Hexapleomera urashima, Tanabe & Hayashi & Tomioka & Kakui, 2017

Tanabe, Yuki, Hayashi, Ryota, Tomioka, Shinri & Kakui, Keiichi, 2017, Hexapleomera urashima sp. nov. (Crustacea: Tanaidacea), a tanaidid epibiotic on loggerhead sea turtles at Yakushima Island, Japan, Zootaxa 4353 (1), pp. 146-160 : 148-156

publication ID	https://doi.org/ 10.11646/zootaxa.4353.1.9
publication LSID	lsid:zoobank.org:pub:45DEC7D4-1EDF-477D-AE6B-10B42FF40841
DOI	https://doi.org/10.5281/zenodo.5688761
persistent identifier	https://treatment.plazi.org/id/03808785-1554-FF8D-FF04-53B7FD6D1F57
treatment provided by	Plazi
scientific name	Hexapleomera urashima
status	sp. nov.

Treatment

Hexapleomera urashima View in CoL sp. nov.

[New Japanese name: Urashima-tanaisu] Figures 2–6 View FIGURE2 View FIGURE 3 View FIGURE4 View FIGURE5 View FIGURE 6

Etymology. The specific name is a noun in apposition referring to Taro Urashima, the lead character in the Japanese fairy tale “Urashima-taro”. In the story, Urashima rides on the back of a sea turtle, as does this tanaidid species.

Material examined. Holotype: female with developed oostegites, ICHUM-5381, nine slides and one vial; other data presented in Table 1. Allotype: male, ICHUM-5382, ten slides and one vial; other data presented in Table 1. Paratypes: six females (ICHUM-5383, six slides and one vial; ICHUM-5384, eight slides; ICHUM-5385, six slides and one vial; ICHUM-5386, seven slides and one vial; ICHUM-5387, eight slides and one vial; ICHUM- 5388, one vial); eight males (ICHUM-5389, seven slides and one vial; ICHUM-5390, six slides; ICHUM-5391, nine slides; ICHUM-5392, nine slides; ICHUM-5393, seven slides and one vial; ICHUM-5394, one slide and one vial; ICHUM-5395, one vial; ICHUM-5396, one vial); other data presented in Table 1.

Diagnosis. Labium with palp fused to outer lobe. Maxilliped with coxa bearing two setae; endite with two tiny dorsosubdistal and two distal spiniform setae. Basal article of pleopod 3 with two outer setae but without inner setae. Uropod with four articles [including basal article].

Description of female. Based primarily on holotype, with some observations from paratypes ICHUM-5383 and 5386.

Body ( Figs 2B View FIGURE2 , 3A, A View FIGURE 3 1 View FIGURE 1 , B) 2.57 mm in length, dorsoventrally flattened, 3.43 times as long as CW, cuticle with red-brown pigmentation ( Fig. 2B View FIGURE2 ), retained in ethanol. Cephalothorax 0.27 times as long as BL, 0.95 times as long as wide, triangular in dorsal view, with pair of mid-lateral simple setae and two long and two short pairs of simple setae posterior to eyes. Pereonites 1–6 with length ratio of 1.00:1.17:1.49:1.92:1.99:1.67 respectively; all wider than long, with several pairs of simple setae. Pleon 0.17 times as long as BL; pleonites all wider than long, with several pairs of simple setae; pleonites 1 and 2 with row of posterior dorsolateral plumose setae; pleonite 2 with row of lateral plumose setae; pleonite 3 with posterior dorsolateral plumose seta. Pleotelson ( Fig. 3A View FIGURE 3 1 View FIGURE 1 ) 0.49 times as long as wide, as wide as pleonite 5, with two pairs of lateral simple setae, two pairs of simple setae anterior to uropodal insertion, and pair of simple setae in apical region.

Antennule ( Fig. 3C, C View FIGURE 3 1 View FIGURE 1 ) 0.84 times as long as cephalothorax; articles 1–4 with length ratio of 1.00:0.46:0.29:0.05 respectively; article 1 with one middle and six distal simple setae and several proximal and distal PSS; article 2 with nine distal simple setae and several distal PSS; article 3 with four distal simple setae and two distal PSS; article 4 ( Fig. 3C View FIGURE 3 1 View FIGURE 1 ) with row of simple setae (more than eight setae) and four aesthetascs. Antenna ( Fig. 3D View FIGURE 3 ) 0.98 times as long as antennule; articles 1–6 with length ratio of 1.00:1.42:0.78:1.47:1.31:0.32 respectively; articles 1 and 3 naked; article 2 with four outer and two inner simple setae; article 4 with four distal simple setae and distal PSS; article 5 with four distal simple setae and three PSS; article 6 with ten distal simple setae.

Labrum ( Fig. 3E View FIGURE 3 ) setulate distally. Mandibles ( Fig. 3F, G View FIGURE 3 ) with well-developed molar process, corrugated on masticatory surfaces; left mandible ( Fig. 3F View FIGURE 3 ) with smooth incisor, two subdistal setae, and denticulate lacinia mobilis; right mandible ( Fig. 3G View FIGURE 3 ) with small process on incisor, two subdistal setae, and peg-like lacinia mobilis. Labium ( Fig. 3H View FIGURE 3 ) with inner and outer lobes setulate on distal margin; labial process (palp) setulate, fused to outer lobe. Maxillule ( Fig. 3I View FIGURE 3 ) endite with eight spiniform setae, outer subdistal setation, and outer serration; palp with two articles; article 2 with six setae. Maxilla ( Fig. 3J View FIGURE 3 ) with small serrations.

Maxilliped ( Fig. 3K, K View FIGURE 3 1 View FIGURE 1 ) with coxa bearing two simple setae; basis with ventral simple seta at insertion of palp; endite with outer serration, two tiny dorsosubdistal and two distal spiniform setae, and two ventrosubdistal circumplumose setae ( Fig. 3K View FIGURE 3 1 View FIGURE 1 ); palp article 1 with outer subdistal seta; article 2 with one outer and four inner simple setae, and three distal spiniform setae; article 3 with five inner simple setae and seven inner plumose setae; article 4 with eleven distal and one outer subdistal serrate setae, and three inner plumose setae. Epignath ( Fig. 3L View FIGURE 3 ) with kidney-shaped lobe, margins finely setulate; terminal seta setulate.

Cheliped ( Fig. 3M, M View FIGURE 3 1 View FIGURE 1 ) with triangular articulation with cephalothorax via sclerite ( Fig. 3B View FIGURE 3 ); basis almost as long as wide, with free posterior portion, and one dorsal and three ventral simple setae; merus with three dorsal and three ventral simple setae; carpus 1.36 times as long as wide, with one dorsal, five dorsodistal, and three ventral simple setae; chela as long and wide as carpus, propodal palm longer than fixed finger, with three simple setae in outer middle region, and four outer and one inner simple setae at insertion of dactylus; fixed finger with four simple setae on ventral margin, eight outer and two inner simple setae, tiny dorsoproximal process, dorsoproximal simple seta, and dorsodistal trilobed lamellar expansion on cutting surface ( Fig. 3M View FIGURE 3 1 View FIGURE 1 ), and triangular claw; dactylus as long as fixed finger, with inner simple seta, ventral process, and row of ventral spiniform setae; unguis triangular.

Pereopods 1–6 cylindrical, with length ratio of 1.00:0.81:0.70:0.84:0.92:0.90 respectively (dactylus-unguis of pereopods 2 and 3 broken, not measured). Pereopod 1 ( Fig. 4A View FIGURE4 ) 0.37 times as long as BL, with length ratio of basis, merus, carpus, propodus, and dactylus-unguis 1.00:0.27:0.34:0.51:0.36 respectively; coxa with three dorsal simple setae and dorsal process; basis cylindrical, narrow, 4.48 times as long as wide, with two dorsal simple setae and dorsal PSS; merus with ventrodistal simple seta; carpus with four distal simple setae; propodus with one dorsodistal and five ventrodistal simple setae, inner plumose seta, and dorsal PSS; dactylus with dorsoproximal simple seta; unguis 1.21 times as long as dactylus, naked. Pereopod 2 ( Fig. 4B View FIGURE4 ) with length ratio of articles from basis to propodus 1.00:0.40:0.31:0.44 respectively; coxa with three dorsal simple setae; basis cylindrical, narrow, 2.67 times as long as wide, with one dorsal and one ventrodistal simple setae, and dorsal PSS; merus with one dorsodistal and two ventrodistal simple setae and ventrodistal spiniform seta; carpus with two dorsodistal and one ventrodistal simple setae, and four distal spiniform setae; propodus with three ventral and one distal simple setae, and dorsal PSS; dactylus naked; unguis broken. Pereopod 3 ( Fig. 4C View FIGURE4 ) with length ratio of articles from basis to propodus 1.00:0.43:0.38:0.53 respectively; similar to pereopod 2, except merus with three ventrodistal setae and propodus without distal seta.

Pereopod 4 ( Fig. 4D, D View FIGURE4 1 View FIGURE 1 ) with length ratio of articles from basis to dactylus-unguis 1.00:0.49:0.39:0.55:0.24 respectively; basis thicker than those of pereopods 1–3, 2.02 times as long as wide, with three ventrodistal simple setae, and two dorsal and two ventro-subdistal PSS; merus with two dorsodistal and two ventrosubdistal simple setae, and two ventrosubdistal spiniform setae; carpus with two dorsodistal simple setae and five distal spiniform setae; propodus with two dorsal, one outer distal, and two ventral simple setae, and dorsal PSS; dactylus-unguis fused to form claw, strongly arched, with outer and inner row of spines, and ventroproximal serration. Pereopod 5 ( Fig. 4E View FIGURE4 ) with length ratio of articles from basis to dactylus-unguis 1.00:0.41:0.40:0.52:0.24 respectively; similar to pereopod 4, except merus with three dorsodistal simple setae, and carpus with two outer and two inner dorsodistal simple setae. Pereopod 6 ( Fig. 4F, F View FIGURE4 1 View FIGURE 1 ) with length ratio of articles from basis to dactylus-unguis 1.00:0.44:0.41:0.52:0.23 respectively; basis, merus, carpus, and dactylus-unguis similar to pereopod 4, except basis with two ventrodistal simple setae but without PSS, merus with five dorsodistal and six ventrosubdistal simple setae, and carpus with two outer and two inner dorsodistal simple setae; propodus ( Fig. 4F View FIGURE4 1 View FIGURE 1 ) with two dorsal, one outer distal, and two ventral simple setae, dorsal PSS, three dorsodistal serrate setae, and seven inner flattened denticulate setae.

Pleopod 1 ( Fig. 4G View FIGURE4 ) with basal article bearing one inner and five outer plumose setae; endopod with one inner and 12 outer plumose setae, and outer distal step-tipped plumose seta; exopod 1.28 times as long as endopod, with 26 outer plumose setae. Pleopod 2 ( Fig. 4H View FIGURE4 ) similar to pleopod 1 except endopod with 11 outer plumose setae. Pleopod 3 ( Fig. 4I View FIGURE4 ) with basal article bearing two outer plumose setae; inner margin of basal article naked; endopod with one inner and nine outer plumose setae, and outer distal step-tipped plumose seta; exopod 1.26 times as long as endopod, with 15 outer plumose setae.

Uropod ( Fig. 3J View FIGURE 3 ) with basal article and ramus of three articles; basal article with eight distal simple setae; ramus article 1 with five distal simple setae and PSS; articles 2 and 3 each with several distal simple setae and PSS.

Description of male. Based primarily on allotype, with some observations from paratypes ICHUM-5390, 5391, and 5393.

Body ( Figs 2C View FIGURE2 , 5A View FIGURE5 ) similar to female but somewhat stouter.

Antennule ( Fig. 5B View FIGURE5 ) 1.42 times as long as cephalothorax; articles 1–4 with length ratio of 1.00:0.43:0.27:0.02 respectively; article 1 with three middle and eight distal simple setae and several proximal and distal PSS; article 2 with ten distal simple setae and several distal PSS; article 3 with four distal simple setae and several distal PSS; article 4 with eight simple setae and five aesthetascs. Antenna ( Fig. 5C View FIGURE5 ) with six articles, 0.90 times as long as antennule; articles 1–6 with length ratio of 1.00:3.74:1.80:3.53:2.70:0.74 respectively; articles 1 and 3 naked; article 2 with six outer and two inner simple setae; article 4 with six distal simple setae and distal PSS; article 5 with four distal simple setae and two distal PSS; article 6 with 13 distal simple setae and distal PSS.

Mouthparts ( Fig. 6A–G View FIGURE 6 ) similar to female, except maxilliped palp ( Fig. 6F View FIGURE 6 ) with article 2 bearing two inner simple setae and three distal spiniform setae; article 3 with five simple setae and eight plumose setae.

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Cheliped ( Fig. 5D–E View FIGURE5 ) with basis, merus, and carpus similar to those of female, except merus with two dorsal setae and carpus with six dorsodistal setae; chela 1.5 times as long and 1.5 times as wide as carpus, propodal palm longer than fixed finger, with two simple setae on outer middle region, proximal process on ventral margin, five outer and one inner simple setae at insertion of dactylus, and dorsoproximal simple seta; fixed finger with five simple setae on ventral margin, eleven outer and two inner simple setae, large dorsoproximal process, dorsodistal bilobed lamellar expansion on cutting surface, and triangular claw; dactylus strongly arched, with inner simple seta and row of ventral spiniform setae; unguis triangular.

Pereopods 1–6 ( Fig. 6H–M, M View FIGURE 6 1 View FIGURE 1 ) with length ratio of 1.00:0.76:0.94:1.02:0.89:0.88 respectively (dactylusunguis of pereopod 2 broken, not measured); pereopod 1 length 0.42 times BL. Pereopods similar to those of female, but differ as follows: pereopod 1, coxa with simple seta, basis with dorsal simple seta, carpus with two distal simple setae, propodus without dorsal simple setae but with three ventrodistal simple setae, and dactylus naked; pereopod 2, propodus with four ventral simple setae; pereopod 3, basis with two ventrodistal simple setae and two dorsal PSS, merus with two ventrodistal simple setae, and propodus with two ventral simple setae; pereopod 4, basis with two ventrodistal simple setae and four dorsal PSS, and merus with three dorsodistal simple setae; pereopod 5, basis with two ventrodistal simple setae and three dorsal PSS, and merus without dorsodistal setae; pereopod 6, basis with two dorsal PSS, merus with three dorsodistal and four ventrosubdistal simple setae, carpus with two dorsodistal simple setae, and propodus with three ventral simple setae and eight flattened denticulate setae.

Pleopod 1 ( Fig. 6N, N View FIGURE 6 1 View FIGURE 1 ) similar to that of female except endopod with two inner plumose setae. Pleopod 2 ( Fig. 6O, O View FIGURE 6 1 View FIGURE 1 ) similar to that of female except basal article with six outer plumose setae and exopod with 24 outer plumose setae. Pleopod 3 ( Fig. 6P, P View FIGURE 6 1 View FIGURE 1 ) similar to that of female except endopod with eight outer plumose setae and exopod with 18 outer plumose setae.

Uropod ( Fig. 6Q View FIGURE 6 ) with four articles, similar to that of female except basal article with four distal simple setae, and ramus article 1 with six distal simple setae and three PSS.

Variation and stability. In addition to the holotype and allotype, five female and five male paratypes of Hexapleomera urashima sp. nov. were dissected and data for twelve characters are listed in Table 2. All specimens shared the following character states: i) uropod with four articles, ii) maxillipedal coxa with two setae (lost during dissection in ICHUM-5383); iii) labial palp fused to outer lobe of labium; and iv) basal article of pleopod 3 with two outer setae but without inner setae. The number of subdistal and distal spiniform setae on the maxillipedal endite was also nearly invariable among the specimens: two tiny subdistal and two distal spiniform setae. In one female (ICHUM-5384), the number differed between the left and right endites, i.e., 2/2 on the right but 0/3 on the left, but since the latter state was observed in only one of 24 cases (one individual bore two endites), this might be a teratological state.

The following setae or aesthetascs varied in number among specimens (ranges in parentheses; Table 2): simple setae posterior to the eye (2–4), setae on the maxillipedal basis (1–2), setae on the maxillular palp (6–7; lost during dissection in ICHUM-5385 and 5387), setae on the ventral margin of the fixed finger (4–6); aesthetascs on the antennule (3–4 in females; 4–5 in males); and inner plumose setae on the endopod of pleopods 1–3 (1–2).

Among males, two cheliped shapes were observed: Type 1 ( Fig. 5D View FIGURE5 ), characterized by a large dorsoproximal process on the fixed finger; and Type 2 ( Fig. 5E View FIGURE5 ), characterized by a slight dorsoproximal process on the fixed finger.

Distribution. At present, known only from the surface of carapaces of nesting loggerhead sea turtles (Caretta caretta) on Yakushima Island, southern Japan.