Stomatopoda (Crustacea: Hoplocarida) from the Shallow, Inshore Waters of the Northern Gulf of Mexico (Apalachicola River, Florida to Port Aransas, Texas)

Six species representing the order Stomatopoda are reported from the shallow, inshore waters (passes, bays, and estuaries) of the northern Gulf of Mexico limited to a depth of 10 m or less, and by the Apalachicola River (Florida) in the east and Port Aransas (Texas) in the west. With the exception of the “live bottom” gonodactylid, Neogonodactylus bredini (Manning), these predatory crustaceans usually inhabit burrows in mud, sand-mud, and sand substrata in coastal and shelf waters. The species treated in this paper are Neogonodactylus bredini (Manning), Lysiosquilla scabricauda (Lamarck), Bigelowina biminiensis (Bigelow), Coronis scolopendra Latreille, Squilla empusa Say, and Gibbesia neglecta (Gibbes). The questionable record of Squilla rugosa Bigelow by Archer (1948) is discussed. A review of the life history, ecology, distribution, and new northern Gulf of Mexico records is provided here for each of these species. Figures and an illustrated key are also presented

Range Extensions and Review of the Caprellid Amphipods (Crustacea: Amphipoda: Caprellidae) from the Shallow, Coastal Waters from the Suwanee River, Florida, to Port Aransas, Texas, with an Illustrated Key

Eight species of the amphipod family Caprellidae sensu Myers and Lowry, 2003 are currently known to occur in the shallow, near shore waters of the northern Gulf of Mexico (GOM), from the Suwannee River, Florida, to Port Aransas, Texas, and to depths of 10 m. They include: Phtisica marina, Hemiaegina minuta, Paracaprella pusilla, Paracaprella tenuis, Deutella incerta, Caprella equilibra, Caprella penantis, and Caprella scaura. Another species, Caprella andreae, is also suspected to occur in this region due to its close association with sea turtles, which nest on the sand beaches of the northern GOM. The occurrence of these 9 species in the northern GOM is discussed; known distributions, new records, synonymies, diagnoses, and remarks on life history and ecology are also presented. In addition, new northern GOM records for 7 of these species are provided along with a simplified identification key

A guide to the Thalassinidea (Crustacea: Malacostraca: Decapoda) of the South Atlantic Bight

Ghost shrimp and mud shrimp in the decapod infraorder Thalassinidea are ecologically important members of many benthic intertidal and shallow subtidal infaunal communities, largely due to the sediment filtration and mixing that result from their burrowing and feeding behavior. These activities considerably modify their immediate environment and have made these cryptic animals extremely interesting to scientists in terms of their behavior, ecology, and classification. Over 20 years ago, seven species of thalassinideans were known from the South Atlantic Bight (Cape Hatteras, NC to Cape Canaveral, FL). During this study, the examination of extensive collections from the National Museum of Natural History (NMNH), the Southeastern Regional Taxonomic Center (SERTC), and regional institutions, resulted in the identification of 14 species of thalassinideans currently known to occur within this region. The family Axiidae is represented by three species: Axius armatus, Calaxius jenneri, and Paraxiopsis gracilimana; the Callianassidae by six: Biffarius biformis, B. cf. fragilis, Callichirus major, Cheramus marginatus, Gilvossius setimanus, and Necallianassa berylae; the Calocarididae by two: Calocaris templemani and Acanthaxius hirsutimanus; and the families Laomediidae, Thomassiniidae, and Upogebiidae are each represented by one: Naushonia crangonoides, Crosniera wennerae, and Upogebia affinis, respectively. An illustrated key is presented for species level identification and supplemental notes on the ecology, distribution, and taxonomy of the species are provided.(PDF file contains 38 pages.

Redescription of Pinnixa arenicola Rathbun, 1922 (Decapoda: Brachyura: Pinnotheridae), with new observations on its range and host

Abstract.-Pinnixa arenicola is redescribed and illustrated on the basis of new collections and reexamined type material. Its occurrence in the burrows of Upogebia vasquezi Ngoc-Ho is reported, along with range extensions that include Florida, Puerto Rico, Aruba, and the Cayman Islands. New collections represent the first reports of P. arenicola since original discoveries in Curaçao and suggest a potentially wide distribution of the species in the tropical western Atlantic. Following publication of the unillustrated original description for the holotype male, females were also noted to occur in Curaçao, but illustrations with limited detail were provided by Rathbun for only the male holotype specimen. Prior to our work, no illustrations have depicted female morphology, unique male gonopods, or some pereopod features of potential value in defining phylogenetic relationships

Transcriptomic effects of dispersed oil in a non-model decapod crustacean

Background. Oil spills are major environmental disasters. Dispersants help control spills, as they emulsify oil into droplets to speed bioremediation. Although dispersant toxicity is controversial, the genetic consequences and damages of dispersed oil exposure are poorly understood. We used RNA-seq to measure gene expression of flatback mudcrabs (Eurypanopeus depressus, Decapoda, Brachyura, Panopeidae) exposed to dispersed oil. Methods. Our experimental design included two control types, oil-only, and oil-dispersant treatments with three replicates each. We prepared 100 base pair-ended libraries from total RNA and sequenced them in one Illumina HiSeq2000 lane. We assembled a reference transcriptome with all replicates per treatment, assessed quality with novel metrics, identified transcripts, and quantified gene expression with open source software. Results. Our mudcrab transcriptome included 500,008 transcripts from 347,082,962 pairend raw reads. In oil-only treatments, we found few significant differences. However, in oildispersant treatments, over 4000 genes involved with cellular differentiation, primordial cellular component upkeep, apoptosis, and immune response were downregulated. A few muscle structure and development genes were upregulated. Discussion. Our results provide evidence that exposure to chemically dispersed oil causes a generalized cellular shutdown and muscular repair attempts. Our results suggest current oil-spill treatment procedures could be detrimental to crustaceans and indicate additional research is needed to evaluate the impact of oil spills in gene expression. Finally, traditional quality metrics such as N50s have limitations to explain the nature of RNA-seq compared to new methods in non-model decapod crustaceans

A new shallow-water mud crab of the genus Hexapanopeus Rathbun, 1898 from Belize (Crustacea: Decapoda: Panopeidae)

Felder, Darryl L., Thoma, Brent P. (2022): A new shallow-water mud crab of the genus Hexapanopeus Rathbun, 1898 from Belize (Crustacea: Decapoda: Panopeidae). Zootaxa 5168 (5): 541-552, DOI: https://doi.org/10.11646/zootaxa.5168.5.

A New Species of the Genus \u3ci\u3eGammarus\u3c/i\u3e (Crustacea: Amphipoda: Gammaridae) From the Low Salinity Habitats in the Northern Gulf of Mexico

In the northern Gulf of Mexico, Gammarus mucronatus sensu lato is represented by at least two forms, G. mucronatus sensu stricto and a less common macromucronate form, which appears to be restricted to low salinity habitats. These two forms have traditionally been separated using the size or angle of projection of the dorsal mucronations (processes). However, because of variability in the development of the processes, it is unclear whether this and other morphological differences between G. mucronatus sensu stricto and the macromucronate form are ecophenotypic or reflect distinct and separate species. Detailed morphological analyses indicate that these two forms represent distinct species; Gammarus lecroyae, new species, is described in detail and a key to the marine and estuarine Gammarus species from the northern Gulf of Mexico is provided

Guinope tiara Thoma & Felder 2020, n. gen., n. sp.

<i>Guinope tiara</i> n. gen., n. sp. <p>(Figs. 1 A–M; 2A–D)</p> <p> <i>Garthiope barbadensis</i>, Thoma <i>et al</i>. 2009: tab. 2, figs 1 & 2, 563. Not <i>Garthiope barbadensis</i> (Rathbun, 1921).</p> <p> “Gen. nov., sp. nov. near <i>Garthiope barbadensis”</i>, Thoma <i>et al</i>. 2014: 90, tab. 1.</p> <p> “nov. gen. nov. sp. near <i>Garthiope barbadensis</i> ”, Thoma <i>et al.</i> 2014: fig. 1, 92.</p> <p> “New genus nr. <i>Garthiope ”</i>, Lai <i>et al.</i> 2011: tab. 1, fig. 1, 421, 422, 432, 442.</p> <p> <b>Type material. Northern Gulf of</b> <b>Mexico:</b> Holotype: male, cw 4.2 mm, Sackett Bank, Louisiana, 28° 37.81´N, 89°</p> <p> 33.32´W, 63–65 m, 28 June 2006, USNM 1577453 (= ULLZ 8183, part, genetic voucher). Paratypes: 2 males, cw 3.4, 3.6 mm, 1 ovigerous female, cw 3.9 mm, Sackett Bank, Louisiana, 28° 37.81´N, 89° 33.32´W, 63–65 m, 28 June 2006, USNM 1543543 (= ULLZ 8183, part, photograph voucher); 1 male, cw 2.2 mm, 3 females, cw 2.6, 3.2, 3.4 mm, Sackett Bank, Louisiana, 28° 37.81´N, 89° 33.32´W, 63–65 m, 28 June 2006, USNM 1543552 (= ULLZ 8210); 1 male, cw 4.2 mm, 1 female, cw 4.0 mm, Sackett Bank, Louisiana, 28° 37.89´N, 89° 33.27´W, 63–68 m, 28 June 2006, USNM 1577531 (= ULLZ 18299); 1 ovigerous female, cw 4.0 mm, Sackett Bank, Louisiana, 28° 38.033´N, 89° 33.387´W, 61–71 m, 7 September 2014, USNM 1549376 (= ULLZ 16150, photograph voucher); 3 males, cw 2.8, 3.7, 4.0 mm, 1 female 3.2 mm, Sackett Bank, Louisiana, 28° 38.125´N, 89° 33.478´W, 60–61 m, 2 December 2010, USNM 1547191 (= ULLZ 13760); 1 ovigerous female, cw 4.5 mm, Sackett Bank, Louisiana, 28° 38.047´N; 89° 35.826´W, 58–80 m, 24 August 2012, USNM 1547740 (= ULLZ 14552, photograph voucher); 1 male, cw 6.9 mm, off Alabama, 29° 24.43´N, 87° 58.63´W, 72-74 m, 29 June 2006, USNM 1543895 (= ULLZ 8581, photograph voucher); 1 male, cw 3.3 mm, 1 female, cw 2.8 mm, off Alabama, 29° 19.57´N, 87° 46.29´W, 96–106 m, 30 June 2006, USNM 1543550 (= ULLZ 8208); 6 males, cw 3.1–3.8 mm, 5 females (1 ovigerous), cw 2.3–5.8 mm, off Alabama, 29° 24.61´N, 87° 58.62´W, 71–73 m, 29 June 2006, USNM 1543544 (= ULLZ 8191); 1 male, cw 5.0 mm, off Alabama, 29° 24.61´N, 87° 58.62´W, 71–73 m, 29 June 2006, USNM 1547121 (= ULLZ 13266 genetic voucher); 1 male, cw 3.7 mm, 2 females, cw 5.6, 5.8 mm, off Alabama, 29° 24.43´N, 87° 58.63´W, 72–74 m, 29 June 2006, USNM 1543849 (= ULLZ 8173, photograph voucher); 4 males, cw 3.1, 3.8, 4.4, 4.9 mm, 1 female, cw 5.1 mm, off Alabama, 29° 24.43´N, 87° 58.63´W, 72–74 m, 29 June 2006, USNM 1543542 (= ULLZ 8170, genetic voucher); 2 males, cw 4.3, 5.2 mm, 3 females, cw 5.9, 3.7, 3.4 mm, off Mississippi-Alabama border, 29° 15.68´N, 88° 20.24´W, 78–86 m, 27 August 2011, USNM 1547899 (= ULLZ 14614). <b>Northwestern Gulf of Mexico:</b> 2 males, cw 5.6, 7.0 mm, off Louisiana, “The Halo” WW II shipwreck, 28° 42.01´N, 90° 08´W, 143 m, 14 August 2004, USNM 1547695 (= ULLZ 14505); 1 male, cw 4.8 mm, off Louisiana, Ewing Bank, 28° 05.011´N, 90° 58.646´W, 79–82 m, 5 December 2010, USNM 1547058 (= ULLZ 13237); 1 male, cw 4.8 mm, Ewing Bank, 28° 05.029´N, 90° 58.656´W, 78–83 m, 5 December 2010, USNM 1547060 (= ULLZ 13242); 1 male, cw 3.7 mm, 1 female, cw 4.0 mm, Fishnet Bank, TAMU submersible dive 74-G-10, 28° 09´N, 91° 49´W, 21 June 1974, USNM 1538101 (= ULLZ 12242); 1 male, cw 3.5 mm, West Flower Garden Banks, diver collection 48 m, 7 May 1972, USNM 1538099 (= ULLZ 12233); 1 male, cw 4.9 mm, off Louisiana, 28° 05.009´N, 91° 09.393´W, 109–110 m, 24 August 2008, USNM 1538097 (= ULLZ 11911); 1 male, cw 3.2 mm, Mysterious Bank, Texas, R / V Falkor ROV, 26° 46´N, 96° 42´W, 26 November 2012, USNM 1547880 (= ULLZ 14592); 1 male, cw 3.6 mm, 1 ovigerous female, cw 4.4 mm, Mysterious Bank, Texas, R / V Falkor ROV, 26° 46´N, 96° 42´W, 27 September 2012, USNM 1548935 (= ULLZ 15560); 2 males, cw 3.7, 2.3 mm, 3 females (2 ovigerous), cw 4.5, 4.8, 2.8, 4 unsexed tentatively identified juveniles, cw 1.6–1.9 mm, Aransas Bank, Texas, R / V Falkor ROV, 27° 36´N, 96° 27´W, 21 September 2012, USNM 1547711 (= ULLZ 14581, photograph voucher); 3 males, cw 3.2, 3.5, 4.4 mm, 1 ovigerous female, cw 4.3 mm, Aransas Bank, Texas, R / V Falkor ROV, 27° 03´N, 96° 43´W, 21 September 2013, USNM 1547888 (= ULLZ 14602); 1 unsexed damaged, cw 3.4 mm, Dream Bank, Texas, R / V Falkor ROV, 27° 03´N, 96° 43´W, 23 September 2012, USNM 1547891 (= ULLZ 14605).</p> <p> <b>Diagnosis</b>. 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.</p> <p> <b>Description</b>. Carapace (Fig. 1A) weakly convex, distinctly wider than long, dorsal regions poorly-defined by shallow grooves, surface sparsely granulate, granules increasing in size and density anteriorly, most dense in hepatic and frontal regions, occasionally forming weak rows or carinae; frontal margin bilobed, downturned, slightly thickened by dense granules, median fissure distinct, lobes broadly convex, antennal sinus shallow, distinct; supraorbital margin granulate, median fissure small, indistinct, lateral fissure obsolete, or nearly so. Pterygostomial and subhepatic regions (Fig. 1B) granulate, granules small; pterygostomial ridge reduced, present as slightly raised line of granules. Branchiostegite below anterolateral teeth with ventral margin nearly straight above coxa of each walking leg, at most slightly cuspate. Second and third pleurites with full width narrowly visible below ventral margin of branchiostegite above pereopod coxae, anterolateral margin of fourth pleurite occasionally visible as small wedge- like prominence. Anterolateral teeth moderately developed, first and second teeth weak to obsolete, often reduced to spinous prominences; third and fourth teeth (appearing as second and third, respectively, given obsolescence to fusion of preceding and counting outer orbital angle as first) anterolaterally directed, typically ending in acute spiniform process distally, third largest; fifth tooth typically small, nearly obsolete, acute to subacute. Eyestalk with distinct raised, coarsely granulate anterior crest.</p> <p>Third maxilliped (Fig. 1 B–D) protopod subcuneate, narrowing laterally, bearing small subtriangular projection proximomesially, external surface with slight notch or groove near distomesial margin, patch of medium length simple setae distolaterally, continuing slightly onto epipod, distal surface deeply grooved to accept ventral edge of carapace, internal surface with two unequal projections on distal margin. Epipod strongly curved posteroventrally near one-third length, distally fringed with long simple setae; podobranch gill typically small, short, lamellae limited to tight terminal bundle (not shown). Endopod basis subtriangular, basis suture with ischium nearly fused, indistinct; ischium broadly subrectangular, proximal portion deflected laterally, external surface with few sparse granules near distomesial corner, mesial margin with irregular fringe of short to medium length simple setae, continued for short distance on internal surface, subtriangular uncalcified region at articulation with merus; merus subquadrate, lateral margin concave, distal margin with indentation mesially, distomesial corner excavated to accommodate carpus, external surface with several large coarse granules near distal and distomesial margins, internal surface deeply excavate to accept endopod of second maxilliped, excavation with fringe of short simple setae, internal surface with raised ridge of setae near mesial margin proximal to articulation with carpus, distomesial uncalcified region at articulation with carpus, mesial margin with sparse fringe of medium length simple setae; carpus appearing subcylindrical externally, subobovate internally, external surface granulate especially near extensor margin, internal surface with fringe of medium-long stout simple setae on distal margin; propodus cylindrical, internal surface with short row of medium-length stout simple setae near midlength; dactylus subcylindrical, tapering distally, nearly twice as long as propodus, flexor margin with short fringe of medium-length stout simple setae proximally, extending about half dactylus length, tip bearing dense tuft of long stout simple setae. Exopod sublanceolate, nearly linear, slightly tapering distally, internal surface mesial margin produced, forming subtriangular projection in distal third, projection fringed with several short to medium length simple setae, external surface mesial margin subtly crenulate, lateral margin with sparse fringe of very short simple setae in proximal one-half, internal surface with short irregular row of short to medium-length setae near mesial margin in proximal one-half; flagellum recurved, multi-articulate distally, bearing numerous long, simple setae.</p> <p>Chelipeds (first pereopods) (Fig. 1 E–G) moderately unequal, sparsely setose, dense broad field of subacute granules covering superior and extensor surfaces, occasionally forming one or more ridges on superior surface of carpus and propodus, especially on major chela; merus superolateral margins with large, broad, subacute, spines, flexor surface granulate, granules larger, sharper near superior and inferior margins, proximo-inferior margin typically fringed with short plumose setae, extensor surface densely granulate, granules decreasing in size and density from superior to inferior margins; carpus densely granulate with broad, subacute granules, strong distal subacute, spiniform, tooth on flexor side of superior surface, two smaller teeth proximally, superior and extensor surfaces with few sparse plumose setae, superodistal margin often with distinct fringe of plumose setae; propodus superior and supero-external surfaces densely granulate with few sparse simple setae, granules broad, subacute, superior surface occasionally with distinct longitudinal groove, flexor surface of palm smooth to micropunctate, distal margin near gape with fringe of small distinct teeth; fixed finger of major chelae short, stout, smooth on both flexor and extensor surface, extensor surface often with two shallow grooves, inferior margin weakly sinuous deflected gently downwards, apex distinctly curved upwards, opposable margin bearing two to three prominent teeth, often with several smaller teeth between, teeth occasionally worn to low rounded lobes; fixed finger of minor chela noticeably longer and more slender than that of major, opposable margin forming slender cutting edge, often with several small teeth proximally, occasionally worn to appear like two distinct platforms or steps; dactylus of major chela curved, slightly longer than fixed finger, superior surface with shallow, longitudinal groove on external side of superior midline, groove widest and deepest proximally, several medium length simple setae on proximal half, cutting edge armed proximally with two large subtriangular teeth, single triangular tooth near mid-length, and numerous small, variably rounded teeth along distal cutting edge, tip strongly curved downwards, forming coniform tooth; dactylus of minor chela curved, longer than fixed finger, superior ridge granulate, granules strongest proximally, shallow narrow groove on external side of superior midline, groove much deeper and broader than on the major chela, cutting edge dentition much weaker than in major chela, appearing as thin, weakly crenulate margin, tip strongly curved downwards to form sharp, coniform tooth.</p> <p>.</p> <p>Pereopods two through five (walking legs) generally similar in form (Fig. 1H), pereopods two through four subequal, fifth smallest; ischium extensor margin about one-half length of flexor margin; merus length slightly less than three times width at widest point, extensor margin bearing single longitudinal row of irregular acute teeth along with four or five long sparsely-plumose setae, excavate subdistally by smooth transverse depression or groove, disto-extensor margin curved upwards appearing as large distal subacute tooth, flexor margin granulate in proximal three-fourths with several simple setae, longest proximal; carpus strongly bent in flexor plane at near right angle, extensor margin densely granulate appearing as several irregular rows of subacute granules, creating elongate sulcus near extensor margin on posterior surface; propodus extensor margin granulate, granules subacute, with several plumose or simple setae, granules continued onto posterior surface above midline, flexor margin with irregular fringe of mixed short stout setae and long thin setae; dactylar-propodal locking mechanism not developed; dactylus subcylindrial, tapering distally, flexor and extensor margins with short dense pubescence intermixed with long simple setae, corneous tip falciform, lacking subterminal, calcareous, raptorial tooth.</p> <p>Thoracic sternum of male (Fig. 1 J–K) narrow, anteriorly projected, length from apex to suture of fourth and fifth sternites (measured at the edge of the pleon) 0.57–0.61 times greatest width of fourth sternite (including episternites); pleonal depression of fourth sternite shallowly concave near midline, just anterior to median sternal groove; fourth through sixth episternites acutely angled posteriorly; seventh episternite broad, round; eighth sternite not visible between lateral margin of flexed second pleonal somite and fifth pereopod condyle; press-button just posterior to suture of third to fourth sternite.</p> <p>Pleon of male (Fig. 1 I–K) with third through fifth somites fused; first somite lateral margins rounded, widest at articulation with carapace, narrowest at articulation with second somite; second somite narrowest proximally, widest distally near articulation with somite three; third somite widest at lateral flange; fused third through fifth somites narrowing distally, width at articulation with sixth somite half or less that at articulation with second somite, sutures between fused somites evident only as slight indentations on lateral margins; sixth somite lateral margins nearly parallel at most slightly convex proximally, swelling slightly near articulation with telson to accept press-button in- ternally; telson terminally rounded, widest near mid-length, distolateral margins slightly excavate to accommodate first gonopod. Pleon of female with first somite narrowing distally, widest at articulation with carapace, second somite with margins nearly parallel, slightly expanded distally; fourth somite widest, lateral margins rounded; fourth through sixth somites each tapering to articulation with the next, narrowest point at the articulation between sixth somite and telson; telson subtriangularly rounded.</p> <p>Male first gonopod (first pleopod) (Fig. 1L) long, sinuous, reaching beyond sternal groove, tips exposed to either side of telson when abdomen flexed in mature; terminal apparatus superficially simple, appearing spatulate with sub-apical microspinulous spines. Male second gonopod (second pleopod) (Fig. 1M) less than one-third length of first gonopod. Female mature gonopore broadly rounded medially, occupying more than half of anterior to posterior transverse width of sixth sternite, largely filled by rounded operculum attached laterally along slightly raised elongate lip, narrow opening to medial side strongly crescentic.</p> <p> <b>Color.</b> Primarily orange to dark orange or reddish brown patterned over whitish to very light orange background, carapace dorsally with broad intricately margined band of orange arched anteriorly from each branchial region, broadest and usually darkest medially where joined over gastric region, arch forming pattern like front of crown or tiara, usually with somewhat lighter medial extension posteriorly to cardiac region, bifurcated from intestinal region to posterior margin of carapace (Fig. 2 A–D). Chelipeds dorsally orange, often darkest on ridges and tubercles, palms with light whitish bands distally, as well as on inner and ventral surfaces, fingers light to dark brown. Walking leg articles with broken bands of orange on whitish background, bands most obvious as orange patches on superior surfaces, usually with three such patches on meri, most proximal of which is smallest and often very diffuse to obsolete. Eggs on ovigerous females reddish magenta.</p> <p> <b>Habitat</b>. 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).</p> <p> <b>Size</b>. The carapace ranges to a maximum of cw 7.0 mm, determined for the largest male among available collections. Juveniles of neither sex were definitively identifiable at less than cw 2.0 mm, though collections included some specimens of cw 1.6 mm that appear to represent the species. The smallest examined ovigerous female was cw 3.9 mm.</p> <p> <b>Distribution.</b> Middle to outer continental shelf waters of the northeastern to northwestern Gulf of Mexico.</p> <p> <b>Etymology.</b> 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.</p> <p> <b>Remarks</b>. While it is at first glance easy to mistake fresh specimens of <i>Guinope tiara</i> <b>n. gen, n. sp.</b> for <i>Garthiope barbadensis</i>, the distinctive dorsal color pattern on the carapace in both sexes and the occurrence of ovigerous females at rather small sizes bearing clutches of bright reddish magenta eggs usually facilitate recognition, even before microscopic examination of the very diagnostic first gonopods. Among small regional xanthoid crabs, a similar dorsal color pattern is found only in some specimens of <i>Scopolius nuttingii</i> (Rathbun, 1898), though it is in that case usually less ornately defined.</p> <p> Lacking knowledge of gene sequences, live coloration, or fine sculpture of mature male first gonopods, identification of <i>Guinope tiara</i> <b>n. gen., n. sp.</b> can be based upon other features in morphology, even though some characters for separations are difficult to quantify. Among other small, regionally distributed xanthoids that occur sympatrically with <i>Guinope tiara</i> <b>n. gen., n. sp.</b>, the only (albeit provisionally assigned) confamilial) <i>Melybia thalamita</i> might be expected to resemble <i>G. tiara</i> <b>n. gen., n. sp</b>., but it is instead among the least likely to be confused with it. <i>Melybia thalamita</i> is immediately separated by its having the merus of pereopod 2 and 3 armed by a unique ventrodistally directed spine on the dis