Animal Biology: Protostomes, Flatworms, Arthropods, Mollusks, and More

protostomes

Animals with 3 germ layers (triploblastic) and bilateral symmetry; blastopore becomes the mouth

Triploblastic

Organisms with three embryonic layers: ectoderm, mesoderm, endoderm

Bilateral symmetry

Body can be split into equal left and right halves

Blastopore

First opening in embryo; becomes mouth in protostomes

Protostome brain

Anterior brain that surrounds entrance to digestive tract

Ventral nervous system

Nerve system located on underside (belly side)

Longitudinal nerve cords

Paired or fused nerve cords running length of body

Protostome diversity

Protostomes make up more than half of all animal species

Ecdysozoans

Protostomes that grow by molting a cuticle

Cuticle

Outer protective layer made by epidermis

Ecdysis

Process of shedding old cuticle to grow

Arthropods

Ecdysozoans with jointed appendages and exoskeleton; most diverse animals

Arthropod species number

Over 1.2 million described species

Exoskeleton

Hard external skeleton made of chitin and proteins

Chitin

Waterproof polysaccharide in arthropod exoskeleton

Exoskeleton limitation

Restricts movement and gas exchange

Arthropod appendages

Used for walking, feeding, gas exchange, mating, sensing

Segment specialization

Each segment has muscles controlling its own parts

Land adaptation

Exoskeleton prevents drying out

Bryozoans

Aquatic animals with tentacles; anus outside tentacle ring; 3-part coelom

Bryozoan feeding

Food moves tip to base of tentacles

Entoprocts

Animals with anus inside tentacle ring; no coelom

Entoproct feeding

Food moves base to tip of tentacles

Flatworms

Flat-bodied animals so all cells are close to surface

Flatworm gas exchange

Happens through skin (no respiratory system)

Flatworm digestive system

Mouth leads to blind gut (no exit)

Blind gut

Digestive system with one opening only

Free

living flatworms - Use cilia to glide and have head region (cephalization)

Cilia

Tiny hair-like structures used for movement

Parasitic flatworms

Tapeworms and flukes that live inside hosts

Tapeworms

Absorb nutrients from host; no digestive system

Flukes

Parasitic flatworms in animals

Schistosomiasis

Disease involving flatworms and snail + mammal hosts

Monogeneans

Flatworm parasites of fish

Turbellarians

Free-living flatworms

Rotifers

Tiny freshwater animals (50-500 µm)

Pseudocoel

Body cavity acting as hydrostatic skeleton

Hydrostatic skeleton

Fluid-filled support system

Corona

Ciliated structure that brings food into mouth

Mastax

Jaw-like grinding organ; can also capture prey

Ribbon worms

Long worms (some up to 20 meters)

Rhynchocoel

Cavity containing proboscis

Proboscis

Explosive feeding tube used to capture prey

Stylets

Sharp hooks used to pierce prey

Toxins

Injected into prey to immobilize it

Phoronids

Small marine worms living in chitin tubes

Lophophore

Ciliated feeding tentacle structure

U

shaped gut - Digestive tract shaped like a U

Phoronid reproduction

Eggs released or fertilized depending on species

Mollusks

Animals with foot, visceral mass, and mantle

Foot

Muscular structure for movement or support

Visceral mass

Contains organs (heart, digestion, reproduction)

Mantle

Tissue that secretes shell and covers organs

Calcareous shell

Calcium-based protective shell

Mantle cavity

Space containing gills for gas exchange

Gills

Organs for breathing; moved by cilia

Open circulatory system

Blood flows into body cavity (hemocoel)

Hemocoel

Body cavity where blood flows freely

Monoplacophorans

Mollusks with repeated organs along body

Gastropods

Snails, slugs, limpets, nudibranchs

Gastropod movement

Glide using muscular foot

Nudibranchs

Sea slugs with no shell

Slugs

Shell-less gastropods

Aposematic coloration

Bright colors warning predators of toxicity

Camouflage

Blending into environment

Bivalves

Clams, oysters, mussels, scallops

Bivalve shells

Two hinged shells

Filter feeding

Feeding by filtering particles from water

Incurrent siphon

Brings water in

Excurrent siphon

Pushes water out

Cephalopods

Squids, octopus, nautilus

Jet propulsion

Movement by forcing water out of body

Cephalopod brain

Highly advanced nervous system

Cephalopod eyes

Similar to vertebrate eyes

Arms/tentacles

Used for movement and prey capture

Nautilus shell

Chambered shell used for buoyancy

Octopus shell loss

No shell allows squeezing through tight spaces

Nematodes

Roundworms with unsegmented bodies

Nematode cuticle

Thick protective layer that is molted

Nematode gas exchange

Through body wall diffusion

Pharynx

Muscular tube that moves food through gut

C. elegans

Model organism used in genetics research

C. elegans traits

Fast life cycle, fixed cell number, genome known

Nematode distribution

Found everywhere in soil, water, organisms

Nematode role

Scavengers, predators, parasites

Nematode diseases

Trichinosis, filariasis, elephantiasis

Arthropods

Animals with jointed appendages and segmented bodies

Chelicerates

Spiders, scorpions, ticks, horseshoe crabs

Chelicerae

Mouth appendages used for feeding

Arachnids

Spiders, scorpions, mites, ticks

Spiders

Predators that inject venom

Silk production

Made from abdominal glands forming webs

Mandibulates

Arthropods with mandibles (jaws)

Mandibles

Used for chewing, biting, holding food

Antennae

Sensory structures on head

Myriapods

Centipedes and millipedes

Centipedes

One pair legs per segment; predators

Millipedes

Two pairs legs per segment; decomposers

Crustaceans

Shrimp, crabs, lobsters, barnacles

Crustacean diversity

Mostly marine but also freshwater and land