Raripagurus roseangelae, Lemaitre & Felder, 2023

Lemaitre, Rafael & Felder, Darryl L., 2023, A new genus and species of micro-pagurid hermit crab (Crustacea, Decapoda, Paguridae) from the rariphotic reef zone in Curaçao Lesser Antilles, Caribbean Sea, Zootaxa 5277 (2), pp. 374-380 : 376-379

Raripagurus roseangelae n. gen., n. sp.

( Figs 1A–F , 2A–F , 3A, B )

Type material. Holotype: female, cephalic shield length 1.8 mm, CURI 17031 , sta CURASUB17–33, 12°04.56′N, 68°53.51′W, Deep Reef Observation Project , Curaçao Sea Aquarium, E of downline, Bapor Kibra, Curaçao, 226– 276 m, 3 Nov 2017, colls. L. Weigt, D.L. Felder, B. Brandt, K. Matterson, USNM 1554278 .

Description. Shield ( Figs. 1A , 3A ) subtriangular, approximately 1.1 times as broad as long; dorsal surface weakly convex, glabrous, semi-translucent, lacking linea or grooves except for short linea-d; lateral lobe narrow, weakly delimited; anterior margin between rostrum and lateral projections weakly concave; anterolateral margins sloping; posterior margin roundly truncate. Rostrum rounded, reaching slightly beyond lateral projections. Lateral projections, broadly subtriangular, terminating bluntly.

Ocular peduncles stout, approximately 0.5 length of shield; dorsal surfaces naked except for short setae dorsodistally; corneas weakly dilated. Ocular acicles subtriangular, each terminating acutely.

Antennular peduncles exceeding distal margins of cornea when fully extended by nearly full length of segment 3 (ultimate). Segments naked or with scattered short setae; segment 1 (basal) with blunt ventromesial distal angle, and small spine on lateral face.

Antennal peduncles, when fully extended, exceeding distal margins of corneas by approximately one-third of segment 5. Segment 5 slender, approximately 4 times as long as wide, unarmed except for scattered short setae. Segment 4 unarmed except for scattered short setae. Segment 3 with blunt ventrodistal angle. Segment 2 with dorsolateral distal angle produced into spine-like process with few short setae distolaterally; dorsomesial distal angle with small spine. Segment 1 unarmed, hidden by shield in dorsal view. Antennal acicles slender, straight, reaching forward to approximately distal two-thirds of corneas, each terminating in strong spine with tuft of setae distally. Flagellum reaching to tip of extended right cheliped, with few short setae 1 or less flagellar article in length.

Mouthparts not dissected. Maxilliped 3 ischium with crista dentata consisting of approximately 14 small subequal teeth, and accessory tooth. Sternite with strong spine on each side of midline.

Chelipeds strongly dissimilar in strength and shape, right distinctly larger and stronger than left. Right cheliped ( Figs. 1B, C , 3A, B ) dorsoventrally flattened, semi-translucent, dorsal and ventral surfaces of ischium to dactyl glabrous except for scattered setae. Chela ovate, approximately 1.7 times as long as broad; dactyl and fixed finger each terminating in inwardly curved blunt calcareous tip overlapping when closed. Dactyl about as long as palm; cutting edge with 3 subtriangular calcareous teeth approximately same size. Fixed finger cutting edge with 3 calcareous teeth increasing in size distally, becoming crenulate near fingertip. Palm slightly broader than long; dorsal surface slightly convex; ventral surface nearly flat; lateral and mesial margins with scattered short setae. Carpus ovate, dorsal surface slightly convex, ventral surface nearly flat; lateral and mesial margins well defined, each with row of short setae; dorsodistal margin unarmed. Merus subtriangular in cross-section and dorsal outline; dorsal margin rounded; dorsodistal margin unarmed; lateroventral and mesioventral margins weakly crenulate distally, setose. Ischium armed dorsally with blunt, setose spine; ventral margin sharply defined. Coxa with few setae on ventromesial distal angle.

Left cheliped ( Figs. 1D , 3A, B ) slender, somewhat dorsoventrally flattened, reaching to approximately midpoint of chela of right cheliped, with surfaces of ischium to dactyl glabrous except for scattered setae; fingers terminating in inwardly curved tips crossed when closed. Dactyl approximately as long as palm; dorsal surface slightly convex; cutting edge with row of minute corneous spinules; lateral margin rounded. Fixed finger with dorsal surface slightly convex; cutting edge minutely crenulate. Palm dorsal surface slightly convex; ventral surface nearly flat; lateral and mesial margins rounded. Carpus approximately as long as merus, dorsal surface slightly convex; ventral surface nearly flat. Merus subtrianguar in cross-section; lateroventral and mesioventral margins weakly crenulate, with few setae. Ischium with small blunt spine dorsally, ventral margin sharply defined. Coxa with few setae on ventromesial distal angle.

Pereopods 2 and 3 ( Fig. 2A, B ) sparsely setose, subequal left from right. Dactyl straight, approximately 0.9 times as long as propodus, with scattered setae dorsally and ventrally, terminating in sharp corneous claw curving ventrally; ventromesial margin with row of 9 distinct corneous spinules. Propodus straight, surfaces smooth, approximately 1.8 times times as long as carpus, unarmed except for few dorsal and ventral setae. Carpus with blunt dorsodistal angle, with scattered setae dorsally. Merus unarmed except for scattered setae dorsally and ventrally. Ischium unarmed. Anterior lobe of sternite XI (of pereopods 3; Fig. 2C ) subovate, glabrous, lacking spines.

Pereopod 4 ( Fig. 2D, E ) semichelate, glabrous except for scattered setae. Dactyl nearly straight, terminating in small corneous spinule; lateral face lacking scales; cutting edge with 4 sharp corneous spinules distally. Propodus ovate (lateral view) lacking scales or rasp; with 4 sharp corneous spines on distal margin opposite to cutting edge of dactyl. Carpus unarmed except for scattered setae dorsally. Merus unarmed.

Pereopod 5 chelate ( Fig. 2F ). Dactyl with 2 minute scales dorsally. Propodus with row of 4 scales on dorsodistal margin. Coxae symmetrical.

Uropods ( Fig. 1E ) nearly symmetrical, with few short setae; exopods each with 2 or 3 rows of minute scales anterodorsally. Telson ( Fig. 1F ) symmetrical, without transverse suture; terminal margin unarmed, weakly divided medially into 2 broadly rounded lobes.

Males unknown. Females with paired gonopores; with paired first pleopods (gonopods), and unpaired left pleopods 2–5.

Genetic data. The barcode fragment of the cytochrome c oxidase subunit I (CO1-5P) is provided under GenBank (www.ncbi.nlm.nih.gov/genbank) accession number OQ211624, BOLD (Barcode of Life Database) specimen number PAGNS9001-23 (dataset dx.doi.org/10.5883/DS-CRUSTACE).

Color ( Fig. 3A, B ). Overall semi-translucent; eyestalks pale rose pink with transverse ventrolateral slash of deep red near midlength, cornea turquoise with distinct spotting of deep red; chelipeds largely translucent, very pale yellow-orange cast darkest near margins of segments and joints, overall with scattered minute red spots; meri of chelipeds and pereopods 2 and 3 with pale bands of yellow-orange at proximal and distal ends in addition to another centered just beyond midlength; translucent anterior thorax with pale mottling of salmon pink to rose red, shield slightly more opaque and somewhat more yellowish with faint reddish spots and mottling; pleon translucent, faint reddish markings on pleopods and uropods.

Etymology. The species name is given to acknowledge and honor Rose Angela Gulledge (Museum Specialist, National Museum of Natural History, Smithsonian Institution), who has assisted the research of both authors in numerous ways during three decades.

Habitat. Found living in the rariphotic zone of the deep reefs of Curaçao, Lesser Antilles. Housing or associations unknown.

Distribution. Southeastern Caribbean Sea, known so far only from Curaçao, Lesser Antilles. Depth: 226– 276 m.

Remarks. The dorsoventrally flattened condition of the segments of the right cheliped, in particular, the carpus and chela, as well as the presence of what appears to be grasping spinules on the propodus and dactyl of pereopod 4, are unique among the Paguridae . Regrettably, the single known specimen of this new species was found loose in the sample without any indication of housing or possible association with another organism. These morphological adaptations are intriguing, and any explanation of their function at present can only be speculative. The armature of the propodus and dactyl of pereopod 4, however, does suggest that this species may grasp onto some housing or perhaps a soft organism while alive in order to protect its pleon or camouflage the body. The virtually symmetrical uropods and telson might suggest a tubular type of housing or association. The semi-transparent cephalothorax and all appendages might represent an adaptation to adopt the color of a possible host or substrate.

The only female known of this new species and type specimen, has paired first pleopods (gonopods), a condition that is considered a defining characteristic of the species in the 13 genera of the Pylopagurus - Tomopagurus group of pagurids ( Lemaitre & McLaughlin 2003). However, the reduced number of gills consisting of eight phyllobranchs in this new species, does not make it possible to assign it to any of the Pylopagurus - Tomopagurus group of genera, all of which have 11 pairs of gills.

Figures

FIGURE 1. Raripagurus roseangelae n. gen., n. sp., female holotype, cephalic shield 1.8 mm, USNM 1554278: A, cephalic shield and cephalic appendages, dorsal; B, right cheliped, dorsal; C, same, ventral; D, left cheliped, dorsal; E, uropods and telson, dorsal; F, telson, dorsal. Scale bars = 0.5 mm (A); 1.0 mm (B–D); 0.25 mm (E); 0.2 mm (F).

FIGURE 2. Raripagurus roseangelae n. gen., n. sp., female holotype, cephalic shield 1.8 mm, USNM 1554278: A, right pereopod 2, lateral; B, right pereopod 3, lateral; C, sternum, coxae of pereopods 1–5, and first pair of pleopods (gonopods); D, right pereopod 4, lateral; E, propodus and dactyl of same, lateral; F, propodus and dactyl of right pereopod 5, lateral. Scale bars = 1.0 mm (A–D); 0.4 mm (E, F).

FIGURE 3. Raripagurus roseangelae n. gen., n. sp., female holotype cephalic shield 1.8 mm, USNM 1554278: A, left dorsolateral; B, right lateral.