A paxilla (plural. paxillae) is a small umbrella-shaped structure sometimes found on Echinoderms, particularly in starfish (class Asteroidea) such as ''

Luidia ''Luidia'' is a genus of starfish in the Family (biology), family Luidiidae in which it is the only genus. Species of the family have a cosmopolitan distribution. Characteristics Members of the genus are characterised by having long arms with ...

'', '' Astropecten'' and '' Goniaster'' that immerse themselves in sediment. They are

ossicles The ossicles (also called auditory ossicles) are three bones in either middle ear that are among the smallest bones in the human body. They serve to transmit sounds from the air to the fluid-filled labyrinth (cochlea). The absence of the auditory ...

composed of

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

microcrystals found on the

aboral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

(upper) surface of the animal. Their stalks emerge from the body wall and their umbrella-like crowns, each fringed with short spines, meet edge-to-edge forming a protective external false skin. The water-filled cavity beneath contains the madreporite and delicate gill structures known as

papulla Papulae (sing. papula; also occasionally papulla, papullae), also known as dermal branchiae or skin gills, are projections of the coelom of Asteroidea that serve in respiration and waste removal. Papulae are soft, covered externally with the e ...

References

Echinoderm anatomy {{Echinoderm-anatomy-stub