MOLLUSCA (IV): DIVERSITY- Bivalves etc.
(Mollusca study images;
a) body plan highly modified for: a) burrowing and b) particle-feeding:
b) two shells joined by flexible ligament (tension or compression); mantle edge fuses to shell margin and links to 2 adductor muscles; may be isomyarian (same size) or anisomyarian (different size)
c) most produce byssal threads as larvae; some still do as adults
d) 1 pair ctenidia inside very large mantle cavity; may be either:
both have compound latero-frontal cilia for particle capture
e) foot is highly modified for burrowing (except attached or swimming species); burrowing involves both shell and foot
f) sexes are separate; gametes spawned freely into water; most have free-swimming trochophore and veliger larval stages
g) classification still debated; 4 Subclasses: Paleotaxodonta, Pteriomorphia, Heterodonta, Anomalodesmata (based on shell hinge teeth, and form of ctenidia and adductor muscle; see lab guide)
Copyright (c) 2007 by A. Richard Palmer. All rights reserved.
(revised Jan. 28, 2007)