Pilumnus mantelattoi, Magalhães & Felder, 2019

Magalhães, Tatiana & Felder, Darryl L., 2019, A new species of the hairy crab genus Pilumnus (Decapoda: Brachyura: Pilumnidae) from Belize, Zootaxa 4711 (1), pp. 175-184 : 178-182

Pilumnus mantelattoi n. sp.

( Figs. 1 , 2 )

Material examined. Holotype, 1 ov. female, USNM 1536868 (= ULLZ 10033 ) (cw 5.92 mm, cws 5.10 mm, cl 3.8 mm, fow 4.5 mm), Twin Cays, Stann Creek, Belize, coll. D.L. Felder, J.M. Felder, H.D. Bracken, & A.M. Windsor, 08 April 2007.

Diagnosis. Carapace outline sub-hexagonal, dorsal surface of the carapace with dense short pubescence concealing surface anteriorly, regions very poorly marked; frontal lobes convex to either side of strong median indentation; supraorbital and infraorbital margins without spines; anterolateral margin with 4 spines, including that of outer orbital angle. Major chela and carpus with superior upper, outer, and inferior lower surfaces covered by with longitudinal rows and fields of heavy spines or spiniform tubercles, between which the rows are coarse interspersed among smaller granules and setae.

Description. Carapace sub-hexagonal ( Figs. 1A , 2A ) with anterior and posterior regions both sloped downwards, dorsum longitudinally arched; dorsal surface with dense short pubescence, densest and, most concealing anteriorly, with few tufts of longer setae, some clavate, on the gastric and branchial regions; dorsal surface overall smooth, bearing few small granules, regions poorly marked; fronto-orbital width more than half the greatest width of carapace, excluding spines; front with two divided into 2 prominent convex lobes, separated by strong median indentation, lobes pubescent, distal margins finely granulate; antennal sulcus between lateral and to frontal lobe rounded, unarmed, sulcus ending terminating laterally in antennal tooth; subhepatic region with single tooth and small granules, otherwise smooth to finely granulate; pterygostomial region smooth; anterolateral margin with 4 spines, anteriormost broad, formed of outer orbital angle, surmounted by short subacute spine, second through fourth distinctly conical, decreasing in size posteriorly; supraorbital and infraorbital margins ( Figs. 1A, 1B , respectively) lacking strong teeth or spines, lined by small rounded to subacute granules. Third maxilliped ( Fig. 1C ) ischium twice length of merus; ischium and merus both with acute distomesial corners, that of merus produced distally. Chelipeds unequal ( Figs. 1D, 1E ), carpus and chela covered with spiniform tubercles, granules and pubescence on upper, lower, and outer surfaces, entirely covering outer surfaces of palms, strong elongate setae, some clavate, especially on outer and upper surface of chela, including dactylus and fixed finger. Major cheliped ( Fig. 1D ) merus upper margin with row of distally inclined teeth, distalmost much the largest, flanged proximally, acute spiniform tip directed distally, lower margin lined by small dentiform tubercles and single strong spiniform tooth distally; carpus with strong tooth at inner upper angle, arched across upper surface and terminated in an elongate, acute, corneous spine; propodus upper margin with longitudinal arched tract of 5 strong spines, outer surface with multiple longitudinal rows of spines to subacute tubercles covering entire palm, becoming obscure on lower surface, row of 4 spines extending onto outer surface of fixed finger; dactylus upper surface bearing strong spiniform tubercles in proximal 2/3, strongest row along outer ridge of upper margin. Ambulatory legs (pereopods 2–5) ( Figs. 1F, 1G , 2A, 2B ) with upper surfaces of distal three articles pubescent; meri with scattered stiff setae marginally, upper margins of most with longitudinal row of 3 or 4 strong, variably hooked, spines, usually in addition to one or more small spinules, margins ending distally in strong corneous terminal spine, lower margins with row of much smaller spines or denticles; carpi upper margins with row or tract of typically 4 or 5 strong corneous spines, often in addition to one or more small spinules, margins ending distally in strong corneous terminal spine, stiff setae of varied lengths on upper and outer surfaces; propodi upper margins with row or tract of typically 3 or 4 strong corneous spines, stiff setae of varied lengths on upper, lower and outer surfaces, this article in pereopod 5 relatively shorter and broader than in other ambulatory legs; dactyli upper and lower surfaces with tracts of short thick stiff corneous setae, those of lower margins larger, the largest forming row of 5–9 heavy hooked spinules, article terminus forming hooked corneous talon 1/4 to 1/3 length of article.

Live coloration. Background dorsal surface of the carapace color whitish to translucent, with dark and light orange and white spots; chelipeds and ambulatory legs with alternating orange and white spots, the orange spots larger than the white; eggs deep orange ( Figs. 2A and B ).

Etymology. The species name “ mantelattoi ” is adopted to honor our colleague Fernando L. Mantelatto, a cherished friend and respected colleague who has made many contributions to molecular phylogenetic studies of western Atlantic decapod crustaceans and also supported all the academic research of one of the authors (T. Magalhães).

Remarks. Among western Atlantic congeners that exhibit convex frontal lobes, P. mantelattoi n. sp. can be distinguished by (1) having 4 (rather than 3 or 5) anterolateral spines ( Figs. 1A, B , 2A ), (2) having the walking pereopod lengths less than twice the carapace width ( Figs. 1A, F, G , 2A ), and (3) having the palm of the major cheliped with the entire outer surface roughened by spines, granules, and/or setae ( Figs. 1D , 2 ). The third character clearly separates it from the somewhat similar appearing and sympatric P. floridanus Stimpson, 1871 , in which lower portions of the palm are relatively bare ( Rathbun 1930; Williams 1965: 170, fig. 160). However, the new species does resemble P. floridanus in both the pubescence concealing the anterior part of the carapace and in the supraorbital margin lacking well-developed teeth or spines. While, as in P. mantelattoi n. sp., the entire outer surface of the major cheliped palm is roughened by tubercles, spines, granules, and/or setation in both P. gemmatus Stimpson, 1860 (see also Rathbun 1930: 483, 513, pl. 207, figs. 1–3) and P. diomedeae Rathbun, 1894 (see also Rathbun 1930: 501, pl. 202, figs. 2, 3), in these two species the upper margins of the orbit are armed with distinct rounded tubercles or acute to subacute teeth.

Interspecific pairwise distance based on COI ranged from 7% ( P. pannosus vs. P. lacteus ) to 20% ( P. mantelattoi n. sp. vs. P. marshi ) ( Table 2 ). The minimum value observed between P. mantelattoi n. sp. and other Pilumnus species was 11%, this being among other interspecific values within the genus ( Table 2 ) and thus supporting validity of this new species. The interspecific pairwise distances based on 16S ranged from 2% ( P. lacteus vs. P. pannosus ) to 8% ( P. gemmatus vs. P.sayi ) ( Table 2 ). The minimum value observed between P. mantelattoi n. sp. and any other Pilumnus species was 3%, again among other interspecific values found within the genus and thus supporting validity of this new species.

The present paper is limited in its comparative scope to congeners known from the western Atlantic, underpinning our species description. While this encompasses most relatives known to be of similar habitus and habitat to our new species, worldwide treatment of the genus is doubtless warranted. Such coverage, including descriptions of putatively undescribed species from other than western Atlantic waters, may be required to assure that P. mantelattoi n. sp. is not an introduction into western Atlantic waters. While such coverage is well beyond the scope of the present paper, we at very least provide insights into morphological and molecular characters of potential utility in such future analyses.

Figures

FIGURE 1. Pilumnus mantelattoi n. sp., holotype, ovigerous female, USNM 1536868.A, carapace, dorsal view; B, right anterolateral margin of carapace, ventral view; C, left third maxilliped, outer view; D, carpus and chela of right major cheliped, outer surface; E, major cheliped, upper surface; F, right fourth pereopod, lateral surface; G, right fifth pereopod, lateral surface.

FIGURE 2. Pilumnus mantelattoi n. sp., ovigerous female holotype, USNM 1536868 showing live coloration. A, dorsal view; B, ventral view.

Tables

TABLE 2. Pairwise genetic distance matrix of COI (below diagonal) and 16S (above diagonal) sequences among specimens of Pilumnus from the western Atlantic. Locality abbreviations: BEL = Belize; BRA = Brazil; GOM = Gulf of Mexico; PAN = Panama.

	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15
1_ P. caribaeus _PAN		0.045	0.051	0.042	0.045	0.058	0.049	0.049	0.047	0.052	0.045	0.056	0.065	0.058	0.054
2_ P. dasypodus _PAN	0.113		0.058	0.049	0.051	0.065	0.060	0.049	0.038	0.054	0.051	0.060	0.056	0.070	0.051
3_ P. floridanus _BEL	0.125	0.132		0.008	0.010	0.065	0.058	0.058	0.052	0.058	0.054	0.063	0.070	0.063	0.063
4_ P. floridanus _BRA	0.125	0.132	0.000		0.002	0.058	0.054	0.054	0.045	0.051	0.047	0.058	0.065	0.058	0.056
5_ P. floridanus _GOM	0.125	0.132	0.000	0.000		0.060	0.056	0.056	0.047	0.054	0.049	0.060	0.067	0.060	0.058
6_ P. gemmatus _PAN	0.137	0.164	0.161	0.161	0.161		0.070	0.056	0.049	0.067	0.058	0.061	0.065	0.084	0.034
7_ P. holosericus _PAN	0.159	0.147	0.136	0.136	0.136	0.156		0.038	0.052	0.052	0.065	0.045	0.049	0.052	0.058
8_ P. lacteus _BEL	0.140	0.144	0.121	0.121	0.121	0.152	0.119		0.051	0.051	0.056	0.019	0.021	0.054	0.047
9_ P. longleyi _BEL	0.141	0.161	0.154	0.154	0.154	0.160	0.195	0.157		0.056	0.043	0.054	0.063	0.065	0.049
10_ P. marshi _BEL	0.123	0.127	0.159	0.159	0.159	0.156	0.167	0.152	0.160		0.070	0.063	0.054	0.056	0.063
11_ P. nudimanus _PAN	0.168	0.164	0.164	0.164	0.164	0.154	0.178	0.163	0.156	0.176		0.054	0.070	0.069	0.056
12_ P. pannosus _GOM	0.131	0.146	0.135	0.135	0.135	0.122	0.127	0.074	0.162	0.154	0.155		0.036	0.061	0.052
13_ P. reticulatus _BRA	0.145	0.135	0.129	0.129	0.129	0.129	0.113	0.098	0.152	0.154	0.150	0.100		0.065	0.056
14_ P. sayi _GOM	0.104	0.150	0.151	0.151	0.151	0.158	0.157	0.162	0.157	0.123	0.183	0.167	0.163		0.065
15_ P. mantelattoi n.sp.	0.156	0.154	0.174	0.174	0.174	0.115	0.184	0.152	0.152	0.202	0.164	0.152	0.145	0.178