Megaesthesius migmus, 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 : 90-91

publication ID	https://doi.org/ 10.11646/zootaxa.4209.1.1
publication LSID	lsid:zoobank.org:pub:849BAB5C-464A-4B4A-A586-5742411EDC01
DOI	https://doi.org/10.5281/zenodo.5617233
persistent identifier	https://treatment.plazi.org/id/F16BFB33-FFFA-FFA1-FF6A-F9E9FC51F995
treatment provided by	Plazi
scientific name	Megaesthesius migmus
status	sp. nov.

Treatment

Megaesthesius migmus View in CoL n. sp.

( Figs. 19 View FIGURE 19 T, X; 20A, B; 27C; 34D; 48D; 55D; 62C; 82D–F; 88G; 92C; 103)

Type material. Holotype male (4.4 × 4.9 mm) ( NMCR) [photographed], Philippines, Bohol Sea, off Pamilacan I., PANGLAO 2005, stn CP2344, 09°28.4’N, 123°50.1’E, 128–142 m, 23.05.2005. GoogleMaps

Paratypes: 1 female (4.6 × 5.2 mm) ( ZRC 2015.243 View Materials ) [photographed], Phillippines, Bohol Sea, off Balicasag I., PANGLAO 2005, stn CP2240, 09°29’N, 123°44'E, 271–318 m, 27.05.2005, 23.05.2005 GoogleMaps ; 1 paratype female (4.7 × 5.7 mm) ( ZRC 2015.244 View Materials ), Bohol Sea, Maribojoc Bay , PANGLAO 2005, stn CP2407, 09°41’N, 123°48'E, 256–268 m, 01.06.2005 GoogleMaps .— 1 female (3.9 × 4.5 mm) ( ZRC 2015.245 View Materials ) [photographed], northwestern Philippines, AURORA 2007, stn CP2711, 15°19’N, 121°32’E, 184–200 m, 28.05.2007 GoogleMaps .

Diagnosis. Carapace ( Figs. 20 View FIGURE 20 A, B; 103A–C) subquadrate, 1.1 wider than long; front bilobed, with deep median cleft; dorsal surface with low, spherical tubercles; post-orbital margins sloping to angular anteroexternal angle marked by small tooth in some specimens. Lateral margins straight, parallel to each other, each with 3 straight, dented regions separated by deep notches, acute or obtuse tooth on posterior third of margin. Posterior margin nearly straight. Long orbits, eye peduncle ( Figs. 27 View FIGURE 27 C; 103D) conspicuously long, immobile, cornea reduced, non-pigmented. Epistome ( Fig. 19 View FIGURE 19 T) compressed, posterior margin with broad median lobe with fissure, narrow, nearly straight lateral margins without fissures. Antennule ( Fig. 27 View FIGURE 27 C) greatly enlarged, particularly in males. Third maxillipeds ( Fig. 34 View FIGURE 34 D) nearly fill buccal cavern when closed; merus subtriangular, outer margin dentate; ischium subquadrate, dentate outer margin, longer than merus; outer margins of merus, ischium dentiform. Chelipeds ( Figs. 20 View FIGURE 20 A, B; 103A–C) subequal in length, nearly similar in both sexes; cutting margins of both chelae ( Fig. 48 View FIGURE 48 D) with broad, shallow teeth in both sexes; ventral margin of palm dentiform; ventral surface of cheliped merus smooth. Proportionally long ambulatory legs ( Fig. 20 View FIGURE 20 A, B), P5 merus not reaching front when folded. Dorsal, ventral margins of meri, dorsal margin of carpus of ambulatory legs with minute teeth. P5 merus 0.7‒0.8 cl. Small, sharp tooth on inner margin of cheliped carpus, ventral surface of cheliped merus smooth in both sexes. Fused thoracic sternites 1, 2 ( Fig. 55 View FIGURE 55 D) broadly triangular, proportionally wide, short. Male pleon with lateral margins of somite 6, fused somites 3–5 nearly straight; postero-lateral regions slightly swollen; telson proportionally short ( Figs. 55 View FIGURE 55 D). Outer (ventral) surface of penis calcified, resembling plate between “supplementary plate”, sternite 8 ( Fig. 19 View FIGURE 19 X). G1 ( Fig. 82 View FIGURE 82 D, E) slender, distal segment, straight, with spinules, apex slanted. G2 ( Fig. 82 View FIGURE 82 F) nearly as long as G1, straight; slender, distal segment long, curved, as long as basal segment, directed inward. Somites of female pleon ( Fig. 88 View FIGURE 88 G) with gently convex margins; telson proportionally short. Sterno-pleonal cavity of female ( Fig. 92 View FIGURE 92 C) deep, vulvae far apart from each other on outer margins of cavity close to suture 5/6.

Colour. The carapace is white to pinkish-white beige in life, with white chelipeds and ambulatory legs ( Fig. 103 View FIGURE 103 ).

Etymology. From the Greek migma for “mixture” in reference to the mixture of characters of the other species of Megaesthesius that characterise the new species.

Remarks. Megaesthesius migmus n. sp. is distinct from M. sagedae in having the carapace proportionately wider ( Fig. 20 View FIGURE 20 A, B versus Fig. 19 View FIGURE 19 A, B), the lateral margin of the carapace having distinct lobiform teeth ( Fig. 20 View FIGURE 20 A, B) (only small spines in M. sagedae , Fig. 19 View FIGURE 19 A, B), the aesthetascs of the antennules are distinctly shorter ( Fig. 27 View FIGURE 27 C versus Fig. 27 View FIGURE 27 B); the fingers of the chela are relatively more slender and longer ( Fig. 48 View FIGURE 48 C versus Fig. 48 View FIGURE 48 D); and the G1 is relatively longer and more slender ( Fig. 82 View FIGURE 82 D, E in contrast to Fig. 82 View FIGURE 82 A, B). As discussed earlier, the calcified plate on the surface of the penis is mobile in the single male of M. migmus examined ( Fig. 19 View FIGURE 19 X) but is immobile in M. sagedae ( Fig. 19 View FIGURE 19 W); but with one male of the former known, it is not clear if this is also a species-specific character.

Compared to M. yokoyai , M. migmus n. sp. is easily distinguished by its proportionately longer ambulatory legs ( Fig. 20 View FIGURE 20 A, B versus Fig. 19 View FIGURE 19 E); the outer margins of the merus and ischium of the third maxilliped are lined with sharp teeth ( Fig. 34 View FIGURE 34 D) (unarmed in M. yokoyai , Fig. 34 View FIGURE 34 B); the fingers of the chela are longer and the ventral margin of the palm is lined with sharp teeth ( Fig. 48 View FIGURE 48 D) (fingers short with the ventral margin of the palm smooth in M. yokoyai , Fig. 48 View FIGURE 48 E); and the G1 is proportionately more slender with the distal part tapering and the opening large ( Fig. 82 View FIGURE 82 D, E) (G1 relatively stouter, with distal part not tapering and the opening rounded in M. yokoyai , Fig. 82 View FIGURE 82 G–I).