Comprehensive Study Guide on Animal Diversity, Vertebrate Evolution, and Neuromuscular Physiology

Choanocytes (Collar Cells)

Flagellated cells lining internal sponge chambers that generate water currents and capture food particles through endocytosis for intracellular digestion.

Diploblastic

Radially symmetrical, diploblastic, endoderm and ectoderm apart of Cnidarians and Ctenophores

Triploblastic

Developing from three embryonic germ layers: ectoderm, mesoderm, and endoderm, which is characteristic of all bilaterians.

Acoelomate

A solid triploblastic body plan lacking a fluid-filled cavity between the body wall and digestive tract, packed instead with mesodermal parenchyma (e.g., flatworms).

Pseudocoelomate

An organism possessing a persistent embryonic blastocoel cavity lined by mesoderm only along the outer body wall and not around the digestive tract (e.g., nematodes).

Coelomate (Eucoelomate)

An animal possessing a true body cavity completely enclosed by mesoderm, which lines both the outer body wall and the visceral surface of the digestive tract.

Protostome

A bilaterian developmental lineage characterized by spiral and determinate cleavage, schizocoelous coelom formation, and the blastopore developing into the mouth.

Deuterostome

A bilaterian developmental lineage characterized by radial and indeterminate cleavage, enterocoelous coelom formation, and the blastopore developing into the anus.

Lophophore

A horseshoe-shaped or circular fold of the body wall bearing ciliated tentacles that surrounds the mouth, used for filter feeding in bryozoans and brachiopods.

Trochophore

A free-swimming, pear-shaped marine larva with an apical tuft of sensory cilia and an equatorial band of locomotory cilia, found in mollusks and annelids.

Ecdysis

The periodic shedding or molting of the rigid, non-living cuticle or exoskeleton, allowing stepwise body growth in ecdysozoans.

Water-Vascular System

A hydraulic network of coelomic fluid-filled canals ending in tube feet, used by echinoderms for locomotion, food gathering, and gas exchange.

Notochord

A flexible, longitudinal rod made of engorged vacuolated cells situated dorsal to the digestive tract, providing skeletal axial support in chordates.

Amniotic Egg

A terrestrial-adapted egg enclosed in a shell and containing four extraembryonic membranes (amnion, yolk sac, allantois, and chorion) that prevent embryonic desiccation.

Sarcomere

The repeating functional contractile unit of striated muscle, delimited by transverse Z lines and composed of interdigitating actin and myosin myofilaments.

Sliding Filament Mechanism

The mechanical process of muscle contraction where thick myosin filaments pull thin actin filaments toward the sarcomere center, shortening the sarcomere without changing individual filament lengths.