Chapter 33 Protostome(Invertebrates)

Bio 202

Protostomes

Most diverse and abundant group of animals; blastopore becomes the mouth

Why study protostomes

They include 22 phyla and show extreme body plan diversity

Urbilaterian

Common ancestor of all bilaterally symmetric animals

When did Urbilaterian evolve

~500 million years ago during the Cambrian Explosion

Cambrian Explosion

Rapid diversification of animal body plans

Diploblastic animals

Animals with ectoderm and endoderm only

Triploblastic animals

Animals with ectoderm, mesoderm, and endoderm

Mesoderm significance

Allows for muscles, organs, and complex body plans

Bilateral symmetry

Left and right sides mirror each other

Coelom

Fluid-filled body cavity completely lined with mesoderm

Synapomorphy

A shared derived trait used to define a group

Protostome blastopore fate

Develops into the mouth

Deuterostome blastopore fate

Develops into the anus

Protostome cleavage

Spiral cleavage

Deuterostome cleavage

Radial cleavage

Protostome nerve cord

Ventral

Deuterostome nerve cord

Dorsal

Protostome body plan traits

Bilateral, triploblastic, coelomate, ventral nerve cord

Monophyletic group

Group that evolved from a single common ancestor

Two protostome superphyla

Lophotrochozoa and Ecdysozoa

Lophotrochozoa

Protostomes with lophophores or trochophore larvae

Ecdysozoa

Protostomes that grow by molting (ecdysis)

Ecdysis

Shedding of the cuticle during growth

Trochophore larva

Free-swimming larval stage in some protostomes

Lophophore

Ring of feeding tentacles

Wormlike protostomes

Have tube-within-a-tube body plan

Hydrostatic skeleton

Coelom provides support for movement

Phylum Annelida

Segmented worms

Annelid traits

Segmentation, coelom, parapodia, chaetae

Chaetae

Bristles used for movement

Phylum Mollusca

Soft-bodied animals with a mantle

Mollusk body plan

Foot, visceral mass, mantle

Mantle

Tissue that secretes the shell

Foot (mollusks)

Used for movement or attachment

Four mollusk classes

Chitons, Bivalves, Gastropods, Cephalopods

Bivalves

Two shells; suspension feeders

Gastropods

Snails and slugs

Cephalopods

Squid, octopus, cuttlefish

Cephalopod adaptations

Tentacles, advanced eyes, jet propulsion

Phylum Nematoda

Roundworms

Nematode traits

Pseudocoelom, cuticle, molting, no appendages

Pseudocoelom

Body cavity not fully lined with mesoderm

Nematode parasite example

Wuchereria bancrofti (elephantiasis)

Phylum Arthropoda

Animals with jointed appendages and exoskeleton

Arthropod exoskeleton

Made of chitin

Chitin

Structural polysaccharide

Hemocoel

Open circulatory cavity replacing the coelom

Tagmata

pecialized body regions

Three arthropod tagmata

Head, thorax, abdomen

Chelicerata

Arthropods with chelicerae and no antennae

Chelicerae

Feeding appendages in chelicerates

Arachnids

Spiders, scorpions, ticks

Myriapoda

Arthropods with many body segments

Crustaceans

Arthropods with two pairs of antennae

Insects (Hexapoda)

Arthropods with three tagmata and six legs

Insect metamorphosis

Change in body form during development