Overview of Mollusca and Annelida Phyla

Mollusca

Second largest animal phylum with diverse species.

Marine Species

Approximately 25% of all marine species.

Soft Bodies

Characteristic feature of mollusks, lacking hard skeleton.

Muscular Foot

Main locomotive structure, can retract and expand.

Visceral Mass

Contains most organs, covered by mantle.

Mantle

Tissue fold producing shell, enclosing gills.

Bivalvia

Class of mollusks with two-part shells.

Umbo

Oldest part of bivalve shell, hinge point.

Gastropoda

Class including snails and slugs, asymmetrical bodies.

Torsion

Embryonic twisting of body in gastropods.

Cephalopoda

Class of mollusks with arms and tentacles.

Chromatophores

Pigment cells for rapid color change in cephalopods.

Closed Circulatory System

Blood circulates within vessels, found in cephalopods.

Annelida

Phylum of segmented worms with true metamerism.

Polychaete

Marine annelids with multiple appendages.

Oligochaete

Earthworms and leeches, some are parasitic.

Setae

Chitinous bristles aiding movement in annelids.

Parapodia

Paired appendages with setae in polychaetes.

Teloblastic Growth

Sequential addition of segments behind the head.

Complete Digestive Tract

Digestive system with distinct mouth and anus.

Hermaphroditic

Most annelids possess both male and female organs.

Fouling

Waste washing back into gills during torsion.