Monday, July 4, 2016

[Ichthyology • 2013] Stiphodon niraikanaiensis • A New Species of Sicydiine Goby (Gobiidae: Sicydiinae) from Okinawa Island, Japan


Stiphodon niraikanaiensis 
Maeda, 2013

Abstract
A new goby species, Stiphodon niraikanaiensis, is described on the basis of three specimens (two females and one male) collected from a freshwater stream in Okinawa Island, Japan. This species can be distinguished from its congeners by nine soft rays in the second dorsal fin, 16 rays in the pectoral fin, a pointed first dorsal fin in male, the premaxilla with 46–50 tricuspid teeth in 27–36 mm SL; no white patch behind the pectoral-fin base in male, the nape and posterior half of the occipital region covered by cycloid scales, broad black band along the distal margin of the second dorsal fin in male, 11 or 12 dusky transverse bars laterally on the trunk and tail of female intersecting with the mid-lateral longitudinal band, several conspicuous black spots on each spine and soft ray on the first and second dorsal fins of female, the anal fin of female lacking remarkable marking, and the pectoral-fin rays with 2–5 and 1–4 black spots, respectively, for male and female. The new species is known only from the type locality.

Keywords: Stiphodon; New species; Ryukyu Archipelago; Dispersal


Fig. 4 Stiphodon niraikanaiensis sp. nov. immediately after fixation.
a NSMT-P 114244, holotype (male, 27.1 mm SL), b NSMTP 114245, paratype (female, 30.0 mm SL), c URM-P 46084, paratype (female, 36.0 mm SL)

Diagnosis. The new species is distinguished by a combination of the following characters: second dorsal-fin rays 9, pectoral-fin rays 16; first dorsal fin pointed with elongate fourth spine in male; premaxilla with 46–50 tricuspid teeth; dentary with 4 (male) or 1 (female) symphyseal teeth and 40–46 unicuspid horizontal teeth in 27–36 mm SL; scales in longitudinal row 30–32; nape and posterior half of occipital region covered by cycloid scales; no white patch behind pectoral-fin base in male; broad black band along distal margin of second dorsal fin in male; lateral side of body and dorsal and caudal fins often tinged with vivid orange in male; eleven or twelve dusky transverse bars laterally on trunk and tail of female intersecting with the mid-lateral longitudinal band; several conspicuous black spots on each of the spines and soft rays on the first and second dorsal, and caudal fins of female; anal fin lacking remarkable marking; pectoral-fin rays with 2–5 and 1–4 black spots, respectively, for male and female.


Distribution. The new species has been known only from the type locality, a freshwater stream on the eastern slope of Okinawa Island (detailed locality is not shown here due to the conservation perspective). Maeda et al. (2012) suggested that the populations of S. alcedo, which has only been reported from Okinawa and Iriomote islands in the Ryukyu Archipelago, recently (a few years ago) colonized the islands after their pelagic larvae were transported from an unknown main range by ocean currents. Possibly, it is also true of S. niraikanaiensis.

Stiphodon niraikanaiensis has unique markings that readily distinguish it from other species. However, only three individuals of this species have been found so far, although the Okinawan fish fauna has been relatively well explored. So, it is very rare on this island.


Ecology. All three individuals were found at the same site. They were observed both in a small pool less than 1 m deep and a rapid just below the pool, located 1.5 km from the stream mouth. There was no major barrier to upstream migration between the stream mouth and this site. They were often shoaled with the abundant congener S. percnopterygionus and observed scratching on the rock surface for feeding with them. Single individuals of S. atropurpureus and S. multisquamus were also observed at the same site. Other abundant fishes at this site were amphidromous gobies, such as Sicyopterus japonicus (Tanaka 1909), Awaous melanocephalus (Bleeker 1849), Rhinogobius nagoyae Jordan and Seale 1906, and Tridentiger kuroiwae Jordan and Tanaka 1927, amphidromous pipefish, Microphis leiaspis (Bleeker 1854), and catadromous flagtail, Kuhlia marginata (Cuvier 1829).

Etymology. Niraikanai is the Okinawan mythical place from which all life originates and to which the spirits of dead person return. It is also said that gods bring fertility to this world from niraikanai. The location of niraikanai is unspecified, but it is usually thought to lie somewhere beyond the ocean. It is thought that, possibly, the main habitat of the new species is somewhere over the ocean and the type specimens were brought to Okinawa from there. Therefore, the new species is named as Stiphodon niraikanaiensis, derived from niraikanai and the Latin suffix -ensis.

Fig. 5 Underwater photographs of Stiphodon niraikanaiensis sp. nov. in a stream on Okinawa Island.
a Male, 14 Nov. 2012 (NSMT-P 114244), b male, 20 Oct. 2012 (NSMT-P 114244), c female, 26 Oct. 2012 (NSMT-P 114245), d female, 7 June 2013 (URM-P 46084)
(a, d photo by K. Maeda, b photo by Y. Yamamoto, c photo by T. Saeki)


Ken Maeda. 2013. Stiphodon niraikanaiensis, A New Species of Sicydiine Goby from Okinawa Island (Gobiidae: Sicydiinae). Ichthyological Research. 61(2); 99–107. DOI 10.1007/s10228-013-0379-2



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