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