Brief Summary
Distribution
Physical Description
Size
Identification Resources
Ecology
Local Distribution
Crypsis
Life History & Behaviour
Feeding
Burrowing
Chemosensory Perception
Reproduction and Larval Biology
Anatomy & Physiology
Morphology
Evolution & Systematics
Fossil History
Phylogeny
Biogeographic Distribution
Conservation & Threats
Human Threats
References & Links
| MORPHOLOGY
Internal Transport
The internal system of a bivalve consists of a heart enclosed in a pericardial cavity with a network of blood sinuses to transport oxygenated blood away from the heart, and numerous veins to return de-oxygenated blood to the heart. The intestine passes through the heart on before ending at the anus.
Gas Exchange
The primary site of gas exchange of M. rufescens is across the gills, but oxygen can also diffuse across the muscular foot. Compared to other molluscs, the uptake of oxygen in bivalves is relatively ineffecient. This ineffeciency is made up for by the increased surface area of their gills.
Excretion
Excretion in bivalves occurs mainly through the heart-kidney complex. This explains why the intestine passes through the heart. In this organ the excretory and circulatory functions are sepatated by the pericardium. There are two nephridia, which act like kidneys and concentrate the waste products. After the available nutrients are absorbed across the pericardium back into the bloodstream, the urine is expelled from one of two nephridiopores.
Nervous System
Bivalve nervous systems are similar to other molluscs, but a lot less cephalized due to their lack on head. The sense organs can be found in around the foot or siphons. Small clusters of nerve cells know as ganglion (like a simplified brain) are present and are generally seperated rather than concentrated in one area. There are three different pairs of ganglia, each being responsible for the co-ordination of a different function.
Figure 1: The anatomy of a standard surf clam (Adapted from Fox et al.) |
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