Two new species of Asellota (Crustacea, Isopoda) from coral reefs on Iriomote Island, Okinawa, Japan

Abstract Pleurocope iriomotensis sp. n. and Prethura tuberculata sp. n. are described from Iriomote Island, Ryukyu Archipelago, southern Japan. These are the first records of Pleurocope from the Pacific and of Prethura from the Asian Pacific coast. Pleurocope iriomotensis differs from its congeners in having lateral spine-like processes on pereonite 4 and coxal plates of pereonite 7. Prethura tuberculata can be distinguished from its single congener in having a lateral short projection of protopod of pleopod 2.


Introduction
Iriomote Island (Fig. 1) in the southwestern part of the Ryukyu Archipelago is located in a subtropical climate zone for terrestrial environments, but its marine fauna is more tropical, being strongly influenced by Kuroshio, a prominent warm ocean current. The island is surrounded by coral reefs and a variety of mangroves, sandy or rocky shores.
The shallow-water crustacean faunal survey of Amitori Bay, Iriomote Island in 2012 by SCUBA, yielded two species of asellote isopods of the families Pleurocopidae and Santiidae. Based on this material, two new species, Pleurocope iriomotensis sp. n. and Prethura tuberculata sp. n are described and illustrated.

Material and methods
Collections of isopods were obtained by the Collaborative Research Program funded by the Ryukyu University in Iriomote Island in 2012. Pieces of coral rubble collected by hand near the coral reefs during SCUBA were washed in a bucket, and isopods were extracted by decanting the suspension through a sieve with a mesh size of 0.3 mm. All specimens obtained were fixed and preserved in 80% ethanol. Each individual was dissected and prepared for observation by a light microscope (Nikon E600). The total length as indicated in "Material examined" was measured from the tip of the head to the end of the pleotelson.

Systematics
Remarks. Walker (1901) established the genus for his new species P. dasyura from a depth of 18 m at the Mediterranean. A second species, P. floridensis, was described by Hooker (1985) from a depth of 30 m at the Florida Middlegrounds in the northeastern Gulf of Mexico. Kensley and Schotte (2002) redefined the genus with the description of the new species of P. wilsoni from a depth of 77 m off Phuket Island, Thailand, and a depth of 6-16 m at Picard Island, Aldabra Atoll.
Description of the holotype. Body (Fig. 2) 1.6 times as long as maximum width (including spine-like processes), widest at pereonite 3, with many small granules on dorsum, without dorsal setae. Head (including eyestalks) 2.4 times as broad as long, head without eyestalks 1.2 times as broad as long, broader than pereonite 1; frontal and posterior margins of head convex. Eyes each with 2 ommatidia; eyestalks slender, long, reaching near distal end of article 1 of antenna 1. Pereonites 1 and 5-7 laterally rounded, without lateral spine-like processes; pereonites 2 and 3 with pair of long lateral spine-like processes bearing 2 or 3 robust setae; lateral spine-like processes of pereonites 2 and 3 reaching to tip of second article of antennula in length; pereonite 4 with pair of short lateral spine-like processes bearing single robust seta and 2 short teeth distally; lateral spine-like processes of pereonite 4 half as long as ones of pereonite 3. Pereonite 1 shortest; pereonite 2 three times as long as pereonite 1; pereonites 3 and 4 longest, subequal in length; pereonite 5 0.7 times as long as pereonite 4, pereonites 5-7 subequal in length. Pereonites 1 to 3 increasing in width; pereonite 4 narrower than pereonites 3; pereonites 4 to 7 decreasing in width. Coxal plates dorsally visible on pereonites 5-7, laterally with spine-like process and 2 robust setae. Pleotelson (Fig. 2) approx. 2.2 times as long as wide, widest at anterior one seventh, tapering to sharply rounded apex, with 12 robust setae distally.
Antennula (Fig. 3A) consisting of 6 articles. Article 1 longest and broadest, twice broader-like than eyestalks, with 1 long and 1 short simple setae laterodistally; article 2 nearly 0.8 times as long as article 1, distally with 1 short and 2 long, stout simple setae and 1 broom seta; article 3 about half as long as article 2, without setae; article 4 approx. 0.6 times as long as article 3, without setae; article 5 approx. 1.8 times as long as article 4, with 1 aesthetasc distally; article 6 shortest, with 1 long simple seta and 1 aesthetasc apically.
Female. Not known.  Remarks. Pleurocope iriomotensis sp. n. can be identified by the following combination of characters: pereonite 1 lacking lateral spine-like processes; pereonites 2-4 and coxal plates of pereonites 5-7 each with lateral spine-like process; pleotelson twice as long longer as wide; flagellum of antenna consisting of 7 articles. Pereonite 1 without a spine-like process links the new species to Pleurocope floridensis Hooker, 1985, from the Gulf of Mexico and to P. dasyura Walker, 1901, from the Gulf of Naples, Italy. Pleurocope iriomotensis is distinguished from P. floridensis by the following characters (those of P. floridensis in parentheses): pereonite 4 and coxal plate of pereonite 7 with spine-like process (without spine-like process); eyestalks not reaching to second article of antennula (surpassing second article of antennula); fifth article of antennula with 1 aesthetasc (with 2 aesthetascs); ischium of pereopod 1 with dorsal projection (without dorsal projection); pleopod 1 apically with 3 pairs of short setae (apically with 5 pairs of short setae). Pleurocope dasyura differs from the new species in having pereonite 4 and coxal plate of pereonite 7 without spine-like processes, pereon with 6 long dorsal setae, antenna with long projection, and pleopod 1 apically with 4 pairs of short setae.
Remarks. This new species differs from the only congener, P. hutchingsae Kensley, 1982, from the Great Barrier Reef, by the following characters (those of P. hutchingsae in parentheses): pleopod 1 lacking any setae (with setae); protopod of pleopod 2 with lateral projection (without projection); epipod of maxilliped with acute apex (blunt apex).
Etymology. From the Latin "tuberculatus", referring to the lateral projection of the protopod of pleopod 1.