BIO 211: Coelomate Invertebrates

Comprehensive vocabulary flashcards covering the morphology, development, organ systems, and diagnostic features of coelomate invertebrates (Annelida, Mollusca, Arthropoda, and Echinodermata) from BIO 211.

Coelom

A secondary fluid-filled body cavity that forms in the mesoderm, completely lined by a mesodermal epithelium known as the peritoneum.

Pseudocoel

A persistent blastocoel-derived body cavity situated between the mesodermal body wall musculature and the endodermal gut wall that completely lacks a peritoneal lining.

Acoelomate

A triploblastic body organization lacking an internal fluid-filled body cavity between the gut and the body wall, with the intervening space filled with solid parenchyma or mesenchyme.

Schizocoel

A coelomic cavity produced during embryonic development by the splitting of the mesodermal bands, characteristic of protostomes including annelids, molluscs, and arthropods.

Enterocoel

A coelomic cavity formed by the outpouching or out-pocketing of the mesodermal layer from the embryonic archenteron, typical of echinoderms, hemichordates, and chordates.

Protostome

A major evolutionary line of coelomates characterized by spiral and determinate (mosaic) cleavage, schizocoelous coelom formation, and the blastopore developing directly into the mouth.

Deuterostome

A major evolutionary line of coelomates characterized by radial and indeterminate (regulative) cleavage, enterocoelous coelom formation, and the blastopore developing into the anus.

Metamerism

The repetition of homologous body segments arranged linearly along the anteroposterior axis, each containing subdivisions of major organ systems such as nerves, muscles, and excretory organs.

Tagmatization

The evolutionary grouping and specialized functional differentiation of adjacent metameric segments into distinct morphological body units known as tagmata.

Prostomium

The pre-segmental anterior lobe of an annelid that contains a nervous ganglion, positioned dorsal and anterior to the mouth.

Peristomium

The first true body segment of an annelid that immediately surrounds the ventral mouth.

Chaetae

Chitinous, bristle-like epidermal structures embedded in individual chaetal sacs and manipulated by protractor and retractor muscles to provide purchase during locomotion.

Clitellum

A conspicuous glandular thickening of the epidermis covering segments $32$ to $36$ or $37$ in sexually mature earthworms that secretes mucus during copulation and forms the cocoon wall.

Calciferous Glands

Paired lateral evaginations of the oesophageal wall in segments $11$ and $12$ of earthworms that convert excess dietary calcium and carbonates into calcite crystals to maintain hemolymph pH.

Typhlosole

A prominent dorsal longitudinal ridge projecting into the intestinal lumen of earthworms to increase the surface area available for digestive enzyme secretion and nutrient absorption.

Chloragogenous Cells

Modified peritoneal cells forming a deep yellow layer around the intestine and major blood vessels in annelids, functioning in food storage, glycogen synthesis, fat synthesis, and nitrogenous excretion.

Metanephridium

A tubular annelid excretory organ spanning two segments; begins with a ciliated funnel (nephrostome) that collects coelomic fluid from the anterior segment and opens ventrolaterally via a nephridiopore.

Hirudin

A potent peptide anticoagulant secreted by leeches into wounds or stored within the crop to prevent host blood from clotting during ingestion and storage.

Epitoky

A reproductive phenomenon in polychaetes involving the morphological transformation and maturation of a benthic non-reproductive worm into a specialized, pelagic swimming form.

Cocoon

A protective, hardened ring of clitellar secretion into which mature eggs and stored partner sperm are deposited, serving as the site of external fertilization and embryo incubation in oligochaetes.

Radula

A chitinous, toothed ribbon supported on an odontophore cartilage in the buccal cavity of molluscs, deployed in a rasping motion to tear or scrape food substrates.

Torsion

An embryonic developmental process in gastropods characterized by a $180^\circ$ counterclockwise twisting of the visceral mass on the foot, rotating the mantle cavity, gills, and anus anteriorly above the head.

Pneumostome

The small, contractile external aperture located on the right side of the body in pulmonate gastropods that admits air into the vascularized mantle cavity (lung).

Osphradium

A specialized molluscan chemoreceptor located near the base of the ctenidia or within the mantle cavity that tests chemical qualities and sediment levels of inhalant water currents.

Glochidium

A specialized bivalve larval stage found in certain freshwater families that temporarily lives as an ectoparasite attached to the gills or skin of fish before dropping off as a juvenile.

Haemocoel

A large secondary internal body cavity composed of expanded blood sinuses derived from the blastocoel, bathing internal organs directly in circulatory fluid.

Apodemes

Internal, shelf-like or spine-like invaginations of the sclerotized arthropod cuticular exoskeleton that serve as rigid anchor points for muscle attachment.

Green Glands

Paired antennary osmoregulatory organs situated at the base of the second antennae in freshwater decapods like Astacus, consisting of an end sac, labyrinth, tubule, and bladder.

Ommatidium

One of the approximately $2,500$ independent photoreceptor units composing the compound eye of crustaceans and insects, containing an external cuticular lens and light-sensitive receptor cells.

Nauplius

The primary free-swimming planktonic larval form characteristic of crustaceans, possessing an unsegmented trunk, a single median eye, and three pairs of appendages (antennules, antennae, and mandibles).

Malpighian Tubules

Slender, blind-ending excretory tubules arising from the junction of the midgut and hindgut in insects and myriapods that extract nitrogenous wastes from hemolymph and deposit uric acid crystals into the digestive tract.

Spiracles

Paired lateral apertures on the thorax and abdomen of insects that lead directly into the cuticular tracheal gas-exchange network.

Water Vascular System

A unique coelomic hydraulic circulatory system in echinoderms consisting of an internal network of canals and pressurized, muscular tube feet (podia) that drives locomotion, food capture, and gas exchange.

Madreporite

A perforated, calcareous sieve plate on the aboral surface of an echinoderm that admits seawater into the stone canal of the water vascular system to balance fluid pressures.

Pedicellariae

Microscopic, jawed, pincer-like calcareous structures on the body surfaces of asteroids and echinoids that function to remove debris and prevent settling organisms from fouling the body wall.