Week 5 material - Zoology

The invertebrates I and II, vertebrates and non-vertebrate chordates, gnathostome vertebrates, mass extinctions

What groups do the bilaterians include?

Acoela (species), deuterostomia, lophotrochozoa, ecdysozoa

Members of Deuterostomia

hemichordates, echinoderms, chordates (vertebrates and invertebrates)

Ecdysozoa characteristics and members

invertebrates that secrete external skeletons that they shed as they grow through ecdysis (molting)

arthropods and nematodes are members

Lophotrochozoa characteristics and members

Either have a lophophore feeding structure or go through trochophore larva development stage

Invertebrates

animals that lack a backbone

What percent of known species do invertebrates make up?

more than 95%

Porifera (sponges)

Outgroup/sister clade of all other animals

sedentary filter feeders

lack tissues; have choanocytes

Choanocyte

one type of cell in sponges

flagellated collar cells that generate a water current through sponge and ingest suspended food

amoebocytes

totipotent cells in the gelatinous noncellular mesohyl layer that play roles in digestion and manufacture skeletal fibers

Eumetozoa

first common ancestor of all true animals

Cnidarian basic body plan features

diploblastic, radial: sac with a central digestive compartment (gastrovascular cavity)

single opening functions as mouth and anus

2 variations of cnidarians

Polyp and medusa

Polyp

sessile - adheres to substrate by the abhoral (away from mouth) end of its bodyf

Medusa

motile - bell shaped body with mouth on underside

Cnidarians - diet + defenses

carnivore that use tentacles to capture prey

tentacles armed with cnidocytes which contain specialized organelles called nematocysts that eject a stinging thread

How many phyla does lophotrochozoa contain?

18

lophophore

feeding structure made up of a crown of ciliated tentacles around the mouth

lophophorates

have a lophophore and a true coelem

two phyla of lophophorates

Ectoprocta and Brachiopoda

Ectoprocts (bryozoans)

Sessile, colonial animals that resemble clumps of moss, encased by a hard exoskeleton

Brachiopods

resemble clams and other hinge shelled molluscs, but the two halves of the shell are dorsal and ventral rather than latera

marine, mostly attached to sea floor by a stalk

What does the phylum mollusca include

snails and slugs, oysters and clams, octopuses and squids

Molluscs

soft bodied animals with most protected by a calcium carbonate shell

Mollusca body plan

3 main parts: muscluar foot, visceral mass, and mantle (secretes shell and is location of respiratory structure)

• visceral mass includes all organs etc

some also have water filled mantle cavity and feed using straplike radula

Class Gastropoda

part of phyla mollusca -snails and slugs

make up around ¾ of all living mollusc species

move slowly by rippling motion of the foot or by cilia

most have single, spiraled shell that functions in protection from injury, dehydration, and predation

most are herbivores

cuticle

tough coat/exoskeleton

two largest phyla of ecdysozoans

nematodes and arthropods

Phylum nematoda (roundworms) - where are they found and body plan

found in most aquatic habitats, soil, moist tissue of plants, body fluids and tissues of animals

have an alimentary canal but lack a circulatory system

longitudinal body wall muscles that produce thrashing motion upon contraction

number of described species of nematode

20-25K

Phylum arthropoda - around how many live on earth? (estimation)

estimated by zoologists to be 1 billion

2/3 known species of animals are arthropods

arthropod body plan

segmented body, hard exoskeleton, jointed appendages; dates back to the Cambrian explosion - 535-525 million years ago

completely covered by the cuticle - molts its exoskeleton when it grows

What helped arthropods be among first animals to colonize land?

Exoskeleton helped prevent desiccation because of its impermeability to water and provided support from its strength without reliance on buoyancy of water

3 major early lineages of arthropods

chelicerates, myriapods, pancrustaceans

Pancrustaceans include:

crustaceans and insects

recent evidence indicates that terrestrial insects are more closely related to crustaceans than myriapods

Crustacean groups (some)

Isopods- one of the largest groups of crustaceans

decapods- relatively large, include lobsters, crabs, crayfish, and shrimp

Hexapoda

large clade including insects and their relatives

rare in marine habitats

When did insects diversify first? what caused subsequent diversifications

359-252 million years ago, following the evolution of flight

radiations of plants on which insects fed

expansion of flowering plants (~100 mya)

what did specialized modes of feeding evolve in response to?

gymnosperm diversification

developmental characteristics of deuterostomes

radial cleavage, formation of the anus from the blastopore

what kind of similarities are deuterostomes primarily defined by?

DNA similarities

What phyla are included in deuterostomes?

Echinoderms and chordates

Echinoderms

slow moving or sessile marine animals

body plan/physical characteristics of echinoderms

endoskeleton of hard calcareous plates covered by a thin epidermis

unique water vascular system, a network of hydraulic canals branching into tube feet that function in locomotion and feeding

Five classes of echinoderms

Asteroidea, ophiouroidea, echinoidea, crinoidea, holothuroidea

Chordates

bilaterally symmetrical coelomates with segmented bodies - have evolved separately from echinoderms for at least 500 million years

Cnidaria (hydras, jellies, sea anemones, corals)

unique stinging structures (nematocysts) housed in specialized cells (cnidocysts); diploblastic; radially symmetrical; gastrovascular cavity

platyhelminthes (flatworms)

dorsoventrally flattened acoelomates; gastrovascular cavity or no digestive tract

syndermata (rotifers and acanthocephalans)

Pseudocoelomates. Rotifers have alimentary canal (digestive tube with mouth and anus) and jaws (trophi); acanthocephalans are parasites of vertebrates

lophophorates: ectoprocta, brachiopoda

coelomates with lophophores

mollusca (clams, snails, squids)

Coelomates with three main body parts; coelom reduced; most have hard shell made of calcium carbonate

annelida (segmented worms)

coelomates with segmented body wall and internal organs (except unsegmented digestive tract)

nematoda (roundworms)

cylindrical pseudocoelomates with tapered ends; no circulatory system; undergo ecdysis

arthropoda (spiders, centipedes, crustaceans, and insects)

coelomates with segmented body, jointed appendages and exoskeleton made of protein and chitin

echinodermata (sea stars, sea urchins)

coelomates with bilaterally symmetrical larvae and fiver part body organization as adults; unique water vascular system; endoskeleton

chordata (lancelets, tunicates, vertebrates)

coelomates with notochord; dorsal, hollow nerve cord; pharyngeal slits; post-anal tail

Coelomates

animals possessing a true, fluid-filled body cavity (coelom) completely lined by mesoderm tissue, located between the gut and the outer body wall.

About how many extant species of vertebrate are there?

70,000

groups comprised by chordates

All vertebrates and two groups of invertebrates, urochordates and cephalochordates

Four key characteristics of chordates

Notochord; dorsal, hollow nerve cord; pharyngeal slits or clefts; muscular, post-anal tail

notochord

longitudinal, flexible rod betwen the digestive tube and nerve cord that provided skeletal support throughout most of the length of a chordate - most species only retain remnants of embryonic notochord

Dorsal, hollow nerve cord

Develops from neural plate/neural tube dorsal to the notochord, and develops into the central nervous system

pharyngeal slits or clefts

grooves that form along the outer surface of the pharynx (throat)

develop into pharyngeal slits that open to the outside of the body

function of pharyngeal slits

suspension feeding structures in many invertebrate chordates

gas exchange in vertebrates except tetrapods (vertebrates with limbs)

develop into parts of the ear, head, and neck in tetrapods

muscular, post anal tail

propelling force in many aquatic species, contains skeletal elements and muscles, greatly reduced during embryonic development in many species

Lancelets (cephalochordata)

Nonvertebrate chordates - bladelike shape - marine suspension feeders that retain characteristics of chordate body plan as adults

Tunicates (urochordata)

Nonvertebrate chordates

more closely related to other chordates than lancelets

most resemble chordates during short larval stage - metamorphosis from larva into adult form involves resorption of the tail and notochord and 90º rotation of remaining organs

vertebrates

chordates that have a backbone

What tasks do a skeletal system and complex nervous system give vertebrates efficiency in

capturing food and evading predators

Agnathans (cyclostomes)

jawless vertebrates - only two lineages remaining today are hagfishes and lampreys

they lack a backbone but presence of rudimentary vertebrae and results of phylogenetic analysis indicate that they are vertebrates

Haikouella

most primitive fossil of early chordates

resembeled lancelets but had well-formed brain, eyes, and muscular segments, but lacked a skull and ear organs

Conodonts

earliest vertebrates in the fossil record (500 mya)

jawless, soft-bodied vertebrates w set of barbed hooks at anterior end of mouth for capturing prey

Gnathostomes

jawed vertebrates

derived characters of gnathostomes

jaws with teeth used to grip and slice food items

hypothesis for evolution of jaws

evolved by modification of the skeletal rods that supported the pharyngeal (gill) slits

Fossil gnathostomes

first appeared 440 mya

early gnathostomes included armored vertebrates called placoderms (ex dunkleosteus)

gnathostome evolution

acanthodians radiated during Silurian and Devonian periods (444-359 mya)

placoderms extinct by 359 mya and acanthodians 70 milllion years later

Chondrichthyans, ray-finned fishes, and lobe finned fishes (3 surviving lineages of jawed vertebrates) evolved by 420 mya

chondrichthyans (sharks, rays, and chimeras)

skeleton composed primarily of cartilage - no bony skeleton

ray-finned fishes

include nearly all the familiar aquatic bony fish

originated 444-419 mya during the Silurian period

fins are supported by long, flexible rays covered by membrane - the fin is just membrane over rays, no blood supply

lobe finned fish

rod-shaped bones surrounded by a thick layer of muscle in pelvic and pectoral fins

Also originated in the Silurian Period

3 surviving lineages of lobe-finned fish

coelacanths, lungfishes, and tetrapods

Lungfishes

all living ones are found in southern hemisphere

gills are main organs for gas exchange, but can also use lungs

Tetrapods - characteristics

Surviving lineage of lobe-finned fish that adapted to life on land

four limbs and feet with digits; a neck allowing separate movement of the head; fusion of the pelvic girdle to the backbone; absence of gills (except some aquatic species); Ears for detecting airborne sounds

Origin of Tetrapods

Tiktaalik- thought to be intermediate step between fish and tetrapods

fish characteristics (fins, gills, lungs, scales) and tetrapod characteristics (ribs to breathe air, neck and shoulders, front fins with bone pattern of tetrapod limb)

First tetrapods appeared 365 mya and diversified rapidly over the following 60 million years

Amphibians - 3 clades

Salamanders (Urodela, “tailed ones”), Frogs (Anura, “tail-less ones”), caecilians (Apoda, “legless ones”)

~6,150 species

Amniotes- definition and derived characters

Tetrapods that have a terrestrially adapted egg - includes reptiles (birds too), and mammals

named for major derived character of the amniotic egg, which contains membranes that protect the embryo

Extraembryonic membranes of the amniotic egg

amnion, chorion, yolk sac, allantois

amnion enclosed embryo in a fluid filed sac that reduces dependence of tetrapods on an aqueous env for reproduction

Reptiles

Have scales that create a waterproof barrier; most lay shelled eggs on land; fertilization occurs internally, before eggshell is secreted

Are diapsids

Origin and evolutionary radiation of reptiles

earliest lived around 310 mya - resembled lizards, were diapsids like all living reptiles

Diapsids

Have a pair of holes on each side of the skull behind the eye sockets through which muscles pass to attach to the jaw

2 main lineages of diapsids

lepidosaurs (tuataras, lizards, snakes, extinct mososaurs)

archosaur (turtles, crocodilians, pterosaurs, and dinosaurs)

Birds - derived characters

Birds are archosaurs but almost every feature of reptilian anatomy has undergone modification in adaptation to flight

Major adaptation is wings with keratin feathers. Weight saving adaptations such as lack of urinary bladder, females with one ovary, small gonads, and loss of teeth to improve flight efficiency

Origin of birds

Likely descended from small theropods (group of carnivorous dinosaurs) about 160 mya

Feather evolved long before powered flight and were likely for insulation, camouflage, or courtship

Archaeopteryx - oldest bird known with feathered wings but retained ancestral characters of teeth, claws, long tail

Ratites

Group of birds that are all flightless

Mammals

Amniotes that have hair and produce milk

Are synapsids

Synapsids

Have a single hole behind eye socket on each side of the skull for attachment of jaw muscle

mammal-like synapsids emerged by end of Triassic (252-201 mya)

First true mammals arose during Jurassic (201-145 mya)

3 living lineages of mammals

Monotremes, marsupials, eutherians

Emerged 140 mya

Monotremes (5 species)

Small group of egg-laying mammals consisting of echidnas and the platypus

females lack nipples and secrete milk from glads on their bellies

Marsupials (324 species)

Embryo develops within mother’s uterus and is nourished by placenta - born very early in development and completes embryonic development while nursing in the marsupium (maternal pouch)

Eutherians (placental mammals) (5010 species)

Have a more complex placenta than marsupials, complete their embryonic development within a uterus, joined to mother by the placenta

Primates - 3 main groups

lemurs, lorises, and bush babies; tarsiers, anthropoids (monkeys and apes)