Tanaopsis japonica Shimada 2017, sp. nov.

Tanaopsis japonica sp. nov.

Figures 1–8

Material examined. Holotype. Female without developed or developing oostegites, ICHUM-5339 (BL 1.43, CW 0.32), 9 slides, 1 vial, and 1 SEM stub; Asari-hama (Asari beach), Higashi-shizunai, Shinhidaka, Hokkaido, Pacific Ocean, 42°17.173'N, 142°27.683'E, muddy sand around roots of the seagrass Phyllospadix iwatensis, intertidal zone, 13 April 2013, coll. by D. Shimada.

Allotype. Male, ICHUM-5340 (BL 1.44, CW 0.32), 6 slides and 1 vial; Kamome-jima (Kamome Island), Esashi, Hokkaido, Sea of Japan, 41°52.198'N, 140°6.958'E, muddy sand around roots of the seagrass Phyllospadix iwatensis, intertidal zone, 29 June 2014, coll. by A. Shibata.

Paratype. Female without developed or developing oostegites, ICHUM-5341 (BL 1.75, CW 0.32), 5 slides, 1 vial, and 1 SEM stab; INSD accession number LC 210598; Oshoro, Otaru, Hokkaido, Sea of Japan, 43°12.886'N, 140°51.304'E, muddy sand, 3 m, SCUBA, 27 August 2016, coll. by K. Kakui.

Diagnosis. Pereonites 4 and 5 subequal in length (length ratio of pereonites 4/5 1.0); mandibular molar absent; uropod with biarticulate endopod and uniarticulate exopod.

Etymology. The specific name is an adjective referring to the type locality.

Description of female. Based on holotype.

Body (Fig. 1A, a1–3) dorsoventrally flattened, 4.4 times as long as CW, translucent, slightly yellowish when alive (Fig. 8). Cephalothorax 0.2 times as long as BL, 0.9 times as long as wide, trapezoidal, with pair of lateral simple setae; eye lobes absent. Pereonites 1–6 with length ratio of 1.0:1.1:1.4:1.9:1.9:1.3; all wider than long, with one or two pairs of simple setae. Pleon 0.3 times as long as BL. Pleonites slightly wider than pereonite 6; all wider than long, similar in shape, with slight lamellar lateral projection (Figs 1a 3, 8), and ventral keel (Fig. 1a 3); pleonite 5 with two pairs of simple setae. Pleotelson 0.6 times as long as wide, narrower than pleonites, with pair of simple setae proximal to uropodal insertion, pair of simple setae and pair of PSS in subdistal region, and pair of simple setae in distal region.

Antennule (Fig. 2A) 0.9 times as long as cephalothorax; articles 1–4 with length ratio of 1.0:0.5:0.3:0.6. Article 1 with two distal simple setae, several PSS, and series of ventroproximal slight grooves (Fig. 7D–F). Article 2 with two distal simple setae and several distal PSS. Article 3 with two distal simple setae. Article 4 with cap-like vestigial article (Fig. 6A), five simple setae and aesthetasc. Antenna (Fig. 2B, C) with six articles, 0.9 times as long as antennule; articles 1–6 with length ratio of 0.4:1.0:0.7:2.0:0.8:0.3. Article 1 naked. Article 2 with inner distal simple seta and series of dorsal denticulate ridges (Figs 2C, 7A, B). Article 3 with inner distal simple seta. Article 4 with three distal simple setae and one mid-inner and several distal PSS. Article 5 with distal simple seta. Article 6 with six distal simple setae.

Labrum (Fig. 2D) naked. Mandibles (Fig. 2E, F) without molar. Incisor of left mandible (Fig. 2E) with blunt tooth and several small teeth; lacinia mobilis widening distally, with several small teeth. Incisor of right mandible (Fig. 2F) with blunt tooth and several smaller teeth. Labium (Fig. 2G) naked. Maxillule (Fig. 2H) endite with one thicker and three thinner spines; palp lost during dissection. Maxilla lost during dissection. Maxillipeds (Fig. 2I) with bases, each bearing simple seta at insertion of palp; distal half of bases separated. Endites flared, separated, reaching beyond distal margin of palp article 1, each with simple seta. Palp article 1 naked; article 2 with two inner and one outer simple setae; article 3 with two inner simple setae; article 4 with three simple and three pinnate setae. Epignath (Fig. 2J) narrow, curved, naked.

Cheliped (Figs 3A, a 1, a 2, B, 6B–E) with triangular articulation with cephalothorax via sclerite (Figs 1a1, 3A, 6B). Basis slightly longer than wide, with free posterior portion and dorsal simple seta. Merus with ventral simple seta. Carpus 1.5 times as long as wide, with one dorsomedial, one dorsodistal, and two ventral simple setae. Chela as long as carpus; propodal palm as long as fixed finger, with one outer, one longer inner, and three shorter inner simple setae at insertion of dactylus (Fig. 3a 1); fixed finger with two simple setae on ventral margin, three simple setae on cutting surface, series of outer smooth ridges (Fig. 6C, D: black arrowheads), outer distal bifurcate process, and bifurcate claw; dactylus as long as fixed finger, with inner simple seta, three spiniform setae on cutting surface, series of denticulate outer dorsal ridges (Fig. 6C–E: white arrowheads), inner hatching with fringed incisions (Fig. 6C–E: arrows), and triangular claw.

Pereopods 1–6 cylindrical, with length ratio of 1.5:1.1:1.0:1.0:1.0:1.0. Pereopod 1 (Fig. 3C, D) 0.4 times as long as BL, with length ratio of basis, ischium, merus, carpus, propodus, and dactylus-unguis 4.5:0.4:1.0:1.4:2.9:3.7. Coxa with dorsal simple seta and acute dorsal process. Basis cylindrical, narrow (4.5 times as long as wide), naked. Ischium with ventral simple seta. Merus naked. Carpus with three dorsodistal and one ventrodistal simple setae. Propodus serrated dorsally, with three dorso-subdistal and one ventro-subdistal setae, and dorsodistal serrations. Dactylus with dorsoproximal simple seta. Unguis twice as long as dactylus, naked. Pereopod 2 (Fig. 3E) with length ratio of articles from basis to dactylus-unguis 5.1:0.4:1.0:1.5:3.1:3.6; similar to pereopod 1, except coxa without dorsal process, basis with one dorsal PSS, carpus with two dorsodistal simple setae, and propodus with two dorso-subdistal setae. Pereopod 3 (Fig. 3F) with length ratio of articles from basis to dactylusunguis 5.3:0.5:1.0:1.4:3.2:3.1; similar to pereopod 2, except basis with one ventral PSS. Pereopod 4 (Fig. 3G) without coxa. Length ratio of articles from basis to dactylus-unguis 3.5:0.3:1.0:1.3:1.7:1.7. Basis thick (2.5 times as long as wide), with one dorsal PSS. Ischium with ventral simple seta. Merus with one outer and one inner serratespiniform setae in ventrodistal region. Carpus with dorsodistal simple seta, and one outer and two inner serratespiniform setae in distal region. Propodus with one dorsal PSS, dorsal serrations on edge in distal half, and one dorsodistal, one outer ventrodistal, and one inner ventrodistal pinnate-spiniform setae. Dactylus naked. Unguis 0.6 times as long as dactylus. Pereopod 5 (Fig. 3H) with length ratio of articles from basis to dactylus-unguis 2.7:0.2:1.0:1.1:1.6:1.4; similar to pereopod 4 except basis with two dorsal and one ventral PSS, and ischium with two ventral simple setae. Pereopod 6 (Fig. 3I, i 1) with length ratio of articles from basis to dactylus-unguis 3.0:0.3:1.0:1.0:1.5:1.1; similar to pereopod 4 except propodus with two dorsodistal serrate setae (Fig. 3 i 1) but lacking dorsal PSS.

Pleopods (Fig. 3J) five pairs, all similar. Basal article naked. Endopod 2.2 times as long as basal article, with one inner subdistal and five outer plumose setae, and outer distal “step-tipped plumose seta” (see Kakui et al. 2010: fig. 5j2). Exopod 1.3 times as long as endopod, with 17–20 outer plumose setae; “vestigial proximal article” (see Bird 2012) with outer plumose seta.

Uropod (Fig. 3K) with basal article naked. Endopod 2.5 times as long as basal article, biarticulate; article 1 with length/width ratio 1.7, with one distal PSS; article 2 as long as article 1, with one subdistal and four distal simple setae, and two distal PSS. Exopod uniarticulate, slightly shorter than endopodal article 1, with one subdistal and two distal simple setae.

Description of male. Based on allotype.

Body (Fig. 1B, b1–4) similar to female but pleon proportionally longer. Pereonites 1–6 with length ratio of 1.0:1.2:1.7:2.4:2.3:1.5; all wider than long; pereonite 6 with pair of genital cones (Fig. 1b 2). Pleon 0.4 times as long as BL.

Antennule (Fig. 4A) as long as cephalothorax, with six articles; thicker than that of female; articles 1–6 with length ratio of 1.0:0.4:0.1:0.1:0.2:0.2. Setation of articles 1–3 similar to those of female. Articles 4 and 5 with ventrodistal row of aesthetascs. Article 6 with six simple setae and aesthetasc; cap-like vestigial article not observed. Antenna (Fig. 4B) 0.8 times as long as antennule, similar to that of female except article 4 with two midouter PSS, and articles 5 and 6 with two and four distal simple setae, respectively.

Mouthparts (Fig. 4C–E) reduced. Vestigial labrum (Fig. 4C: arrowhead) observed. Labium (Fig. 4D) narrowing distally, naked. Maxillipeds (Fig. 4E) similar to those of female, except endites not flared and all setae on palp-article 4 simple.

Cheliped (Fig. 4F, f 1, G) similar to that of female, except propodal palm with six shorter inner simple setae at insertion of dactylus, fixed finger with outer distal trifurcate process, and dactylus with two spiniform setae on cutting surface.

Pereopods 1–6 (Fig. 5A–F) with length ratio of 1.4:1.1:1.0:1.1:1.1:1.1 (note that pereopod-6 unguis broken); pereopod 1 length 0.38 times BL. Pereopods similar to those of female, but differ as follows: coxa of pereopod 1 without acute dorsal process; basis of both pereopods 4 and 5 with two ventral PSS; ischium of pereopods 4 and 6 with two ventral simple setae; carpus of pereopods 4–6 with two dorsodistal simple setae.

Pleopods (Fig. 5G) five pairs, all similar. Basal article naked. Endopod 1.8 times as long as basal article, with five longer and one shorter outer plumose setae, and one inner subdistal and one outer distal step-tipped plumose setae. Exopod 1.2 times as long as endopod, with 10–14 outer plumose setae; vestigial proximal article naked.

Uropod (Fig. 5H) similar to that of female, except endo- and exopod proportionally shorter (endopod twice as long as basal article) and endopodal article 2 with two distal simple setae.

Variation and stability. One additional female (paratype) was observed. The ratio of BL/CW was different among specimens, i.e., 4.4 (female holotype; BL 1.43), 4.5 (allotype; BL 1.44), and 5.5 (paratype; BL 1.75), but pereonites 4 and 5 were subequal in length in all specimens, i.e., the length ratio of pereonites 4/5 was 1.0. In the two females, the numbers of simple, spiniform, serrate-spiniform, pinnate-spiniform, and serrate setae on the antenna, cheliped, and pereopods were constant. The number of setae on the pleopodal endopod was constant among the five pairs in each specimen and between the two females; that on the exopod varied, ranging from 16 to 18 in the paratype. All specimens lacked setae on the basal article of all pleopods. All specimens had a biarticulate uropodal endopod.

Genetic Information. The nearly complete 18S-gene sequence (2275 nt) was determined from the paratype specimen; INSD accession number LC 210598. The three sequences in the International Nucleotide Sequence Database most similar to our sequence, as determined by BLAST searches (Altschul et al. 1990), were from the tanaidaceans Chauliopleona sp. KK-2011 (identity score [IS] 97%; query cover [QC] 65%; Akanthophoreidae; Kakui et al. 2011), Paratanais sp. KK-2011 (IS 98%; QC 63%; Paratanaidae; Kakui et al. 2011), and Paratanais malignus Larsen, 2001 (IS 98%; QC 66%; Paratanaidae; Spears et al. 2005).

Distribution. So far known only from three localities around Hokkaido Island, at depths of 0– 3 m.

Remarks. Tanaopsis japonica sp. nov. is the seventeenth species described in this genus and family. In having the uropod with the endopod biarticulate and the exopod uniarticulate, this species closely resembles T. chotkarakde Bird & Bamber, 2000 from around Hong Kong and T. rawhitia Bird, 2011 from New Zealand waters (Bird & Bamber 2000; Bird 2011). Female T. japonica differs from T. chotkarakde in the following characters (character state of T. chotkarakde in parentheses): the length ratio of pereonites 4/5 is 1.0 (1.2); antennal article 4 has three simple distal setae (two); the propodal palm of the cheliped has one longer and three shorter inner simple setae at the insertion of the dactylus (one longer and two shorter setae); the chelipedal dactylus has three spiniform setae on the cutting surface (one); and the pleopodal basis is naked (one outer seta) (Bird & Bamber 2000). Males have not yet been described for T. chotkarakde.

Tanaopsis japonica differs from T. rawhitia as follows (character state of the latter in parentheses). In both sexes, T. japonica has the dactylus of pereopods 1–3 with a dorsoproximal simple seta (naked). In females, the mandible lacks a molar (point-tipped molar present); pereonites 4 and 5 are all wider than long (as wide as long), antennal article 2 lacks outer setae (one outer seta), and the pleopodal endopod has six outer setae in total (eight or nine). In males, T. japonica has the antennule with six articles bearing two rows of aesthetascs (seven articles and three rows), the propodal palm of the cheliped has one longer and six shorter inner simple setae at the insertion of the dactylus (two longer and 11 shorter setae), and the uropodal exopod is uniarticulate (biarticulate) (Bird 2011).

Our male specimen of T. japonica is unique within Tanaopsidae in that its antennule consists of six articles and bears two rows of aesthetascs. Including male T. laticaudata (Sars, 1882) sensu Sars (1886), which Lang (1967: p. 350) suggested might have been misidentified as to genus, males have previously been reported in nine congeners, all of which have seven-articulate antennule with three rows of aesthetascs (Sars 1886; Lang 1967; Shiino 1970; Kudinova-Pasternak 1984; Sieg & Dojiri 1991; Bird 2011; Segadilha & Araújo-Silva 2015). To determine whether the six-articulate antennule is restricted to T. japonica, males must be examined from additional species.

Among congeners, T. cadieni Sieg & Dojiri, 1991 and T. gallardoi (Shiino, 1970) include descriptions of the male mouthparts. Although the maxillipedal endites are flared in these species, they are not flared in male T. japonica. While Shiino (1970) observed mandibles in male T. gallardoi, we found only a simple opening in place of the mandibles (Fig. 4C). This suggests that, as observed in Nototanoides (Nototanaidae; Kakui & Yamasaki 2013), the degree of reduction of the male mouthparts can vary among species in Tanaopsis.