The Echinoid Directory

Glossary

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Glossary terms beginning with: L

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labral plate
The first, unpaired plate in interambulacrum 5 (red, 1) in atelostomates. This forms the anterior part of the plastron. (show image)
labrum
The labral plate (show image)
labyrinthic (stereom)
A stereom arrangement which results in calcite struts and pore spaces are haphazardly arranged. (show image)
lantern
See Aristotle's lantern.
lantern
latero-anal (fasciole)
A fasciole band that runs from just behind the anterior paired petals and passes beneath the periproct. At its anterior it connects to the peripetalous fasciole. (show image)
levator muscles
Muscles in the suckered disc of tube-feet used in adhesion. (show image)
Loven's system
The standard reference system by which the various ambulacral (amb) and interambulacral (Iamb) zones are numbered. The key tie point is that the madreporic plate lies in Iamb 2. (show image)
lumen (spine)
A central space running up the length of the shaft of a spine (cross-section of spine illustrated). (show image)
lunule
An ovate to slit-like perforation through the test, either interradial or perradial in position. These perforations are lined with tubercles and spines and are used to sieve sediment for its organis content and as a pressure release channel. Confined to Clypeasteroida. There are two types of lunule; cross-linked lunules formed by resoption, with upper and lower series of plates vertically stacked; and festooned lunules, formed by secondary closure of notches and with plate sutures highly oblique (show image)