Limnoria furca, Yoshino & Ohsawa, 2019

Yoshino, Hiroki & Ohsawa, Takeshi A., 2019, Description of new species of algal-boring Limnoria (Crustacea, Isopoda, Limnoriidae) from Japan and redescription of Limnoria segnoides Menzies, 1957 and L. nagatai Nunomura, 2012, Zootaxa 4550 (2), pp. 236-250 : 237-242

Limnoria furca , sp. nov.

Figs. 1–4

Material examined. Holotype: male 2.4 mm, Oki Islands , Shimane Prefecture, Japan, 36°06’33’’ N, 133°07’50’’ E, subtidal zone, Eisenia bicyclis holdfasts, Takeshi A. Ohsawa and Hiroki Yoshino, 14 March 2014 (KMNH IvR 500953).

Paratypes: male 2.2 mm, Oki Islands, Shimane Prefecture, Japan, 36°06’33’’, N 133°07’50’’ E, subtidal zone, Eisenia bicyclis holdfasts, Takeshi A. Ohsawa and Hiroki Yoshino, 14 March 2014 (KMNH IvR 500953); nonovigerous females, 2.1–3.2 mm (KMNH IvR 500954), same as KMNH IvR 500953; non-ovigerous female, 3.1 mm, Munakata-shi, Fukuoka prefecture, Japan, 33°53’22’’ N, 130°31’29’’ E, subtidal zone, Eisenia bicyclis holdfasts, Takeshi A. Ohsawa A. Takeshi and Hiroki Yoshino, 4 March 2014 (KMNH IvR 500950); males, 2.5–2.6 mm, Karatsu-shi in Saga prefecture, Japan, 33°33’24’’ N, 129°50’46’’ E, subtidal zone, Eisenia bicyclis holdfasts, Takeshi A. Ohsawa A. Takeshi and Hiroki Yoshino, 22 June 2013 (KMNH IvR 500951); females, 2.5–3.1 mm (KMNH IvR 500952), same as KMNH IvR 500951.

Type locality. Oki Island, Shimane prefecture, Japan.

Description. Body oblong and pale yellow in 70% ethanol. Head almost globular. Eyes black in color, each with 7–8 ommatidia. Most of dorsal surface of pereonite, pleon and pleotelson covered with small pores. Pleonite composed of 5 distinct segments. Pereonal segment 1 longest, approximately 1.5 times longer than segment 2. Segments 2–4 subequal length. Posterior pereonal segments 4–7 progressively shorten. Coxal plates of pereonal segments 2–4 rectangular in shape and those of posterior segments prolonged acutely at posterior angle. Pereonites 6, 7 and pleonites 1–4 each with transverse row of many small setae.

Pleonite 5 0.5–0.6 times as long as pleotelson ( Fig. 1 , 2A ). Pleonite 5 medially with 1 strong tubercle and 1 weaker tubercle posteriorly ( Fig. 1 ), sometimes imperceptible ( Fig. 2A ). Pleonite 5 dorsomedially with often illdefined Y-shaped carinae on which few scale spikes form line. These spikes continuing laterally and pleonite 5 fringed with spikes.

Pleotelson 0.6–0.9 times as long as wide, medially with 1 large median tubercle followed by faint pair of subparallel, inverted V-shaped carinae on which few scale spikes follow its line. Pleotelson dorsally with 0–6 shallow pits between carinae and lateral crest. Lateral crests and posterior margin of pleotelson margined with sets of about 2–5 directed upward tubercles. Posterior edge of pleotelson with a fringe of long sheathed setae and many short setae.

Antenna 1 with 4 flagellar articles; second article with 4–5 aesthetascs ( Fig. 2C ). Flagellum of second antenna with 3 articles ( Fig. 2D ).

Mandibular palp lacking, replaced by single long stout seta ( Fig. 2G ). Mandibular incisors lack rasp and file. Lacinia mobilis of right mandible branched at intermediate point, the branches gradually curving 90-degrees and serrated on anterior side. Posterior branch slightly longer than or almost same length as anterior branch.

Epipod of maxilliped, clavate, approximately 2 times as long as wide, reaching articulation of palp, with simple true setae ( Fig. 2B ).

Secondary unguis on pereopod 1 bifid or trifid ( Fig. 3A, B ), of pereopods 2–6 bifid ( Fig. 3 C–G). Pereopod 7 bifid or trifid ( Fig. 3H ). Ventral comb seta absent on merus and present on carpus of pereopods 6 and 7.

Pleopod 2 with plumose setae up to 0.8 times length of exopod ( Fig. 4B ). Appendix masculina long, reaching beyond endopod tip, articulating near midlength of endopod. Endopod of pleopod 5, oval ( Fig. 4E ). Peduncle of pleopod 5 with simple seta laterally. Peduncles with coupling hook sequence 32220.

Uropod exopod with laterally recurved apical claw ( Fig. 4F ). Row of simple long setae on endopod placed apically and laterally. Uropod peduncle about 1.6 times as long as endopod. Exopod about 0.3 times as long as peduncle.

Molecular data. COI sequences obtained from the holotype and paratype were deposited in GenBank (accession number: LC146617 – LC146632 ).

Substrate. Eienia bicyclis holdfasts.

Distribution. Oki Island, Sea of Japan coast of Honshu Island and Kyushu Island

Etymology. From the Latin for fork, furca , referring to the secondary unguis on pereopod 1.

Remarks. Although most Limnoria , for example, L. japonica and L. saseboensis , have a mandibular palp, the mandibular palp of L. furca sp. nov. is reduced to a seta, a condition also found in 6 other species: L. bacescui , L. bituberculata , L. nagatai , L. segnoides , L. uncapedis and L. zinovae ( Cookson 1991, Pillai 1957, Kussakin 1963, Menzies 1957, Nunomura 2012, Ortiz & Lalana 1988). L. bacescui , L. bituberculata , L. segnoides , and L. uncapedis differ from L. furca sp. nov. by the shape of the secondary unguis on the pereopods, and the sculpturing of pleonite 5 and pleotelson. L. nagatai has a bifid secondary unguis on all pereopods and clearly marked carinae on pleonite 5 and the pleotelson, while L. furca sp. nov. has bifid or trifid secondary unguis on pereopods 1 and 7 and weak or absent carinae on pleonite 5 and the pleotelson. L. zinovae can be separated from L. furca sp. nov. by carinae on the pleotelson, the shape of the uropod, lacinia mobilis of right mandible, and the secondary unguis on pereopod 1.

All of our samples of L. furca sp. nov. were collected from the Sea of Japan side of Honshu and Kyushu Islands, while L. nagatai has been collected from the Pacific Ocean side of Honshu and Kyushu Islands. The genetic study of L. nagatai and of specimens now identified as L. furca sp. nov. showed that mitochondrial COI sequence of L. furca sp. nov. differed from L. nagatai by approximately more than 15% in p -distance ( Yoshino et al. 2018).

Figures

FIGURE 1. Limnoria furca sp. nov. Male KMNH IvR 500951. Dorsal view of pleonite 5, pleotelson. Scale bars: 0.1 mm.

FIGURE 2. Limnoria furca sp. nov. Holotype male KMNH IvR 500856. A, pleonite 5 and pleotelson. B, maxilliped. C, antenna 1. D, antenna 2. E, maxilla 1. F, maxilla 2. G, right mandible. Scale bars: A–D, F = 0.1 mm, E = 0.05 mm.

FIGURE 3. Limnoria furca sp. nov. Holotype male KMNH IvR 500856. A, pereopod 1. B, dactylus of pereopod 1. C, pereopod 2. D, pereopod 3. E, pereopod 4. F, pereopod 5. G, pereopod 6. H, pereopod 7. Scale bars: A–H = 0.1 mm.

FIGURE 4. Limnoria furca sp. nov. Paratype male KMNH IvR 500857. A, pleopod 1. Holotype male KMNH IvR 500856. B, pleopod 2. C, pleopod 3. D, pleopod 4. E, pleopod 5. F, uropod. Scale bars: A–G = 0.1 mm.