Image Key > Ostracoda

• Pelagic ostracods are small, usually less than 2mm.

• On first appearance have some resemblance to cladocerans. However, ostracods differ in that the body is completely enclosed in a clam-like bivalve shell that is hinged dorsally.
• A transverse adductor muscle, similar to that in clams and mussels, closes the shell.
• The carapace (shell) can have various shapes but is typically circular, elliptical, or almost rectangular.
• There is often an anterior antennal notch (not clearly visible on image).
• The carapace can be smooth, thin, and transparent in planktonic ostracods, while benthic forms have more robust, ornate shells.
• The trunk is reduced and unsegmented with 2 or less appendages, much fewer than other adult crustaceans. The abdomen is also reduced.
• Both the first and second antennae are well developed, extend beyond the carapace, and are the main swimming appendages.

• They are not particularly common in coastal plankton samples.
• Benthic samples may be collected when sampling close to the bottom or close in to the shore.