Zoology Exam 3

Zoology

 

Phylum Arthropoda Part 3

 

Subphylum Hexapoda

§     Six legs

§     All legs are uniramous

§     Three tagmata (regions): Head, thorax, and abdomen

§     Along with Crustacea, the hexapods are grouped in the clade Pancrustacea

§     Two classes:

l     Entognatha (“ento”: inside,  “gnatha”: jaw)

l     Insecta

 

Class Entognatha

 

§     Bases of the mouthparts enclosed within the head capsule

§     Small group

§     Example: Order Collembola – Springtails

l     Live in the soil or in freshwater

l     Are able to spring from place to place (name = springtails)

l     Some species emerge from the snow and people call them “snow fleas”

 

Class Insecta

 

§     The most diverse and abundant of all groups of arthropods

l     There are more species of insects than species of all other animals combined

l     1.1 million insects have been classified, but some project that as many as 30 million species exist

§     Entomology: study of insects

 

§     Insects are ectognathous which means the bases of the mouthparts are outside of the head capsule

§     Usually have two pairs of wings and they are attached to the thorax

l     Some insects have one pair of wings and some have no wings

§     Distribution:

l     Occur in almost every terrestrial and freshwater habitat

       Only a few occur in marine habitats

 

§     The exoskeleton is formed of a system of plates called sclerites

l     The sclerites are connected by concealed, flexible hinge joints

§     Muscles between sclerites enable insects to make precise movements

§     The exoskeleton contains mostly chitin which provides rigidity, but is also light enough to allow for flight (not much calcium carbonate because it would be too heavy)

l     Chitin is also waterproof

 

§     Head usually bears:

l     Two compound eyes

l     A pair of antennae – vary greatly in form and function

       Can act as: tactile (touch) organs, olfactory (smell) organs and/or auditory (hearing) organs

 

 

 

l     Mouthparts – Made of exoskeleton (cuticle) and vary greatly

       The type of mouthpart that an insect possesses determines how it feeds

      Chewing mouthparts – Example: Grasshopper

      Sucking mouthparts – Example: Mosquito

      Siphoning mouthparts – Example: Butterfly

      Sponging mouthparts – Example: House fly

 

§     Alimentary canal – digestive system

l     Foregut- esophagus and crop (lined with cuticle)

l     Midgut – stomach & gastric ceca

l     Hindgut – Intestine & rectum (lined with cuticle)

§     Malpighian tubules – Excretory system

l     Tubules that attach between the midgut and the hindgut

l     Take nitrogenous wastes out of the hemolymph and placed in the posterior part of the alimentary canal

l     Also control water balance

 

§     Circulatory system:

l     A tubular heart, located posteriorly in the insect, creates peristaltic waves that moves the hemolymph (blood) forward through the only blood vessel, the dorsal aorta

l     The brain receives the freshest hemolymph

l     The hemolymph then passes major muscle masses (legs, wings, etc.)

l     It moves posteriorly pass the alimentary canal where it receives nutrients

l     Further past the Malpighian tubules which cleanses the hemolymph of metabolic waste

l     And then back into the heart through the ostia

§     The hemolymph contains plasma and amebocytes, but usually carries no oxygen (so it usually contains no hemoglobin)

 

§     Gas exchange in terrestrial insects

l     Tracheal system:  A network of thin walled tubes that branch to every part of the body

l     The system opens to the outside through spiracles

l     The tracheae are lined with cuticle and must be shed during molting along with the insects exoskeleton

l     Tracheoles are smaller tubes and are not lined with cuticle

       Tracheoles are not shed with molting

       O2 diffuses from the tracheoles to the cells and CO2 diffuses from the cells to the tracheoles

 

§     Gas exchange in aquatic insects

l     Most aquatic insects have closed tracheal system

l     There are no spiracles, the gases cross the thin exoskeleton and move into the tracheae

       Gases move through the body wall and / or gills

       Gills in aquatic insects are just areas with high surface to volume ratios

l     The rest of the tracheal system remains the same as for terrestrial insects

 

§     Metamorphosis:  Change in form during postembryonic development

l     A/metabolous (direct) development:  Young are similar to adults except in size and sexual maturity

       Example: Silverfish

l     Hemimetabolous (Incomplete) metamorphosis: Gradual changes in form during growth from an immature to adulthood

       Nymphs to adult

       Wings develop externally in pads and then a winged adult develops

       Examples: grasshoppers and mayflies

l     Holometabolous (Complete) metamorphosis: Drastic changes in form during growth from an immature to adult

       Larva to Pupa to Adult

       Wings develop internally during pupa stage

       88% of all insects

       Examples: Butterfly and Beetles

 

l     Classification of insects:

l     Subclass A/pterygota

       Order Thysanura – Silverfish

      Long antennae and three terminal cerci

l     Subclass Pterygota

       Infraclass Paleoptera

      Order Ephemeroptera – Mayflies

»      Membranous forewings longer than hindwings

      Order Odonata – Dragonflies and damselflies

»      Long, narrow, membranous wings on a long slender body

 

       Infraclass Neoptera

      Order Orthoptera – Grasshoppers, etc

»      Hindwings folded like a fan under thickened forewings

-       Order Hemiptera: Leaf bugs, stink bugs, etc.

»      Piercing sucking mouthparts

»      Forewing - Front half thick, back half membranous

 

      Order Coleoptera – Beetles

»      Front wings hard and thick

»      Hindwings membranous

      Order Lepidoptera – Butterflies and moths

»      Membranous wings covered with overlapping scales

»      Mouthparts form a sucking tube

 

      Order Diptera – True flies

»      Single pair of wings

»      Halteres for balancing

      Order Hymenoptera - Ants, bees, wasps

»      Wings coupled distally

»      Hindwings smaller

 

 

Zoology

 

Insect Metamorphosis

(A challenge to Evolution)

 

Molting is not so simple

 

       Molting for growth or for metamorphosis is an intricate process

       The initiation of molting and the timing of the various processes must be exact otherwise the insect will not survive

 

       A number of hormones control the molting process

      Brain hormone (Prothoracicotropic hormone) initiates molting

      Ecdysone activates the epidermal cells to produce a new exoskeleton and molting fluid

      Juvenile hormones interact with ecdysone to determine which stage of metamorphosis the insect should be in

      Bursicon triggers the sclerotization of the exoskeleton

 

·       Molting not only requires the shedding of the old cuticle and the making of the new cuticle that surrounds the insect, but also:

      The cuticle in the tracheal system

      The cuticle that lines the foregut and hindgut

 

Metamorphosis is Complex

 

       Before a caterpillar becomes a butterfly pupa (chrysalis) tiny packets of cells called imaginal discs begin forming in different places

      imaginal discs: undifferentiated cells that are set aside during embryonic development and carried through the larval stages

       Some differentiate to form pupal characteristics

       Some wait and then differentiate to form adult features

 

       Certain imaginal discs become attached underneath the caterpillar’s exoskeleton and then form the pupal exoskeleton

       Once the pupal exoskeleton is completed most of the insides of the caterpillar are broken down except for a few nerves and muscles

 

       The imaginal discs then begin generating an adult butterfly

      Leaf chewing mouthparts must be replaced by nectar siphoning mouthparts

      Simple eyes are replaced by compound eyes

      They must produce four wings covered with scales where no wings occurred before

      A new respiratory system that can sustain flight is created

      The digestive system changes from digesting plant food to digesting nectar

 

 

 

      A new thorax and abdomen are formed

       New nerves and muscles are created

       Some nerves and muscles are reused, but must be rearranged

      Some imaginal disks cling to the inside of the pupal exoskeleton to produce an adult exoskeleton

 

       Since the pupa doesn’t feed, all of these new features must come from the materials accumulated during the larval stage

       Finally n adult butterfly emerges from the pupa

 

       In many ways, the creation of a holometabolous insect is the creation of three “different” organisms

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Zoology

 

Phylum Chaetognatha & Phylum Echinodermata

 

Phylum Chaetognatha – Arrow worms

 

       Marine animals that are highly specialized for planktonic environments

       A small group of animals that fall between the protostome and deuterostome clades

       Mouth does not arise from the first opening, but development is different from the deuterostomes

       They are coelomates and the coelom is used as a hydrostatic skeleton

 

       Small (1 to 12 cm), straight bodies resemble torpedoes

       Planktonic predators that spend much of the time floating, but can dart quickly after prey

       Complete digestive system and a nervous system

       But no respiratory or excretory system

 

       Beneath the head is a large depression called a vestibule that leads to the mouth

       The vestibule contains teeth

       On both sides of the vestibule are sickle-shaped, chitinous spines for grasping prey

       The only invertebrates with a multi-layered epidermis

 

       Fossils of chaetognatha have been found in the Cambrian rock layers

       The fossil forms are very similar to modern forms

 

Phylum Echinodermata
(Prickly – skin)

 

       Marine coelomates

       Deuterostomes: Develop mouth from the second opening

       Spiny endoskeleton of plates

       No ability to osmoregulate

 

       Most have radial symmetry (there are some exceptions with bilateral symmetry)

       Basic pentaradial symmetry in most adults

       Pentaradial symmetry: Any one-fifth "pie slice" of an echinoderm should have all of the same structures as any other

       Water vascular system

       Unique to echinoderms

       A set of canals and specialized tube feet that work with the dermal ossicles to form a hydraulic system

 

Class Asteroidea - Sea stars

 

       A central disc that merges with the tapering arms (rays)

       Body covered with a ciliated, pigmented epidermis

       A ventral ambulacral groove runs from the mouth to the tip of the arm

       The groove is bordered by rows of tube feet which usually have suckers

        The groove and tube feet are not covered with ossicles (open)

 

       The aboral (dorsal) side

       Covered with spines (often flattened)

       Around the bases of the spines are minute, pincerlike pedicellariae

       Keep the body free of debris

       Papulae (dermal gills): Soft projections covered with only epidermis are involved with respiration

       Madreporite: A circular sieve leading to the water vascular system

 

       Endoskeleton

       Ossicles, calcareous plates, bounded together by catch collagen

       Catch collagen:  Collagen that is under neurological control

       Changes collagen from “liquid” to “solid” very quickly allowing the sea star to hold various postures without muscular effort

       Spines project from the ossicles

 

       Spacious body coelom filled with fluid which bathes internal organs and moves into the papulae

       Exchange of respiratory gases and excretion of ammonia occurs by diffusion through the thin walls of the papulae and tube feet

       Water-vascular system

       A ring canal surrounds the mouth

       Radial canals diverge from the ring canal and run up the ambulacral groove of each ray

       A series of lateral canals connects the radial canals to the tube feet

 

       Many sea stars feed on molluscs especially bivalves

       They use their tube feet in relays to pull apart the valves

       When the bivalve’s adductor muscles fatigue a small gap opens

       The sea star inserts its stomach in between the valves and around the bivalves soft parts and begins digestion

       Most sea stars are dioecious

       Fertilization is external

 

       In addition to regeneration, sea stars exhibit autotomy and can cast off an injured arm near its base and then regenerate it

       Autotomy: Detachment of a part of the body by an organism

       Most sea stars produce free-swimming, planktonic larvae

       The free-swimming larvae have cilia arranged in bands and are called bipinnaria

       When the bipinnaria develop three arms and a sucker it is called a brachiolaria

 

Class Ophiurodea – Brittle stars

 

       Largest class of echinoderms in both number of species and individuals

        Most active at night

       Differ from sea stars:

       Arms are slender and sharply set apart from the central disc

       Tube feet without suckers

       No pedicellariae or papulae

       Ambulacral grooves are closed and covered with arm ossicles

       Madreporite is located on the oral surface

       Most brittle stars are dioecious although a few are monoecious

       Regeneration and autotomy occur often

 

Class Echinoidea – Sea urchins and sand dollars

 

       Have a compact body enclosed in a test or shell

       Dermal ossicles are closely fitted plates that form the test

       The plates bear small tubercles on which the round ends of spines articulate as ball-and-socket joints

       Spines are moved by small muscles

 

       No arms but tube feet with suckers are arranged in five ambulacral grooves

       Ambulacral grooves are closed

       Like sea stars, they have pedicellariae to keep their bodies clean

       Aristotle’s lantern is a complex chewing mechanism with 5 pairs of retractor muscles and 5 pairs of protractor muscles

       Dioecious

 

       Regular Echinoidea

       Most species

       Radial symmetry

       Medium to long spines

       Rocky and hard substrates

 

       Irregular Echinoidea

       Sand dollars and heart urchins

       Bilateral symmetry

       Short spines

       Burrow into sandy substrates

 

Class Holothuroidea – Sea cucumbers

 

       Elongate, cucumber-shaped bodies

       No arms or spines

       Ossicles greatly reduced and so they are more soft bodied

       Tube feet with suckers

       Ambulacral grooves are closed

 

       Oral tentacles are used for feeding

       Pedicellariae absent

       Most are dioecious although some are monoecious

       Defense mechanism

       Can cast out its viscera through the ruptured body wall or evert its contents out the anus

 

Class Crinoidea – Sea lilies and feather stars

 

       The fossil record reveals crinoids were once far more prevalent than they are now

       Crinoids remain attached to a substrate during much of their lives

       Body disc (calyx) is covered with leathery skin containing calcareous plates

       Five flexible arms branch to form many more arms

       The calyx and the arms form the crown

 

       Ambulacral grooves are open and ciliated to carry food to the mouth

       Tube feet without suckers line the grooves

       No pedicellariae

 

       No madreporite

       Therefore, no exchange of fluid with the environment

       Water-vascular system must function entirely on existing coelomic fluid

 

       Sea lilies have a flower-shaped body at the tip of an attached stalk

       Feather stars have long, many branched arms

       Larvae are sessile

       Adults are free-moving, but tend to stay in the same place for long periods of time

 

 

 

Zoology

 

Ecology

 

§     Environment: All external factors, living and nonliving, that affect a living organism

 

§     Ecology: The study of the interactions of living organisms with each other and the nonliving (physical) environment

 

§     Environmental Science

l     The study of the interaction of humans with the earth

l     Uses the physical, biological (especially ecology) and social sciences to assess and develop solutions to environmental problems

 

§     An organism’s habitat is where it lives in the community (bog, forest floor, swift river, or ocean’s edge)

§     An ecological niche is the role an organism plays in the community:

       Habitat

       Interaction with other species

 

§     Terrestrial and aquatic habitats for animals are described differently

l     When describing habitat terrestrial ecologists often focus on plants because they dominate a community and strongly influence the physical environment

l     Aquatic ecologists, however, emphasize physical and chemical factors instead of biological factors when describing habitat because organisms less conspicuously affect aquatic habitats

       Four physical factors that are often measured when describing aquatic habitats are light penetration, dissolved oxygen, temperature, and pH

 

Major Ecological Themes

 

§     Population: all the organisms within an area belonging to the same species.

       Interested in:

      Growth:

»      Endangered species, fish and game animals

      regulation

»      Predators, disease, hunting

 

§     A community consists of all the various populations at a locale and the structure that results

l     The analysis and classification of communities is important in the preparation of maps that form the basis of natural resource management

 

§     Ecological Succession: a change in community composition over time

l     An area goes through many predetermined communities before reaching the climax community

       Example: see picture

l     Pioneer species: first species to colonize area

l     Climax community:  the final community to occupy an area.  Often determined by climate

       Coniferous forest (northern zone)

       Deciduous forest (temperate zone) (winters and summers are different)

       Tropical rain forest (tropics)

 

l     Primary succession - Bare earth or rock is colonized by organisms

       Volcanic, glacier retreat, sand dune

l     Secondary succession - Previously vegetated areas that are disturbed

       A soil already occurs here

       Examples:

      abandoned farmland

      areas burned by fire

 

§     An ecosystem is the community of populations and the abiotic (nonliving) environment.

l     Two important principles:

       Energy flows

       Chemical cycling

 

§     Ecosystem composition

l     Producers (autotrophs) - produce food for themselves and others

       Most use photosynthesis

l     Consumers (heterotrophs) - Eat producers

       Herbivores (primary consumers) -

       Eat plants

       i.e. Deer

       Carnivores (secondary consumers)

      eat consumers

       i.e. mountain lions

       Omnivores

      eat plants and herbivores

       i.e. Opossums, Humans

       Decomposers

      Break down and absorb dead material

      i.e. fungi

      Although decomposers have been ignored for a long time by ecologists it is becoming apparent that they play an extremely important role in chemical cycling

 

Relationships within ecosystems

 

§     Food chains (linear) - Simplistic picture of who eats whom.

§     Food web

l     More complicated but more realistic

l     Allows for multiple relationships

§     These feeding relationships form pyramids of energy

l     Energy pyramid- Energy does NOT cycle, it flows. Light energy captured by the sun is eventually lost to work or heat.

       Only about 10% of the energy is passed from one trophic level to the next

 

§     Biogeochemical cycles: Chemicals circulate through ecosystems and involve components that are:

l     Living (biosphere)

l     Nonliving (geological)

l     Biogeochemical cycles help us to understand where important nutrients and pollutants travel

§     Biogeochemical cycles have the following parts

l     A reservoir: chemicals unavailable to producers i.e. rocks

l     An exchange pool: organisms can obtain these chemicals

       Atmosphere (gaseous cycle)

       Soil (Sedimentry cycle)

l     Biotic community - chemicals move along the food chains

l     Carbon cycle

       Includes greenhouse gasses such as carbon dioxide and methane

 

§     The biosphere is the thin layer of water, land, and air inhabited by living organisms

§     Biomes - The largest units of the biosphere and these are primarily defined by climate:

l     Temperature

l     rainfall

§     Influenced also by topographical features

l     \rain shadows

§     Biomes change with latitude and altitude

§     Biome Example: Grasslands

        Savanna (e.g. Africa) - Cool dry season, hot rainy season

       Temperate grasslands - prairies of North America

      Most have been converted to farming because of very fertile soils

      Plants

»      tall grass prairie - wetter

»      short grass prairie – drier

 

 

Climate diagrams

 

§     The distribution of terrestrial ecosystems is closely related to regional climate

§     Climate diagrams describe:

l     Temperature (Mean annual & Mean monthly)

l     Precipitation (Mean annual & Mean Monthly)

l     Topography (Elevation above sea level)

§     It is especially important to contrast the seasonality of temperature and precipitation

l     Example: Various grasslands

 

§     Biogeography: is the study of the distributions of organisms   

l     Its goal is to describe and understand the many patterns found in the distribution of species

(biodiversity hotspots)

§     The eight biogeographical realms of the world:

l     Eastern Hemisphere:

        Palearctic (Russia and Europe)

       Afrotropic (Ethiopian)

       Indo-Malay (Oriental)

l     Western Hemisphere

       Nearctic (North America and Canada)

       Neotropic (South America)

l     Australasia

l     Oceana (islands of the Pacific Ocean)

l     Antarctic

 

 

The proper relationship between a Christian and creation

 

§     Francis A. Schaeffer - Pollution and the Death of Man: The Christian View of Ecology 1970 –Tyndale House Publishers

§     Two important points:

l     Since humans, animals and plants are all created by God

       We are all equally separated from God in that He is the Creator

       Man, therefore is united to all other creatures as being created

l     Man’s relationship with God, however, is different from the rest of creation in that people have been made in the image of God

 

Stewardship of Creation

 

§     God is the creator and is the sustainer of Creation (Gen. 1, Psalm 104, etc.)

§     We are to use the creation

l     Everything that lives and moves will be food for you.  Just as I gave you the green plants, I now give you everything. Genesis 9:3

§     Stewardship - responsibility

l     The Lord God took the man and put him in the Garden of Eden to work it and take care of it. Genesis 2:15

§     God maintains ownership of His Creation (Deut. 10:14, Psalm 24:1, Psalm 95:4-5)

l     The earth is the Lord’s, and everything in it, the world, and all who live in it. Psalm 24:1

§     God cares about his creation (Not just in Genesis but other Books talk about His creation)

l     God saw all that he had made, and it was very good. … Genesis 1:31

l     Look at the birds of the air; they do not sow or reap or store away in barns, and yet your heavenly Father feeds them … Matt 6:26

l     Are not five sparrows sold for two pennies?  Yet not one of them is forgotten by God   Luke 12: 6

§     God is still in control of his creation

l     Are not two sparrows sold for a penny.  Yet not one of them will fall to the ground apart from the will of your Father. Matt 10: 29

§     Human life is sacred

l     So God created man in His own image …” Genesis 1:27

§     Accountability

l     And if you have not been trustworthy with someone else’s property, who will give you property of your own? Luke 16:12

 

 

 

Zoology

 

Phylum Chordata

 

l     Coelomates

l     Deuterostomes

l     Five chordate characteristics

      Notochord

      Dorsal tubular nerve cord

      Pharyngeal pouches and slits

      Endostyle or thyroid gland

      Postanal tail

 

l     Notochord

      Flexible, rodlike structure

      First part of the endoskeleton to appear in an embryo

      Contains fluid-engorged cells

      Muscles attached to the notochord provide undulatory movements of the body

      In most vertebrates, the notochord is replaced by vertebrae

l     Dorsal tubular nerve cord

      Dorsal to the digestive tract

·       Most invertebrate phyla have a ventral nerve cord

      Begins as a tube

·       Most invertebrate nerve cords start out solid

      The anterior end is enlarged to form a brain among vertebrates

 

l     Pharyngeal slits and pouches

      Slits are openings that lead from the pharyngeal cavity to the outside

·       Aquatic chordates

·       Work as filter feeding mechanisms or as gills

      Pouches

·       Do not open to the outside

·       In terrestrial (tetrapod) vertebrates the pouches give rise to:

      Eustacean tube

      Middle ear

      tonsils

      Parathyroid glands

 

l     Endostyle or thyroid gland

      Endostyle

·       Found in protochordates and lamprey larvae

·       Some cells secrete iodinated ….

      Thyroid gland

·       Adult lampreys and all other vertebrates

·       Secretes iodinated hormones

 

l     Postanal tail

      A structure added behind the digestive system

      Many vertebrates have postanal tails, but not all

·       I would not call the coccyx in humans a tail

      Coccyx: A series of small vertebrae at the end of the spinal column

      An important attachment for various muscles, tendons and ligaments

 

Subphylum Urochordata - Tunicates

      Adults are sessile

      Larvae bear the characters of chordates

      Class Ascidiacea – sea squirts

·       Incurrent and excurrent siphons

·       Endostyle secretes a mucous net

      Food particles that are brought in by the incurrent siphon are trapped on the mucous net

 

Subphylum Cephalochordata – Lancelets (Amphioxus)

      Slender and laterally compressed

      Inhabit sandy coastal waters

      Water enters the mouth, driven by cilia in the buccal cavity and pharynx

·       The water then passes through numerous pharyngeal slits where the food is trapped in mucus secreted by the endostyle

      The nervous system is centered around a hollow nerve cord lying above the notochord

 

      Closed circulatory system is fairly complex for such a simple organism

·       There is no heart, but the flow is similar to a fish’s circulatory system

·       Blood is pumped forward in the ventral aorta by peristaltic-like contractions of the vessel wall

      It then passes upward through branchial arteries (aortic arches) in the pharyngeal bars to paired dorsal aortas which join to become a single dorsal aorta

      From there blood is distributed by microcirculation and then collected in veins and returned to the ventral aorta

      There are no gills specialized for respiration in the pharynx

»      Gas exchange occurs over the surface of the body

 

l     Subphylum Vertebrata (Craniata)

      Most possess both an exoskeleton and endoskeleton of cartilage or bone

·       Exoskeleton develops from the skin

      Reptilian scales, hair, feathers, claws and horns

·       A living endoskeleton

      Allows continuous growth

      Permits almost unlimited body size

      A framework for efficient muscle action and attachment

      Most vertebrates have central discs that surround the spinal cord instead of a notochord

·       Dorsal projections called neural spines are present and provide more area for attachment of segmented muscles

 

      Anterior end of the nerve cord is enlarged to form a tripartite brain

·       Forebrain

·       midbrain

·       Hindbrain

·       Protected by a cartilaginous or bony cranium

      Vastly increased respiratory efficiency

      Muscularized gut

      Chambered heart

 

l     Extinct vertebrates found in the fossil layers

      Conodonts: Microscopic toothlike fossils used to classify geologic layers

·       In the early 1980s a complete conodont fossil was discovered

·       Resemble lancelets, but have eyes and greater cephalization

      Ostracoderms – Armored jawless fish

·       Heterostracans:  Armed with bone in the dermis and lack paired fins

·       Osteostracans: 

      Single piece headshield

      Paired pectoral fins

·       Anaspids:  More streamlined than other ostracoderms

 

      Armored jawed fish

·       Placoderms

      Paired fins

      Heavily armored

      Diamond shaped scales or large plates of bone

·       Acanthodians

      Paired fins with large spines

      Larger anterior set eyes

      Less armor than placoderms

 

Vertebrate Tissue types

 

l     Four types of tissues in vertebrates:

      Epithelial tissues

      Connective tissues

      Muscular tissues

      Nervous tissues

 

Epithelial tissue

 

l     Epithelial tissue: a sheet of cells that covers external and internal surfaces

      Act as chemical and/or physical barriers

      Simple (a single layer)

·       Squamous: flattened cells

·       Cuboidal:  Short, boxlike cells

·       Columnar: Cells are taller with elongated nuclei

      The columnar cells that line the intestine are an example of a chemical barrier

      They are selective as to which chemicals they let through to the tissues

 

      Stratified: Two or more layers of cells

·       The stratified squamous cells of the skin are keratinized and act as a physical barrier to scratching, etc.

·       Transitional:  Cells can be greatly stretched

      Example: As the bladder fills, the cells expand and as it empties the cells compress

 

      Microvilli vs cilia

»      Microvilli:

·       Non-motile

·       Are used in the absorption process

·       Located on the surfaces of the columnar epithelial cells of the small intestine and kidney tubules

»      Cilia:

·       Motile

·       Are used to move cell bodies and other sweeping processes

·       Example: Fallopian tube cilia move the eggs

 

      Blood vessels never penetrate into epithelial tissues

      All types of epithelia are supported by an underlying basement membrane

»      Basement membrane: A condensed region of connective tissue matrix

·       It is secreted by both the epithelial and connective tissue cells

 

Connective tissues

 

l     Connective tissue is composed of relatively few cells and a matrix (lots of extracellular fibers suspended in a ground substance)

      Fibers are often composed of collagen

·       Collagen is a protein of great tensile strength

      Is the most abundant protein in the animal kingdom

l     Connective tissue types:

      Loose: anchors blood vessels, nerves and body organs

      Dense: forms tendons, ligaments and fasciae

·       Fasciae: sheets or bands of tissue surrounding skeletal muscles

      Specialized connective tissue: blood, lymph, adipose (fat), cartilage and bone

·       Fibrin and platelets form a blood clot

 

Muscular tissues

 

l     The basic unit of the muscular tissues is the muscle fiber (or cell)

l     Striated muscle

      Appears transversely striped (striated) with alternating dark and light bands

      The appearance results from repeating bands of the proteins, actin and myosin

      Two types of striated muscle:

·       Skeletal: Extremely long, cylindrical fibers which are multinucleated

      Voluntary:  Can consciously control its movement

·       Cardiac: Shorter with only one nucleus per cell (uninucleated)

      Involuntary:  Cannot consciously control movement

      Found only in the vertebrate heart

 

l     Smooth (or visceral) muscle:

      Lack striated bands

      Involuntary

      Long and tapering, contain a single nucleus

      Surrounds blood vessels and internal organs such as the intestines

 

Nervous tissue

 

l     Two basic cells in nervous tissue:

      Neurons:  receive stimuli and conduct impulses

»      It is the functional unit of the nervous system

»      A neuron consists of:

·       Cell body (soma)

      The soma produces the enzymes needed to make the neurotransmitters

·       Nerve fibers: thin processes

      Axon: Carries impulses away from the soma

·       There is usually one axon per neuron

      Dendrites: Transmit incoming electrical impulses toward the soma

·       There can be one or many dendrites

 

      Neuroglia:  Non-neuron cells that insulate neuron membranes, provides nutrients to the neurons and many other functions

 

 

Zoology

 

Fish

 

n     Aquatic vertebrates

n     Gill breathing

n     fins

n     Heart (except in jawless fish) consists of a sinus venosus, atrium, ventricle and conus (bulbus) arteriosus

      Sinus venosus: a thin-walled sac that collects blood from the fish’s veins and assures smooth delivery of blood to the heart

      Conus arteriosus: dampens blood pressure oscillations before blood flows into delicate blood capillaries

 

n     Single cycle circulation

      Blood makes a single circuit through a fish’s vascular system

      Blood is pumped from the heart to the gills, where it is oxygenated

      Then it flows into a dorsal aorta to the body organs

      The blood returns to the heart by veins

      The heart must provide sufficient pressure to push the blood through two sequential capillary systems (the gills and the remainder of the body)

      The disadvantage of the single circuit system is that capillaries offer so much resistance to blood flow that blood pressures to the body tissues are greatly reduced

 

n     Consists of five classes of vertebrates

      With close to 28,000 species

 

n     Two large groupings:

      Agnatha:  Jawless fish

      Gnathostomes:  Jawed fish

 

Agnatha: Jawless fish

 

n     Jaws absent

n     Brain small, but distinct

n     Cranium present

n     Slender, eel-like, with no paired fins

n     No scales

n     Cartilaginous skeleton

n     Notochord present and vertebrate reduced or absent

n     Heart consists of a sinus venosus, atrium and ventricle

      Sinus venosus: a thin-walled sac that collects blood from the fish’s veins

 

 

n     Includes:

      Class Myxini:  Hagfish

      Class Petromyzontida:  Lampreys

 

Class Myxini: Hagfish

 

n     Entirely marine

n     Feed on annelids, molluscs, crustaceans and dead animals

      Almost completely blind, but have keen senses of smell and touch

      Are quickly attracted to food

      A dead whale at the bottom of the ocean will attract thousands of hagfish

      The hagfish will feed on the whale for several years

n     Hagfish enter into a dead animal through a hole or by digging into the body

      The two toothed, keratinized plates on the tongue fold together in pincerlike action

n     The hagfish uses this to rip bits of flesh away from the animal

      The hagfish ties a knot in its tail, then passes the knot forward along its body

n     It presses the knot against the side of the animal for extra leverage

 

n     Hagfish produce enormous amounts of slime

      If a hagfish is disturbed it exudes a milky fluid from special glands along the sides of its body

n     When the milky substances contacts seawater, the fluid forms a slime so slippery that the hagfish is almost impossible for a predator to grab

 

n     Have a low pressure circulatory system with a heart positioned behind the gills

      There are three additional accessory hearts

n     The body fluids of the hagfish are in osmotic equilibrium with seawater

      This is true of no other vertebrates

      This is generally the case for most marine invertebrates

 

Class Petromyzontida – Lampreys

 

n     All lampreys swim up streams to breed

n     Marine forms are anadromes

      They spend most of their lives at sea, but ascend streams to spawn

 

n     Small larvae, called ammocoetes, hatch from eggs

      The larvae resemble amphioxus (lancelets) and are a model for chordate characters

n     They look more like lancelets than they look like their parents

      The larvae are suspension feeders

 

 

 

 

n     Eventually the larvae metamorphosize into adults:

      Eyes erupt

      An oral disc with keratinized teeth develops

      Fins are enlarged

      Gonads mature

      Gill openings are modified

 

n     Parasitic lampreys

n     Freshwater species remain in freshwater, but often move from streams to lakes

n     Parasitic lampreys attach themselves to fish by their keratinized teeth located in the buccal funnel

      The buccal funnel also provides suction

      The keratinized tongue protrudes out and rasps an opening through the hosts skin

n     Body fluid and muscle are then eaten

 

      To promote blood flow, lampreys inject anticoagulant into the wound

      After the lamprey has gorged on the fish it releases its hold and migrates to a spawning area

      This leaves the fish with a gaping wound and can kill the fish especially if it gets infected

 

n     Nonparasitic lampreys, least brook lamprey, do not feed after metamorphosis

      Their digestive systems degenerate to nonfunctional tissue

      Within a few months they spawn and die

 

n     Sea lampreys do not naturally occur in the Great Lakes

      In the early 1900s the Welland Ship Canal was constructed to allow ships to go around the Niagara Falls

      This also allowed sea lampreys to go around the Niagara Falls and enter the Great Lakes

      Great Lakes fish such as lake trout, rainbow trout, lake whitefish and other species were very susceptible to attack by the lampreys

      In combination with overfishing, the invasion of the sea lamprey led to a collapse of fisheries for the above species

      The number of sea lampreys in Great Lakes has been reduced in recent years by an aggressive program that releases chemical larvicides into the main sea lamprey spawning streams

      Sea lampreys still take their toll on Great Lakes fish

 

 

Zoology

 

Gnathostomes

 

       Superclass: Gnathostomata – Jawed fish

       Jaws present

       Paired fins

       Three classes:

       Class Chondrichthyes – Sharks, rays and chimaeras

       Class Actinopterygii – Ray-finned fish

       Class Sarcopteryii – Lobe-finned fish

 

       Gnathostomes appear in the Silurean layer with jaws fully formed with no “intermediates” between jawless and jawed fish

 

Class Chondrichthyes – Cartilaginous fish

 

       Cartilaginous skeleton and vertebrae distinct

       Skeleton made of cartilage and there is no bone

       The cartilage is extensively calcified

 

       Large jaws

       Teeth not fused to jaw

       Powerful swimming musculature

       Most are predators

       Well-developed sense organs

 

       Two subclasses:

       Elasmobranchii

       Holocephali

 

Subclass Elasmobranchii – Sharks, skates, and rays

 

       Paired ventral nostrils connected to a large olfactory organ

       Allows for long distance detection of prey (1 part per 10 billion)

       Lidless eyes

       Two dorsal spiracles open into the pharynx to bring water in

       Five pairs of external gill slits allow the water to exit

       The gills are not covered by an operculum (gill cover)

 

       The front row of functional teeth on the edge of the jaw is backed by rows of developing teeth that replace worn teeth throughout the life of the shark

       Polyphyodont: Several sets of teeth in succession

 

       Heterocercal caudal fin

       Upper lobe larger than lower lobe

       The vertebral column turns upward and extends into the dorsal lobe of the caudal fin

       Provides thrust and some lift as it sweeps back and forth

       The medial part of each pelvic fin is modified to form a clasper which is inserted in the female during copulation

 

       Placoid scales (denticles) covering a tough, leathery skin

       Placoid scale:  A rectangular basal plate embedded in the skin.  Protruding from the basal plate is a backward pointing spine

       Consists of a central pulp cavity supplied with blood vessels surrounded with dentine.  The dentine of is enclosed by enamel

       Reduces the turbulence of water flowing along the body surface during swimming

 

       Lateral line system

       Neuromasts: Receptor organs that consist of interconnected tubes and pores along the sides of the body and over the head

       Mechanoreceptors:  Sense low-frequency vibrations

       Ampullae of Lorenzini:

       Electroreceptors that sense the bioelectric fields that surround all animals

       Located primarily on the shark’s head

 

       The straight intestine contains a spiral valve that slows the passage of food and increases the absorptive surface

       Large livers that contain a lipid called squalene which is low in density and helps keep the fish afloat

       Rectal Gland

       Secretes a highly concentrated sodium chloride fluid that assists the kidneys in regulating the salt concentration of the blood

 

       Reproduction (all three types):

       Oviparous: Eggs are laid soon after fertilization, the embryo develops and then hatches

       Ovoviviparous: Developing young are retained in the uterus while they are nourished by their yolk sacs until they are born

       Viviparous: Embryos receive nourishment through a placenta or from nutritive secretions, “uterine milk,” produced by the mother

 

       Sharks

       Chondrichthyes with a fusiform body

       Includes:

       Whale sharks

       Great white sharks

       Hammerhead sharks

       Carpet sharks

       Pygmy sharks

 

       Rays:

       Includes rays, skates, and sawfish

       Most specialized for bottom dwelling

       Dorsoventrally flattened body

       Greatly enlarged pectoral fins

       Large spiracles on top of head

 

       Stingrays: Have slender, whiplike tail armed with one or more spines with venom glands at the base

       Electric rays: Contain large electric organs on each side of the head which put out a high amperage current to stun prey or predators

 

Subclass Holocephali – Chimaeras

 

       No teeth, jaws bear large flat plates                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               

       Upper jaw completely fused to the cranium (unique in fishes)

       Gills covered by a cartilaginous operculum to create a single external respiratory opening

       Less abundant now than in the fossil layers

 

Osteichthyes – Bony fish

 

       Endochondral bone

       Bone that develops by replacing embryonic cartilage

       An operculum made of bony plates covers the gills

       Increases respiratory efficiency

       Outward rotation of the operculum creates negative pressure so that water is drawn across the gills

 

       Most have swim bladders

       By displacing water with gas the fish can achieve neutral buoyancy

       The fish can remain suspended indefinitely at any depth with no muscular effort (no energy)

       Reproduction: Oviparous, ovoviviparous or viviparous

 

       Two classes:

       Actinopterygii - Ray-finned fish

       Sarcopterygii – Lobe-finned fish

 

Actinopterygii – Ray-finned fish

 

       Most have a homocercal caudal fin

       Homocercal: Upper and lower lobes symmetrical

       Vertebral column ending near the middle of the base

       Fins supported by bony rays

       Muscles controlling fin movement are within the body

       Larval stage often very different from adult

 

       Teleost fish – Modern bony fish (96% of all living fish, almost ½ of all vertebrates)

       Cycloid scales or ctenoid scales or naked

       Cycloid and ctenoid scales:

       Of dermal origin

       Made of bone, but light and flexible

       Cycloid: Posterior margins are smooth

       Ctenoid: Posterior margins have fine, toothlike spines

       Naked: eels and catfish lack scales

       Many teleost fish have pharyngeal teeth

       Pharyngeal teeth are located on the last gill arch at the posterior region of a fish's head (under the operculum)

 

 

       Nonteleost ray-finned fish

       Sturgeons and paddlefish

       A mostly cartilaginous endoskeleton

       The only ossified bones are found in the skull, jaws, and pectoral girdle

       Fins positioned towards the posterior and a heterocercal caudal fin

       Lateral line and scales are absent

       Gars and bowfin

       Can surface to gulp air

       This fills their vascularized swim bladder with air to supplement oxygen obtained from the water by gills

 

Sarcopterygii – Lobe-finned fish

 

       Fins supported by stout bones and bony rays

       Muscles controlling fin movements are within the fin

       Diphycercal caudal fin

       Tapers to a point

       Vertebral column extends to the tip without upturning

       Oviparous

       Lungfish and coelacanths

 

       Lungfish

       Swim bladder used for respiratory gas exchange (“lung”)

       Some species can live out of water for a long time

       Coelacanths

       Thought to be extinct since the Mesozoic fossil layer

       Rediscovered in 1938

       Swim bladder filled with fat

 

 

Zoology

 

Additional Bony Fish Features

 

Hearing in Fish

 

„  Fish, like other vertebrates, detect sound as a vibration in the inner ear

„  The semicircular canals are attached to three chambers

„  The lagena is the hearing receptor in fish

 

„  Most fish, however, do not hear well

„  The body of a fish is similar in density to the surrounding water

„  The sound waves tend to pass through the fish’s body nearly undetected

„  Catfish, minnows, and suckers hear better than most fish

„  Weberian ossicles: a set of small bones that allow them to hear faint sounds over a broader range of frequencies

 

„  Reception of sound begins at the swim bladder which is easily vibrated because it contains air

„  Vibrations are transmitted from the swim bladder to the inner ear (semicircular canals and lagena) by the Weberian ossicles

 

Taste

 

„  Fish have taste buds both internally and externally

„  The mouth and gill rakers are packed with taste buds

„  In catfish, the barbels, fins, back, belly, sides and even the tail contain taste buds

„  A channel catfish just 6 inches long has more than a quarter-million taste buds on its body (humans have 10,000 taste buds in their mouth)

„  Not surprising, catfish have the best sense of taste among the vertebrates

„   For instance, a catfish can taste a single drop of coke in an Olympic size swimming pool

 

„  Catfish tend to live in dark, murky waters where their vision isn't very useful

„  The taste buds on the barbels and other parts of the body help the fish search out food using their senses of touch and taste

 

„  A taste bud consists of a cluster of receptor cells surrounded by supporting cells

„  It has a small external pore through which slender tips (microvilli) of the sensory cells project

„  Chemicals being tasted interact with specific receptor sites on the microvilli

 

 

 

 

Fish Gills

 

„  There are four gill arches on each side of the fish

„  Each bears numerous thin gill filaments that project to the rear

 

„  The thin gill filaments are each covered by an epidermal membrane folded repeatedly in platelike lamellae

„  The lamellae are richly supplied with blood vessels

 

„  The flow of water is opposite the direction of blood flow (countercurrent flow)

„  This is the best arrangement for extracting the greatest possible amount of oxygen from water

 

„  Gill rakers project forward from the gill arches and strain out food and debris

„  Filter feeding fish such as herring have well developed gill rakers for capturing food

„  Most fish are carnivores as compared to filter feeders

„  Only a small proportion of fish are herbivores (feeding on plants or macroalgae)

 

„  Fish such as salmon, mackerel, herring, lake trout, sardines and albacore tuna contain large amounts omega-3 fatty acids (fish oil)

„  Omega-3 fatty acids from fish have been proposed to have numerous human health benefits such as reducing triglycerides and relieving rheumatoid arthritis

 

„  Fish, however, can not synthesize omega-3 fatty acids

„  Microalgae such as plankton produce the omega-3 fatty acids

„  The fish obtain the omega-3 fatty acids by feeding on microalgae or by feeding on fish that feed on microalgae

„  The fish then store the omega-3 fatty acids

„  This also true of krill oil (a source of omega-3 fatty acids), krill cannot produce oil, but obtain it by feeding on microalgae

 

Fish Migration

 

„  Freshwater eels are catadromous

„  They spend most of their lives in freshwater

„  Migrate to the ocean to spawn in the Sargasso Sea

 

„  Pacific salmon are anadromous

„  The salmon hatch out of eggs in freshwater streams and then migrate toward the ocean

„  As they move down the streams and rivers, they molt several times

„  While doing this they imprint on the vegetation and soil odors of those streams and rivers so that they can return to them

„  Pacific salmon live much of their adult lives in the ocean

„  They return to freshwater to spawn after which they die

 

„  Pacific salmon populations are threatened throughout the world

„  Siltation from logging and agriculture

„  Hydroelectric dams which block adults returning from the ocean to spawn

„  The lakes formed from the dams increase mortality of the juvenile salmon migrating to the ocean

 

Growth

 

„  Fish growth is temperature dependent

„  Poikilothermic (ectothermic): Body temperature fluctuates with environmental temperature

„  Fish in temperate regions (warm and cold seasons) grow rapidly in the summer when temperatures are high and food is plentiful

„  Growth in the winter nearly stops

 

„  Annual rings in scales, otoliths and other bony parts reflect this seasonal growth

„  Each year’s increment in scale growth is a ratio of the annual increase in body length

„  Otoliths: Small oval calcareous plates in the inner ear for sensing gravity and movement

„  Most reproductively mature fish continue to grow (although more slowly) for as long as they live

„  The annual rings can be used to determine the age of many fish

 

Reproduction

 

„  Most ray finned fish are dioecious, but are often difficult to sex using external features

„  Males usually have two long, rectangular testes that occupy a large majority of the posterior coelomic cavity especially during breeding season

„  Females typically possess a single ovary posterior to the stomach which varies in size depending on the season

 

„  Some species of fish, including some of the clown fish and grouper species, are hermaphrodites,

„  They naturally have both male and female sex organs

„  They are born with the ability to change their gender

„  Which can increase their chances of mating and passing on their genes

 

„  Intersex

„  Feminization of male fish

„  Can happen in species of fish that aren’t hermaphroditic,

„  It doesn’t help reproduction

„  In severe cases, it can make fish sterile

„  The intersex males do not outwardly appear different from normal males

„  This can interfere with mating behavior

„  In severe cases it can lead to death

„  The presence of female eggs in male testes is an indicator of intersex

„  Evidence suggests that intersex in fish may be the result of pharmaceuticals (Ex: birth control pills), pesticides (Ex: the herbicide, Atrazine), and personal care products that move into aquatic environments

 

„  A survey of fish in 19 national wildlife refuges in the Northeastern U.S. indicted that 60 to 100 percent of all the male smallmouth bass had intersex conditions

„  Another study of the Shenandoah and Potomac Rivers found intersex conditions in more than three-quarters of male smallmouth bass

„  Higher than normal levels of vitellogenin occured in the blood of the male fish

„  Vitellogenin is a protein produced by female fish to form egg yolk and is normally absent in males

„  The gene that tells the body to produce vitellogenin is usually “turned off,” in male fish

„  That gene only “switches on” in the presence of estrogen, a female sex hormone

 

Tremendous Variation in Teleost Fish

 

„  Three groups of deep-sea fishes, tapetails, bignose fishes, and whalefishes, were so different in morphology that they were assigned to three different taxonomic families

„   It has now been determined that they are the larvae, males, and females, respectively, of a single species

 

 

 

 

 

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