Limnoria magadanensis Jesakova, 1961

Yoshino, Hiroki, Watabe, Hikari & Ohsawa, Takeshi A., 2017, A new species of seagrass-boring Limnoria (Limnoriidae, Isopoda, Crustacea) from Japan, Zootaxa 4232 (2), pp. 251-259 : 256-257

Limnoria magadanensis Jesakova, 1961

Limnoria magadanensis Jesakova, 1961: 180 –186, fig. 1, 2, 5. — Kussakin, 1963: 287, fig. 1c, 4. — Kuhne, 1976: 548 –549, fig. 10. — Kussakin, 1979: 329 –333, fig. 196–198.

Limnoria japonica Richardson. — Nunomura, 2011: 51 -56, fig. 2.

Material examined. male, 7.0 mm (2.3 mm wide pleotelson, with 1 slide, TOYA Cr-22281); male, 8.1 mm (2.5 mm wide pleotelson, with 1 slide, TOYA Cr–22282); male, 6.4 mm (2.0 mm wide pleotelson, with 1 slide, TOYA Cr–22283); male, 6.7 mm (2.0 mm wide pleotelson, with 1 slide, TOYA Cr–22284); male, 7.4 mm (2.5 mm wide pleotelson, with 25 slides, TOYA Cr–22285); male, 6.4 mm (2.2 mm wide pleotelson, with 1 slide, TOYA Cr- 22286); non-ovig. female, 6.5 mm (2.0 mm wide pleotelson, with 1 slide, TOYA Cr–22287); non-ovig. female, 7.3 mm (2.2 mm wide pleotelson, with 1 slide, TOYA Cr–22288); non-ovig. female, 7.4 mm (2.1 mm wide pleotelson, with 1 slide, TOYA Cr–22289); non-ovig. female, 8.1 mm (2.3 mm wide pleotelson, with 1 slide, TOYA Cr– 22290); ovig. female, 8.4 mm (2.2 mm wide pleotelson, with 1 slide, TOYA Cr–22291), Uozu City , Toyama Prefecture, Japan, submerged pinewood, Kano Yasuo, 21 January 1987.

Type locality. Magadan port on the Sea of Okhotsk, Russia, collected by O. B. Mokievsky.

Note. Body oblong and pale yellow in 70% ethanol. Head globular. Eyes black in color, each with 8 ocelli. Maximum length is 8.5 mm ( Jesakova 1961). Most of dorsal surface of pereonite, pleonite, and pleotelson covered with many small hairs. Pereonal segment 1 longest, approximately 1.9 times longer than segment 2 with 2 obvious lateral grooves. Segments 2–4 nearly equal. Posterior pereonal segments become shorter than anterior ones among segments 4–7.

Pleonite 5 0.43 times as long as pleotelson. Pleonite 5 with 2 medially located tubercles, anterior tubercle separated from posterior by prominent sulcus. Two tubercles followed by crests laterally.

Pleotelson dorsomedially with single prominent anterior medially located tubercle, followed by pair of large tubercles with no accompanying carinae. Lateral crests emerge anteriorly and their accompanying weak crests connect with anterior tubercle. Posterior margin of pleotelson with dorsally directed row of spike-like setae, and fringe of stout sheathed setae. Lateral crests lack tubercles, but have numerous dorsally directed spike-like setae.

Antenna 1 with 4 flagellar articles; second article with more than 20 aesthetascs. Flagellum of antenna 2 with 4 articles.

Mandibular palp with 3 articles; second article longest with 2 apical setae and distal article shortest with 8 plumose setae. Mandibular incisors with rasp and file. Lacinia mobilis of right mandible broad apically and curved distally, with 2 or 3 branched and spinulate projections at apex. Spine row of right mandible composed of 11 stout and serrated setae progressively increasing in length from first to last. Inner seta on inner lobe of maxilla 2 slightly S-shaped.

Epipod of maxilliped semi-triangular, apically rounded, approximately 2.7 times as long as wide, reaching past palp articulation; epipod lacking simple setae.

Secondary unguis of all pereopods clearly bifid. Ventral comb seta on merus of pereopods 6 and 7 and carpus of pereopods 5–7.

Pleopod 2 with plumose setae, up to 0.4 times as long as exopod. Appendix masculina long, reaching beyond endopod tip, articulation near midlength of endopod. Endopod of pleopod 5 anterior to exopod, oval, 1.3 times as long as endopod of pleopod 2. Peduncles of pleopods with coupling hook sequence 32220. Simple seta located on lateral peduncle of pleopod 5.

Uropod exopod with laterally recurved apical blunt claw. Row of simple setae on endopod only placed apically. Many lateral tubercles present on uropod peduncle and exopod. Uropod endopod 0.5 times as long as peduncle and exopod 0.25 times as long as peduncle.

Substrate. Wood.

Distribution. Toyama Bay, Honshu Island, Japan. Previously detected at a depth of 4 to 145 m in the Sea of Okhotsk and the north part of the Sea of Japan.

Remarks. Jeskova (1961) described L. magadanensis , and Kussakin (1979) provided additional description. This species was recorded from the Sea of Okhotsk and the north part of the Sea of Japan off mainland Russia and Karafuto Island . The specimens examined here were collected from Toyama Bay off Honshu Island , Japan and incorrectly identified as L. japonica . L. magadanensis might be distributed throughout the Sea of Japan .

The three tubercles on the pleotelson of L. magadanensis are similar to those of L. borealis , L. japonica , L. orbellum , L. tripunctata , and L. tuberculata . L. orbellum , L. tripunctata , and L. tuberculata are very similar, with 5 flagellar articles on antenna 2, and a triangular epipod of maxilliped with simple setae, but L. magadanensis has 4 flagellar articles on antenna 2, and a semi-triangular epipod of maxilliped lacking simple seta. L. magadanensis is also distinguished from these 3 species by the sculpturing of pleonite 5, the bifid secondary unguis of all pereopods, the presence of ventral comb seta on merus of pereopods 6 and 7 and carpus of pereopods 5–7, and the small length ratio of endopod/peduncle.

L. magadanensis seems more similar to L. borealis and L. japonica for antenna 2 with 4 flagellar articles, 2 distinct transverse parallel carinae on pleonite 5, and margin of pleotelson with sheathed setae and dorsally directed numerous spike-like setae. However, L. magadanensis differs from L. borealis in the semi-triangular epipod of maxilliped, the absence of accompanying carinae behind the pair of tubercles on pleotelson and the absence of an anterior median projection on the posterior carina of the fifth pleonite. Also, L. magadanensis has an apically rounded semi-triangular epipod of maxilliped reaching palp articulation, absence of accompanying carinae behind the pair of tubercles on pleotelson, and 2 or 3 branched lacinia mobilis of right mandible. L. japonica has a triangular epipod maxilliped not reaching palp articulation, presence of accompanying carinae behind the pair of tubercles on pleotelson, and 4 branched apexes on lacinia mobilis of right mandible.