protostomes

Protostome

Triploblastic animals with bilateral symmetry where the blastopore becomes the mouth; have an anterior brain and ventral nerve cords

Lophotrochozoan

Protostome clade that includes groups with a lophophore or trochophore larva and often spiral cleavage

Ecdysozoan

Protostome clade that molts a cuticle to grow (ecdysis)

Coelom

Fluid-filled body cavity fully lined by mesoderm; modified many times among protostomes

Pseudocoelom

Body cavity not fully lined by mesoderm; functions as a hydrostatic skeleton

Incomplete gut (blind gut)

Digestive cavity with one opening (mouth) for ingestion and egestion

Complete gut

Alimentary canal with separate mouth and anus for one‑way flow

Spiral cleavage

Embryonic cell division pattern common in many lophotrochozoans

Trochophore larva

Free‑swimming ciliated larva that helps capture plankton and disperse

Lophophore

Ciliated ring of hollow tentacles around the mouth used for feeding and gas exchange

Lophophorate

Group with a lophophore: bryozoans, entoprocts, brachiopods, phoronids

Bryozoan (Ectoproct)

Colonial lophophorate; anus outside tentacle ring; three‑part coelom; colonies form a secreted 'house'

Entoproct

Colonial filter‑feeder; anus inside tentacle ring; lacks a coelom

Brachiopod

Solitary marine animal with dorsal/ventral shells and a lophophore; many fossil species

Phoronid

Sessile tube‑dwelling worm with a U‑shaped gut and lophophore; secretes chitinous tube

Flatworm (Platyhelminth)

Dorsoventrally flattened; no specialized gas transport; many have blind gut; many are parasitic

Turbellarian

Mostly free‑living flatworms that glide on cilia; show cephalization

Monogenean

External parasitic flatworms of aquatic animals

Fluke (Trematode)

Parasitic flatworm; complex life cycles; some cause disease (e.g., schistosomiasis)

Tapeworm (Cestode)

Endoparasitic flatworm lacking its own digestive system; absorbs nutrients through body surface

Rotifer

Tiny pseudocoelomate with complete gut; ciliated corona drives feeding; mastax grinds food

Corona (rotifer)

Ciliated wheel‑like structure that draws food into the mouth

Mastax

Muscular pharyngeal organ that grinds ingested particles in rotifers

Bdelloid rotifer

All‑female lineage; eggs develop without fertilization; tolerates desiccation

Gastrotrich

Tiny ciliated ventral surface animals in water/soil; often simultaneous hermaphrodites

Ribbon worm (Nemertean)

Worm with rhynchocoel housing an eversible proboscis; can pierce prey with stylets

Annelid

Segmented worm; compartmentalized coelom and segmental ganglia; moist or aquatic habitats

Polychaete

Mostly marine annelids with many setae and paired parapodia for gas exchange/movement

Parapodia

Paired lateral outgrowths on polychaetes used for gas exchange and locomotion

Clitellate

Annelid group including oligochaetes and leeches; has clitellum for reproduction

Oligochaete (earthworm)

Terrestrial/freshwater annelid; few setae; hermaphroditic; burrows and ingests soil

Leech

Ectoparasitic or predatory annelid lacking parapodia; has anterior/posterior suckers; secretes anticoagulant

Pogonophoran (Siboglinid)

Tube‑dwelling annelid lacking a gut; harbors chemoautotrophic endosymbionts in a trophosome

Trophosome

Specialized organ in pogonophorans housing bacteria that oxidize H2S to fix carbon

Mollusk

Invertebrate with foot, visceral mass, and mantle that secretes shell; mantle cavity houses gills

Mantle

Sheet of tissue covering the visceral mass; secretes shell and forms the mantle cavity

Foot (mollusk)

Muscular structure for locomotion or manipulation; modified in many groups

Open circulatory system

Fluid (hemolymph) bathes organs in hemocoel; typical of most mollusks (not cephalopods)

Monoplacophoran

Primitive mollusks with repeated organs along body; few living species

Chiton

Mollusk with 8 overlapping plates and a girdle; scrapes algae with radula; clings to rocks

Girdle (chiton)

Tough mantle margin surrounding chiton plates for protection and adhesion

Radula

Toothed ribbon in many mollusks used to scrape or cut food

Gastropod

Snails/slugs/nudibranchs; foot for gliding; many have torsion; land forms use a lung‑like mantle

Bivalve

Clams/mussels/oysters; two hinged shells; filter‑feed using large gills and siphons

Cephalopod

Squids/octopuses/nautiluses; jet propulsion via mantle cavity; complex eyes; arms/tentacles capture prey

Nautilus

Cephalopod with external chambered shell used for buoyancy control

Pen (gladius)

Internal support in many cephalopods; octopuses lack a shell entirely

Cuticle (ecdysozoan)

External nonliving layer secreted by epidermis; must be molted for growth

Ecdysis

Molting process where the old cuticle is shed and a new one expands and hardens

Priapulid

Unsegmented marine burrower with an eversible, toothed pharynx

Kinorhynch

Microscopic segmented ecdysozoan with molted cuticular plates; feeds via retractable proboscis

Loriciferan

Minute marine ecdysozoan encased in a protective 'lorica' of six plates

Nematode (roundworm)

Unsegmented ecdysozoan with thick multilayered cuticle; complete gut; moves by longitudinal muscles

C. elegans

Model nematode used in genetics/development; short life cycle and fixed cell number

Nematode diseases

Parasitic species cause trichinosis, filariasis, and elephantiasis in humans

Horsehair worm

Very thin ecdysozoan; larvae are insect/crayfish parasites; adults may lack a functional mouth

Arthropod

Ecdysozoans with jointed appendages and chitinous exoskeleton; most diverse animal group

Exoskeleton (arthropod)

Protein‑ and chitin‑reinforced covering that supports, protects, and reduces water loss

Segmented appendage

Jointed limb segments with muscles attached to inner exoskeleton enabling precise movement

Tardigrade (water bear)

Microscopic animal with unjointed legs; survives desiccation via dormant state (cryptobiosis)

Onychophoran (velvet worm)

Tropical leaf‑litter predator with unjointed legs and flexible chitinous cuticle

Trilobite

Extinct Paleozoic arthropods; first to show jointed legs with specialized appendages

Chelicerate

Arthropods with chelicerae mouthparts and two body regions: cephalothorax and abdomen

Sea spider (pycnogonid)

Marine chelicerate; long legs; feeds on small invertebrates

Horseshoe crab

Marine chelicerate with ancient body plan; spawns on beaches; scavenger/predator

Arachnid

Chelicerates including spiders/scorpions/mites/ticks; mostly terrestrial

Spider

Predatory arachnid; hollow chelicerae inject venom; many spin silk webs from abdominal glands

Mite/Tick

Small arachnids; many are ectoparasites and disease vectors

Mandibulate

Arthropods with mandibles and antennae; includes myriapods, crustaceans, hexapods

Centipede

Predatory myriapod with one leg pair per segment

Millipede

Detritivorous myriapod with two leg pairs per apparent segment

Crustacean

Mostly aquatic mandibulates with head, thorax, abdomen and diverse specialized appendages

Decapod

Crustaceans like shrimp, lobsters, crabs with five pairs of walking legs

Isopod

Crustaceans including sow bugs; dorsoventrally flattened body

Copepod

Abundant small crustaceans important in marine food webs

Barnacle

Sessile crustacean with calcareous plates; filter‑feeds with cirri

Carapace

Expanded exoskeleton fold covering head/thorax in many crustaceans

Hexapod

Arthropods with six legs; includes insects and close wingless relatives

Insect body plan

Head with antennae; thorax with three leg pairs and usually two wing pairs; abdomen without appendages

Tracheae (insect)

Tubular airways from spiracles delivering oxygen directly to tissues

Pterygote

Winged insects (or secondarily wingless lineages descended from winged ancestors)

Halteres

Reduced hindwings in true flies used as gyroscopic stabilizers

Incomplete metamorphosis

Gradual change from nymph to adult (e.g., grasshoppers, true bugs)

Complete metamorphosis

Distinct larva–pupa–adult stages (e.g., beetles, flies, butterflies, wasps)

Neopteran

Most winged insects that can fold wings over the abdomen

Odonate/Mayfly condition

Early winged lineages that cannot fold wings; aquatic larvae

Insect diversification

Major radiation tied to land plants; flight opened pollination and new niches

Protostome vs Deuterostome

Protostomes form the mouth from the blastopore and often show spiral cleavage; deuterostomes form the anus first

Adaptations to land (arthropods)

Exoskeleton prevents desiccation; jointed legs enable movement; tracheae/book lungs enable gas exchange

Coelom types

Coelomates have a true coelom; pseudocoelomates have a partially lined cavity; acoelomates lack a cavity

Feeding modes (protostomes)

Filter feeding (bryozoans/bivalves), scraping with radula (mollusks), absorption across body surface (parasitic flatworms)

Reproduction strategies

External fertilization in many lophophorates; complex parasitic life cycles in flatworms; hermaphroditism in earthworms

Brachiopods vs Bivalves

Brachiopods have dorsal/ventral shells and lophophore; bivalves have left/right valves and gill filter‑feeding

Flatworms vs Nematodes

Flatworms lack a molted cuticle and often have blind guts; nematodes molt a thick cuticle and have a complete gut

Protostome diversity drivers

Segmentation, complex life cycles, parasitism, diverse feeding structures, hard coverings, locomotion