Nesotanais ryukyuensis, Kakui & Kajihara & Mawatari, 2010

Kakui, Keiichi, Kajihara, Hiroshi & Mawatari, Shunsuke, 2010, A new species of Nesotanais (Crustacea, Tanaidacea) from Japan, with a key to species and a note on male chelipeds, ZooKeys 33 (33), pp. 1-17 : 3-10

Nesotanais ryukyuensis sp. n.

urn:lsid:zoobank.org:act:287D87E6-70DB-496B-B8C9-319B1D581F29

Figs 4–8

Material examined. Holotype, male (ZIHU-3822), 26°11'13.38"N, 127°41'8.84"E, Noha River (near Ishihiyabashi bridge), Naha, Okinawa, Japan, muddy bottom sediment, 50 cm depth, salinity 0‰, 29 February 2008 (dissected) . Allotype, ovigerous female (ZIHU-3823), same data as holotype (dissected). Paratypes: non-ovigerous female (ZIHU-3824), same data as holotype (dissected) ; ovigerous female (ZIHU- 3825), same data as holotype ; ovigerous female (ZIHU-3826), almost the same locality as holotype, salinity not recorded, 23 May 2008 ; non-ovigerous female (ZIHU- 3827), almost the same locality as holotype, salinity 20‰, 29 July 2008. All specimens were collected by Keiichi Kakui.

Accompanying fauna. Longiflagrum nasutus ( Nunomura, 2005) and Sinelobus sp. ( Tanaidacea ); Victoriopisa ryukyuensis Morino, 1991 and Corophium sp. ( Amphipoda ).

Diagnosis (male). Nesotanais with maxillipedal basis with one pair of simple setae, the latter being apparently longer than maxillipedal palp. Maxillipedal palp without any spiniform setae. Carpus of cheliped without any outer ridges. Dactylus of cheliped with one small and two toothed processes on cutting surface. Cheliped flange short, distally rounded. Plumose setae of pleopod rami on both distal and outer margins. One “step-tipped plumose seta” on inner margin of pleopod endopod.

Etymology. The specific epithet, noun in apposition, is after “Ryukyu”, the old name of the type locality, Okinawa.

Description of male (holotype, ZIHU-3822). Body ( Fig. 4A, 4B ). Cylindrical, but slightly flattened dorsoventrally; 1.97 mm in length, about 4.9 times as long as wide, white in ethanol, without any pigmentation.

Cephalothorax about 0.25 of total body length, with one pair of lateral simple setae near eyes. Eyes well defined, black. Anterior edge obtuse triangular in shape from dorsal view. Posterior end laterally swollen, with large sclerite where cheliped is attached.

Pereon. Each pereonite with pair of lateral simple setae; pereonite 1 with one pair of dorsolateral simple setae. All pereonites laterally rectangular; pereonite 1 shortest, pereonites 2 and 3 shorter than succeeding; pereonites 4–6 subequal in length.

Pleon about 0.26 times total body length, with five pleonites and pleotelson, as wide as pereon. Pleonites all wider than long, with one pair of lateral simple setae. Pleotelson wider than long, gradually tapering posteriorly from uropodal insertion; with one pair of lateral, one pair of dorsal, and two pairs of posterior setae.

Antennule ( Fig. 5A, 5a 1) four-articled, about 0.9 times as long as cephalothorax. Article 1 about 0.55 times as long as cephalothorax, with two medial and two distal simple setae, several broom setae, and five proximal "feeble branching setae" ( Fig. 5a 1). Article 2 0.6 times length of article 1, with one simple seta and two broom setae. Article 3 shortest, naked. Article 4 with six simple setae and three aesthetascs at tip.

Antenna ( Fig. 5B ) six-articled, narrow, about 0.85 times as long as antennule. Article 1 naked. Article 2 long, 2.3 times as long as article 3, with one distal simple seta. Article 3 with one distal simple seta. Article 4 longest, with one distal simple seta, one medial and five distal broom setae. Article 5 with one distal simple seta. Article 6 with six simple setae.

Mouthparts reduced. Maxilliped ( Fig. 5C ) bases completely fused, proximally widened, pear-shaped, each with one ventrodistal simple seta apparently longer than length of palp. Endites reduced. Articulation between palp articles 1–2 obscure; palp article 4 small; all palp articles naked. Epignath ( Fig. 5C ) falciform, tip broken.

Cheliped ( Fig. 6 A–C) basis with broad articulation with cephalothorax via sclerite, as long as wide, with no free posterior portion, and one outer simple seta. Merus triangular, with one ventral simple seta and one ventrodistal process. Carpus hexagonal, 1.27 times as long as wide, with two ventral setae, one ventroinner and one ventral processes. Chela as long as carpus, twisted about 90-degrees with dactylus situated inwards. Propodal palm with seven short and one long inner simple setae at dactylus insertion, and longitudinal parallel series of cuticular ridges in inner region. Fixed finger with one dorsoproximal, three dorsosubdistal, and two ventrosubdistal simple setae, and several inner small teeth and one inner subdistal toothed process; curving ventrally at a position just distal to the ventrosubdistal setae. Flange short, 0.67 times as long as wide, with round end, bearing inner crenulations. Dactylus slightly longer than fixed finger, gradually curving ventrally, with one ventromedial simple seta; three spiniform setae, one small and two toothed processes on cutting surface, and longitudinal parallel series of cuticular ridges in inner region.

Pereopod 1 ( Fig. 5D, 5d 1) about 0.7 mm long, longest among pereopods. Coxa with one long simple seta. Basis 0.34 times as long as total pereopod length, narrow (6.6 times as long as wide), cylindrical, and slightly arched; with slight dorsoproximal projection, bearing one simple seta. Ischium wider than long, with one ventral seta. Merus with one ventrodistal seta. Carpus longer than merus, with one dorsodistal, one inner distal, and one ventrodistal simple setae. Propodus longer than carpus, distally setulated ( Fig. 5d 1), with one ventrodistal simple seta and dorsodistal serration. Dactylus and unguis as long as propodus, falciform. Dactylus with one medial seta. Unguis 1.5 times as long as dactylus.

Pereopod 2 ( Fig. 5E ) 0.7 times as long as pereopod 1. Coxa like that of pereopod 1. Basis 0.4 times as long as total length, cylindrical, slightly curved; with slight dorsoproximal projection, bearing two broom setae. Ischium like that of pereopod 1. Merus with one ventrodistal simple and one spiniform setae. Carpus longer than merus, with one dorsodistal seta and two ventrodistal spiniform setae. Propodus as long as carpus, distally setulated, with one ventrodistal spiniform seta and dorsodistal serration. Dactylus and unguis slightly shorter than propodus, falciform. Dactylus naked; unguis as long as dactylus.

Pereopod 3 ( Fig. 5F ) shorter than pereopod 2. Otherwise like pereopod 2, except basis with one dorsoproximal broom seta.

Pereopod 4 ( Fig. 5G ) shorter than pereopod 3, without separate coxa. Basis 0.38 times as long as total length, inflated (1.95 times as long as wide) with two dorsoproximal and two (one lost in dissection) ventrodistal broom setae. Ischium like that of pereopod 3. Merus with two ventrodistal spiniform setae. Carpus as long as merus, with one dorsodistal simple seta, and two dorsodistal and two ventrodistal spiniform setae. Propodus longer than carpus, with one long spiniform and two ventrodistal spiniform setae, and dorsodistal serration. Dactylus and unguis shorter than propodus, claw-shaped. Dactylus naked. Unguis slightly shorter than dactylus.

Pereopod 5 ( Fig. 5H ) longer than pereopod 4, without separate coxa. Otherwise like pereopod 4, except basis with one dorsoproximal broom seta, and ischium with two ventrodistal simple setae.

Pereopod 6 ( Fig. 5I ) longer than pereopod 5, without separate coxa. Otherwise like pereopod 5, except basis naked, and propodus with three dorsodistal pinnate setae.

Pleopods ( Fig. 5J, 5j 1, 5j2) biramous, in five pairs, all similar. Basal article naked. Exopod uniarticulate, with 23 or 24 outer plumose setae. Endopod uniarticulate, with seven or eight outer plumose setae, and one inner and one distal “step-tipped plumose setae” ( Fig. 5j 2 ).

Uropod ( Fig. 5K ) basal article naked. Exopod biarticulate. Article 1 with one distal simple seta. Article 2 with two simple setae at tip. Endopod biarticulate, 1.5 times as long as exopod. Article 1 with one distal simple and two distal broom setae. Article 2 with five simple setae at tip.

Description of ovigerous female (allotype, ZIHU-3823; partially based on paratype, non-ovigerous female, ZIHU-3824): Body ( Fig. 4C, 4D ). Somewhat narrower than in male, 2.02 mm (1.70 mm in ZIHU-3824) in length, about 5.9 times as long as wide.

Cephalothorax similar to that of male, except posterior end not as swollen and anterior not as narrow behind the eyes.

Pereon and Pleon similar to those of male.

Antennule ( Fig. 7A ) three-articulated, about 0.7 times as long as cephalothorax. Article 1 about 0.45 times as long as cephalothorax, with two medial and two distal simple setae, several broom setae, and three proximal feeble branching setae. Article 2 one quarter length of article 1, with two simple setae and one broom seta. Article 3 as long as article 2, with six simple setae and one aesthetasc at tip.

Antenna ( Fig. 7B ) about 0.8 times as long as antennule; setation of articles 1–6 like those of male.

Mouthparts. Labrum ( Fig. 7C ) rounded, naked. Mandibles ( Fig. 7D, 7E ) molar process well developed, bearing distal row of denticles. Body with bumpy outer margin. Left mandible ( Fig. 7D ) incisor with several distal denticles; lacinia mobilis well developed, with seven teeth. Right mandible ( Fig. 7E ) crenulate at subdistal margin, incisor apex bifid. Labium (ZIHU-3824; Fig. 7F ) inner lobe tapering distally, naked. Outer lobe rounded, naked. Maxillule ( Fig. 7G, 7g 1) endite with nine distal spiniform setae and outer subdistal row of simple setae. Palp articulation obscure, with two setae. Maxilla lost during dissection. Maxilliped ( Fig. 7H ) bases completely fused, triangular, widest anteriorly, with one pair of distal simple setae over-reaching endites. Endites partly fused, triangular, widest anteriorly, each with one ventrodistal simple seta and two distal tubercles. Palp article1 parallelogram in shape, naked; article2 with one distal and two ventrodistal simple setae; article 3 with inner extension, bearing one inner simple and three inner ventral setulate setae; article 4 with two simple, two pinnate, and two setulate setae. Epignath ( Fig. 7I ) falciform, setulate at tip.

Cheliped ( Fig. 7J, 7j 1) basis with broad articulation with cephalothorax via sclerite, slightly longer than wide, with no posterior free portion, and one outer simple seta. Merus triangular, with one ventral simple seta. Carpus gradually widening distally, about 1.35 times as long as wide, with one short dorsodistal and two ventral simple setae. Chela as long as carpus, in general orientation. Propodal palm with seven short and one long inner, and one outer simple setae at dactylus insertion. Fixed finger with two ventral and three dorsal simple setae, one distal bifurcate process, and one distal lamella. Dactylus slightly longer than fixed finger, with one inner proximal simple seta and three small teeth on cutting surface.

Pereopods 1–6 ( Fig. 8 A–G) somewhat thicker and shorter than in male, setation like those of male.

Pleopods ( Fig. 8H, 8h 1) biramous, in five pairs, all of them similar and like those of male.

Uropod ( Fig. 8I ) similar to that of male, except endopod article 2 with three simple and two broom setae at tip.

Habitat. Specimens of Nesotanais ryukyuensis were collected from muddy sediment together with the parapseudid Longiflagrum nasutus ( Nunomura, 2005) and tanaid Sinelobus sp. The sediment consisted of upper soft and bottom stiff layers. All three tanaidacean species occurred in the upper soft layer.

Figures

Figure 2. Photograph of the sampling point, Noha River, taken from Ishihiyabashi Bridge spanning the river.

Figure 4. Nesotanais ryukyuensis sp. n. A, B holotype, male (ZIHU-3822) C, D allotype, ovigerous female (ZIHU-3823). A body, lateral view B body, dorsal view C body, lateral view D body, dorsal view. Scale bar equals 0.5 mm.

Figure 5. Nesotanais ryukyuensis sp. n. Holotype, male (ZIHU-3822). A right antennule aļ feeble branching seta B right antenna C maxillipeds and right epignath D right pereopod 1 dļ same, distal setulation of propodus E right pereopod 2 F right pereopod 3 G right pereopod 4 H right pereopod 5 I right pereopod 6 Ì right pleopod 1, most ornaments of setae not shown jļ same, endopod, most ornaments of setae not shown j2 same, distal part of step-tipped plumose seta K right uropod. Scale bar equals 0.1 mm.

Figure 6. Nesotanais ryukyuensis sp. n. Holotype, male (ZIHU-3822). A right cheliped, outer view B same, inner view of chela C same, anterodorsal view of chela. Scale bars equal 0.1 mm.

Figure 7. Nesotanais ryukyuensis sp. n. A–E, G–Ì allotype, ovigerous female (ZIHU-3823) F paratype, non-ovigerous female (ZIHU-3824). A right antennule B left antenna C labrum D left mandible E right mandible F labium G left maxillule gļ same, endite H maxillipeds, right palp not shown I epignath Ì right cheliped, outer view jļ same, inner view of chela. Scale bars equal 0.1 mm.

Figure 8. Nesotanais ryukyuensis sp. n. A–F, H, I allotype, ovigerous female (ZIHU-3823) G paratype, nonovigerous female (ZIHU-3824). A right pereopod 1 B right pereopod 2 C right pereopod 3 D right pereopod 4 E right pereopod 5 F right pereopod 6 G right pereopod 1 H right pleopod 1, most ornaments of setae not shown hļ same, endopod, most ornaments of setae not shown I left uropod. Scale bar equals 0.1 mm.