The fourth segment of a crab's walking leg, which is attached to the carpus.

The body cavity of a cnidaria and ctenophore, which is used as a stomach, an excretory organ and as a primitive vascular system. Cnidaria included the jellyfish, corals and anemones

Operated by hydraulic (liquid) pressure along tubes.

The bottom plate of an echinoderm. Contains the mouth, reproductive and excretory organs. Abdominal relates to the belly, or digestive area.

To do with the digestive system. Between the stomach and the anus.

Areas of a body surface in which tube feet are situated. In sea urchins and sea stars.

Appendages, in pairs, often jointed, extending from the head. One group of antennae are tactile for touch, while the other group are chemosensory, for taste.

Excretory opening of the digestive system.

A form of calcium carbonate.

Animal within the Phylum Arthropoda, which contains the insects, spiders, ticks and mites, crustaceans. Arthro = jointed; pod = foot.