Invertebrate Diversity: Porifera, Cnidaria & Platyhelminthes

Vocabulary flashcards covering essential terms and definitions from the lecture on sponges (Porifera), cnidarians, and flatworms (Platyhelminthes).

Phylum Porifera

Aquatic phylum of about 5,500 sponge species that are filter-feeding animals lacking true tissues.

Ostia

Small incurrent pores through which water enters a sponge’s body.

Spongocoel

Central cavity inside a sponge where water collects and food particles are trapped.

Osculum

Large excurrent opening at the top of a sponge through which water exits.

Filter-feeder (suspension feeder)

Organism that draws water through its body and extracts suspended food particles.

Sessile

Fixed in place; attached to a substrate and non-motile as an adult.

Gastrula stage

Embryonic phase that forms germ layers; absent in sponges, so they never develop true tissues.

Cell specialization (Sponges)

Organization level where distinct cell types perform unique functions without forming tissues.

Pinacocyte

Flat outer surface cell covering a sponge’s body.

Porocyte

Tubular sponge cell that surrounds an ostium and can contract to regulate water flow.

Choanocyte (collar cell)

Flagellated cell lining the spongocoel; traps food with a mucus-covered collar and drives water currents.

Mesohyl

Gelatinous, collagen-rich matrix between a sponge’s cell layers through which amoebocytes crawl.

Amoebocyte

Mobile sponge cell that digests food, distributes nutrients, and secretes skeletal spicules or spongin.

Spicule

Rigid skeletal element of calcium carbonate or silica produced by sponge amoebocytes.

Spongin

Flexible protein fibers that form the supportive skeleton in many sponges.

Fragmentation (sponges)

Asexual reproduction in which a detached piece grows into a new, genetically identical sponge.

Gemmule

Internal, resistant bud of cells produced by sponges during harsh conditions for asexual reproduction.

Hermaphrodite (sponges)

Individual containing both sperm-producing and egg-producing cells.

Amphiblastula larva

Motile, flagellated larval stage released by sponges before settlement.

Phylum Cnidaria

Aquatic phylum of about 10,000 radially symmetrical animals such as hydra, jellies, corals, and anemones.

Diploblastic

Having two embryonic germ layers—ectoderm and endoderm; characteristic of cnidarians.

Epidermis (Cnidaria)

Outer tissue layer derived from ectoderm that covers the cnidarian body.

Gastrodermis

Inner tissue layer lining the gastrovascular cavity in cnidarians; secretes digestive enzymes.

Nerve net

Diffuse network of interconnected nerve cells that coordinates movement in cnidarians.

Mesoglea

Thick, gelatinous, collagen-containing layer between epidermis and gastrodermis in cnidarians.

Incomplete digestive tract

Digestive system with a single opening that functions as both mouth and anus.

Cnidocyte

Specialized stinging cell on cnidarian tentacles housing a nematocyst.

Nematocyst

Coiled, harpoon-like stinging organelle inside a cnidocyte that injects neurotoxin into prey.

Polyp

Sessile cnidarian body form with upward-facing mouth and tentacles.

Medusa

Motile, bell-shaped cnidarian body form with downward-facing mouth and tentacles.

Class Hydrozoa

Cnidarian class whose dominant adult form is a polyp; juveniles are medusae; includes hydra and Portuguese man-o-war.

Class Scyphozoa

Cnidarian class with adult spherical medusae; juveniles are polyps; includes true sea jellies.

Class Cubozoa

Cnidarian class with box-shaped medusae; juveniles are polyps; includes box jellies.

Class Anthozoa

Cnidarian class existing only as polyps throughout life; includes corals, sea fans, and sea anemones.

Planula larva

Free-swimming, ciliated cnidarian larval stage that settles to form a new polyp.

Budding (cnidarians)

Asexual reproduction in which a new polyp forms as an outgrowth of the parent.

Phylum Platyhelminthes

Bilateral phylum of about 20,000 flatworm species including planaria, flukes, and tapeworms.

Cephalization

Evolutionary trend toward concentration of sensory and nerve structures at the anterior end.

Triploblastic

Having three germ layers—ectoderm, mesoderm, and endoderm; feature of flatworms and more complex animals.

Acoelomate

Animal lacking a body cavity between gut and body wall; flatworms are acoelomates.

Longitudinal muscles

Muscle fibers running from head to tail in flatworms, enabling motion; absence of circular muscles keeps body flat.

Ganglia

Clusters of nerve cells in the head of flatworms acting as a primitive brain.

Protonephridia

Excretory system of branching tubules ending in flame bulb cells that remove waste in flatworms.

Flame bulb cell

Ciliated cell in protonephridia that propels fluid through excretory tubules of flatworms.

Class Turbellaria

Free-living, ciliated flatworm class that includes planaria.

Ocellus (ocelli)

Light-sensitive eyespot on turbellarians that detects presence or absence of light.

Class Trematoda

Parasitic flatworm class known as flukes; possess two suckers and a protective cuticle.

True host

Host harmed by a parasite and in which sexual reproduction occurs; e.g., humans in blood fluke life cycle.

Intermediate host

Secondary host, often unharmed, where a parasite asexually reproduces or matures; commonly snails for flukes.

Class Cestoda

Parasitic flatworm class comprising tapeworms.

Scolex

Anterior attachment organ of a tapeworm equipped with hooks and/or suckers; not a head.

Proglottid

Repeating, self-contained reproductive segment of a tapeworm containing both male and female organs.

Cuticle (parasitic flatworms)

Protective outer covering that shields flukes and tapeworms from host digestive enzymes and acids.

Hooks (tapeworm)

Attachment structures on a scolex that anchor a tapeworm to the host’s intestinal wall.

Suckers (tapeworm/fluke)

Muscular adhesive organs that enable parasitic flatworms to cling to host tissues.

Regeneration (tapeworm)

Ability of a tapeworm to regrow lost proglottids.

High egg output

Parasitic adaptation where producing vast numbers of eggs increases chances that some offspring reach adulthood.