Microtopsis teschi, Ng, Peter K. L. & Castro, Peter, 2016

Ng, Peter K. L. & Castro, Peter, 2016, Revision of the family Chasmocarcinidae Serène, 1964 (Crustacea, Brachyura, Goneplacoidea), Zootaxa 4209 (1), pp. 1-182 : 86-87

Microtopsis teschi n. sp.

( Figs. 18 B, C; 80C–F; 81G–N)

Camatopsis rubida Forma B—Tesch 1918: 235 (part) [ Indonesia] (other Forma B specimens = Camatopsis minor n. sp.).

Type material. Holotype male (1.5 × 2.1 mm) (NNM-ZMA), Indonesia, northwest of Kei Is. , Siboga Expedition , stn 260, 90 m, 0 7.1899.

Paratype: 1 male (1.5 × 1.9 mm) (NNM-ZMA), collected with holotype.

Diagnosis. Carapace ( Fig. 18 B, C) subtrapezoidal, 1.3‒1.4 wider than long; front bilobed, with shallow median cleft; anterolateral margins arcuate, minutely granular, without distinct lobes or teeth, those on anterior part spiniform; dorsal surface covered with minute granules, more prominent on lateral surfaces. Epistome slightly depressed; posterior margin with widely semicircular median lobe with median fissure, semicircular lateral margins without fissures. Eye peduncle filling orbit, proportionally long, mobile; cornea reduced, pigmented. Third maxillipeds ( Fig. 80 C, D) apparently not filling buccal cavern when closed (left maxillipeds incomplete); merus subcircular, anteroexternal angle rounded; ischium subquadrate, about same length as merus. Chelipeds subequal in length, slightly heteromorphic in males; cutting margin of pollex of larger chela with dense short setae, less prominent on minor chela; ventral surface of cheliped merus almost smooth. Meri of ambulatory legs unarmed; proportionally long, slender dactyli; P5 merus 0.6 cl. Fused thoracic sternites 1, 2 broadly triangular, proportionally narrow, long; fused sternites 3, 4 relatively broad. Male pleon ( Fig. 80 F) broad, subtriangular, telson proportionally short. G1 ( Fig. 81 G‒L) relatively stout, longer, median part distinctly twisted, distal part slightly twisted, distal segment with short, spirally arranged spinules. G2 ( Fig. 81 M, N) straight, slender, distal segment with short, flaplike apex, almost as long as G1. Female unknown.

Etymology. The species is named after J. J. Tesch, whose seminal work on the Siboga goneplacoids has been so important in our study.

Remarks. This new species resembles M. takedai , but can easily be distinguished by the form of the carapace, male pleon, and G1 structure. In M. teschi n. sp., the dorsal surface of the carapace is covered with distinct small granules ( Fig. 18 B, C) (surface relatively smooth in M. takedai , Fig. 18 A), the anterior part of the lateral carapace margin has short spiniform granules ( Fig. 18 B, C) (granules lower, not spiniform in M. takedai , Fig. 18 A), the male telson is more triangular in shape ( Fig. 80 F) (relatively more semicircular in M. takedai , Fig. 80 B), male pleonite 6 is proportionally broader ( Fig. 80 F) (less broad in M. takedai , Fig. 80 B), and the G1 is proportionately longer, with the median twist more substantial and the tip more hook-shaped ( Fig. 81 G‒L) (cf. Fig. 81 A‒E for M. takedai ).

Microtopsis teschi n. sp. is only known from two very small but fully mature males that Tesch (1918) had identified as “ Camatopsis rubida forma B”. As discussed above, some of his B form belongs to a small-size species of Camatopsis , C. minor n. sp. The carapace of the paratype male of M. teschi n. sp. is relatively more spinular, especially along the posterolateral regions. The G1s of the two male specimens are, however, almost identical.

Distribution. Known only from Indonesia (Kei Is.). Depth: 90 m.

Figures

FIGURE 18. Overall dorsal view of species of Microtopsis. A, M. takedai, Japan: paratype female 3.6 × 2.7 mm (ZRC 2012.0146); B, M. teschi n. sp., Indonesia: holotype male 1.5 × 2.1 mm (NNM-ZMA); C, M. teschi n. sp., Indonesia: paratype male 1.5 × 1.9 mm (NNM-ZMA).

FIGURE 80. Third maxilliped and male pleon of species of Microtopsis. A, B, M. takedai, Japan: holotype male 2.4 × 3.1 mm (after Komai et al. 2012: figs. 3 A, 2 H, respectively); C, D, F, M. teschi n. sp., Indonesia: holotype male 1.5 × 2.1 mm (NNM- ZMA); E, M. teschi n. sp., Indonesia: paratype 1.5 × 1.9 mm (NNM-ZMA). A, left third maxilliped; B, F, male pleon; C, right third maxilliped (denuded, exopod not drawn); D, left third maxilliped (denuded, exopod not drawn); E, right third maxilliped (denuded). Scales = 0.5 mm.

FIGURE 81. Gonopods of species of Microtopsis. A ‒ F, M. takedai, Japan: holotype male 2.4 × 3.1 mm (after Komai et al. 2012: fig. 4); G ‒ N, M. teschi n. sp., Indonesia: holotype male 1.5 × 2.1 mm (NNM-ZMA). A ‒ C, G ‒ I, left G 1; D, E, J ‒ L, distal part of left G 1; F, M, left G 2; N, distal part of left G 2. Scales: G ‒ I, M = 0.1 mm; J ‒ L = 0.05 mm; N = 0.01 mm.