''Davidaster discoideus'' or the beaded crinoid is a
species of
feather star
Crinoids are marine animals that make up the class Crinoidea. Crinoids that are attached to the sea bottom by a stalk in their adult form are commonly called sea lilies, while the unstalked forms are called feather stars or comatulids, which are ...
in the
family Comatulidae
Comatulidae is a family of comatulid crinoids. Since 2015, it replaces the family Comasteridae.
Description and characteristics
This family is of recent restoration, and still has no consensual description. However the description of the fam ...
. It was previously known as ''Nemaster discoidea'' but the World Register of Marine Species has determined that the valid name is ''Davidaster discoideus''.
[ It is found on reefs in the Caribbean Sea and northern coast of South America.
]
Description
The beaded crinoid has a cup shaped body, usually hidden from sight, from which about twenty arms project. Only a few of these are usually visible at one time and each can be curled up in a coil. Short pinnules extend from either side of the arms like vanes on a feather. Both the arms and the pinnules are formed from a large number of jointed plates which gives them great overall flexibility. There is an ambulacral groove
Ambulacral is a term typically used in the context of anatomical parts of the phylum Echinodermata or class Asteroidea and Edrioasteroidea. Echinoderms can have ambulacral parts that include ossicles, plates, spines, and suckers. For example, sea ...
along the oral surface of each pinnule which is continuous with grooves on the arms. These are linked to grooves leading to the mouth forming feeding channels. The grooves have flap-like lappets overhanging them. At each plate junction on the pinnules there are three tube feet of different length used in food capture and manipulation. The arms can be long and are the only part of the crinoid normally visible as its body is generally concealed in a crevice or inside a sponge. At the base of the crinoid are several cirri
Giovanni Battista Cirri (1 October 1724 – 11 June 1808) was an Italian cellist and composer in the 18th century.
Biography
Cirri was born in Forlì in the Emilia-Romagna Region of Italy. He had his first musical training with his brother ...
, unbranched appendages with which it grips the rock or other substrate
Substrate may refer to:
Physical layers
*Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached
** Substrate (locomotion), the surface over which an organism lo ...
. The arms are orange or red and the pinnules are grey or banded in black and white and have a beaded appearance.
Distribution and habitat
The beaded crinoid is found in the Caribbean Sea and the Gulf of Mexico. It is found at depths between and is generally uncommon. These crinoids often live in the same concealed spot for several years and should not be moved by divers as they are very sensitive to changes in water temperature and illumination.[
]
Biology
The beaded crinoid extends its arms and pinnules in slow flowing water.[ The longest tube feet on the pinnules trap planktonic particles and push them into the ambulacral groove. They are prevented from leaving this by the remaining tube feet and the lappets. Cilia lining the groove form particles into boluses and move these along to the mouth.]
References
{{Taxonbar, from=Q5241533
Comatulidae
Animals described in 1888