Amphigymnas Walsh, 1891

O’Loughlin, P. Mark, Mackenzie, Melanie & VandenSpiegel, Didier, 2013, New sea cucumber species from the seamounts on the Southwest Indian Ocean Ridge (Echinodermata: Holothuroidea: Aspidochirotida, Elasipodida, Dendrochirotida), Memoirs of Museum Victoria 70, pp. 37-50 : 38

Amphigymnas Walsh, 1891

Amphigymnas Walsh, 1891: 199 .— Deichmann, 1930: 106–107.

Diagnosis (this work). Genus of large synallactid species, up to at least 140 mm long; body wall calcareous, brittle, similar to that of the elasipodid family Deimatidae ; mouth ventral, about 20 peltate tentacles; dorsal and lateral body with long conical calcareous papillae, including a ventrolateral series; body flat ventrally, tube feet in ambulacral series or scattered; anus subdorsal posterior; ossicles in body wall large table discs with many perforations, discs variably with or lacking spires comprising 3 or 4 pillars, sometimes cross-bars, pillars lacking distal spines or teeth, spires sometimes reduced to short unconnected pillars.

Type species. Amphigymnas multipes Walsh, 1891 , by monotypy (= Pannychia woodmasoni Walsh, 1891 , by priority according to the synonymy by Koehler and Vaney 1905) (Indian Ocean, Andaman Sea, 344–896 m). Synallactes reticulatus Sluiter, 1901 is a junior synonym (according to the synonymy by Koehler and Vaney, 1905).

Other included species. Amphigymnas bahamensis Deichmann, 1930 (Atlantic Ocean, Bahamas, 480 m); A. staplesi O’Loughlin sp. nov. (Southwest Indian Ocean Ridge, Atlantis Bank , 740 m).

Remarks. Koehler and Vaney (1905) examined numerous relevant specimens and judged that A. multipes Walsh, 1891 and S. reticulatus Sluiter, 1901 were junior synonyms of P. woodmasoni Walsh, 1891 , the senior synonym based on the name sequence priority in Walsh (1891). They referred P. woodmasoni to Synallactes Ludwig, 1894 . Deichmann (1930) examined the holotype of A. multipes and considered Amphigymnas Walsh, 1891 to be a good monotypic genus with A. multipes Walsh, 1891 the type species based on the single type specimen. She did not examine any P. woodmasoni specimens and acknowledged that she was not able to judge whether A. multipes and P. woodmasoni were conspecific. She rejected the referral of the species to Synallactes by Koehler and Vaney (1905) and wrote: ‘ Amphigymnas is as good a genus as Synallactes and Bathyplotes with neither the solid rod-like spire of the typical Synallactes nor the long spire with the numerous cross beams of Bathyplotes . The deposits remind one so much of those found in certain Deimatidae that at first one would be inclined to place it in that group. It is only when one notes the presence of respiratory trees as well as smaller tables with more or less complete spire and the long synallactidlike supporting rods that one realizes that the genus belongs in the Synallactidae’. She added the species A. bahamensis Deichmann, 1930 . Solís-Marín and Laguarda-Figueras (2004) listed Pannychia woodmasoni Walsh, 1891 (incorrectly as Synallactes woodmasoni Koehler and Vaney, 1905 ) and Synallactes reticulatus as junior synonyms of A. multipes . We uphold the work of Deichmann (1930) by recognizing the genus Amphigymnas Walsh, 1891 , and the work of Koehler and Vaney (1905) by confirming Pannychia woodmasoni Walsh, 1891 as the type species.

Walsh (1891) diagnosed his genus Amphigymnas as: ‘Body ovoid with narrow tail-like extremities; soft and appears to have been surrounded by a jelly-like material when fresh. Feet very numerous over the whole of the trivium and placed more or less irregularly. Lateral margins with two or three rows of long processes. Back covered with processes except near the mouth and anus where the body tapers and where the dorsal surface is naked; mouth terminal, small; tentacles 15, very small and retracted; anus terminal, small. Calcareous bodies moderate sized, irregularly rounded, many-holed plates somewhat like those of Pannychia . Calcareous ring of 5 small pieces loosely connected.’ The type specimen of A. multipes was 80 mm long, 22 mm wide midbody, the lateral processes about 15 mm long, shorter processes on the back. Koehler and Vaney (1905) examined the type specimen and judged that it was damaged and incomplete. This may explain why Walsh (1891) could describe the type specimen as being ‘soft’ and the calcareous ring as comprising ‘five small pieces loosely connected’, neither of which is true for a synallactid.

Deichmann (1930) diagnosed Amphigymnas as: ‘Closely related to Synallactes , but in its texture resembling a Deimatid. Skin thin, glass-like, filled with large deposits, derived from tables; spires 3–4 pillared with 1–2 cross beams and no teeth on top, often reduced or entirely absent, so the large plates resemble the plates found in the Deimatiids; dorsally large, conical papillae, ventrally a lateral row of large and conical pedicels, and a midventral row of smaller ones, filled with numerous supporting rods and a rudimentary endplate’.

The distinctive diagnostic characters of Amphigymnas are: long, conical, dorsal calcareous papillae, including a ventrolateral series; flat ventrally with small tube feet in ambulacral series or scattered over ventrum; brittle calcareous outer body wall texture resulting from the presence of many large table discs with variably complete spires. We suspect that the three species assigned to Amphigymnas are not congeneric. The dorsal table discs with their central cross, four large central perforations, and four-pillared spires, are similar for A. multipes Walsh and A. staplesi O’Loughlin sp. nov., but quite different from the table discs with numerous small perforations and predominantly three-pillared spires illustrated for A. bahamensis Deichmann. And we judge that species with a distinctly ambulacral series of tube feet would not be congeneric with species that have tube feet scattered over the ventrum.

We note that the first description of S. reticulatus was in Sluiter (1902). This paper was published after Sluiter (1901) provided an illustrated description of S. reticulatus in the Siboga report. Sluiter, 1901 is given here as the date of authorship of the species.