''Xyloplax turnerae'' is a sea daisy, a member of an unusual group of marine

taxa In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...

belonging to the phylum

Echinodermata An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the s ...

. It has been found living on decaying timber in a deep oceanic trench in the Bahamas.

Discovery

An enigmatic new species of echinoderm, ''Xyloplax medusiformis'', was discovered in the South Pacific near New Zealand and first described in 1986 by Baker, Rowe and Clark. Further deep sea exploration by the same team using a submersible vehicle led to the discovery of a new species of ''

Xyloplax Sea daisies (infraclass Concentricycloidea; order Peripodida) make up an unusual group of deep-sea taxa belonging to the phylum Echinodermata, with three species described in the genus ''Xyloplax''. Intestine and anus are absent. Distribution S ...

''. Pieces of timber were deposited at a depth of in an oceanic trench known as the

Tongue of the Ocean The Tongue of the Ocean (TOTO) is the name of a region of much deeper water in the Bahamas separating the islands of Andros and New Providence. Features The TOTO is a U-shaped, relatively flat-bottomed trench measuring approximately . Its depth ...

between the Bahamian islands of

Andros Andros ( el, Άνδρος, ) is the northernmost island of the Greek Cyclades archipelago, about southeast of Euboea, and about north of Tinos. It is nearly long, and its greatest breadth is . It is for the most part mountainous, with many ...

and New Providence. When recovered nearly two years later they yielded more than two hundred specimens of ''Xyloplax turnerae''. In 2004, another species in this genus was collected in a similar way from a depth of in the north east Pacific Ocean. It has since been named ''

Xyloplax janetae ''Xyloplax janetae'' is a ''Xyloplax'' of the family Xyloplacidae. It lives on the surface of wood sunken to abyssal depths. Morphology ''Xyloplax janetae'' is a flattened disk, from in diameter, and about thick. It has adambulacral spines wh ...

''.

Description

''Xyloplax turnerae'' is very much like ''Xyloplax medusiformis'' in appearance. It is shaped like a flattened disc and is fringed by a row of short spines which are all of approximately equal length in the range 300–400 μm. The aboral (upper) surface is clad in a series of concentric plates each bearing three spines. The

tube feet Tube feet (technically podia) are small active tubular projections on the oral face of an echinoderm, whether the arms of a starfish, or the undersides of sea urchins, sand dollars and sea cucumbers; they are more discreet though present on br ...

have rounded bulbous tips. On the oral (lower) side the mouth leads to an eversible stomach but there is no gut or anus. There is a single row of tube feet circling the mouth and these number up to 110 while ''X. medusiformis'' has fewer than 65. The females grow to about in diameter and the males to . All the embryos found in the females were small, less than 180 μm in diameter, and it seems unlikely that this species broods its young in the same way that ''X. medusiformis'' does. The marginal spines are mobile and are disproportionally longer in smaller individuals than they are in larger ones. It is thought that juveniles may use them to "parachute" and that this may aid in their dispersal.

References

{{Taxonbar, from=Q2089789 Peripodida Animals described in 1988