Plesionika semilaevis Bate, 1888

Chan, Tin-Yam, Hsu, Chia-Yu, Kumar, Appukuttannair Biju & Chang, Su-Ching, 2020, On the “ Plesionika martia ” (A. Milne-Edwards, 1883) species group in Indian waters, Zootaxa 4729 (1), pp. 67-76 : 71-74

Plesionika semilaevis Bate, 1888

( Figs. 1B, D, E , 2 )

Plesionika semilaevis Bate, 1888: 644 , pl. 113-fig. 3 (type locality: Moro Gulf east of Basilan Strait, Philippines); Chace 1985: 113, figs 51-52; Hanamura & Takeda 1987: 116, fig. 3c, d; Ohtomi & Hayashi 1995: 1035, fig. 1; Hanamura & Evan, 1996: 15; Chan & Crosnier 1997: 213; De Grave & Fransen 2011: 450; Li & Chan 2013: 147, fig. 4A; Kuberan et al. 2017: 21, fig. 1.

Pandalus (Plesionika) martius— Alcock 1901: 95 (in part).[not A. Milne-Edwards, 1883]

Plesionika martia —George & Rao 1967: 330 (? in part); Suseelan 1974: 500, fig. 2 (? in part); Holthuis 1980: 146 (in part); Rajool Shanis et al. 2012: 40 (in part); Radhakrishnan et al. 2012: 68 (? in part); Samuel et al. 2016: 8985 (in part). [not A. Milne-Edwards, 1883]

Material examined. Sakthikulangara fishing harbour, Kollam district, Kerala, 20 March 2017, 1 ovigerous female cl 18.6 mm ( DABFUK /AR-PLE-25); 4 March 2019, 1 ovigerous female cl 20.7 mm ( DABFUK /AR-PLE-26), 1 ovigerous female cl 19.4 mm ( DABFUK /AR-PLE-27), 1 ovigerous female cl 18.1 mm ( DABFUK /AR-PLE-28), 4 ovigerous females cl 17.7-20.8 mm ( DABFUK /AR-PLE-29-32).

Diagnosis. Rostrum long and far overreaching scaphocerite, 1.8–2.1 times longer than carapace, curved downwards at basal part but curved upwards and straight distal to antennular peduncle; dorsal margin only with basal part bearing 6-8 teeth and all situated behind distal end of antennular peduncle, none with barbed tip, posterior 2 or 3 teeth situated behind orbital margin while posterior 1 or 2 teeth with incomplete basal suture; ventral margin bearing 41–50 closely spaced teeth. Carapace postrostral ridge extending to about middle of carapace, distinctly elevated and laminate along entire length. Lateral carapace without carina or groove, only with hepatic region more or not depressed as a small pit; antennal and pterygostomian spines moderately large, former spine longer than latter; orbital margin with upper part slightly convex and strongly inclined backwards, lower part convex. Eye kidney shaped and with distinct ocellus. Stylocerite obtuse but distally pointed, laterally strongly folded upwards, extending to second segment of antennular peduncle. Scaphocerite slender, 0.8–0.9 times carapace length and 4.2–5.0 times as long as maximum width; distolateral tooth more or less reaching distal margin of lamina; basicerite spine long and slightly overreaching proximal end of lateral margin of scaphocerite. Maxilliped III and anterior 4 pereiopods bearing well developed, strap-like epiopods. Maxilliped III with penultimate segment1.2–1.4 times longer than terminal segment. Pereiopod II subequal, carpus divided into 19–29 articles. Pereiopod III overreaching scaphocerite by length of 0.2–0.8 carpus, propodus and dactylus; dactylus 0.3 times as long as propodus, somewhat paddle-shaped, terminal spine minute, accessory spine on flexor margin absent. Abdomen with posterior margin of tergite III rounded, pleuron IV posteroventrally rounded and pleuron V posteroventrally pointed, somite VI 2.2–2.5 times as long as maximum height; telson more or less as long as somite VI, usually with 3 pairs of dorsolateral spines (excluding pair adjacent to posterior margin of telson).

Coloration. Body semitransparent and molted with pinkish red color ( Fig. 2 ). Anterior carapace, basal part of rostrum and scaphocerite somewhat whitish. Eyes black brown. Basal segments of pereiopods somewhat pale pink. Chela of pereiopod II somewhat pale yellowish. Exopod of uropod with distal white spot. Eggs bright blue but becoming dark red when near hatching.

Distribution. Indo-West Pacific; reported from India, Indonesia, the Philippines, South and East China Sea, Japan, Australia and French Polynesia, at depths of 164–888 m (see Li & Chan 2013).

Remarks. The southwestern Indian material has the upper part of the orbital margin strongly inclined backwards, and therefore fits well with the definition of P. semilaevis instead of P. martia according to both Chace (1985) and Chan & Crosnier (1997). Thus, the present work supports Kuberan et al. (2017) in considering those P. martia records from southwestern India are misidentification of P. semilaevis . Nevertheless, there are several discrepancies in the description provided by Kuberan et al. (2017) with the present material. The rostrum is slightly longer (2.2 times carapace length versus maximum 2.1 times) and may have less ventral teeth (35 versus minimum 41), and the pereiopod III only overreaching the scaphocerite by dactylus (versus by the combined length of 0.2–0.8 carpus, propodus and dactylus) in Kuberan et al. (2017). The differences in the rostrum likely represent normal variations but the much shorter pereiopod III is likely abnormal or incorrect. Of the present eight specimens examined, two specimens have a complete pereiopod III while only one specimen has a complete pereiopod IV. The only complete pereiopod IV in the present material overreaches the scaphocerite by about half carpus plus propodus and dactylus and has the dactylus 0.1 times as long as the propodus. None of the present material has an intact pereiopod V.

Genetic comparisons between the present Indian and topotypic Philippines material of P. semilaevis reveal an interesting situation. The present Indian material has 95.4% sequence similarities with one of the two Philippines specimens analyzed, and there are 13.8–14.3% sequence divergences from the other Philippines specimen. On the other hand, the genetic divergence of the two Philippines P. semilaevis specimens is as high as 14.0%. Although species of Plesionika often found to have high genetic differences (see Matzen da Saliva et al. 2013; Chakraborty et al. 2015; Chan et al. 2018), more than 10% COI sequence divergence is generally considered as interspecific differences in crustaceans ( Jones & Macpherson, 2007; Cabezas et al. 2008; Chang et al., 2014; Zheng et al. 2019). Therefore, it is highly likely that topotypic Philippines material of P. semilaevis actually containing two species. Which form is the true P. semilaevis will need a full revision of the “ P. martia ” groups with the re-examination of at least the types of P. semilaevis , P. orientalis and P. cottei . On the other hand, the present Indian material has 97.6–97.7% COI sequence similarities with two other Indian P. semilaevis sequences also from the southwestern coast (Kalamukku) in the GenBank ( KX364192 , KX364193 ) but 19.5% sequence divergence from another Indian P. semilaevis sequences ( KX781157 , no specific locality). Moreover, this KX781157 sequence has 19.2–22.7% sequence divergence from all other “ P. martia ” group material analyzed. Such great genetic difference implies that the specimen for the KX781157 sequence is misidentified and this species even does not belong to the “ P. martia ” group, though it has no positive match with any other COI sequence available in the GenBank. Hence, the four Indian sequences considered by the present work as belonging to P. semilaevis have 97.6–100% similarities and with 4.6–5.7% divergence from one of the topotypic Philippines specimens. Such a genetic difference is moderately high but still lower than the 5.8–8.4% reported between the Indian and topotypic Philippines P. quasigrandis Chace, 1985 material ( Chakraborty et al. 2015) that without noticeable morphological and color difference. The coloration of the Indian material ( Fig. 2 ) is almost identical with a P. semilaevis specimen from the Philippines ( Li & Chan 2013: fig. 4A) and only with the pale markings at the tips of the uropod exopods more yellowish.

Figures

FIGURE 1. A, C, Plesionika martia (A. Milne-Edwards, 1883), Great Nicobar Islands, ovigerous female cl 20.0 mm (DAB- FUK/AR-PLE-24). B, D, E, P. semilaevis Bate, 1888, Sakthikulangara fishing harbour, Kerala: B, ovigerous female cl 18.6 mm (DABFUK/AR-PLE-25); D, E, ovigerous female cl 18.1 mm (DABFUK/AR-PLE-28).A, B, carapace and cephalic appendages, lateral; C, D, abdominal somites III to VI and tail fan, lateral; E, left pereiopod III propodus and dactylus, lateral. Scales: A-D = 5 mm, E = 2 mm.

FIGURE 2. Plesionika semilaevis Bate, 1888, Sakthikulangara fishing harbour, Kerala, ovigerous female cl 19.4 mm (DAB- FUK/AR-PLE-27).