Nototanoides ohtsukai, Kakui & Yamasaki, 2013

Kakui, Keiichi & Yamasaki, Hiroshi, 2013, Nototanaids (Crustacea: Tanaidacea) from Japan, with the Description of a New Species of Nototanoides, Species Diversity 18, pp. 245-254 : 246-251

Genus Nototanoides Sieg and Heard, 1985 Nototanoides ohtsukai sp. nov.

( Figs 2–5 )

Material examined. Holotype. Ovi female, ZIHU-4401; BL 2.75, CW 0.45; five slides and one vial; R / V Soyo-maru , Yaku-Shin-Sone Bank, North Pacific Ocean, 29°47.0′N, 130°22.6′E to 29°47.6′N, 130°23.0′E, 155–175 m depth, biological dredge, 2 August 2008, collected by Ken Fujimoto and Takami Morita (sorted by Hironori Komatsu).

Allotype. Male, ZIHU-4402; BL 2.46, CW 0.39; three slides and one vial; same collection data as for holotype.

Paratypes. PO female, ZIHU-4403; BL 2.70, CW 0.36; four slides and one vial . Ovi female, ZIHU-4404; BL 2.66, CW 0.43; four slides and one vial . Ovi female, ZIHU-4405; BL 2.63, CW 0.36; one slide and one vial . Female , ZIHU- 4408; BL 1.58, CW 0.23; one vial . Female , ZIHU-4409; BL 2.46, CW 0.30; one vial . Male , ZIHU-4406; BL 2.54, CW 0.37; four slides and one vial . Male , ZIHU-4407; BL 2.11, CW 0.27; one slide and one vial . Four individuals, ZIHU- 4410; all intact, one vial . Four individuals, NSMT-Cr 22361; all intact, one vial . ZIHU-4403–4406, ZIHU-4410, and NSMT-Cr 22361, same collection data as for holotype; ZIHU-4407–4409, TR/ V Toyoshio-maru , Yaku-Shin- Sone Bank, North Pacific Ocean, 29°49.26′N, 130°24.55′E to 29°48.75′N, 130°24.45′E, 201– 198 m depth, biological dredge, 18 May 2011, collected by Susumu Ohtsuka and Hiroshi Yamasaki .

Diagnosis. Relative length of distal article to article 2 in antennule 0.42–0.49 in females, 0.38–0.39 in males. Row of aesthetascs on distal article of antennule located on midventral region.

Description of female. Based primarily on holotype, with some observations from paratypes ZIHU-4403–4405. Body ( Fig. 2A, C ) dorsoventrally flattened, 6.11 times as long as wide. Cephalothorax 0.24 times BL, with one pair of lateral simple setae posterior to eyes; rostrum blunttriangular; dorsal region of carapace smooth. Pereonites each with one pair of dorsolateral simple setae; pereonites 4–6 each with one pair of lateral simple setae. Pleon 0.27 times BL. Pleonites as wide as pereon; all similar in shape, each with one pair of dorsolateral simple setae and row of lateral simple setae. Pleotelson slightly narrower than pleonites, wider than long, trapezoidal, with one pair each of lateral, posteriolateral, and posterior simple setae.

Antennule ( Fig. 3A, a 1 ) 0.72 times cephalothorax length; length ratio of articles 1–3 3.52: 1.00:0.49. Article 1 with two outer and two inner simple setae and several plumose sensory setae. Article 2 with two simple setae and one plumose sensory seta. Article 3 with six distal simple setae, one distal plumose sensory seta, and one distal and four mid-ventral aesthetascs. Antenna ( Fig. 3B ) with six articles; length 0.82 times antennule length; length ratio of articles 1–6 1.00: 2.16:0.81: 3.98: 0.52: 0.11. Article 1 naked. Articles 2 and 3 each with one dorsodistal setulate seta. Article 4 with one simple seta and several plumose sensory setae. Article 5 with one simple seta. Article 6 with five simple setae.

Labrum (ZIHU-4405; Fig. 3C ) rounded; distal region setulate; distolateral region with several teeth. Mandibles ( Fig. 3D, E ) with broad masticatory region bearing several teeth. Left mandible ( Fig. 3D ) with several teeth on incisor and five teeth on lacinia mobilis; right mandible ( Fig. 3E ) with bifurcate incisor. Labium ( Fig. 3F ) with inner lobe bearing tiny ventrolateral spine; outer lobe well developed, rounded, with outer serration. Maxillule (ZIHU-4404; Fig. 3G ) with outer clumps of short setae; endite with nine spiniform setae. Maxillular palp with two setae at tip. Maxilla (ZIHU- 4404; Fig. 3G ) subovate, naked. Maxillipeds ( Fig. 3H, h 1 , h 2 , I) with bases fused, bearing one ventral simple seta (reaching beyond distal margin of endite) at insertion of palp. Endites distally separated; outer margin setulate; each distal margin with one shorter (shorter than 0.33 times longer simple seta length) and one longer simple setae, and two flat tubercles or “membranous hemispherical structures” ( Sieg and Heard 1985); flat tubercles large, partly overlapping ( Fig. 3h 1 ). Maxillipedal palp ( Fig. 3h 2 ) with article 1 naked; article 2 with two inner simple setae and one multifurcate spiniform seta; article 3 with one simple seta and three thick bipinnate setae in inner region; article 4 with one subdistal simple seta and five inner thick bipinnate setae. Epignath (ZIHU-4405; Fig. 3J ) narrow, curved, with one distal circumplumose seta.

Cheliped ( Fig. 4A, a 1 , a 2 ) with basis slightly longer than wide, bearing small free posterior portion and one outer simple seta. Merus triangular, with one ventral simple seta. Carpus 1.6 times as long as wide, with one dorsoproximal, one dorsodistal, and two ventral simple setae. Chela with four ventral simple setae. Propodal palm with one outer and one inner simple setae, and inner row of minute setae at insertion of dactylus. Fixed finger with claw; cutting surface with two middle simple setae, one middle sinuate spiniform seta ( Fig. 4a 1 ), and one outer distal rectangular lamellar projection. Dactylus 1.5 times as long as fixed finger, with one inner proximal bipinnate seta; cutting surface with one small mid-ventral process (not illustrated) and several teeth.

Pereopods 1–6 with length ratio of 1.55: 1.00:1.01: 1.07: 1.14: 1.18. Pereopod 1 ( Fig. 4B ) 0.36 times BL. Coxa with one simple seta. Length ratio of basis, ischium, merus, carpus, propodus, and dactylus-unguis 3.38: 0.21:1.00: 1.07: 1.66: 1.76. Basis cylindrical, narrow (6.0 times as long as wide), with one dorsal simple seta and one dorsal plumose sensory seta. Ischium and merus each with one ventral simple seta; merus obliquely articulated with carpus. Carpus with four distal simple setae. Propodus with one dorsal and one ventral simple setae, and dorsodistal setulation. Dactylus with one simple seta. Unguis twice as long as dactylus. Pereopod 2 (ZIHU-4403; Fig. 4C ) with length ratio of basis, ischium, merus, carpus, propodus, and dactylus-unguis 3.28: 0.20: 1.00: 1.28: 1.41: 0.94. Coxa, basis, and ischium like those of pereopod 1, except basis shorter. Merus with one ventral simple seta and one ventral spiniform seta. Carpus with four distal spiniform setae. Propodus with one ventral spiniform seta and dorsodistal setulation. Dactylus naked. Unguis 1.9 times as long as dactylus. Pereopod 3 ( Fig. 4D ) similar to pereopod 2, except basis with one additional plumose sensory seta, and carpus with only three distal spiniform setae. Pereopod 4 ( Fig. 4E, e 1 ) with length ratio of basis, ischium, merus, carpus, propodus, and dactylus-unguis 3.13: 0.21: 1.00: 1.16: 1.69: 0.93. Basis thick (2.6 times as long as wide), with two dorsoproximal and two ventrodistal plumose sensory setae. Ischium with two ventral simple setae. Merus with two ventrodistal spiniform setae. Carpus with one dorsodistal simple seta and three distal spiniform setae. Propodus with one mid-dorsal plumose sensory seta, one dorsodistal pinnate seta ( Fig. 4e 1 ), two ventrodistal spiniform setae, and dorsodistal setulation. Dactylus-unguis curved ventrally, with thick basal part bearing dorsoproximal setulation. Unguis 0.70 times as long as dactylus. Pereopod 5 ( Fig. 4F ) similar to pereopod 4, except ischium bearing one additional simple seta, and carpus with four distal spiniform setae. Pereopod 6 ( Fig. 4G, g 1 ) similar to pereopod 4, except basis bearing only one dorsoproximal plumose sensory seta, carpus with four distal spiniform setae, and propodus with two dorsodistal serrate setae ( Fig. 4g 1 ).

Pleopods ( Fig. 4H ) all similar. Basal article naked. Endopod with 10–12 plumose setae and one distal “step-tipped plumose seta” (see Kakui et al. 2010: fig. 5j2) on outer margin, and one inner subdistal step-tipped plumose seta. Exopod longer than endopod, with 23–25 outer plumose setae; “outer process” ( Larsen and Froufe 2013) [=“vestigial proximal article” ( Bird 2012a)], with one outer plumose seta.

Uropod ( Fig. 4I ) with basal article naked. Endopod article 1 with one simple seta and four plumose sensory setae; article 2 with five simple setae and one plumose sensory seta. Exopod article 1 with one simple seta; article 2 slightly shorter than article 1, with two simple setae.

Description of male. Based on allotype. Body ( Fig. 2B, D ) 6.30 times as long as wide. Otherwise similar to females, except cephalothorax more slender in anterior half, all pereonite articulations more constricted than those of female, and pereonite 6 with pair of genital cones.

Antennule ( Fig. 5A, a 1 ) with four articles, 0.73 times cephalothorax length; length ratio of articles 1–4 3.45: 1.00: 0.16: 0.38. Articles 1 and 2 similar to those of female. Article 3 with three ventrodistal aesthetascs. Article 4 with six distal simple setae, one plumose sensory seta, and one distal and four mid-ventral aesthetascs. Antenna ( Fig. 5B ) 0.82 times antennule length, with six articles; length ratio of articles 1–6 1.00: 2.39: 0.86: 4.76: 0.69: 0.18. Articles 1, 2, 4, and 5 similar to those of female. Article 3 with exoskeleton thickened in part of distal half ( Fig. 5B : arrowhead), bearing one dorsodistal setulate seta. Article 6 with six simple setae.

Labrum ( Fig. 5C ) naked. Maxillule ( Fig. 5D ) with naked endite; palp with one seta. Maxillipeds ( Fig. 5E, e 1 ) with bases completely fused, bearing one ventral simple seta at insertion of palp. Endites completely fused medially but distal margin slightly concave, each with one ventral small simple seta and one small process. Palp with four articles; article 3 with one distal simple seta.

Cheliped ( Fig. 5F, f 1 ) with basis and merus similar to those of female. Carpus 1.75 times as long as wide, with one dorsoproximal, one dorsodistal, and two ventral simple setae, and one ventral process. Chela otherwise similar to that of female, except fixed finger lacking distal rectangular lamellar projection, and process on dactylus larger than that of female.

Pereopods 1–3 ( Fig. 5H–J ) similar to those of female, except basis bearing outer dorsodistal lamellar projection ( Fig. 5H–J : arrowheads). Pereopods 4–6 ( Fig. 5K–M ), pleopods, and uropod generally similar to those of female.

Variation. The length of the antennule’s distal article relative to article 2 varies: in females, 0.49, 0.43, or 0.42 (ZIHU-4401, 4403, 4404, respectively); in males, 0.38, 0.39, or 0.39 (ZIHU-4402, 4406, 4407, respectively). The distal article of antennule bears five simple setae in three paratypes (ZIHU-4404, 4406, 4407). The number of aesthetascs in the mid-ventral region of the antennule’s distal article varies: two (in ZIHU-4407), three (in ZIHU-4403, 4406), or four (ZIHU-4401, 4402, 4405). Antennal article 6 has four (ZIHU-4404), five (ZIHU-4401, 4403, 4406), or six (allotype) simple setae. The shape of the multifurcate seta on article 2 of the maxillipedal palp varies in females: bifurcate in two individuals (ZIHU-4401, 4405; Fig. 3h 2 ); trifurcate in two individuals (ZIHU-4403, 4404; Fig. 3I ). The number of simple setae on article 2 of the maxillipedal palp varies in males: one in two individuals (ZIHU-4402, 4407); two in ZIHU-4406. The number of ventral simple setae on the chela is three in two paratypes, ZIHU-4403 and 4407. The carpus of pereopod 3 has four distal spiniform setae in one female (ZIHU-4403). Three ventral simple setae are present on the pereopod 5 ischium of two specimens (ZIHU-4401 and 4403), and on the ischium of pereopod 6 ischium of the allotype. Article 2 of the uropodal endopod bears four simple setae in ZIHU-4404, but two plumose sensory setae in ZIHU-4403. Two plumose sensory setae are present in the dorsoproximal region on the basis of pereopod 2 in ZIHU- 4402 and 4404.

The carpus of pereopod 4 has four distal spiniform setae, except in the holotype; four may thus be the usual condition.

In addition to the antennule, mouthparts, and chelipeds, marked sexual dimorphism is evident in the bases of pereopods 1–3, which bear an outer dorsodistal lamellar projection in males.

Etymology. The specific name honours Susumu Ohtsuka, organizer of serial benthos/plankton surveys in southwestern Japan by the TR/V Toyoshio-maru, which procured many tanaidaceans.

Remarks. Nototanoides ohtsukai sp. nov. is the second species described in this genus. The type species, N. trifurcatus Sieg and Heard, 1985 , was originally described from the Gulf of Mexico; Araújo-Silva and Larsen (2012) subsequently reported N. cf. trifurcatus from the North Chain Banks, Brazil, adding brief remarks. Nototanoides ohtsukai can be distinguished from N. trifurcatus by the length of the distal article (article 3 for females; article 4 for males) of the antennule and the position of the row of aesthetascs on this article (character states of N. trifurcatus are in parentheses): relative length of distal article to article 2 0.42–0.49 in females [0.66; measured from fig. 2 in Sieg and Heard (1985)], 0.38–0.39 in males [0.57 for “male Type 1”, 0.63 for “male Type 2”; measured from fig. 2 in Sieg and Heard (1985)]; two to four aesthetascs in mid-ventral region (four in ventroproximal region). Note that Sieg and Heard (1985: p. 60) described that “second segment smaller, about 2 times longer than broad, sternal margin distally with 4 aesthetascs” for the female antennule; based on their fig. 2 and the condition in female N. ohtsukai , however, the four aesthetascs appear to be in the proximal region of article 3, or on the “vestigial segment” as Bird (2012a) suggested. In addition to the previous two characters, the chela of N. ohtsukai bears one sinuate spiniform seta, which is lacking in N. trifurcatus .

Females of N. ohtsukai differ from those of N. trifurcatus in some maxillipedal features. The former have endites with a short simple seta and the large, overlapping flat tubercles; the latter have a medium-long simple seta [longer than half the length of the longer simple seta; measured from Sieg and Heard (1985: fig. 3)] and an apparent gap between the two flat tubercles. The number of ventral simple setae on the chela also differs between the two species (three or four in N. ohtsukai ; six in N. trifurcatus ).

Males of N. ohtsukai have maxillipeds that are not strongly reduced and bear endites and palps with four articles. In contrast, males of N. trifurcatus have strongly reduced maxillipeds lacking palps. The fixed finger of the chela in males of N. ohtsukai bears a triangular claw, instead of the reduced, rounded tooth of N. trifurcatus . Sieg and Heard (1985) illustrated outer and inner broad lamellar projections on the bases of pereopods 1–6 of male N. trifurcatus , with those on the pereopods 4–6 being strongly developed. Males of N. ohtsukai bear similar structures, but only the outer one is well developed (triangular) on pereopods 1–3 ( Fig. 5H–J : arrowheads) whereas those on the pereopods 4–6 are not well developed.

Sieg and Heard (1985) recognized two male morphs, large “male Type 1” and small “male Type 2”, in male N. trifurcatus , which differ in body size and the shape of the cheliped. Diandry (cf. Sadovy and Domeier 2005) has been demonstrated ( Bückle Ramírez 1965) or strongly indicated ( Gardiner 1975) in some tanaidomorphs such as Heterotanais oerstedii (KrØyer, 1842) and Neotanais micromopher Gardiner, 1975 . Bückle Ramírez (1965) showed that, in addition to primary males (“Primärmännchen”), three other types of males (“Sekundärmännchen”, or secondary males) that differ in body size, cheliped shape, and cephalothorax shape, arise by sex change from females in different developmental stages (see his table 10 and fig. 42). Based on this knowledge, Sieg and Heard (1985) suggested that the two types of male in N. trifurcatus might likewise result from that species’ diandric reproductive mode. We found large (ZIHU- 4402, 4406) and small (ZIHU-4407) males in N. ohtsukai , which might similarly indicate diandry, but more data such as from breeding experiments are necessary to confirm this interpretation.

Distribution. So far, this species is known only from the type locality.

Figures

Fig. 2. Nototanoides ohtsukai sp. nov. A, C, holotype, female; B, D, allotype. A, B, body, dorsal view; C, D, body, lateral view. Scale bars: 1mm.

Fig. 3. Nototanoides ohtsukai sp. nov., female. A, B, D–F, H, holotype; C, J, paratype (ZIHU-4405); G, I, paratype (ZIHU-4404). A, right antennule, ventral view; a1, same, distal portion; B, right antenna, outer view; C, labrum, anterior view; D, left mandible, anterior view; E, right mandible, anterior view; F, labium; G, right maxillule and maxilla (arrowhead); H, maxillipeds, dorsal view (right palp removed); h1, same, distal region of endite, ventral view; h2, same, left palp; I, multifurcate spiniform seta (in trifurcate case); J, right epignath. Scale bars: A, B, 0.1mm; C–J, h1, h2, 0.05mm.

Fig. 4. Nototanoides ohtsukai sp. nov., female. A, B, D–I, holotype; C, paratype (ZIHU-4403). A, right cheliped, outer view (outer ventral view for chela); a1, same, sinuate spiniform seta; a2, same, inner dorsal view of chela; B–G, right pereopods 1–6, outer view; e1, pinnate seta; g1, serrate seta; H, right pleopod 1, dorsal view, most setal ornamentation omitted; I, right uropod, ventral view. Scale bars: A–I, a2, 0.1mm; a1, e1, g1, 0.05mm.

Fig. 5. Nototanoides ohtsukai sp. nov., male. A–F, H–J, allotype; G, paratype (ZIHU-4406). A, right antennule, ventral view; a1, same, distal portion; B, right antenna with region of thickened exoskeleton in article 3 (arrowhead), outer view; C, labrum, D, right maxillule; E, maxillipeds, ventral view; e1, same, distal region of endite, ventral view; F, right cheliped, outer view (outer ventral view for chela); f1, same, chela, inner dorsal view; G, right cheliped dactylus, outer view. H–J, right pereopods 1–3 with outer dorsodistal lamellar projection (arrowheads), outer view; K–M, right pereopods 4–6 (basis, ischium, and merus only), outer view. Scale bars: A–M, f1, 0.1mm; a1, e1, 0.05mm.

Fig. 1. Maps showing nototanaid distributions. A, global distribution of nototanaids, including the sampling sites for Nototanoides ohtsukai sp. nov.; B, nototanaid records in Japan, with the sampling sites for Nototanoides ohtsukai sp. nov. Symbols: red diamonds, Nototanoides; green triangles, Nesotanais; blue circles, Nototanais; black circles (1–4), Gamboa, Birdotanais, Paranesotanais, and Stachyops, respectively.