Hexapleomera sasuke, Tanabe & Kakui, 2019

Tanabe, Yuki & Kakui, Keiichi, 2019, Two Hexapleomera species from Japan, with a new species description and discussion of phylogenetic relationships within Hexapleomera (Crustacea: Tanaidacea), Zootaxa 4648 (2), pp. 318-336 : 322-332

publication ID	https://doi.org/ 10.11646/zootaxa.4648.2.7
persistent identifier	https://treatment.plazi.org/id/545387AE-FFE9-B923-FF74-5B40FD5CCE67
treatment provided by	Plazi
scientific name	Hexapleomera sasuke
status	sp. nov.

Treatment

Hexapleomera sasuke View in CoL sp. nov.

[New Japanese name: Shinobi-urashima-tanaisu]

Figures 1B View FIGURE 1 , 2 View FIGURE 2 –6, 7A

Sinelobus View in CoL sp. [cf. stanfordi ( Richardson, 1901)]: Saito & Higashi 2000, 2–4, figs 1, 2.

Hexapleomera View in CoL sp.: Kakui et al. 2011, 751; Kakui et al. 2012, 128–130, fig. 1C.

Etymology. The specific name, treated as a noun in apposition, is the name of a famous ninja, Sasuke, in reference to the specimens having sneaked into buildings (= public aquaria) without being noticed by anyone.

Material examined. Holotype, female (ICHUM-5849, eight slides and one vial) . Allotype, male (ICHUM- 5850, nine slides and one vial) . Paratypes: seven females (ICHUM-5853, seven slides ; ICHUM-5854, one vial ; ICHUM-5856, one vial ; ICHUM-5859, one vial ; ICHUM-5862, one vial ; ICHUM-5865, one vial ; and ICHUM- 5866, one vial) and nine males (ICHUM-5851, seven slides and one vial ; ICHUM-5852 ; eight slides and one vial ; TOYA Cr-23768, six slides and one vial ; ICHUM-5855 ; seven slides and one vial ; ICHUM-5857, eight slides and one vial ; ICHUM-5858, one vial ; ICHUM-5860, one vial ; ICHUM-5861, one vial ; ICHUM-5863, nine slides and one vial ; and ICHUM-5864, one vial). See Table 1 for detailed specimen information.

Diagnostic characteristics. Labium with palp fused to outer lobe. Maxilliped with coxa bearing two setae; endite with two tiny dorso-subdistal and two distal spiniform setae. Cheliped with three or four dorsodistal simple setae on carpus; region between bases of dactylus and fixed finger with three or four simple setae. Propodus of pereopod 1 with inner subdistal plumose seta. Pleopodal rami with deep pigmentation (retained in ethanol). Basal article of pleopod 3 with three outer setae. Uropod with four articles, including basal article.

Description of female. Based primarily on holotype, with some observations from paratype ICHUM-5853.

Body ( Figs 2A View FIGURE 2 , 3A, B View FIGURE 3 ) 2.28 mm in length, 4.89 times as long as CW, covered with dark pigmentation ( Fig. 2A View FIGURE 2 ), retained in ethanol. Cephalothorax 0.23 times as long as BL, 1.15 times as long as wide, triangular in dorsal view, with pair of mid-lateral simple setae and one pair each of long and short simple setae posterior to eyes. Pereonites 1–6 with length ratio 1.00:1.37:1.59:2.17:2.26:1.65; all wider than long, with several pairs of simple setae. Pleon length 0.17 times of BL. Pleonites all wider than long, with several pairs of simple setae and lateral plumose setae; pleonites 1 and 2 with row of posterior dorsolateral plumose setae. Pleotelson 0.75 times as long as wide, as wide as pleonite 5, with pair of lateral simple setae, pair of subposterior simple setae, and pair of posterior simple setae.

Antennule ( Fig. 3C View FIGURE 3 ) 0.70 times as long as cephalothorax; articles 1–4 with length ratio 1.00:0.33:0.29:0.02. Article 1 with one middle and four distal simple setae and several proximal and distal PSS. Article 2 with six distal simple setae and three distal PSS. Article 3 with three distal simple setae and two distal PSS. Article 4 with row of simple setae, one PSS, and three aesthetascs. Antenna ( Fig. 3D View FIGURE 3 ) with six articles, 0.92 times as long as antennule; articles 1–6 with length ratio 1.00:2.16:1.05:1.78:1.68:0.72. Articles 1–3 dorsally depressed.Article 1 naked. Article 2 with two dorsal and two ventral simple setae. Article 3 naked. Article 4 with three distal simple setae. Article 5 with three distal simple setae and four PSS. Article 6 with 12 distal simple setae and one PSS.

Labrum ( Fig. 3E View FIGURE 3 ) setulate distally. Mandibles ( Fig. 3F, F View FIGURE 3 1 View FIGURE 1 , G) with well-developed molar process, corrugated in masticatory region. Left mandible ( Fig. 3F, F View FIGURE 3 1 View FIGURE 1 ) with weakly denticulate incisor, two subdistal serrate spiniform setae, and wide lacinia mobilis with distal tooth. Right mandible ( Fig. 3G View FIGURE 3 ) with smooth incisor, two subdistal serrate spiniform setae, and peg-like lacinia mobilis with distal denticles. 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 and outer subdistal fine setae. Palp with two articles; article 2 with four simple setae. Maxilla ( Fig. 3J View FIGURE 3 ) with fine serration. Maxilliped ( Fig. 3K View FIGURE 3 ) coxa broken. Basis with ventral simple seta at insertion of palp; endite with two tiny dorso-subdistal and two distal spiniform setae, and two ventro-subdistal circumplumose setae. Palp article 1 with outer subdistal seta; article 2 with one outer, four inner simple setae, and three distal spiniform setae; article 3 with four dorsal and one ventral simple setae, and seven ventral plumose setae on inner margin; article 4 with two distal and one outer subdistal simple setae, four inner plumose setae, and six serrate setae. Epignath ( Fig. 3L View FIGURE 3 ) kidney shaped (distal portion broken), setulate proximally.

Cheliped ( Fig. 4A View FIGURE 4 ) with triangular articulation to cephalothorax via sclerite. Basis 1.33 times as long as wide, with free posterior portion, and one dorsal and two ventral simple setae. Merus with two dorsal and two ventral simple setae. Carpus 1.40 times as long as wide, with one dorsal, three 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 inner simple seta at insertion of dactylus; region between bases of dactylus and fixed finger with three simple setae. Fixed finger with three simple setae on ventral margin, six outer and two inner subdistal simple setae, and dorsodistal lamellar expansion on cutting surface, and triangular claw. Dactylus 1.10 times as long as fixed finger, with inner simple seta and row of ventral spiniform setae. Unguis triangular.

Pereopods 1–6 cylindrical, with length ratio 1.00:0.85:0.75:0.68:0.74:0.82. Pereopod 1 ( Fig. 4B View FIGURE 4 ) 0.31 times as long as BL, with length ratio (basis, merus, carpus, propodus, and dactylus–unguis) 1.00:0.30:0.39:0.58:0.36. Coxa with two simple setae but without anterior process. Basis cylindrical, narrow, 4.05 times as long as wide, with dorsal simple seta and dorsal PSS. Merus with ventrodistal simple seta. Carpus with three distal simple setae. Propodus with one dorsodistal and four ventrodistal simple setae, inner subdistal plumose seta, and dorsal PSS. Dactylus with dorsoproximal seta. Unguis 1.31 times as long as dactylus, naked. Pereopod 2 ( Fig. 4C View FIGURE 4 ) with length ratio of articles from basis to dactylus–unguis 1.00:0.46:0.29:0.45:0.29. Coxa with simple seta. Basis cylindrical, narrow, 2.61 times as long as wide, with one dorsal and one ventrodistal simple setae, and dorsal PSS. Merus with ventrodistal simple seta and ventrodistal spiniform seta. Carpus with two dorsodistal and one ventrodistal simple setae, and four distal spiniform setae. Propodus with one ventral, one dorsodistal, and one ventrodistal simple setae, and dorsal PSS. Dactylus with dorsoproximal simple seta. Unguis 1.41 times as long as dactylus, naked. Pereopod 3 ( Fig. 4D View FIGURE 4 ) with length ratio of articles from basis to dactylus–unguis 1.00:0.43:0.32:0.52:0.32; similar to pereopod 2, except coxa with two simple setae, basis with two dorsal PSS, merus with two ventrodistal setae, and carpus with dorsal simple seta. Pereopod 4 ( Fig. 4E View FIGURE 4 ) with length ratio of articles from basis to dactylus–unguis 1.00:0.46:0.32:0.47:0.29. Coxa with simple seta. Basis thick, 2.11 times as long as wide, with two ventrodistal simple setae. Merus with two dorsodistal and one ventro-subdistal simple setae, and two ventro-subdistal spiniform setae. Carpus with two dorsodistal simple setae and five distal spiniform setae. Propodus with two dorsodistal, one outer distal, and one ventral simple setae, and dorsal PSS. Dactylus–unguis fused to form claw. Claw strongly arched, with outer and inner rows of spines, and ventroproximal serration. Pereopod 5 ( Fig. 4F View FIGURE 4 ) with length ratio of articles from basis to dactylus–unguis 1.00:0.4 7:0.34:0.53:0.22; similar to pereopod 4, except basis with ventrodistal simple seta, and carpus with two outer and one inner dorsodistal simple setae. Pereopod 6 ( Fig. 4G View FIGURE 4 ) with length ratio of articles from basis to dactylus–unguis 1.00:0.42:0.37:0.51:0.26. Basis, merus, carpus, and dactylus–unguis similar to pereopod 4, except basis with ventrodistal simple seta, merus with dorsal simple seta, carpus with two outer and one inner dorsodistal simple setae. Propodus with two dorsodistal, one outer distal, and one ventral simple setae, dorsal PSS, two dorsodistal serrate setae, and six inner flattened denticulate setae.

Pleopodal rami with deep pigmentation (retained in ethanol). Pleopod 1 ( Fig. 4H View FIGURE 4 ) with basal article bearing one inner and five outer plumose setae. Endopod with one inner and ten outer plumose setae, and outer distal step-tipped plumose seta. Exopod 1.22 times as long as endopod, with 26 outer plumose setae. Pleopod 2 ( Fig. 4I View FIGURE 4 ) similar to pleopod 1. Pleopod 3 ( Fig. 4J View FIGURE 4 ) with basal article bearing three outer plumose setae. Endopod with one inner and eight outer plumose setae, and outer distal step-tipped plumose seta. Exopod 1.30 times as long as endopod, with 21 outer plumose setae.

Uropod ( Fig. 4K View FIGURE 4 ) with four articles (basal article and triarticulate ramus). Basal article with five distal simple setae. Ramus article 1 with two distal simple setae and PSS, article 2 with five distal simple setae and PSS, and article 3 with five distal simple setae and PSS.

Description of male. Based primarily on allotype, with some observations from paratype ICHUM-5857.

Body ( Figs 2B, C View FIGURE 2 , 5A, B View FIGURE 5 ) similar to female.

Antennule ( Fig. 5C, C View FIGURE 5 1 View FIGURE 1 ) 1.15 times as long as cephalothorax; articles 1–4 with length ratio 1.00:0.41:0.25:0.02. Article 1 with two middle and six distal simple setae and several proximal and distal PSS. Article 2 with eight distal simple setae and several distal PSS. Article 3 with four distal simple setae and several distal PSS. Article 4 ( Fig. 5C View FIGURE 5 1 View FIGURE 1 ) with rows of simple setae and five aesthetascs. Antenna ( Fig. 5D View FIGURE 5 ) with six articles, 0.81 times as long as antennule; articles 1–6 with length ratio 1.00:2.06:1.33:2.47:1.76:0.63. Articles 1–3 dorsally depressed. Articles 1 and 3 naked.Article 2 with six simple setae. Article 4 with four distal simple setae and distal PSS.Article 5 with four distal simple setae and three distal PSS. Article 6 with 14 distal simple setae and distal PSS.

Mouthparts ( Fig. 5 View FIGURE 5 E–L) similar to female, except maxillular palp ( Fig. 5J View FIGURE 5 ) with article 2 bearing five setae; maxilliped ( Fig. 5K View FIGURE 5 ) with coxa bearing two setae, basis bearing two ventral simple setae at insertion of palp, and palp article 3 bearing five dorsal simple setae.

Cheliped (Fig. 6A) with basis, merus, and carpus similar to those of female, except merus with dorsal seta and carpus with four dorsodistal setae. Chela 1.25 times as long and 1.1 times as wide as carpus. Propodal palm longer than fixed finger, with two simple setae in outer middle region, and inner simple seta at insertion of dactylus; region between bases of dactylus and fixed finger with four simple setae. Fixed finger with four simple setae on ventral margin, nine outer and two inner subdistal simple setae, large dorsal process, dorsodistal bilobed lamellar expansion on cutting surface, and triangular claw. Dactylus strongly arched, with ventral process, inner simple seta, and row of ventral spiniform setae. Unguis triangular.

Pereopods 1–6 (Fig. 6B–G) with length ratio 1.00:0.77:0.67:0.78:0.80:0.73 (unguis of pereopod 3 broken, not measured); pereopod 1 length 0.38 times of BL. Pereopods similar to those of female, but differ as follows: pereopod 1, propodus with four ventrodistal simple setae; pereopod 2, coxa with two simple setae, basis with two ventrodistal simple setae, merus with one dorsodistal and two ventrodistal simple setae, propodus with two ventral and two dorsodistal simple setae, and dactylus naked; pereopod 3, coxa with simple seta, basis with two ventrodistal simple setae and dorsal PSS, merus with dorsodistal simple seta, and carpus with two dorsodistal simple setae; pereopod 4, basis with two dorsal and two ventro-subdistal PSS, merus with three dorsodistal simple setae, and propodus with two outer distal simple setae; pereopod 5, basis with two ventrodistal simple setae and two dorsal and two ventrosubdistal PSS, merus with three dorsodistal and two ventro-subdistal simple setae, carpus without dorsodistal inner seta, and propodus with two ventral simple setae; pereopod 6, basis with two ventrodistal simple setae, merus with two dorsodistal and two ventro-subdistal simple setae, and propodus with two ventral simple setae, three dorsodistal serrate setae and nine flattened denticulate setae.

Pleopodal rami with deep pigmentation (retained in ethanol; Fig. 1B View FIGURE 1 ). Pleopod 1 (Fig. 6H) similar to that of female except exopod with 26 outer plumose setae. Pleopod 2 (Fig. 6I) similar to that of female except exopod with 23 outer plumose setae. Pleopod 3 (Fig. 6J) similar to that of female except endopod with nine outer plumose setae and exopod with 20 outer plumose setae.

Uropod (Fig. 6K) with four articles (basal article and triarticulate ramus). Basal article similar to that of female. Ramus article 1 with three distal simple setae and two PSS, article 2 with seven distal simple setae and two PSS, and article 3 with four distal simple setae and two PSS.

Variation and stability. We dissected and observed the holotype female, allotype male, and one female and six male paratypes. Table 4 View TABLE 4 lists the states of eleven selected characters. All specimens shared the following character states: i) the uropod with four articles; ii) two dorso-subdistal and two distal spiniform setae on the maxillipedal endite; iii) the maxillipedal coxa with two setae (lost during dissection in ICHUM-5849 and 5852); iv) the labial palp fused to the outer lobe of the labium; v) the pereopod-1 propodus with one inner subdistal plumose seta; vi) the basal article of pleopod 3 with three outer setae but without inner setae; and vii) the pleopodal rami with deep pigmentation ( Fig. 1B View FIGURE 1 ).

The following setae or aesthetascs included in the list varied in number among specimens (ranges in parentheses; Table 4 View TABLE 4 ): the setae in the region between bases of the chelipedal dactylus and fixed finger (3–4); the dorsodistal setae on the chelipedal carpus (3–4); the setae on the ventral margin of the fixed finger (3–4); and the aesthetascs on the antennule (3 in females; 5–6 in males).

Among males, two cheliped types were observed. Type 1 (Fig. 6A, L) is characterized by a large dorsal process on the cutting surface (Fig. 6L) or in the region between the bases of the chelipedal dactylus and fixed finger (Fig. 6A). Type 2 (Figs 6M, 7A) is characterized by a slight dorsoproximal process in the region between the bases of the chelipedal dactylus and fixed finger.

Genetic information. Part of the COI gene (655 nt, translating to 218 amino acids) was sequenced for 18 specimens of H. sasuke ( INSD accession numbers LC474840 View Materials –474857, Table 1 View TABLE 1 ), and only one haplotype was detected. A partial 18S sequence of one specimen collected from Okinawa Churaumi Aquarium (1878 nt; INSD accession number AB618191 View Materials ) was determined by Kakui et al. (2011).

Distribution. At present, this species has been found among the fouling community on tether lines at Yakushima Island and Ishigaki Island (this study); from the inner surface of the wall of aquarium tanks in Okinawa Churaumi Aquarium and Yokohama Hakkeijima Sea Paradise ( Saito & Higashi 2000; this study); and among epiphytic algae on the carapace of the loggerhead sea turtle ( Caretta caretta ) bred in Okinawa Churaumi Aquarium ( Kakui et al. 2011).

Remarks. Hexapleomera sasuke sp. nov. is the tenth species described in this genus. It has a 4-articulate uropod, which it shares with H. bultidactyla Esquete & Fernandez-Gonzalez, 2016 , H. edgari Bamber, 2012 , H. robusta ( Moore, 1894) , H. satella Bamber, 2012 , and H. urashima Tanabe et al., 2017 ; the other four congeners, namely H. moverleyi ( Edgar, 2008) , H. ulsana Wi et al., 2018a , H. wombat Bamber, 2012 , and H. yokjidona Wi et al., 2018b , have a 5-articulate uropod.

Among the species bearing a 4-articulate uropod, H. sasuke most closely resembles H. urashima in having the maxillipedal endite with two tiny dorso-subdistal and two distal spiniform setae, the maxillipedal coxa with two simple setae, the pereopod-1 propodus with a single inner subdistal plumose seta, and the labial palp fused to the outer lobe of the labium ( Table 5 View TABLE 5 ). These two species differ in the number of setae in the outer region of the pleopod-3 basal article (three in H. sasuke , two in H. urashima ), in the dorsodistal region of the chelipedal carpus (3–4 in H. sasuke , 5–7 in H. urashima ), and in the region between bases of the chelipedal dactylus and fixed finger (3–4 in H. sasuke , 5–6 in H. urashima ). Additionally, the degree of dark pigmentation on the pleopods also differs between two species (deep in H. sasuke , slight in H. urashima ; Fig. 1 View FIGURE 1 ). This character state may help in identifying the two Japanese species without using dissection. Partial sequences of the COI gene (655 nt, translating to 218 amino acids) from H. sasuke were 15.0–15.3% divergent (K2P distance) from those of H. urashima ; also, in partial 18S sequences (1888 nt after alignment), 0.8% divergent (K2P distance) was detected between two species. These support the conclusion of our morphological analysis, that H. sasuke and H. urashima are different species.

Kakui et al. (2011) reported this species (as Hexapleomera sp.) from the surface of a loggerhead sea turtle bred in the Okinawa Churaumi Aquarium. The turtle had been kept in an open-air backyard pool of the aquarium after the removal of epiphytic organisms, but at the time we conducted sampling, its carapace was covered with filamentous algae ( Cladophora sp.) and sac like algae (a species of Colpomenia or Hydroclathrus ). The water in the pool was taken unfiltered from the sea (Atsushi Kaneko, Okinawa Churaumi Aquarium, pers. comm.), and tanaidaceans and algae may have entered the aquarium along with the seawater. There are no other records of this tanaidacean species from sea turtles, either in captivity or in the wild.