Echinodermata Glossary

Echinodermata: Glossary

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Aboral side The side of the body opposite the mouth is called the aboral side. This is normally dorsal.

Ambulacra Structures located in the middle of each arm along a features called the ambulacral groove.

Ambulacral groove In many echinoderms, this groove carries small captured food particles to the mouth of the organism, although in some types the feature has been altered to serve other functions.

Ambulacral system same as the water vascular system.

Arms long, flexible mobile limbs - usually containing a feeding groove


Brachioles Delicate arm-like appendages coming off their ambulacra in stalked echinoderms like Blastoids.


Calyx At the top of this stem of echinoderms like Crinoids and Cystoids is the main part of the animal, a cup-shaped body, to which arms are attached.

Columnals stacked, articulated plates that make up the stem.

Crown The calyx and the arms together are sometimes referred to as the crown.


Madreporite a structure located on the aboral surface, in some species looking rather like a drain cover in a sink. The madreporite is a perforated platelike structure which acts as the inlet for the water vascular system.


Oral side The side with the mouth in echinoderms is defined as the oral side. Depending on the group, the oral side can point up or down. In starfish it points down, in crinoids up.

Ossicles The numerous small plates that constitute the echinoderm skelton. These ossicles are composed of a form of calcium carbonate known as calcite.


Pinnules Small, feather-like structures on the arms which form the filtration fan which stalked echinoderms (crinoids, cystoids, and blastoids) use to feed. The pinnules which are used to filter small food particles from the water.


Stem The calyx is usually connected to the bottom via a stem. The stem is either circular or pentagonal (five-sided) in section and composed of numerous disc-like plates called columnals. Stemmed forms frequently have a holdfast composed of small, polygonal plates, although some species wrapped their stem around other organisms, and thus didn't need a holdfast.


Test many echinioderms to have fused calcite ossicles forming a rigid, external skeleton referred to as a test.


Water vascular system The water vascular system maintains communication with the surrounding sea water through a group of pores in the madreporite.  It serves for food transport in some forms, but has been adapted to assist in locomotion and as a kind of  internal, hydrostatic skeleton.  

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