Richardina ohtsukai, Saito, Tomomi & Komatsu, Hironori, 2009

Saito, Tomomi & Komatsu, Hironori, 2009, Two new species of Richardina A. Milne-Edwards, 1881 (Crustacea: Decapoda: Stenopodidea: Stenopodidae), representing the first occurrences of the genus from the Pacific, Zootaxa 2154, pp. 30-46 : 31-38

publication ID	https://doi.org/ 10.5281/zenodo.188854
DOI	https://doi.org/10.5281/zenodo.5691367
persistent identifier	https://treatment.plazi.org/id/03EB87A1-7E17-3A49-0FE8-FB99FC1E13BA
treatment provided by	Plazi
scientific name	Richardina ohtsukai
status	sp. nov.

Treatment

Richardina ohtsukai View in CoL n. sp.

[New Japanese name: ohtsuka-ryu-jin-ebi] ( Figs. 1–6 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 )

Type material. HOLOTYPE: NSMT-Cr 20835, female (cl 5.0 mm), TV Toyoshio-maru, 2007-05 cruise, stn 0 9, Kerama Islands, N of Nagan-nu Island, 26° 23.15N, 127° 30.09E, 730– 728 m, 26 May 2007, coll. H. Komatsu.

PARATYPES: NSMT-Cr 20836, 6 males (cl 3.6–4.9 mm), 4 females (cl 4.5–5.1 mm), 1 ovigerous female (cl 4.4 mm), same data as holotype. NSMT-Cr 20837, male (cl 4.0 mm), TV Toyoshio-maru, 2007-05 cruise, stn 0 7, Amami-oshima Island, W of Utsuzaki, 28° 24.88N, 129° 14.57E, 655 m, 28 May 2007, coll. H. Komatsu. NSMT-Cr 20838, 4 males (cl 2.6–5.1 mm), ovigerous female (cl 5.1 mm), TV Toyoshio-maru, 2008-04 cruise, stn 08(1), Kerama Islands, N of Kuroshima Island, 26° 20.00N, 127° 23.53E, 722– 715 m, 25 May 2008, coll. H. Komatsu.

Description of females. Body slender and compressed. Integument of carapace and pleon glabrous ( Figure 1 View FIGURE 1 ).

Rostrum ( Figure 2 View FIGURE 2 A, B) slender, directed forward, reaching proximal third of antennal scale, 0.34 of cl, narrowly triangular in dorsal view; dorsal margin armed with 8–11 teeth, proximal tooth posterior to postorbital margin; ventral margin with 1–2 teeth subdistally; lateral margin often with 1–2 tiny teeth at midlength.

Carapace ( Figure 2 View FIGURE 2 A, B) with postrostral median ridge extending to gastric region; postrostral submedian spine relatively small, straight, directed anteriorly; postorbital region armed with a few stout spines directed anteriorly; orbital margin concave, inferior orbital angle rounded; antennal spine small and acuminate, marginal; anterolateral margin rounded with several minute spines; cervical groove distinct, posterior margin armed with cincture of many spines of various sizes, large in lateral part, small in dorsal part, directed anteriorly; hepatic groove present.

Sixth thoracic sternite ( Figure 2 View FIGURE 2 C) with paired narrow lobes, each lateral margin unarmed, ventral surface concave. Seventh sternite with paired, broad trapezoid lobes, each distolateral angle weakly produced, ventral surface concave, unarmed. Eighth sternite with paired narrow plates, each distolateral angle rounded, ventral surface concave, unarmed.

Pleonal somites ( Figure 1 View FIGURE 1 ) not sculptured; ventral margins unarmed. First pleonal somite short, divided in two sections by distinct transverse carina; anterior section with pleuron unarmed laterally, posterior section with pleuron unarmed laterally, posteroventral margin unarmed. Second somite with anterior transverse carina ending at base of pleuron. Third somite longest, posterodorsal margin somewhat posteriorly produced; pleuron unarmed laterally. Sixth somite ( Figures 1 View FIGURE 1 , 2 View FIGURE 2 E) armed with 2–4 strong lateral spines on either side. Telson ( Figure 2 View FIGURE 2 E) lanceolate, proximally narrowed between widest part and basal joint, tapering distally, 2.6 times longer than broad; dorsal surface with median groove flanked by two dorsolateral carinae, each provided with row of usually 5 strong, rather symmetrically situated spines, inner margin with 2–3 spines subproximally; lateral margins convex subproximally, armed with strong spine at midlength; posterior margin convex, unarmed, posterolateral angle armed with posterolateral spine.

Eye ( Figure 2 View FIGURE 2 A, B) well developed, cornea hemispherical, red pigmented; eyestalk armed with 5–7 small spines along base of cornea, dorsally with several scattered small spines, 0.7 of cornea in length. Antennular peduncle ( Figures 2 View FIGURE 2 B, 3A) reaching to midlength of antennal scale; first segment subequal to distal two segments combined, with longitudinal, distolateral row of setae; stylocerite acute, curved; second segment armed with 1 strong dorsolateral and 2 strong ventromesial spines; third segment with rounded distal margin. Antenna ( Figures 2 View FIGURE 2 B, 3B) with stout basicerite armed with moderately large spine at distolateral angle, and with few additional small spines on ventrolateral margin; antennal scale 3.2 times longer than broad, lateral margin nearly straight, armed with 5–7 teeth, dorsal surface with 2 distinct longitudinal carinae; carpocerite short, reaching to level of first segment of antennular peduncle, armed with 1 spine.

Epistome ( Figure 2 View FIGURE 2 D) triangular anteriorly, armed with 2 distolateral spines and 2 smaller subdistal spines; labrum normally developed. Paragnath bilobed, separated by median fissure.

Mandible ( Figure 3 View FIGURE 3 C) robust, with palp consisting of 3 articles, distal article oval, furnished with dense setae, intermediate article longest, distally with tuft of setae; molar and incisor processes clearly separated; molar surface oval, without distinct tooth, distal margin of incisor process truncated, armed with short, stout teeth. Maxillule ( Figure 3 View FIGURE 3 D) with simple, slender endopod tapering distally; basial endite moderately broad, truncated distally with several slender spines and sparse, long spiniform setae; coxal endite suboval, with submarginal row of stiff setae on outer surface. Maxilla ( Figure 3 View FIGURE 3 E) with curved, slender endopod; basial and coxal endites both bilobed; scaphognathite well developed, anterior lobe rounded distally, posterior lobe short, widened posteriorly. First maxilliped ( Figure 3 View FIGURE 3 F) with broad endopod consisting of 2 articles, distal article narrow, tapering distally with blunt distal spine; proximal article subquadrate; basial endite large, subtriangular, with concave mesial margin; coxal endite bilobed; exopod with well-developed flagellum; epipod large, feebly bilobed. Second maxilliped ( Figure 3 View FIGURE 3 G) with endopod composed of 7 segments; dactylus tapering distally; propodus anteromesially truncated, 0.7 of dactylus in length; carpus cap-shaped, subequal in length to propodus; merus about twice as long as carpus, oblong, mesial margin pectinate; ischium and basis very short, obliquely demarcated; coxa with small tubercles laterally, epipod cylindrical with small podobranch; exopod with well-developed flagellum. Third maxilliped ( Figure 4 View FIGURE 4 A) with slender endopod, composed of 7 segments, reaching tip of antennal scale by lengths of dactylus and half of propodus; dactylus tapering distally, lateral margins of dactylus and propodus furnished with long setae, distomesial surface with shallow depression fringed with dense grooming setae; carpus unarmed, ventrodistal margin somewhat produced; merus with distolateral row of 4–6 stout spines; ischium compressed, armed with ventral row of several small spines, interspaced with pectines, and with 1 dorsolateral spine; basis short; coxa with short epipod; exopod with well developed, unsegmented flagellum, distally with dense setae.

Branchial formula shown in Table 2.

Maxillipeds Pereopods

1 2 3 1 2 3 4 5 Pleurobranchs - - 1 1 1 1 1 1 Arthrobranchs 1 1 2 2 2 2 2 - Podobranch - 1 - - - - - - Epipods 1 1 1 1 1 1 1 - Exopods 1 1 1 - - - - - First pereopod ( Figure 4 View FIGURE 4 B) small, slender, unarmed, reaching tip of antennal scale by length of dactylus, with well developed grooming apparatus; dactylus 0.4 of chela length; palm subcylindrical; carpus slender, 1.7 of chela length; merus 0.9 of carpal length; ischium 0.6 of meral length. Second pereopod ( Figure 4 View FIGURE 4 C) longer than first pereopod, unarmed, overreaching tip of antennal scale by lengths of chela and half of carpus; dactylus 0.4 of chela length; palm subcylindrical; carpus slender, about twice as long as chela length; merus 0.8 of carpal length; ischium about half of meral length. Third pereopod ( Figure 4 View FIGURE 4 D, E) strongest of pereopods, overreaching tip of antennal scale by lengths of chela and carpus; dactylus 0.4 of chela length, terminating hooked unguis, unarmed on dorsal and lateral margins, cutting edge armed proximally with stout, triangular tooth, remaining parts entire; fixed finger generally similar to dactylus, cutting edge armed with blunt teeth opposed into depression on dactylus; palm subcylindrical, 2.5 times longer than wide, mesial margin armed with row of several small spines, lateral surface armed with 1–2 rows of several small spines mesially and laterally, ventrolateral margin armed with short row of a few small spines anteriorly; carpus slightly widened distally, about 4.2 times longer than wide, 0.6 of chela length, dorsal surface armed with two rows of 2–9 stout spines, ventral margin armed with 2 rows of 5–6 smaller spines; merus subequal to carpus, dorsal margin armed with row of 7 spines, ventral margin armed with row of 9 smaller spines; ischium 0.6 of meral length, unarmed.

Fourth and fifth pereopods ( Figure 4 View FIGURE 4 F, G, H) similar, very long and slender; fourth pereopod reaching tip of antennal scale by lengths of dactylus, propodus and carpus; dactyli ( Figure 4 View FIGURE 4 G, H) compressed laterally, about 4 times longer than wide, uniunguiculate, dorsal margin usually with 1 movable spine at midlength; propodi 4 times as long as dactyli, subdivided into 8–15 articles, ventral margin armed with small spine on Pleopods without any appendices. First pleopods uniramous ( Figure 4 View FIGURE 4 I), shortest. Second to fifth pleopods biramous. Second pleopod ( Figure 4 View FIGURE 4 J) with basipodite shorter than exopodite, but as long as endopodite, mesial margin unarmed. Third to fifth pleopods generally similar, decreasing in size posteriorly, often armed with a few teeth on ventral margins of basipodites.

Uropod ( Figure 2 View FIGURE 2 E) with protopodite stout, lateral margin terminating in acute process; exopod broad, falling slightly short of posterior margin of endopod, lateral margin nearly straight, terminating in acute tooth, with row of 7–10 acute teeth, dorsal surface with 2 smooth longitudinal carinae, unarmed; endopod tapering distally, falling slightly short of posterior margin of telson, lateral margin unarmed, dorsal surface with 2 smooth longitudinal carinae, unarmed.

Eggs counting 2, diameter 1.5–1.6 mm (example: ovig. female, cl 4.4 mm, NSMT-Cr 20836).

Male characteristics. Rostrum ( Figure 5 View FIGURE 5 ) relatively longer than that of female, 0.36 of cl; dorsal margin armed with 9 teeth, proximal 2 teeth posterior to postorbital margin; ventral margin with 2 subterminal teeth; lateral margin with few tiny teeth at midlength. Sixth thoracic sternite ( Figure 6 View FIGURE 6 A) with slender, strongly bifurcated lobes, lateral angle terminating in acute spine, mesial angle denticulate; seventh sternite with relatively broad subquadrangular lobes directed anterolaterally, each anterolateral angle terminating in acute spine; eighth sternite with triangular lobes directed anterolaterally, each anterolateral angle terminating in acute spine. Pleura of first to sixth pleonal somites ( Figure 5 View FIGURE 5 ) armed with several teeth anteroventrally and/or posteroventrally. Third pereopod ( Figure 6 View FIGURE 6 B, C) with palm about twice as long as wide, dorsal margin armed with a few irregular rows of several spines of various sizes, basal surface of immovable finger armed with some small spines or tubercles, ventrolateral surface of palm armed with 1–2 rows of several small spines; carpus widened distally, about 3.1 times longer than wide, 0.6 of chela length, dorsolateral surface armed with 1 distal spine and two rows of 1–4 spines, mesial margin armed with row of 5 smaller spines; merus subequal to carpus, dorsal margin armed with row of 5–7 spines, ventral margin armed with row of 7 spines; ischium 0.7 of meral length, unarmed. Second to fifth pleopods ( Figure 5 View FIGURE 5 ) armed with some teeth on ventral margins of basipodites.

Color in life. Body and appendages generally pinkish transparent. Rostrum transparent. Carapace generally transparent with anterolateral to hepatic regions of cephalothorax reddish and with red spots on posterior margin. First to sixth pleonal somites each with red transverse band posteriorly. Eyestalk red. Second and third maxillipeds almost red. Telson and uropods generally transparent but with lateral margins and carinae red.

Etymology. Specifically named after Prof. Susumu Ohtsuka of Hiroshima University, the project leader of TV Toyoshio-maru Research Cruise, for his great contributions to the phylogeny and systematics of Crustaceans.

Distribution. So far known from off Amami-oshima Island and Kerama Islands, southwestern Japan.

Ecological notes. Richardina ohtsukai n. sp. is collected from the gastric cavity of hexactinellid sponges.

Remarks. Richardina ohtsukai n. sp. appears unique within the genus in having the additional movable spine on the dorsal margins of the dactyli of the fourth and fifth pereopods. R. ohtsukai is most similar to the Atlantic species R. spinicincta in the median row of spines on the posterior margin of the cervical groove and its numbers. Comparison with the type material of R. spinicincta has revealed that the new species is easily distinguished from R. spinicincta by the following characters: (1) lateral teeth on the rostrum are present in R. ohtsukai , whereas they are entirely absent in R. spinicincta ; (2) the length ratio of cornea and eyestalk is 1: 0.7 in R. ohtsukai , whereas it is 1: 2.7 in R. spinicincta ; (3) the eyestalk has relatively reduced armament in R. ohtsukai , but it is armed with many large spines in R. spinicincta ; (4) the propodi and carpi of the fourth and fifth pereopods are subdivided into 8–15 and 10–12 articles, respectively, in R. ohtsukai , rather than into the 4 and 5 articles in R. spinicincta (cf. Kemp 1910; Forest & Holthuis 1997).