General Zoology BIO 251 – Vocabulary Review (Lectures 6/24 – 7/6 2025)

A comprehensive set of vocabulary flashcards covering key zoological terms, taxa, anatomical structures, life-cycle stages, and physiological concepts discussed in Dr. Nesreen Aljahdali’s General Zoology (BIO 251) lectures from 6/24 to 7/6 2025.

Subkingdom Metazoa

All multicellular animals, distinguished from single-celled Protozoa.

Diploblastic animals

Organisms whose bodies develop from two germ layers—ectoderm and endoderm.

Triploblastic animals

Animals with three embryonic germ layers: ectoderm, mesoderm, and endoderm.

Ectoderm

The outermost germ layer forming epidermis, nerves and related structures.

Endoderm

Innermost germ layer giving rise to the gut lining and associated organs.

Mesoderm

Middle germ layer that forms muscles, connective tissues, and many organs.

Acoelomate

Triploblastic animal lacking a body cavity; solid mesoderm fills space between gut and body wall.

Coelomate

Triploblastic animal with a true mesoderm-lined body cavity (coelom).

Peritoneum

Mesodermal membrane lining the coelom and covering visceral organs.

Nephridium

Excretory tubule opening to the exterior, characteristic of many coelomates.

Coelenteron (gastrovascular cavity)

Single internal cavity in Cnidaria that functions in digestion and circulation.

Phylum Coelenterata (Cnidaria)

Diploblastic, radially symmetrical animals such as jellyfish, hydra, and corals.

Radial symmetry

Body plan arranged around a central axis, typical of Cnidaria and echinoderms.

Class Hydrozoa

Cnidarian class containing Hydra, Obelia, and related forms with polyp and/or medusa stages.

Class Scyphozoa

True jellyfish; dominant medusa form exemplified by Aurelia (moon jelly).

Class Anthozoa

Cnidarians lacking a medusa stage; includes sea anemones and corals.

Hydra

Freshwater hydrozoan polyp that reproduces by budding and possesses stinging tentacles.

Obelia

Marine colonial hydrozoan with alternating hydroid (polyp) and medusa stages.

Sea anemone (Actinea)

Solitary anthozoan polyp lacking a skeleton; possesses tentacles and siphonoglyphs.

Polyp

Sessile, cylindrical cnidarian body form with mouth and tentacles facing upward.

Medusa

Free-swimming, umbrella-shaped cnidarian stage with downward-facing mouth.

Tentacle

Flexible appendage surrounding the mouth, bearing nematocysts for capture and defense.

Basal disc

Adhesive structure at hydra’s base allowing attachment to substrates.

Nematoblast (nematocyte)

Specialized cnidarian cell containing a stinging capsule (nematocyst).

Interstitial cell

Undifferentiated cell in Hydra capable of regenerating various cell types.

Mesoglea

Jelly-like, largely acellular layer between ectoderm and endoderm in cnidarians.

Nutritive-muscle cell

Endodermal cell in Hydra combining digestive and contractile functions.

Glandular cell (Hydra)

Endodermal cell that releases digestive enzymes into the gastrovascular cavity.

Sensory cell

Receptor cell linked to nerve net, allowing cnidarians to detect stimuli.

Holozoic nutrition

Ingestion of solid food particles followed by internal digestion; seen in Hydra.

Somersaulting (Hydra)

Locomotory behavior where hydra flips end-over-end using tentacles and basal disc.

Budding

Asexual reproduction by outgrowth of a new individual from the parent’s body.

Planula larva

Ciliated, free-swimming cnidarian larva that settles to form a new polyp.

Hydrorhiza

Root-like horizontal stolon anchoring an Obelia colony to the substrate.

Hydrocaulus

Vertical branching stem of an Obelia colony carrying polyps and gonangia.

Perisarc

Chitinous protective covering secreted by hydrozoan ectoderm around colony stalks.

Blastostyle

Hollow branch in Obelia that buds off medusae within the gonotheca.

Gonotheca

Protective cup around blastostyle and medusa buds in Obelia colonies.

Medusa bud

Immature medusa developing asexually on hydrozoan blastostyles.

Morula

Solid ball of cells produced by early cleavage of a zygote.

Blastula

Hollow sphere of cells (blastoderm) surrounding a fluid-filled blastocoel.

Aurelia (moon jelly)

Common scyphozoan jellyfish characterized by four horseshoe-shaped gonads.

Nematocyst

Eversible stinging organelle housed in cnidarian nematocytes.

Velarium

Shelf-like membrane at margin of some scyphozoan bells aiding propulsion.

Scyphistoma

Polyp stage in scyphozoan life cycle that undergoes strobilation.

Strobilation

Transverse fission of a scyphistoma producing stacked ephyrae.

Ephyra

Juvenile medusa released from a strobilating scyphistoma.

Hydra-tuba

Initial scyphozoan polyp (scyphistoma) formed from settled planula.

Order Alcyonaria (Octocorallia)

Anthozoan order whose polyps bear eight pinnate tentacles and mesenteries (e.g., Alcyonium).

Order Zoantharia (Hexacorallia)

Anthozoan order with polyps having multiples of six tentacles and mesenteries.

Alcyonium

Soft coral forming large colonies; each polyp has eight tentacles.

Mesentery (Anthozoa)

Internal sheet of tissue partitioning the gastrovascular cavity and bearing gonads or muscles.

Stomodaeum

Ectoderm-lined tubular pharynx connecting mouth to gastric cavity in anthozoans.

Siphonoglyph

Ciliated groove(s) at sea-anemone mouth that generate internal water currents.

Phylum Platyhelminthes

Acoelomate, dorsoventrally flattened worms including planarians, flukes, tapeworms.

Class Turbellaria

Mostly free-living flatworms such as planaria; body ciliated and leaf-like.

Class Trematoda

Parasitic flukes with suckers and incomplete digestive tract (e.g., Fasciola).

Class Cestoda

Endoparasitic tapeworms lacking digestive tract, composed of scolex and proglottids.

Planaria

Freshwater turbellarian noted for regeneration and ladder-type nervous system.

Rhabdites

Rod-like secretory bodies in planarian epidermis that produce protective mucus.

Parenchyma (platyhelminthes)

Loose mesodermal tissue filling space between organs in flatworms.

Flame cell

Ciliated excretory cell driving fluid through protonephridial tubules of flatworms.

Fasciola gigantica

Large liver fluke infecting sheep and cattle; has oral and ventral suckers.

Oral sucker

Anterior attachment organ surrounding the mouth of a trematode fluke.

Ventral sucker

Secondary attachment organ on ventral surface of trematode body.

Miracidium

Ciliated larval stage of trematodes that infects a snail host.

Cercaria

Fork-tailed larval stage that leaves snail and encysts or infects second host.

Metacercaria

Encysted, infective stage of trematodes on vegetation or in second host tissues.

Lymnaea

Freshwater snail genus serving as intermediate host for Fasciola species.

Hexacanth embryo (oncosphere)

Six-hooked tapeworm larva developing within the egg before hatching.

Cysticercus

Bladder-worm larval stage of Taenia species encysted in host muscle.

Taenia saginata

Beef tapeworm of humans; scolex has four suckers but no hooks.

Scolex

Anterior head of a tapeworm bearing suckers and/or hooks for attachment.

Proglottid

Individual reproductive segment of a tapeworm strobila.

Gravid proglottid

Mature tapeworm segment packed with fertilized eggs.

Ootype

Region in tapeworm female system where yolk and egg are assembled and shelled.

Vitelline gland

Yolk-producing gland associated with flatworm and tapeworm reproduction.

Bursa copulatrix

Copulatory pouch at male posterior end in some nematodes (Order Strongylata).

Copulatory spicules

Hard needle-like structures aiding sperm transfer in male nematodes.

Phylum Nematoda (Nemathelminthes)

Roundworms with cylindrical bodies, pseudocoel, complete digestive tract, and cuticle.

Ascaris lumbricoides

Large intestinal nematode parasite of humans.

Pseudocoel (perivisceral cavity)

Fluid-filled body cavity not lined by peritoneum, characteristic of nematodes.

Cuticle (nematode)

Tough, elastic, non-cellular outer layer secreted by underlying epidermis.

Pharynx (nematode)

Muscular pumping organ immediately behind the mouth that draws in food.

Lung migration (Ascaris)

Phase where larvae travel via bloodstream to lungs before re-entering gut.

Phylum Annelida

Segmented, coelomate worms including earthworms, leeches, and polychaetes.

Metamerism (segmentation)

Serial repetition of body segments and organ systems in annelids.

Chaetae (setae)

Chitinous bristles projecting from annelid body wall for locomotion or anchorage.

Clitellum

Glandular saddle on oligochaetes and leeches that secretes cocoon during reproduction.

Metanephridium

Segmentally arranged excretory organ opening into coelom and to exterior in annelids.

Pseudoheart (earthworm)

Contractile lateral vessel connecting dorsal and ventral blood vessels for circulation.

Allolobophora (earthworm)

Common European earthworm genus used to illustrate oligochaete anatomy.

Parapodium

Paired, fleshy lateral appendage on polychaete segments bearing chaetae.

Notopodium

Dorsal lobe of a polychaete parapodium.

Neuropodium

Ventral lobe of a polychaete parapodium.

Aciculum

Stiff supportive chaeta embedded within each lobe of polychaete parapodia.

Nereis

Free-living polychaete sandworm with well-developed parapodia and sensory structures.

Prostomium

Anterior, pre-oral lobe of polychaete head bearing eyes and tentacles.

Peristomium

First true segment of a polychaete surrounding the mouth.

Class Hirudinea

Leeches; annelids with fixed segment number, two suckers, and no chaetae.