Trypaea oblonga ( Le Loeuff & Intès, 1974 ) Le Loeuff & Intes, 1974

De Matos-Pita, Susana S. & Ramil, Fran, 2015, Additions to thalassinidean fauna (Crustacea: Decapoda) off Mauritania (NW Africa) with the description of a new genus and a new species, Zootaxa 4020 (3), pp. 571-587 : 576-578

Trypaea oblonga ( Le Loeuff & Intès, 1974) n. comb.

( Figs. 2 A–D)

Callianassa oblonga Le Loeuff & Intès, 1974: 38 , figs. 9a–r.— Saint Laurent & Le Loeuff, 1979: 55.—Sakai, 1999: 18; 2005a: 32, figs. 2E, 3E, 4E.

Cheramus oblongus .— Manning & Felder, 1991: 780.— Tudge et al., 2000: 145.— Sakai, 2011: 369.

Material examined. Expedition Maurit0911: Stn. MU215, off S Nouakchott ( Mauritania) (17°29´44″– 17°28´06″N; 16°39´31″–16°40´10″W), 358–364-m depth, muddy fine sand, commercial trawl, 2.II.2009; one male TL/CL: 19.09/ 4.52 mm, both pereiopods 1 missing, left P4 merus to dactylus detached and both pleopods 3 missing. Expedition Maurit1011: Stn. MUDR 26, off S Nouakchott ( Mauritania) cold-water coral reef (17°29´42″N, 16°41´04″W), 441-m depth, mud with coral rubble and shell debris, rock dredge, 12.XII.2010; one incomplete female, TL/CL: +12.23/ 4.94 mm, right pereiopod 1 carpus and chela, both pereiopods 3–5, abdominal segments 3–5 and telson are all missing.

Description. Our male specimen mostly corresponds to the type description provided by Le Loeuff & Intès (1974). Both specimens present a rudimentary, uniramous and bisegmented pleopod 1 (as shown in Le Loeuff & Intès 1974: fig. 9r). While the type specimen was described with pleopods 2–5 missing, in our male specimen, although no scar or trace of pleopods can be appreciated on pleomere 2, a conspicuous scar is present in place of pleopod 3; pleopods 4 and 5 are biramous and foliaceous ( Fig. 2 A), with an appendix interna projecting from the distal proximal third of the endopod inner border, and with distal margin obliquely truncate and furnished with hooks ( Figs. 2 A, B).

Our incomplete female specimen also corresponds to the original description. Differences observed are those referring to the sex: conspicuous gonopore on both pereiopod 3 coxa, pleopod 1 uniramous and bisegmented ( Fig. 2 C), and pleopod 2 slender, biramous, with endopod bearing a terminal appendix interna ( Fig. 2 D).

Habitat. The type specimen was collected at 200 m with a DRB: drague à dents (72× 30 cm); no bottom was specified ( Le Loeuff & Intès 1974). Our specimens were captured off South Nouakchott, at two geographically close stations, on muddy fine sand and muddy coral rubble, at depths between 358–364 and 441 m.

Distribution. Previously reported only from the type locality ( Ivory Coast) and now from Mauritania, this species seems to be restricted to the West African tropical region.

Remarks. To date, the type specimen (male CL: 3.5 mm) from Ivory Coast (200 m) is the only one ever recorded. After its original description as Callianassa oblonga , the species was included in the genus Cheramus Bate, 1888 as C. oblongus by Manning & Felder (1991), and accepted by Tudge et al. (2000) in this genus. However, Sakai (2005: 20) was unable to find enough morphological characters that reliably separated both genera; he therefore synonymized the genus Cheramus with Callianassa .

On the other hand, a tendency to group Callianassa species based on pleopod morphology, among other characters, led Saint Laurent and Le Loeuff (1979: 55) to recognize three groups: one including species with pleopod 1, but not pleopod 2; a second group of species lacking either pleopod 1 or pleopod 2; and a third group with ‛des pléopodes présents, bien que faiblement développés, sur les deux premiers segments abdominaux du mâle’ (pleopods on male absominal segments 1 and 2 present, although reduced). These authors included only one species, Callianassa oblonga , in the last group, although this species was originally described as with ‛pléopode 1 réduit, en forme de doigt de gant à extrémité courbe; les autres pléopodes manquent.’ (pleopod 1 reduced, fingerlike and with tip curved; pleopods 2–5 absent) ( Le Loeuff and Intès 1974: 40); however, although a reduced pleopod 1 is present (and bisegmented as shown in Le Loeuff and Intès (1974): fig. 9r), there is no clear evidence of an existing pleopod 2.

In his synopsis of the family Callianassidae, Sakai (1999) first associated C. oblonga with Callianassa species without pleopod 2 (Sakai 1999: 5). However, in his account of the species (Sakai 1999: 18), he described it as having male pleopods 1 and 2, as did Saint Laurent and Le Loeuff (1979). Some years later, with the revision of the Callianassoidea of the world, Sakai (2005a) arranged the Callianassa species into four groups according to the morphology of pleopods l and 2, including C. oblonga within the group with uniramous and two-segmented pleopod l, and with pleopod 2 absent (Sakai 2005: 25, 32). The same author ( Sakai 2011: 355) later considered the morphology of male pleopods 1 and 2 as the single valid character for callianassid genera classification, redescribing, among others, the genera Callianassa (to include species with male pleopod 1 uniramous and bisegmented, and with male pleopod 2 uniramous, in which the protopod rarely protruded short distolaterally), Trypaea (male pleopod 1 uniramous, uni-, bi- or trisegmented, and male pleopod 2 absent), and Cheramus (male pleopod 1 absent, or uniramous and bisegmented, and with slender, biramous male pleopod 2), and subsequently, returning Callianassa oblonga to the genus Cheramus (as Cheramus oblongus ).

All the foregoing propositions of classification were based on pleopod morphology. However, neither of the only two males ever recorded (the type specimen and the one captured during the Maurit surveys) displayed pleopod 2, and there is no evidence of their existence (at least in our material). In consequence, we propose here the relocation of C. oblonga to the genus Trypaea as Trypaea oblonga ( Le Loeuff & Intès, 1974) n. comb.

Figures

FIGURE 2. Trypaea oblonga (Le Loeuff & Intès, 1974) n. comb. Male MU 215: A) Left pleopod 4; B) Left pleopod 4 appendix interna detail. Female MUDR 26: C) Left pleopod 1; D) Left pleopod 2, mesial view. Scale bars: A, 2 mm; B, 0.2 mm; C, D, 1 mm.