[Crustacea • 2020] Lithopanopeus truesdalei • A New Genus and Species of Mud Crab (Brachyura, Panopeidae) from Shoreline Waters of the western Gulf of Mexico
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| Lithopanopeus truesdalei Felder & Thoma, 2020 |
Abstract
Several specimens of a small panopeid crab from coastal waters of the western Gulf of Mexico were long suspected to represent an undescribed species and are herein designated as representatives of a new genus. While the originally collected specimens from over four decades ago were not of gene-sequence quality, later collections from the same locality produced materials that yielded sequence data for inclusion in molecular phylogenetic studies. Building on results of those analyses, the present taxonomic description draws upon morphology to support the description of a unique species in which especially the male first gonopods differ from those of all other described panopeid genera. To date, the species remains known from only two western Gulf of Mexico sites, both of which are wave-washed intertidal rocky habitats where substrates are heavily burrowed by boring bivalves and sipunculans. While we cannot exclude the possibility that the species was introduced, recurrent collections show its populations to be at very least persistent, the species most likely being a long-overlooked among a confusing hard-substrate assemblage of small panopeid crabs.
Several specimens of a small panopeid crab from coastal waters of the western Gulf of Mexico were long suspected to represent an undescribed species and are herein designated as representatives of a new genus. While the originally collected specimens from over four decades ago were not of gene-sequence quality, later collections from the same locality produced materials that yielded sequence data for inclusion in molecular phylogenetic studies. Building on results of those analyses, the present taxonomic description draws upon morphology to support the description of a unique species in which especially the male first gonopods differ from those of all other described panopeid genera. To date, the species remains known from only two western Gulf of Mexico sites, both of which are wave-washed intertidal rocky habitats where substrates are heavily burrowed by boring bivalves and sipunculans. While we cannot exclude the possibility that the species was introduced, recurrent collections show its populations to be at very least persistent, the species most likely being a long-overlooked among a confusing hard-substrate assemblage of small panopeid crabs.
Keywords: Crustacea, Xanthoidea, mud crab, western Atlantic, shoreline
Taxonomy
Superfamily Xanthoidea MacLeay, 1838
Family Panopeidae Ortmann, 1893
Lithopanopeus n. gen.
Type species. Lithopanopeus truesdalei n. sp., by present designation.
Diagnosis. Carapace outline ovoid to subhexagonal, length about ¾ greatest width (including lateral extremes of anterolateral teeth, slightly less in large females), fronto-orbital width less than ¾ greatest carapace width, front more than twice width of orbit, with deep median V-shaped notch, laterally forming lobiform tooth; dorsal surface appearing nearly smooth with scattered fine granules, coarser near margins, across front, or where forming rows across anterior carapace regions; areolations weakly marked, separated at most by shallow depressed furrows anteriorly, anterior regions surmounted by elongate ridges of low granules; anterolateral margin with five distinct anterolateral teeth (counting as first the outer orbital), second anterolateral tooth rounded subtriangular to lobiform, partially coalesced to first tooth, third and fourth teeth subtriangular, acute to subacute tips directed anteriorly to anterolaterally, fifth tooth smallest, distinctly developed, subtriangular; lacking subhepatic tubercle below margin. Eyestalk short, ending in globular cornea about width of eyestalk shaft. Distalmost article of antennal peduncle elongate, rectangular in outline, reaching to and filling orbit hiatus. Chelipeds unequal, dorsal surface finely granulate with some enlarged granules in short rows and ridges; carpus dorsal surface irregular, distal furrow extending from superior to distolateral surface, deeply depressed, inner corner marked by enlarged blunt, distally directed tooth; propodus upper surface weakly convex longitudinally, granulation slightly coarser, some in short transverse rows dorsally, weakly defined broken dorsal furrow between very low to obsolete longitudinal ridge to internal side and stronger rounded longitudinal ridge to external side; major chela dactylus opposable margin bearing enlarged, lobiform, basal tooth. Ambulatory pereopod merus, carpus, and propodus superior margin bearing narrow tract of subacute granules or small tubercles, superior margin of merus including row of long, closely set, plumose, feathery setae, these less dense on more distal articles, distalmost articles bearing broad tracks of very short, densely plumose setae on margins, densest on inferior and especially superior surface of dactylus; dactylar-propodal locking mechanism not developed, dactyl inferior margin lacking calcareous prehensile tooth. Male thoracic sternum length from apex to suture between fourth and fifth sternites (measured at edge of pleon near or exceeding 0.7 greatest width of fourth sternite (including episternites), sternopleonal cavity in fourth sternite not sculpted or excavate to accommodate first gonopod tips; fifth sternite with granulate press button to each side of sternopleonal cavity; male pleonal margins thick, reflected toward thoracic sternum, edges appearing heavy, press-button depression deep, thick; third to fifth somites of male pleon fused, second somite spanning almost full width of sternum, narrow tract of eighth sternite exposed between lateral margin and condyle of fifth pereopod coxa, third somite about 1.2 width of second, lateral flange reaching to base of fifth peropod condyle. Male first gonopod tip of modified trifid panopeid form, sternomesial side of trunk lined by heavy teeth in distal half and subterminally with broad, acute, bladelike subterminal tooth. Male second gonopod less than 1/3 length of first. Female gonopore (including opening and surrounding lips or vulva) centered in anterior half of sixth thoracic sternite, in spanning more than half of sixth thoracic sternite adjacent length.
Etymology. The generic name Lithopanopeus merges the prefix “litho”, for its rocky habitat, with the suffix “panopeus”, derived from the type genus of Panopeidae. The gender is masculine. The few known specimens all have been found in association with calcareous intertidal rocks eroded by burrowing molluscs and sipunculan worms. Appropriately, the species bears close general resemblance to a number of other small panopeid crabs.
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