Tetralia muta ( Linnaeus, 1758 )

PETER CASTRO, PETER K. L. NG & SHANE T. AHYONG, 2004, Phylogeny and systematics of the Trapeziidae Miers, 1886 (Crustacea: Brachyura), with the description of a new family, Zootaxa 643, pp. 1-70 : 29-30

Tetralia muta ( Linnaeus, 1758)

Cancer mutus Linnaeus, 1758: 625 .

Tetralia armata Dana, 1852: 264 , pl. 16, fig. 4.

Tetralia vanninii Galil & Clark, 1988: 146 , figs. 1C, 2B, 3C, 4C, 4H, 6C.

Remarks. Cancer mutus Linnaeus, 1758 , is a name which has hardly been used since 1758. When naming this species, Linnaeus described it as having a brown frontal margin and a smooth carapace with a flattened, truncated posterior margin ("... thorace laevi integerrimo, margine antico transverso brunneo ... postice complanato­truncata ..." ( Linnaeus, 1758: 625). The name was subsequently used by Herbst (1783: 116), who merely listed this species, but without any figures. This species was then forgotten until the name was used again by Sakai (1999: 14), this time for a dromiid. Sakai (1999: pl. 4A, fig. F) figured a specimen in the Zoologisch Museum, Humboldt­Universität, Berlin which apparently had been identified and labelled as " Conchoecetes mutus Linnaeus, 1758 ". The specimen figured is clearly conspecific with Conchoecetes intermedius Lewinsohn, 1984 , as currently understood and bears absolutely no resemblance to the description of Linnaeus (1758). Clearly, Herbst (or someone else) had misidentified the Berlin specimen and Sakai (1999) had followed suit without question. The type specimen(s) of Cancer mutus Linnaeus, 1758 , is no longer extant (S. H. Tan, pers. comm.).

The characters noted by Linnaeus (1758) for Cancer mutus are clearly that of a Tetralia (or Tetraloides ). He recorded it from the Mediterranean with doubt. This is important as the Mediterranean does not have any known records of trapeziids or tetraliids, and this probably confused workers or caused them to ignore the name. In the present instance, we believe that the locality data Linnaeus obtained was incorrect. Certainly there is no crab we know of from the Mediterranean which has the characters Linnaeus described for C. mutus .

The characters enumerated by Linnaeus, although brief, clearly indicate that C. mutus could be one of the following recognised trapeziid species: Tetralia armata Dana, 1852 , Tetralia vanninii Galil & Clark, 1988 , or Tetraloides nigrifrons ( Dana, 1852) .

Tetralia armata Dana, 1852 , itself is a problem, especially since the type is lost. Although described from Tonga in the central Pacific Ocean, the name has somehow been ignored by almost all workers, even though Dana provided a reasonably detailed description (for the time) and an uncoloured figure. It was described as "pale, with anterior margin brownish black" ( Dana 1852: 264). The specimen illustrated by Dana (1852: pl. 16, figs. 4 a–c) was a juvenile or small adult with one anterolateral spine on each side of the carapace and two pointed spines on the inner side of each cheliped carpus. Dana's drawing also showed the outer margin of the cheliped merus having thin, spine­like teeth. The colour pattern and morphological characters of T. armata are shared with T. vanninii , which has been collected through most the Indo –West Pacific region (see Castro 1997b: 113, fig. 1; 1999b: 103). Tetralia vanninii Galil & Clark, 1988 , is thus likely to be a junior subjective synonym of T. armata Dana, 1852 .

All of the characters used to describe C. mutus , most particularly the brown frontal margin, could also apply to Tetraloides nigrifrons ( Dana, 1852) , although the brown frontal margin of this species often extends along the anterolateral sides of the carapace.

Therefore, as things are, the name Cancer mutus Linnaeus, 1758 , can be used for either Tetralia armata Dana, 1852 (= Tetralia vanninii Galil & Clark, 1988 ) or Tetraloides nigrifrons ( Dana, 1852) . Tetraloides nigrifrons ( Dana, 1852) , however, is a relatively common species and the name has been used more frequently used by taxonomists and ecologists than either T. armata or T. vanninii . In addition, Tetraloides nigrifrons is also the designated type species of Tetraloides Galil, 1986 . Since the name T. vanninii Galil & Clark, 1988 , has to be replaced by the senior but hardly used name T. armata Dana, 1852 , anyway, and since this species is generally less common, replacing both names with Cancer mutus Linnaeus, 1758 , seems to be the most parsimonious action to take and will cause the least problems for taxonomy.

To this effect, we hereby select an ovigerous female specimen (ZRC 2000.2330; cl 8.0 mm, cw 8.8 mm) from Pago Bay, Guam (13º30’N, 144º40’E), Mariana Islands, as the neotype for both T. armata and C. mutus . It was collected by G. Paulay from Acropora at a depth of 20–25 m on 1 May 1997. Cancer mutus Linnaeus, 1758 , and Tetralia armata Dana, 1852 , thus become objective synonyms. The holotype of T. vanninii Galil & Clark, 1988 , a male specimen from Somalia, western Indian Ocean, is supposedly extant (ZMF 1263) but is now apparently lost or misplaced. It has been unsuccessfully searched in Florence by the first author and more recently by S. Trautwein (pers. comm.). In the event future studies show that the Indian and Pacific Ocean populations of Tetralia muta ( Linnaeus, 1758) are separate taxa, the name T. vanninii Galil & Clark, 1988 , is still available.