Guinope, Thoma & Felder, 2020

Thoma, Brent P. & Felder, Darryl L., 2020, A new genus and species of xanthoid crab (Decapoda: Brachyura) from offshore hard bank habitats in the Gulf of Mexico, Zootaxa 4731 (3), pp. 403-413 : 404-405

Guinope n. gen.

Type species. Guinope tiara n. sp.

Diagnosis. Carapace broader than long, weakly convex, regions poorly defined by shallow grooves, surface granulate, granules increasing in size and density anteriorly in each region; frontal margin bilobed, slightly thickened by dense granules, median fissure distinct; anterolateral teeth moderately-well developed, arrayed in arc, first and second fused, nearly obsolete, giving appearance of three teeth, third and fourth acute to subacute with third directed anteriorly to anteromedially, fourth directed anteriorly to anterolaterally, fifth tooth reduced to small acute process. Chelipeds densely granulate on superior and extensor surfaces, carpus with superoflexor margin having two distinct acute to subacute processes, largest near distal margin, apex directed dorsally. Pereopods two through five (walking legs) with merus extensor margin bearing distinct row of distally-directed, subacute, triangular teeth, strongest distal. Male pleon anteriorly elongate, reaching beyond first pereopod condyle; second somite width subequal to that of first, obscuring seventh sternite except for, at most, small sliver to either side; third through fifth fused, sutures visible externally only as small notches laterally; telson rounded. Male first pleopod (gonopod) long, sinuous, reaching beyond anterior end of median sternal groove in pleonal depression, visible to either side of flexed pleon distally, apex narrowly spatulate. Male second pleopod one-third or less length of first.

Etymology. The generic name Guinope honors our greatly admired colleague, Danièle Guinot, for her extensive contributions to studies of xanthoid and other brachyuran crabs over a very distinguished career.

Assigned species. Guinope tiara n. gen., n. sp. (monotypic)

Remarks. Previous molecular genetic analyses showed that the species now assigned to Guinope n. gen. shared little phylogenetic affinity with other xanthoid genera, though it did appear closely related to Melybia thalamita ( Stimpson, 1871) in a clade sister to panopeids and pseudorhombilids ( Thoma et al. 2014). Analyses based on three mitochondrial markers, 12S rDNA, 16S rDNA, and cytochrome oxidase I (COI), along with three nuclear markers, 18S rDNA, enolase (ENO) and histone H3 (H3) recovered Guinope tiara n. gen., n. sp. (then under “Gen. nov., sp. nov. near Garthiope barbadensis ”) as sister to Melybia thalamita in a clade proposed to represent Linnaeoxanthidae Števčić, 2005 . This clade (i.e., now Guinope tiara n. gen., n. sp. + Melybia thalamita ) was in turn sister to a clade comprised of Panopeidae Ortmann, 1893 and Pseudorhombilidae Alcock, 1900 ( Thoma et al. 2014), though without these molecular phylogenetic analyses having included the Indo-West Pacific type species of the family, Linnaeoxantho acanthomerus ( Rathbun, 1911) (see Mendoza et al. 2012; Thoma et al. 2014). Morphologically, Guinope n. gen. shares few of the diagnostic features proposed by Mendoza et al. (2012) to join the linnaeoxanthid genera Linnaeoxantho and Melybia , and differs from them in lacking any evidence of a ventrodistally directed spine on the posterior (inferoventral) margin of any ambulatory pereopod. For the present, we regard its assignment to the family Linnaeoxanthidae as provisional, pending molecular genetic analyses that include the type of the family.

In a previous study of the group, focused on Old World xanthoids, analyses inferred from four loci (12S, 16S, COI, and H3) recovered a similar arrangement with Guinope tiara n. gen., n. sp. (therein “new genus nr. Garthiope ”) as sister to a clade comprised of taxa now considered to represent the families Panopeidae and Pseudorhombilidae ( Lai et al. 2011, fig. 1). While support for this arrangement was poor (BS 56 / pP 62), it must be noted that Guinope tiara n. gen., n. sp. was represented by only two (12S and 16S rDNA) of the four genes applied to most other species in this particular analysis.

In earlier analyses of the group, the relationship between Guinope tiara n. gen., n sp. and other representatives of Xanthoidea varied by loci, with analyses of 12S and 16S rDNA inferring somewhat different relationships. In analysis of 16S rDNA, Guinope tiara n. gen., n. sp. (therein as “ Garthiope barbadensis ”) was recovered as sister to a poorly supported clade (BS <50/ pP 68) comprised of Glyptoplax smithii A. Milne-Edwards, 1880b and Eucratopsis crassimanus ( Dana, 1851) ( Thoma et al. 2009, fig. 1). In the same study, analyses of 12S rDNA recovered Guinope tiara n. gen., n. sp. (again as “ Garthiope barbadensis ”) near the root as sister to all other xanthoids + pilumnoids, but support values for this arrangement were generally poor as well (BS <50 / pP <50) ( Thoma et al. 2009, fig. 2). While not recognized at the time (nor in Felder & Thoma 2010), that analysis did include Garthiope spinipes (A. Milne-Edwards, 1880) , type species of its genus, albeit as a juvenile originally misidentified as Batodaeus urinator . In the analyses of Thoma et al. (2014), labeling the type-species of Garthiope was corrected, showing that genus to be well separated from the clade herein assigned to the Guinope n. gen.

Although phylogenetic relationships Guinope tiara n. gen., n. sp. to other xanthoids remain somewhat unresolved, molecular genetic analyses unambiguously show that Guinope tiara n. gen., n. sp. is part of the superfamily Xanthoidea and that it has affinities to both panopeids and pseudorhombilids. While current analyses indicate that Guinope tiara n. gen., n. sp. is more closely related to Melybia thalamita than to any other genetically compared xanthoid, it clearly represents a separate genus from Melybia , both as inferred from molecular phylogenetic analyses and as readily evident in morphology. Guinope n. gen. shares with Melybia a generally quadridentate anterolateral carapace margin, but the overall carapace shape and marginal tooth development, proportions of the chelipeds, and armor of the pereopods is not similar in the two genera. Further morphological comparisons of the sympatric species representing these two monotypic genera are undertaken under Remarks following the description of Guinope tiara n. gen. n. sp. that follows.