Plesionika martia (A. Milne-Edwards, 1883 )

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 : 68-71

Plesionika martia (A. Milne-Edwards, 1883)

( Fig. 1A, C )

Pandalus martius A. Milne-Edwards, 1883 , pl. 21 (type locality: northeastern Atlantic); Forest & Holthuis 1997: 54, pl. 21.

Panalus prox. martius— Wood-Mason & Alcock 1892: 369.

Pandalus (Plesionika) martius— Alcock 1901: 95 (in part).

Plesionika martia — Crosnier & Forest 1973: 212 , figs. 63d, 64e, 66; Holthuis 1980: 146 (in part); Hanamura 1986: 63, figs. 9- 11; Hanamura & Evans 1996: 13; Chan & Crosnier 1997: 213; De Grave & Fransen 2011: 449; Rajool Shanis et al. 2012: 40 (in part); Samuel et al. 2016: 8985 (in part).

Not Plesionika martia —George & Rao 1967: 330 (? in part); Suseelan 1974: 500, fig. 2 (? in part); Radhakrishnan et al. 2012: 68 (? in part). [= Plesionika semilaevis Bate, 1888 ]

Material examined. Great Nicobar Islands, Andaman Sea, 9º37.159’N, 92º44.011’E, 17 November 2017, 1 ovigerous female cl 20.0 mm ( DABFUK /AR-PLE-24).

Diagnosis. Rostrum extending far beyond scaphocerite, 1.9 times longer than carapace, basal part descending but curved upwards and straight distal to antennular peduncle; dorsal margin armed only with 7 teeth, including 3 on rostrum proper behind tip of antennular peduncle and 4 on carapace posterior to orbital margin, posteriormost tooth bearing incomplete basal suture, none with barbed tip; ventral margin with 57 closely spaced teeth. Carapace with postrostral ridge distinct but not elevated as lamina, extending to about posterior 2/3 of carapace; hepatic region having small pit-like depression; antennal spine moderately large while pterygostomian spine small; orbital margin with upper part faintly convex and almost vertically straight, lower part slightly convex. Eye with distinct ocellus. Antennular peduncle basal segment with stylocerite obtuse but distally pointed, laterally strongly folded upwards, extending just beyond distal margin of basal peduncular segment. Scaphocerite slender, 0.9 times as long as carapace and 5.6 times as long as maximum width; distolateral tooth more or less extending to distal margin of lamina; basicerite spine moderately long and slightly overreaching proximal end of lateral margin of scaphocerite. Maxilliped III bearing well developed, strap-like epipods; penultimate segment 1.2 times as long as ultimate segment. Anterior 4 pereiopods bearing well developed, strap-like epipods. Pereiopod II subequal, carpus divided into 25–28 articles. All posterior 3 pereiopods incomplete and with distal segments lost. Abdomen with posterior margin of tergite III rounded, pleuron IV posteroventrally rounded while pleuron V posteroventrally pointed, somite VI 2.2 times longer than maximum height; telson 1.1 times longer than somite VI and bearing 3 pairs of dorsolateral spines (excluding pair adjacent to posterior margin of telson).

Coloration. Body pinkish red with eggs blue for the East Atlantic topotypic material ( Fransen 2014). No information available on the coloration of the present Andaman Sea specimen.

Distribution. Widely reported from the Atlantic and the Indo-West Pacific, at depths of 190 to 2195 m, mostly less than 700 m (see Crosnier & Forest 1973; Holthuis 1980; Chan & Crosnier 1997; Fransen 2014).

Remarks. Chace (1985) regarded that P. martia was restricted to the Atlantic while the Indo-West Pacific population was a subspecies P. martia orientalis . Most of the differences between the two subspecies, as well as those for distinguishing the species of the “ P. martia ” group proposed by Chace (1985; such as the eye shape, pereiopod and pleopod length) are rather difficult to use in addition to these rather fragile body parts are often damaged or incomplete. Moreover, it is highly likely that forms most closely related to P. martia martia are present at least in Australia ( Hanamura 1989, Hanamura & Evans 1996), Taiwan and French Polynesia ( Chan & Crosnier 1997). Therefore, the subspecies P. martia orientalis is now generally treated as a distinct species P. orientalis (e.g. Hanamura & Evans 1996; Li 2006; Hayashi 2009; Komai 2011, De Grave & Fransen 2011; Li & Chan 2013).

On the other hand, Chan & Crosnier (1997, also see Li & Chan 2013) proposed that the shape of the postrostral carina, orbital margin and the size of antennal basicerite spine are more useful in separating the species of the “ P. martia ” group. Plesionika martia has the postrostral carina not laminar, upper part of the orbital margin almost vertically straight, and the antennal basicerite spine overreaching the posterior end of the lateral margin of the scaphocerite. Plesionika orientalis has the postrostral carina elevated and distinctly laminar, upper part of the orbital margin more or less vertically straight or slightly convex, and the basicerite spine more or less extending to the posterior end of the lateral margin of the scaphocerite. Plesionika semilaevis has the postrostral carina elevated and distinctly laminar, upper part of the orbital margin strongly convex and curved backwards, and the basicerite spine far overreaching the posterior end of the lateral scaphocerite margin. Plesionika parvimartia differs from the other three species of the group in having a much smaller size and with the anteriormost dorsal rostral tooth generally situated anterior to the antennular peduncle (the other three species of the “ P. martia ” group have dorsal rostral tooth generally restricted behind the tip of the anennular peduncle), the postrostral carina elevated and laminar, orbital margin vertical but regularly convex, and the basicerite spine just overreaching the posterior end of the lateral scaphocerite margin. Nevertheless, the abundant material of this group recently collected from various Indo-West Pacific locali- ties by the French MUSORSTOM-TDSB expeditions (see Richer de Forges et al. 2013) indicates that there are highly likely more species in the “ P. martia ” group according to the variations in the living coloration, shape of the orbital margin and the size of the basicerite spine.

Plesionika martia was firstly reported in Indian waters from the western side of the Andaman Islands (Wood- Mason & Alcock 1892) and subsequently off the various coasts of India ( Alcock 1901; George & Rao 1967; Suseelan 1974; Rajan et al. 2001; Kurup et al. 2008; Rajool Shanis et al. 2012). The present specimen was collected from the Andaman Sea in a locality (west of Great Nicobar Islands) adjacent to the first record of this species in Indian waters. To provide more insights on the taxonomic status of the present Andaman Sea specimen, its COI sequence was compared with topotypic material of the four species in the “ P. martia ” group as well as an Indian specimen from the Laccadive Sea registered as P. martia ( KU708836 ) in the GenBank ( Table 2 ). There are very high genetic divergences (14.7-22.1%) amongst the topotypic material of the four species in the “ P. martia ” group as defined by Chan & Crosnier (1997). The Andaman Sea specimen, though with high sequence divergence, is more similar to P. martia than P. orientalis . Moreover, the very high genetic differences (20.4-22.1%) between the topotypic specimens of P. orientalis and P. martia confirm that they are indeed distinct species instead of subspecies. The other sequence from a specimen from India, identified with P. martia ( KU708836 ) in the GenBank, have more than 20% sequence divergence from both the present specimen and the Atlantic material. On the other hand, this KU708836 sequence showed 99.5% sequence similarity with two sequences ( KX530799 , KX530800 ) referred to P. alcocki in the GenBank, and therefore, is most probably a misidentification of P. alcocki . The high genetic difference of the Andaman Sea specimen from the topotypic P. martia material also suggested that it represents a distinct species. However, taxonomy of the P. martia group is quite complicate as P. cottei Kotte, 1903 described from the Indian Ocean is sometimes treated as a synonym of P. martia or P. orientalis ( Holthuis 1980; Chace, 1985; De Grave & Fransen 2011). Moreover, the types of P. semilaevis contains the holotype of P. orientalis (see Chace 1985) and there are at least two species present in the topotypic P. semilaevis Philippines material as defined by Chan & Crosnier (1997) (see Remarks under P. semilaevis ). A full revision of the “ P. martia ” group including the re-examination of the types of P. cottei , P. orientalis and P. semilaevis are necessary to determine the taxonomic status of the Andaman Sea material. For the time being, the present Andaman Sea specimen is assigned to P. martia following the definition of Chan & Crosnier (1997). Whether those P. martia material reported before from off the India mainland is assignable to this species remains to be confirmed.

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.