Solenotheres, Ng, Peter K. L. & Tri, Ngo Van, 2010

Ng, Peter K. L. & Tri, Ngo Van, 2010, Solenotheres prolixus, a new genus and new species of pinnotherid crab (Crustacea: Decapoda: Brachyura) associated with the razor clam, Solen corneus Lamarck, 1818 (Solenidae) in Vietnam, Zootaxa 2570, pp. 61-68 : 61-63

Solenotheres , new genus

Type species. Solenotheres prolixus , new species, by present designation.

Diagnosis (female). Carapace very broad, subquadrate, width 1.5 times length; weakly calcified; dorsal surface smooth, glabrous; regions poorly defined; anterior part gently raised medially but without distinct ridge; anterolateral margin rounded. Eyes small, cornea pigmented; not visible in dorsal view. MXP3 with ischium, merus completely fused, no trace of suture; palp 3 segmented; carpus shorter than propodus; propodus spatuliform; dactylus elongate, spatuliform, subequal in length to propodus, inserting just before base of propodus. Chelae relatively long, slender. P2, 4, 5 symmetrical from left to right, right P3 with proportionately longer merus, propodus, dactylus than left P3; dactyli relatively stout, hooked with sharp apices, subequal (except on right P3), similar, falcate with spiniform apices. Abdomen with 6 free somites, telson. Male unknown.

Etymology. Derived from an arbitrary combination of the genus name of the host, Solen , and the Latin suffix, - theres, often used as a suffix for pinnotherid genera. Gender masculine.

Remarks. Solenotheres , new genus, is unusual in having a very broad and subquadrate carapace (cw 1.5 times cl), the antero-dorsal part of the carapace is gently vaulted, and P3 is asymmetrical. It is nevertheless clearly a member of the subfamily Pinnotherinae De Haan, 1833. Campos (2009) questioned the current classification of the Pinnotherinae which he argues is not monophyletic. Campos (2009) commented that “consistent and distinct characters ….. particularly the soft, thin carapace and the protuberance in the basal antennal article … allow for the differentiation of a presumably monophyletic group that comprises the subfamily Pinnotherinae de Haan, 1833 sensu stricto ” (Campos 2009: 42). Of the 43 genera now listed under the Pinnotherinae , he argued that 25 genera either did not belong or only doubtfully belonged to the Pinnotherinae (Campos 2009: table 1). In a preliminary study, done mainly with American taxa, Palacios- Theil et al. (2009) also supported the heterogeneity of the Pinnotherinae . Solenotheres , new genus, fits clearly into Pinnotherinae sensu Campos (2009). That been said, even if the Pinnotherinae is almost certainly not a natural grouping, much more work will still need to be done on how it should be separated, and more characters will need to be checked. Even with the removal of “aberrant” pinnotherids into other families (see Ng et al. 2008; Palacios-Theil et al. 2009; Ahyong & Ng 2009), the classification of the Pinnotheridae remains a challenge.

With regard to the relatively broad and subquadrate carapace which is slightly vaulted as well as the long and spatuliform MXP3 dactylus, Solenotheres , new genus, most closely resembles Afropinnotheres Manning, 1993 (from West Africa) and Raytheres Campos, 2004 (replacement name for Raymondia Campos, 2002 ) (from California). Compared to Solenotheres , new genus, Raytheres has a relatively longer and more slender ischium with the dactylus relatively shorter and inserted more medially on the propodus, and P3 is not asymmetrical ( Campos 2002: fig. 5). Afropinnotheres on the other hand, has a proportionately shorter MXP3 propodus ( Manning 1993: figs. 1a, 2b, 4b, 5b, 7e, 11b), a carapace which is less quadrate and relatively less broad ( Manning 1993: figs. 2a, 3a, 7b, 8a); the P3 is symmetrical and not slender or elongate ( Manning 1993: figs. 2d–g, 4d–g, 5b–e, 7g –j, 10d–g); and a proportionately more rounded female abdomen ( Manning 1993: fig. 3b).

With regards to the very broad and subquadrate carapace, the only other pinnotherine species with a similar feature is Alainotheres leloeuffi ( Crosnier, 1969) , described from the Ivory Coast in West Africa ( Crosnier 1969; Manning 1993). In this species (which is only known from one male), however, the front is more produced and the eyes are visible in dorsal view ( Crosnier 1969: fig. 1), the MXP3 dactylus is short and inserted submedially on the propodus ( Crosnier 1969: fig. 2-7), the inner margin of the ischiomerus is angled ( Crosnier 1969: figs. 2-7), P2–P5 are proportionately shorter with the dactylus almost straight ( Crosnier 1969: fig. 2-3–6), and the chela is relatively short and stout ( Crosnier 1969: fig. 2-2). In Solenotheres , new genus, the front and eyes are not visible in dorsal view ( Figs. 1 , 2 A), the MXP3 dactylus is as long as the propodus and inserted sub-basally on the propodus ( Fig. 2 C, D), the inner margin of the ischiomerus is convex ( Fig. 2 C), P2–P5 are proportionately longer with the dactylus hooked ( Figs. 1 , 3 ), and the chela is slender and elongate ( Figs. 1 A, 2E). Comparisons, however, are not easy as Alainotheres known only from one male while Solenotheres , new genus, is based on just one female specimen.

The general carapace shape of Solenotheres , new genus, is superficially similar to some species of Pinnotheres like P. dilatatus Shen, 1932 , and P. serrignathus Shen, 1932 , from China, but those of the latter are proportionally less broad and less quadrate. In addition, they symmetrical P3 and the MXP3 have short simple dactylus. The carapace proportions of Solenotheres , new genus, is also similar to Orthotheres Sakai, 1969 , notably taxa like O. turboe Sakai, 1969 (type species) and O. haliotidis Geiger & Martin, 1999 , although their carapaces are more ovoid in shape and the eyes are visible in dorsal view. All species of Orthotheres , however, have a 2-segmented MXP3 palp (see also Campos 1989). Superficially, Solenotheres , new genus, also resembles the American Opisthopus Rathbun, 1893 , in carapace shape and form of the MXP3 ( Crosnier 1969: figs. 11-11, 13, 16) but the carapace of Opisthopus is more rounded, the MXP3 dactylus relatively shorter and inserted submedially on the propodus. The gently vaulted carapace of Solenotheres , new genus, superficially resembles the Indo-West Pacific Durckheimia De Man, 1889 , and Tridacnatheres Ahyong & Ng, 2005 , and Visayeres Ahyong & Ng, 2007 . The form of the P2–5 dactyli is also similar, although none of them have asymmetrical P3. The carapace condition in Solenotheres , new genus, however, is less pronounced and there is no clear ridge or swelling on the carapace; but when viewed frontally, the vaulting is obvious ( Fig. 1 B). There are, however, numerous differences in the structures of the carapace and MXP3 ( Ahyong & Ng 2005, 2007b). The form of the MXP3 dactylus also resembles Pinnaxodes Heller, 1865 , which is known from Chile and the northwestern Pacific ( Takeda & Masahito 2000; Ng & Manning 2003). In Pinnaxodes , however, the dactylus is inserted sub-medially and there is still a faint suture separating the ischium from the merus ( Ng & Manning 2003: fig. 6B, F).

The form of the MXP3 dactylus and the structure of the ambulatory dactyli of Solenotheres , new genus, also superficially resemble those of pinnotherine genera that live in holothurians, notably the Indo-West Pacific Holotheres Ng & Manning, 2003 , and American Holothuriophilus Nauck, 1880 . Holotheres , however, has a more rounded carapace, the front is visible in dorsal view and the MXP3 dactylus is inserted basally on the propodus ( Ng & Manning 2003; Ahyong & Ng 2007a). In terms of width, the carapace of Holothuriophilus resembles Solenotheres , new genus, but the length of the latter is relatively greater (cf. Ahyong & Ng 2007a: fig. 20A), and the MXP3 dactylus is relatively longer and inserted sub-basally ( Fig. 2 C, D) rather than medially ( Ng & Manning 2003: fig. 7C; Ahyong & Ng 2007a: fig. 20C).

Figures

FIGURE 1. Solenotheres prolixus, new genus, new species, holotype ovigerous female, cl 4.40 mm, cw 6.58 mm (ZRC), southern Vietnam. A, overall view; B, frontal view of carapace; C, ventral view of carapace.

FIGURE 2. Solenotheres prolixus, new genus, new species, holotype ovigerous female, cl 4.40 mm, cw 6.58 mm (ZRC), southern Vietnam. A, dorsal view of carapace; B, frontal view of carapace showing orbits, antennules and antennae; C, left MXP 3 (setae not drawn); D, MXP 3 palp, drawn from angle to show position of dactylus on propodus; E, left cheliped (setae not drawn); F, abdominal somites 5, 6 and telson. Scales: A = 1.0 mm; B – F = 0.5 mm.

FIGURE 3. Solenotheres prolixus, new genus, new species, holotype ovigerous female, cl 4.40 mm, cw 6.58 mm (ZRC), southern Vietnam. A – D, right P 2 – P 5, respectively (setae not drawn); E, left P 3 (setae not drawn). Scales = 0.5 mm.