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| Guinope tiara Thoma & Felder, 2020 |
Abstract
Speciose populations of small xanthoid crabs on offshore banks and reefs of the northern Gulf of Mexico include a new species that is not assignable to presently named genera. Morphological diagnoses of the new genus and species are underpinned by previously published gene sequence analyses, originally misattributed to another species but now known to apply to this taxon. Herein named Guinope tiara n. gen., n. sp., the species shows molecular phylogenetic affinities with the family Linnaeoxanthidae Števčić, 2005, an ally of panopeid and pseudorhombilid crabs. Specimens from Occulina banks off the Florida Atlantic coast, previously regarded to represent Garthiope barbadensis (Rathbun, 1921), are not that species but instead morphologically assignable to Guinope n. gen. Whether they represent variants of Guinope tiara n. gen, n. sp. or a second species of the genus awaits the collection of fresh materials for DNA analyses.
Keywords: Decapoda, Xanthoidea, Linnaeoxanthidae, Guinope tiara, deep reef
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| Guinope tiara n. gen., n. sp. A–F, H, J, L, M = male holotype, cw 4.2 mm, northern Gulf of Mexico, Sackett Bank, Louisiana, 28° 37.81´ N, 89° 33.32´ W, 63–65 m, 28 June 2006, USNM 1577463 (= ULLZ 8183, part); G, I, K = male paratype, cw 5.2 mm, northern Gulf of Mexico, 120 km south of Mississippi-Alabama state border, 29° 15.68’ N, 88° 20.24’ W, 78–86 m, 27 August 2011, USNM 1547899 (= ULLZ 14614): A, carapace, left half only; B, buccal region; C, left third maxilliped, external surface; D, left third maxilliped, internal surface, E, right (major) chela, extensor surface; F, right (major) cheliped, superior surface; G, left (minor) chela, extensor surface; H, right second pereopod, anterior surface; I, pleon, external surface; J, posterior sternum overlain by flexed pleon, postero-ventral surface; K, anterior sternum overlain by flexed pleon, ventral surface; L, right first gonopod, pleonal-mesial surface; M, right second gonopod, lateral surface. Scale bars A, B, E–I = 2.0 mm; C, D, J, L, M = 1.0 mm; K = 0.4 mm. |
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| Guinope tiara n. gen., n. sp., color variants, northern Gulf of Mexico: A, female, cw 5.8 mm (USNM 1543849 = ULLZ 8173); B, male, cw 6.9 mm, USNM 1543895 (= ULLZ 8581); C, male, cw 3.7 mm, USNM 1543849 (= ULLZ 8173); D, ovigerous female, cw 4.5 mm, Sackett Bank, Louisiana, USNM 1547740 (= ULLZ 14552). |
Superfamily Xanthoidea MacLeay, 1838
Family Linnaeoxanthidae Števčić, 2005
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.
Guinope tiara n. gen., n. sp.
Diagnosis. Carapace wider than long (length near 2/3 width), dorsal surface weakly convex, regions poorlydefined, granulate, size and density of granules increasing anteriorly in each region; frontal margin bilobed, median fissure distinct; anterolateral teeth arrayed in arc, first and second often fused, appearing as weakly spiniform lobes to nearly obsolete, third and fourth acute to subacute, third directed anteriorly to anteromedially, fourth directed anteriorly to anterolaterally, fifth at most a denticle or subacute process. Chelipeds densely granulate on superior and extensor surfaces, carpus superoflexor margin with two distinct acute to subacute processes, largest distal, apex directed dorsally. Pereopods two through five (walking legs) with merus superior margin bearing distinct row of small distally directed, triangular teeth, strongest distal. Male pleon anteriorly elongate, reaching beyond first pereopod condyle; second somite width subequal to that of first, seventh sternite obscured or at most visible as small sliver to either side; third segment proximo-lateral extremities broadly subtriangular, unevenly rounded, slightly overreaching fifth pereopod coxa proximally; third through fifth fused, sutures visible externally only as small notches laterally; sixth segment slightly broader than long; telson rounded. Male first pleopod (gonopod 1) long, sinuous, reaching beyond anterior end of median sternal groove, visible to either side of pleon distally, apex narrowly spatulate. Male second pleopod less than one-third length of first. Applicable GenBank sequence accession numbers for USNM 1543542 (= ULLZ 8170) and USNM 1577463 holotype (= ULLZ 8183, part) are as follow: (16s) EU863367, EU863366; (12s) EU863301, EU863300.
Habitat. Abundant on offshore reefs and banks, especially in small cavities and interstices of eroded hard substrates as well as among sponges, bryozoans, corals, encrusting algae, and other epibiota of fouling communities. Confirmed depth records range from 58–143 m; some additional collections are from within sponges taken at depths estimated to be 200–300 m (Aransas Bank, TX).
Distribution. Middle to outer continental shelf waters of the northeastern to northwestern Gulf of Mexico.
Etymology. The name “tiara” alludes to the reddish pattern that typically spans the dorsal carapace, the shape of which suggests the elevated front of a tiara or crown.
Brent P. Thoma and Darryl L. Felder. 2020. A New Genus and Species of Xanthoid Crab (Decapoda: Brachyura) from offshore hard bank habitats in the Gulf of Mexico. Zootaxa. 4731(3):403-413. DOI: 10.11646/zootaxa.4731.3.8
