Cymonomus windsorae, Felder & Tavares, 2024

Felder, Darryl L. & Tavares, Marcos, 2024, A new species of Cymonomus A. Milne-Edwards, 1880, from the deep waters of the Gulf of Mexico (Crustacea: Brachyura: Cymonomidae), Zootaxa 5471 (2), pp. 261-267 : 262-265

Cymonomus windsorae n. sp.

( Figs 1A–E , 2A–D )

Material examined. Holotype: Ovigerous female, cw 3.9 mm, pcl 3.5 mm, USNM 1546450 (= ULLZ 12698 A), trawl sample, LGL Stn 3, Cruise I, off Louisiana, northwestern Gulf of Mexico , 27°48’N, 90°03.3’W, 850 m, 27 November 1983 . Paratype: Ovigerous female, cw 4.0 mm, pcl 3.7 mm, USNM 1705285 (= ULLZ 12698 B), collection data same as for holotype .

Diagnosis. Carapace regions well marked, irregularly granulate; broad gastric region delimited laterally by distinct arched furrow. Eyestalks elongate, untapered, subcylindrical with slight dorsoventral flattening proximally, directed anteriorly, nearly straight, freely articulated at base, no evident fusion to one another or frontal margin of carapace. Cornea translucent, unfaceted, no remaining evidence of pigment, distinctly bulbous, separation from adjacent heavily sclerotized eyestalk cuticle distinctly evident.

Description. Carapace outline subquadrate, lateral margins sinuous, subparallel, widest posteriorly at lateral margin of slightly inflated branchial region, irregularly granulate anterolateral margin slightly extended mesially above base of outer orbital process ( Figs 1A–C , 2A–D ). Carapace regions dorsally indicated, shallow cervical groove evident; hepatic region with lateral supramarginal crest bearing irregular coarse granules and small denticles; broad gastric region slightly elevated anteriorly above level hepatic regions, delimited laterally by distinct arched furrow, frontal and fronto-orbital margins upturned, posteriorly with distinct pair of small gastric pits near median line; pattern of four shallow depressions framing intestinal region, two near posterolateral limits of gastric region, two near anterolateral limits of cardiac region; cardiac region distinctly inflated, elevated above thicken posterior margin of carapace; surfaces overall with well-separated small granules and weak rugae marking regional furrows, cervical groove, branchial grooves, also as irregular patterns on hepatic region, branchial region, and near carapacial margins. Anterolateral spine low, anteriorly directed, slightly enlarged among other acute to subacute marginal granules of anterolateral margin. Fronto-orbital margin reaching anteriorly little if any beyond anterolateral margins; width about half that of anterior carapace; outer orbital process narrowly digitiform, positioned below plane of rostrum, dorsoventrally thickened by raised granulate margins proximally, mesial margin continued from upturned fronto-orbital margin, raised margins obsolete distally. Rostrum (fractured from carapace at base, appearing crushed terminally) narrowly elongate, extending anteriorly at least as far as eyestalk corneas, lacking subrostral tubercle; rostral margins parallel at sides, divergent at base. Carapace ventrally with pterygostomian region swollen, finely granulate, forming elongate boss.

Eyestalks narrow, elongate, subcylindrical with slight dorsoventral flattening proximally, directed anteriorly, nearly straight, freely articulated at base, no evident fusion to one another or frontal margin of carapace ( Figs 1A, B , 2A, B, D ); cornea reaching to just beyond midlength of antennular peduncle first article; dorsal surface of stalk with scattered granules, granules denser, stronger along mesial margin; cornea well defined, translucent, unfaceted, no remaining evidence of pigment, terminally inflated, separation from adjacent heavily sclerotized cuticle distinctly evident.

Epistome surface produced anteriorly below rostral base, bearing several small, elongate granules, one centered on midline, transverse row of four enlarged granules between bases of antennules; flattened subtriangular lobe mesial to base of antenna.

Antennular peduncle length (paratype) about 0.82 carapace width ( Fig. 1B ); first article granulate dorsally and laterally; second and third articles mostly smooth. Antennal peduncle first to third articles minutely granulate; fourth and fifth articles minutely granulate to smooth.

Third maxilliped ischiobasis subquadrate, with distinct longitudinal sublateral groove, mesial margin coarsely granulate, granules dentiform to spiniform distally ( Figs 1D , 2C, D ); lateral margin mostly smooth, ending distally in sharp corner; fusion of ischium and basis marked by distinct groove. Merus length near equal that of ischium, elongate, weakly bent toward midline in distal half, terminally rounded; margins bearing a few dentiform granules and short, blunt spines; external surfaces with scattered denticles. Carpus heavy, subtriangular, with sparse marginal dentiform granules, propodus subcylindrical, dactylus subconiform, weakly arched, tapering to subacute tip. Exopod reaching to distal quarter of endopod merus; exopod flagellum well developed, multi-segmented.

Except for coxae ( Fig. 2A–D ), chelipeds and other pereopods unknown, missing from holotype and paratypes.

Thoracic third sternite subpentagonal, thickened granulate anterolateral margins converging to anterior point at small terminal tubercle; thickened lateral margins slightly concave, weakly divergent posteriorly, posterior width about one and one-half times median length ( Figs 1E , 2C ). Fourth sternite lateral margin thickened, forming strongly raised coarsely granulate swollen lip along concavity accommodating first pereopod coxa.

Pleon with raised median longitudinal crest on pleonites and pleotelson, otherwise faintly patterned by low anastomosed weakly granular elevations and shallow sulci ( Figs 1C , 2A–D ); pattern of transverse sulci evident on especially second to fourth pleonites. Pleotelson subtriangular, width slightly less than twice length, sixth pleonite and telson completely fused with no evidence of separating suture along entire width; obtuse angle of terminus rounded.

Etymology. This species is named for our colleague, Amanda M. Windsor, in recognition of her substantial contributions to phylogenetic and systematic studies of brachyuran crabs.

Distribution and habitat. Known at present from only the type locality, northwestern Gulf of Mexico, western Atlantic, at a depth of 850 m.

Remarks. Specimens herewith described as C. windsorae n. sp. were originally referred to one of us for study (DLF) by Dr. Linda Pequegnat, a consultant to LGL Ecological Research Associates, Bryan, Texas. As both specimens lacked appendages and exhibited varied degrees of damage to the rostrum, description was long deferred in hopes of making additional collections that might include intact and perhaps male specimens, or even DNA sequence-quality representatives as methods progressed. However, despite repeated collection efforts at similar depths in the northwestern Gulf of Mexico, no additional specimens have been found.

Both specimens are unfortunately now in a very poor state of preservation. Initially fractured, missing appendages, and not well preserved, they were among a few specimens that became dried in the course of the ULLZ collections being shipped to and temporarily stored at (without routine curation during the covid pandemic) the USNM, where they are now curated with other of the former ULLZ holdings. However, most of the line drawings, specimen photographs, and morphological notes were fortunately prepared by DLF prior to the specimens’ drying. Having now been rehydrated by standard protocols and returned to alcohol, essential features at very least remain recognizable in the type materials. However, both the holotype and paratype females of C. windsorae n. sp. initially carried eggs that have now somewhat shriveled and disintegrated. The holotype bore fourteen and the paratype six relatively large eggs, 0.9–1.1 mm in greatest diameter.

Assignment of C. windsorae n. sp. to the genus Cymonomus is based upon a combination of characters, which include ocular peduncles not covered by the long slender rostrum, so that the peduncles are fully exposed in dorsal view; absence of an interantennular septum; third maxilliped merus remarkably elongated distally with the palp articulating at its subdistal inner surface and exopod with well-developed flagellum; and pleon of five pleonites and pleotelson without any trace of suture separating the sixth pleonite from the telson. This is in contrast to members of the closely related genus Cymonomoides , in which the rostrum is vestigial or very short and all six pleonites and the telson are freely articulated, thus facilitating ready separation of Cymonomus windsorae n. sp. from species of Cymonomoides , also known to occur in the Gulf of Mexico and adjacent waters (Tavares 1993; Lemaitre & Bermúdez 2000; Felder et al. 2009).

Cymonomus windsorae n. sp. can be readily distinguished from all other species in the genus by having an untapered rostrum with rostral margins parallel at the sides and divergent at the base and perhaps distally (though damaged there), and its unique eye morphology with well-developed bulbous terminal corneas of the nearly straight eyestalks, the smooth integumental covering of which is clearly demarcated from that of the eyestalk itself. It superficially resembles the Mediterranean Cymonomus granulatus (Norman in Wyville Thompson, 1873) and the Tasmanian Cymonomus karenae Ahyong, 2019 , in having the transparent cornea similarly demarcated, but in the latter two species the cornea is less bulbous and in C. karenae , it is centered on the distoventral terminus of a stout, strongly divergent stalk ( Ahyong 2019: 58, fig. 22C, D). Additionally, the two aforementioned species can be easily set apart from C. windsorae n. sp. by the ornamentation of the dorsal and lateral surfaces of the carapace, which is densely covered with prominent spination or coarse granulation in C. granulatus and C. karenae , respectively. In C. windsorae n. sp. it is instead irregularly granulate with surfaces overall bearing well-separated small granules and weak rugae marking regional furrows.

Among the three known species of Cymonomus that range into at least eastern extremes of the Gulf of Mexico ( Felder et al. 2009), the cornea and eyestalks readily separate these species from C. windsorae n. sp., as it shares neither the absence of cornea as in C. rostratus Chace, 1940 , and C. caecus Chace, 1940 , the distinct lateral curvature of the stalks as in C. quadratus A. Milne-Edwards, 1880 , nor the strong taper toward the apices as found in C. caecus . Cymonomus windsorae n. sp. can be further separated from C. rostratus by the anterolateral shoulder of the carapace that appears more produced or angular in dorsal perspective, often forming a rounded, sometimes spined corner as opposed to a more broadly rounded margin as in C. rostratus .

Cymonomus is essentially a deep-water group currently consisting of 45 species, of which 33 are Indo-West Pacific and 12 Atlanto-Mediterranean/East Pacific in distribution. It also includes one species from the Late Eocene of Hungary, C. primitivus Müller & Collins, 1991 . A number of descriptive and distributional accounts over the last two decades have markedly expanded documented diversity of Cymonomus in Indo-Pacific waters ( Ahyong & Brown 2003; Ahyong 2008, 2014, 2019; Ahyong et al. 2020; Ahyong & Ng 2009, 2011, 2017; Takeda et al. 2021; Ahyong & Ng 2023). The Atlanto-Mediterranean/East Pacific species of Cymonomus are under revision by one of us (MT) so that further additions are anticipated in the course of this effort, as well as range extensions building on previous work ( Tavares 1991, 1993a, 1994; Campos Junior 1997). Additional insights into the cymonomid assemblage of the Gulf of Mexico region are, however, constrained by limited appropriate sampling in the region over recent decades, which also limits insight into microhabitats and substrate dependencies of Cymonomus and its confamilials.

Figures

FIGURE 1. Cymonomus windsorae n. sp.: A, D, E, USNM 1546450 (= ULLZ 12698A) ovigerous female holotype; B, C, USNM 1705285 (= ULLZ 12698B) ovigerous female paratype.A, carapace and eyestalks, dorsal; B, anterior carapace, eyestalks, antennules, and antennae, dorsal; C, carapace, extended pleon, and pleotelson, dorsal; D, left third maxilliped, external; E, anterior thorax, proximal articles of third maxillipeds, first pereopod coxae, and anterior sternum, ventral. Scale bars = 1.0 mm

FIGURE 2. Cymonomus windsorae n. sp.: A, USNM 1546450 (= ULLZ 12698A) preserved ovigerous female holotype, cw 3.9 mm, northwestern Gulf of Mexico; B–D, USNM 1705285 (= ULLZ 12698B) preserved ovigerous female paratype, cw 4.0 mm, northwestern Gulf of Mexico.