Acaudina is a genus of sea cucumbers of the family Caudinidae. They are small, smooth and spindle-shaped, with a thin body wall and are distinguished by their absence of a Tail.
Acaudina are found in tropical and subtropical waters, with habitats ranging from Intertidal zone and Estuary zones including reefs, sandbars, Seagrass meadow or within soft-bottom and Anoxic waters Mudflat, where salinity is slightly reduced.
Etymology
The genus was established by Hubert Lyman Clarke in 1907, to accommodate a species that is markedly different from other related genera within the order
Molpadida. Its name is derived from the Latin “
a”, combined with “
caudina”, referring to the absence of a caudal (tail)
appendage that is present in similar
Genus such as
Caudina. This notable difference in the posterior body region was what led to its recognition as a separate genus.
It has been synonymized with the name Aphelodactyla (H. L. Clark, 1908), but this name is unaccepted.
Taxonomy
Source:
Acaudina belong to the order Molpadida of sea cucumbers which do not have feeding feet apart from their tentacles. They are considered as apodous holthurians, which are slim, vermiform and have thin body walls.
The type species is Molpadia demissa Sluiter, 1901, later recognised as Acaudina demissa. This was originally described from a preserved specimen collected from the Madura Strait in Java. The species listed on WoRMS are as follows:
-
Acaudina bacilla (Cherbonnier & Féral, 1981)
-
Acaudina demissa (Sluiter, 1901)
-
Acaudina leucoprocta (H.L. Clark, 1938)
-
Acaudina molpadioides (Semper, 1867) (syn. Aphelodactyla delicata, Clark 1908, unaccepted)
-
Acaudina pellucida (Semper, 1867)
-
Acaudina punctata (Sluiter, 1887)
-
Acaudina rosettis (O'Loughlin & Ong, 2015)
-
Acaudina spinifera (Teoh & Woo, 2022)
-
Acaudina suspecta (Cherbonnier & Féral, 1981)
Many species have been synonymized in the past. For instance, opinions have been divided as to whether A. australis is distinct from A. molpadioides and whether A. hualoeides constitutes a valid species. Conflicting assessments by various authors have led to ongoing taxonomic discussion, however WoRMS currently lists A. Australis and A. hualoeides as valid species.
Morphology
Acaudina is characterized by a
cylindrical stout body that does not taper toward a
Tail region. Unlike
Caudina, the posterior end is not distinctly set off as a tail or appendage, but rather blunt and rounded.
They range from being of a darker grayish color,
to semi-translucent,
though some species may contain orange, brown or purple pigment.
The lengths vary across species and specimen in the genus. The lengths of observed specimen of
Acaudina molpadioides in
Java were reported to range from 150-200
mm.
species possess 15 tentacles, each with a lateral digits pair.
The radial pieces of the
calcareous rings that are common across the genus show subtle, posterior prolongations.
Unlike many related genera, these deposits are formed into thick plates, which feature few and small
, with a number of sharp projections. Ossicles are present primarily in the posterior body wall and in the fingerlike
Anus ,
which come in five sets, of two to four.
Genus-level traits
Source:
The following characteristics can be observed in specimen across species in Acaudina.
| +
!Characteristic
!Description |
| Body surface | Smooth, lacking any external appendages |
| Skin deposits | Calcareous particles arranged in thick plates, each with few sharp projections and small perforations |
| Calcareous ring | Well-developed, with posterior prolongations |
| Tentacle count | 15 |
| Tentacle morphology | Each bears 2-4 |
| Ampullae | Present on the tentacles |
| Posterior end | Blunt and rounded |
| Caudal appendage | Absent |
Species-level traits
One report by Teoh and Woo provides an
identification key to distinguish the species in the genus.
Distribution
Acaudina species can be found in the
Indo-Pacific Littoral zone region.
Some species, (
Acaudina leucoprocta, Acaudina molpadioides) found in shallow
Intertidal zone along the Johor Straits (4), while others
(Acaudina bacilla) are found at greater depths of around 168-287m.
The distribution of species across the genus extends to but is not limited by the waters of India, Thailand, Malaysia, Australia, Indonesia, Iran, Singapore, Philippines and China.
