Class Bivalvia Two Shells

Bivalves Examples: oysters, clams, scallops, freshwater mussels No head Entire body is enclosed within the two valves (shells)

So, how does this work? Characteristic umbo= large hump on the anterior end on the dorsal side. The umbo is the oldest part of the shell. The shells are connected together on the dorsal side, anterior end, by a hinge ligament.

Movement The muscular foot is used modified for digging Scallops propel themselves through the water by jet propulsion: rapid closing of the valves squirts water out of the mantle cavity, thereby allowing him to “swim” along

Feeding Bivalvia is the only Molluscan class characterized by the absence of a radula Filter feeding, some are scavengers

Internal Systems Circulatory Three- chambered heart Two atria and one ventricle Nervous Three pairs of ganglia Sense organs are poorly developed Tentacles may have tactile and chemoreceptor cells

Internal Systems Reproduction and Development Sexes are usually separate External fertilization

Bivalves- Pet or Pest? Huge economic impact Good Used as sources of food all over the world Pearl oysters and the jewelry market Bad Larvae of mussels can be parasites of fish Some marine bivalves bore through wood, causing serious damage to ships, pilings, and other wooden structures

Bivalve Digestion and Anatomy Bivalves are filterfeeders- they draw water through their body and filter out organic matter within the water.

Bivalve Digestion and Anatomy 1. They draw the water in through an incurrent siphon which is located on the posterior end of the animal

Bivalve Digestion and Anatomy 2. The organic rich water passes over the gills. 3. The food particles adhere to the mucus that covers the gills. The smaller particles in the mucus are carried by cilia covering the gills

Bivalve Digestion and Anatomy 4. The food particles are passed to the Labial palps (B)- flaps of tissue surrounding the mouth and serves as a sorting mechanism that selects material to be used for food.

Bivalve Digestion and Anatomy 5. After the food enters the Mouth (A), it passes into a short Esophagus (C), which leads into the Stomach (D).

Bivalve Digestion and Anatomy 6. The stomach is connected to a Large Digestive Gland (F) by several ducts; it produces enzymes that help to digest food.

Bivalve Digestion and Anatomy 7. The digestive food passes into the intestine where it is absorbed. A Any food NOT absorbed passes back into the stomach and into the intestine again.

Bivalve Digestion and Anatomy 8. The intestine carries the waste to the Rectum (H) which is then released out through the Anus (I).

Did you catch that? Incurrent siphon- hollow tube that allows for the intake of oxygenated water and food Excurrent siphon- hollow tube that permits the outflow of waste products Siphon- tubular organ in an aquatic animal through which water is drawn in or expelled Rectum- final section of the large intestine, leading to the anus Anus- opening through which solid waste matter leaves the body