Pseudopanopeus pusillus (A. Milne-Edwards, 1880) Felder, 2020

Felder, Darryl L., 2020, A new crab of the genus Nanoplax from the Gulf of Mexico, and assignment of Micropanope pusilla to a new genus (Crustacea, Brachyura, Pseudorhombilidae), Zootaxa 4810 (3), pp. 531-545 : 541-544

Pseudopanopeus pusillus (A. Milne-Edwards, 1880) n. comb.

( Fig. 4 A–F; 5A–D)

Micropanope pusilla A. Milne-Edwards 1880: 327 , pl. 54, figs. 4–4b; Rathbun 1930: 427, 431, 434, 435, 585, pl. 179 (figs. 7, 8); 1933: 66; Wass 1955: 137 (key), 157; Powers 1977: 98–99; Garth 1978: 326; Lemaitre 1984: 438, 440, 441, 443, fig. 7A–I, fig. 8A–C; Abele & Kim 1986: 58, 609 (key, as “pusilus” [sic]), 624, 625 (text figures a–c); Melo 1996: 363, 365 (with text figure); Ng et al. 2008: 203; Felder et al. 2009: 1085; Thoma et al. 2014: 95, table 1, fig. 1; Poupin 2018: 218, 219, fig. 246.

Glyptoplax pusilla, Rathbun 1899: 628 ; 1901: 33; A. Milne-Edwards & Bouvier 1923: 328.

Material examined. Atlantic coast of Florida. 1 male, damaged ( ULLZ 9023 = USNM 1536349 ) off Fort Pierce Inlet , 27˚ 29.01’ N, 80˚ 10.93’ W, 15 m, 9 September 2003 . Northeastern Gulf of Mexico . 2 males, 1 female (fragmentary syntypes, MCZ 2984 ), west Florida shelf, Bache Expedition, 17 m, 1872–1874 ; 1 male, cw 3.6 mm ( ULLZ 7587 = USNM 1536341 ) northwest Florida shelf, 28˚ 55.12’ N, 85˚ 09.62’ W, 54 m, 3 July 2006 ; 2 males, cw 4.1, 5.2 mm ( ULLZ 2388 = USNM 1536336 ) west of Sanibel Island , Florida, 26˚ 25.5’ N, 83˚ 23.7’ W, 53 m, 30 July 1980 ; 3 males, cw 2.7, 3.6, 4.1 mm, 1 female, cw 3.2 mm ( ULLZ 1929 = USNM 1536334 ) west of Sanibel Island , Florida, 26˚ 24.5’ N, 83˚ 22.5’ W, 53 m, 31 July 1980 ; 2 males, cw 3.8, 4.7 mm, 2 females, cw 3.6, 3.8 mm ( ULLZ 1940 = USNM 1536335 ) west of Sanibel Island , Florida, 26˚ 26.5’ N, 83˚ 01.8’ W, 40 m, 31 July 1980 ; 1 male, cw 5.7 mm ( ULLZ 8058 = USNM 1536348 ) west Florida shelf, 27˚ 37.41’ N, 84˚ 01.99’ W, 60 m, 6 July 2006 ; 1 male, cw 4.4 mm ( ULLZ 8134 = USNM 1536346 ) west Florida shelf, 27˚ 37.41’ N, 84˚ 01.99’ W, 60 m, 6 July 2006 ; 1 male, cw 5.9 mm ( ULLZ 7178 = USNM 1536345 ) west Florida shelf, 28˚ 37.26’ N, 84˚ 28.38’ W, 45 m, 4 July 2006 ; 1 male, cw 3.7 mm, 1 ov female, cw 3.5 mm ( ULLZ 8139 = USNM 1536349 ) northwest Florida shelf, 29˚ 17.48’ N, 85˚ 38.79’ W, 56 – 58 m, 8 July 2006 ; 3 males, cw 5.2, 5.4, 5.6, 5.2 mm ( ULLZ 14362 = USNM 1536353 ) northwest Florida shelf, 29˚ 49.62’ N, 86˚ 08.83’ W, 42 – 44 m, 8 June 2012 ; 6 males, cw 5.0 – 6.4 mm, 4 females, cw 3.1 – 5.1 mm ( ULLZ 14349 = USNM 1536354 ) northwest Florida shelf, 29˚ 49.62’ N, 86˚ 08.83’ W, 42 – 44 m, 8 June 2012 ; 1 male, cw 5.0 mm, 1 ovi female, cw 4.0 mm ( ULLZ 14360 = USNM 1536352 ) northwest Florida shelf, 30˚ 01.00’ N, 86˚ 36.54’ W, 55–57 m, 7 June 2012 ; 1 female, cw 5.3 mm ( ULLZ 2386 = USNM 1536342 ) in muricid gastropod shell, northwest Florida shelf, 30˚ 02’ N, 86˚ 20’ W, 25 m, 5 April 1973 . Southwestern Gulf of Mexico . 1 male, cw 4.5 mm ( ULLZ 6803 = USNM 1536338 ) Campeche Bank , rubble, 21˚ 36.44’ N; 91˚ 04.66’ W, 20–30 m, 15 June 2005 ; 1 male, cw 3.9 mm ( ULLZ 7539 = USNM 1536343 ) Campeche Bank , 22˚ 15.88’ N, 90˚ 35.64’ W, 42 – 43 m, 6 June 2005 ; 1 female, cw 4.0 mm ( ULLZ 7335 = USNM 1536337 ) Campeche Bank , 22˚ 05.05’ N, 90˚ 43.23’ W, 51 m, 7 June 2005 ; 1 male, cw 6.1 mm, 2 female, cw 4.5, 4.3 mm ( ULLZ 12313 = USNM 1536351 ) Campeche Bank , calcareous rubble, 21˚ 34.18’ N, 91˚ 04.71’ W, 33 m, 12 June 2005 ; 1 male, cw 5.0 mm ( ULLZ 6776 = USNM 1536339 ) Campeche Bank , 22˚ 14.04’ N, 90˚ 41.63’ W, 37–43 m, 18 June 2005 ; 1 ov female, cw 3.9 mm ( ULLZ 7558 = USNM 1536340 ) Campeche Bank , 21˚ 15.29’ N, 90˚ 36.15’ W, 47 m, 12 June 2005 . Southeastern Gulf of Mexico . 1 male, cw 3.8 mm ( ULLZ 16618 = USNM 1536355 ) off Dry Tortugas, 24˚ 45.72’ N, 83˚ 35.31’ W, 67–68 m, 10 September 2014 ; 1 male, cw 3.8 mm ( ULLZ 8735 = USNM 1536350 ) off Dry Tortugas, 24˚ 43.19’ N, 83˚ 13.88’ W, 61 – 62 m, 3 June 2004 .

Rediagnosis. Carapace fronto-orbital width less than ¾ maximum width of carapace (between lateral extremes of anterolateral teeth), front wider than orbit; dorsal surface slightly convex, areolations distinct, separated by smooth furrows, dorsal surface otherwise with uniform fine granulation except where coarser across front; anterolateral margin with three prominent triangular anterolateral teeth (counting as one the outer orbital plus strongly coalesced obsolescent second tooth), fourth (posteriormost) anterolateral tooth dimunitive or obsolescent; larger two teeth sometimes directed anteriorly into acute tips; lacking subhepatic tubercle below margin. Eyestalk short, heavy, not narrowed terminally, ending in globular, rounded cornea, corneal diameter equal to or exceeding greatest width of eyestalk shaft. Chelipeds slightly heterochelous in most specimens, dorsal surfaces finely granulate; propodus upper surface elevated, broadly inflated, depressed weakly (if at all) between low ridge of inner border and slightly developed outer border; carpus dorsal surface irregular, with deeply depressed distolateral furrow, inner corner usually with at least one moderately enlarged acute tooth, distalmost usually largest if two or more present, major chela dactylus opposable margin bearing enlarged basal tooth. Ambulatory pereopod with merus superior margin texture nearly smooth, finely granulate to minutely denticulate, small denticles very low if present. Male third through fifth pleonites fused ( Fig. 4E ), second pleonite spanning almost full width of sternum when flexed, narrow tract of eighth sternite exposed between lateral margin and condyle of fifth pereopod coxa, third pleonite spanning full width of sternum. Male first gonopod (first pleopod) ( Fig. 4 A–C) subterminal spination including enlarged, proximally directed, articulated, very enlarged, elongate spine (usually one, sometimes two; length near 1/5 length of first gonopod trunk), distal to which shaft terminates in weakly flexed, narrow, distally directed, microspinulous finger of similar length. Male second gonopod (G2) ( Fig. 4D ) about two-thirds length of first, terminating in spiniform tip, 3 or 4 minute subterminal spinules at base of tip. Female gonopore (= vulva) ( Fig. 4F ) forming elongate oval, positioned obliquely to occupy anterior half of sixth sternite. Applicable GenBank sequence accession numbers from Thoma et al. (2014) are as follow for ULLZ 6776 = USNM 1536339: (12S) KF683050 ; (16S) KF682991 ; (18S) KF682887 ; (COI) KF682795 ; (ENO) KF682634 ; (H3) KF682556 .

Remarks. In the course of revising the genus Micropanope and suggesting its restriction to M. sculptipes and M. lobifrons, Guinot (1967, 1971 ) did not provide a definitive alternate generic assignment for M. truncatifrons and M. pusilla . As noted at the outset of the present study, addressing this issue for M. truncatifrons is herein deferred for lack of gene-sequence quality tissues to use in molecular phylogenetic comparisons and absence of a mature male specimen to exemplify gonopods and pleonal structures. The same cannot be said for Micropanope pusilla , which was included in the analyses of Thoma et al. (2014: fig. 1) and shown there to be widely divergent from the two species of Micropanope s.s. While regarded to be a poorly known species when reported upon by Lemaitre (1984), extensive collections of this small brachyuran have now been accumulated from the Gulf of Mexico, as well as Caribbean waters extending to Brazil ( Melo 1996; Felder et al. 2014; Poupin 2018). Access to a selection of these, as listed above, was essential to drafting of a diagnosis that applied broadly to the type species of the genus, building on the species diagnosis of Lemaitre (1984). Of particular relevance, morphological studies consulted for diagnosis of Pseudopanopeus n. gen. included the male voucher specimen (ULLZ 6776, herein = USNM 1536339) that had been sequenced for the phylogenetic analysis of Thoma et al. (2014), thus assuring that both sequence data and morphology correctly applied to an archived specimen of the new genus.

The characters applied by Rathbun (1930) in her identification key and in her diagnosis of M. pusilla were based upon a set of examined specimens that included three extant “cotypes” archived as two males and one female and cataloged under MCZ 2984. Recent reexamination of these fragmentary materials confirms that a relatively unarmed superior margin is found on the meri the ambulatory pereopods (especially pereopods three and four). This character usually separates the species (and thus the genus) from Micropanope s.s. as well as from most species formerly placed in that now restricted genus (members of Batodaeus , Garthiope, Microcassiope , Nanoplax , and Scopolius ), whatever genus might eventually accommodate M. truncatifrons , and the recently described Guinope . In contrast to the unarmed walking leg meri in Pseudopanopeus n. gen., which at most bears a few enlarged dentiform granules, the others have those meri armed by short but erect (often weakly hooked) spinules or conspicuously enlarged teeth or tubercules.

As shown in the above cited line figures of A. Milne-Edwards (1880) and Lemaitre (1984) other features of the anterolateral teeth and chelipeds represent additional characters that collectively separate Pseudopanopeus n. gen. from Micropanope s.s. and most species formerly placed in that now restricted genus. Owing to the obsolescent posteriormost (positionally fifth) anterolateral tooth and strong coalescence of the outer orbital tooth with an obsolescent second tooth, the anterolateral margin appears armed by only three prominent angular teeth (noting that one margin is obviously broken or misshapen on a possible syntype, MNHN-IU-2014-22611, in the Muséum national d’Histoire naturelle, Paris, as depicted in web accessible photographs at http://coldb.mnhn.fr/catalognumber/mnhn/ iu/2014-22611). In present and former Micropanope spp., either the second or fifth teeth (if not both), while often small, are more strongly expressed than in Pseudopanopeus n. gen.

It should also be noted that the chelae in Pseudopanopeus pusillus n. comb. are strongly developed in mature specimens, especially males, being dorsally elevated or swollen to the point of resembling those of Milnepanopeus Thoma & Felder, 2012 or Glyptoplax Smith, 1870 , the latter being a genus to which this species was at one point assigned ( Rathbun 1899, 1901; A. Milne-Edwards & Bouvier 1923). However, mature males of Pseudopanopeus pusill us n. comb. can be easily separated from these species, other present and former Micropanope spp., or the recently described Guinope tiara Thoma & Felder, 2020 , by the very unique sculpture and armor of the first gonopod ( Fig. 4 A –C ), herewith confirmed to match that of the fragile male syntypes (MCZ 2984). The shape of the first gonopod tip combined with the large, heavy, bluntly tipped, articulated, subterminal spine (sometimes double) is unlike any other first gonopod described for pseudorhombilid crabs. Garth (1978) commented on the utility of this character in his report of the species from Hogsty Reef, Bahamas, as did Lemaitre (1984: figs 7, 8), who provided line illustrations of the gonopods, carapace, sternum, pleon, and pereopods in his later report of the species from Cal Sal Bank, Bahamas. More recently, Poupin (2018) included a photograph of the first gonopod for a specimen from the Lesser Antilles.

The second gonopod ( Fig. 4D ) may also prove to be somewhat unique in Pseudopanopeus pusillus n. comb., at least in the degree to which subterminal microspination is developed at the base of the concave tip. To date, however, too few examples of this appendage are described at a level of detail that facilitates further comparisons. For mature females, the relatively narrow obliquely oriented ovoid gonopore (= vulva) ( Fig. 4F ) appears to distinguish the species from at least some other species of comparably sized pseudorhombilid crabs in which the pore is of more crescentic or circular shape or in which it spans a greater portion of the sixth sternite, but variations before and after embryonated egg deposition remain to be documented.

Figures

FIGURE 4. Pseudopanopeus pusillus n. comb. A–E, male, cw 3.8 mm (ULLZ 8735 = USNM 1536350); F, female, cw 4.3 mm (ULLZ 12313 = USNM 1536351).A, left first gonopod, sternal surface; B, same, pleonal surface; C, right first gonopod, pleonal surface; D, left second gonopod, pleonal surface; E, flexed proximal pleon, posterior pereopod coxae, and exposed sternites, posteroventral surfaces; F, fifth and sixth sternites, pleon extended to show female gonopores, ventral. Scale bars = 0.5 mm.