Limnoria nagatai Nunomura, 2012

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 : 244-249

Limnoria nagatai Nunomura, 2012

Figs 9–10

Limnoria nagatai Nunomura, 2012: 80 –82 fig. 2

Material examined. Holotype: male, 4.2 mm, Sumiyoshizaki , Kunimi-cho (now Kunisaki-shi), Oita Prefecture, Japan, Nagata Kizo, 13 June 1978 (TOYACr-23340)

Allotype: ovigerous female, 4.7 mm, Ryozaki , Kunimi-cho (now Kunisaki-shi), Oita Prefecture, Japan, Nagata Kizo, 1976 or 1977 (TOYA Cr-23345).

Paratypes: 4 males, 3.0– 5.1 mm, Ryozaki , Kunimi-cho (now Kunisaki-shi), Oita Prefecture, Japan, Nagata Kizo, 19 May 1977 (TOYA Cr-23341–23344; Cr-23341 lost, Cr-23342 lost, Cr-23343 head lost, Cr-23344 lost) .

Other material: female 2.6 mm (with 26 slides), Kamogawa-shi, Chiba prefecture, Japan, 35°07’N, 140°10’E, subtidal zone, Eisenia bicyclis holdfasts, Takeshi A. Ohsawa and Hiroki Yoshino, 23 April 2012 (KMNH IvR 500790); 3 males, 2.2–2.7 mm, 4 ovigerous females, 2.6–3.3 mm, 6 non-ovigerous females, 1.9–3.4 mm (KMNH IvR 500791), same as KMNH IvR 500790; 1 male, 2.7 mm, 4 non-ovigerous females, 1.9–3.5 mm, Tokura , Minamisanriku-cho, Miyagi prefecture, Japan, 38°38'N, 141°26'E, subtidal zone, Eisenia bicyclis holdfasts, Takeshi A. Ohsawa and Hiroki Yoshino, 9 April 2013 (KMNH IvR 500792) ; 1 female, 2.5 mm, Oppa-wan , Kitakami-machi, Ishinomaki-shi, Miyagi prefecture, Japan, 38°36'N, 141°30'E, subtidal zone, Eisenia bicyclis holdfasts, Takeshi A. Ohsawa and Hiroki Yoshino, 9 April 2013 (KMNH IvR 500793) ; 1 male, 2.4 mm, 1 ovigerous female, 2.9 mm, 2 non-ovigerous females 1.9 (head lost)–2.0 mm, Hiraiso-cho , Hitachinaka-shi, Ibaraki prefecture, Japan, 36°21'N, 140°36'E, subtidal zone, Eisenia bicyclis holdfasts, Hiroki Yoshino, 8 April 2013 (KMNH IvR 500794) ; 1 male, 1.8 mm, 1 non-ovigerous female, 2.8 mm, Mizuki-cho , Hitachi-shi, Ibaraki prefecture, Japan, 36°31'N, 140°38'E, subtidal zone, Eisenia bicyclis holdfasts, Takeshi A. Ohsawa and Hiroki Yoshino, 2 June 2013 (KMNH IvR 500795) ; 1 male 1.8 mm, 1 ovigerous female, 3.3 mm, 2 non-ovigerous females, 1.8–3.2 mm, Choshi-shi , Chiba prefecture, Japan, 35°41'N, 140°51'E, subtidal zone, Eisenia bicyclis holdfasts, Takeshi A. Ohsawa and Hiroki Yoshino, 3 June 2012 (KMNH IvR 500796) ; 4 males 1.7–2.5 mm, 2 nonovigerous females, 1.9–2.3 mm, Okinoshima Island park, Tateyama-shi, Chiba prefecture, Japan, 34°59'N, 139°49'E, subtidal zone, Eisenia bicyclis holdfasts, Takeshi A. Ohsawa and Hiroki Yoshino, 9 June 2013 (KMNH IvR 500797) ; 1 male, 1.8 mm, 1 non-ovigerous female, 2.2 mm, Hagiu , Futtsu-shi, Chiba prefecture, Japan, 35°11'N, 139°49'E, subtidal zone, Eisenia bicyclis holdfasts, Hiroki Yoshino, 23 December 2013 (KMNH IvR 500798); 1 ovigerous female, 2.5 mm, 1 non-ovigerous female, 2.2 mm, Kisami Ohama Beach, Shimoda-shi, Shizuoka prefecture, Japan, 34°39'N, 138°55'E, Takeshi A. Ohsawa and Hiroki Yoshino, 13 April 2013 (KMNH IvR 500799) ; 3 males, 2.7 mm, 4 females, 3.0–4.0 mm, Hamajima-cho , Shima-shi, Mie Prefecture, Japan, 34°18'N, 136°44'E, subtidal zone, Eisenia arborea holdfasts, Takeshi A. Ohsawa and Hiroki Yoshino, 3 July 2012 (KMNH IvR 500856) ; 4 males, 1.8–3.0 mm, 5 females, 2.5–3.4 mm, Hiwasaura , Minami-cho, Kaifu-gun, Tokushima Prefecture, Japan, subtidal zone, Eisenia bicyclis holdfasts, Takeshi A. Ohsawa and Hiroki Yoshino, 28 April 2013 (KMNH IvR 500857) ; 1 male, 2.8 mm, 1 female, 3.0 mm, Abe port, Minami-cho, Kaifu-gun, Tokushima Prefecture, Japan, subtidal zone, Eisenia bicyclis holdfasts, Takeshi A. Ohsawa and Hiroki Yoshino, 28 April 2013 (KMNH IvR 500858) .

Type locality. Sumiyoshizaki, Kunimi-cho (now Kunisaki-shi), Oita Prefecture, Japan

Description. Body oblong and pale yellow to pale red in 70% ethanol. Head almost globular, some samples red in color, about 1.4 times broader than long. Eyes black in color, each with 7 ommatidia. Most of dorsal surface of pereonite, pleon and pleotelson covered with small pores. Pleonites with 5 distinct segments. Pereonal segment 1 longest, about 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 to 4 each with transverse row of many small setae.

Pleonite 5 0.65 times as long as pleotelson ( Fig. 8A ). Pleonite 5 dorsomedially with Y-shaped or nearly Xshaped carinae on which scale spikes form line ( Fig. 7 ). These spikes continuing laterally and pleonite 5 fringed with spikes. Posterior margin of pleonite 5 with sparsely populated scale-spikes. Pleonite 5 medially with 1 strong tubercle and 1 weaker tubercle posteriorly.

Pleotelson approximately 0.55–0.8 times as long as wide, medially with 1 strong tubercle followed by 1 pair of subparallel carinae on which scale spikes form line that appears as an inverse V-shaped structure on the pleotelson ( Fig. 8A ). Pleotelson dorsally with 0–6 shallow pits between carinae and lateral crest. Lateral crests and posterior margin of pleotelson margined with sets of about 3–4 directed upward tubercles. Posterior edge of pleotelson with a fringe of long stout setae and many short setae.

Antenna 1 with 4 flagellar articles; second article with 5 aesthetascs ( Fig. 8B ). Flagellum of second antenna with 3 articles ( Fig. 8C ).

Mandibular palp lacking, replaced by single stout long seta ( Fig. 8D ). Mandibular incisors lack rasp and file. Lacinia mobilis of right mandible branched at intermediate point, the branches gradually curving 90-degrees or more and serrated on anterior side. Anterior and posterior branches almost same length.

Epipod of maxilliped, clavate, approximately 2–3 times as long as wide, slightly reaching articulation of palp ( Fig. 8G ).

Secondary unguis on all pereopods bifid ( Fig. 9 ). Exceptionally, only right pereopod 1 of one individual from Ibaraki prefecture (KMNH IvR 500794), slightly trifid. Ventral comb seta absent on merus and present on carpus of pereopods 6, 7.

Pleopod 2 with plumose setae up to 0.8 times length of exopod ( Fig. 10B ). Appendix masculina long, reaching beyond endopod tip, articulating near midlength of endopod. Endopod of pleopod 5, oval, 0.8 times as long as endopod of pleopod 2 ( Fig. 10E ). Peduncle of pleopod 5 with simple seta laterally. Peduncles with coupling hook sequence 32220.

Uropod peduncle 1.6 times as long as endopod. Exopod 0.3 times as long as peduncle ( Fig. 10F ).

Molecular data. COI sequences obtained from our materials were deposited in GenBank (accession number: LC146527 - LC146632 ).

Substrates. Eisenia bicyclis and E. arborea . Unknown in type locality.

Distribution. Pacific coast of Honshu Island, Shikoku Island and Kyushu Island.

Remarks. This work has provided some morphological and substrate details omitted in the original description of Limnoria nagatai ( Nunomura, 2012) . Nunomura (2012) did not describe the substrate, and that the mandibular palp was reduced to a seta although they described, “Palp not found.” Most of needed notes are added in the above description.

The mandibular palp of L. nagatai is reduced to a seta. L. nagatai is most similar to L. furca sp. nov. and L. segnoides in that they share a bifid lacinia mobilis of the right mandible, inverse V-shaped carinae on pleotelson, and similarly shaped uropods. L. nagatai is separated from L. furca sp. nov. and L. segnoides by bifid secondary unguis on all pereopods, Y-shaped carinae on pleonite 5 and clear and strong carinae on pleonite 5 and pleotelson.

L. nagatai feeds on the holdfasts of Eisenia in Honshu Island and east side of Shikoku Island. L. nagatai tended to live in bigger holdfasts of E. bicyclis . They may bore into the substrates, making long pits and, finally, causing the holdfasts to look like a sponge. More than 100 individuals have been found from a single holdfast.

Figures

FIGURE 7. Limnoria nagatai Female KMNH IvR 500790. Dorsal view of pleonite 5, pleotelson. Scale bars: 0.1 mm.

FIGURE 8. Limnoria nagatai Female KMNH IvR 500790 A, pleotelson. Holotype male TOYACr-23340. B, antenna 1. C, antenna 2. D, right mandible. female KMNH IvR 500796. E, maxilla 1. Holotype male TOYACr-23340. F, maxilla 2. G, maxilliped. Scale bars: A–C= 0.1 mm, D–G = 0.05 mm,

FIGURE 9. Limnoria nagatai Holotype male TOYACr-23340. A, pereopod 1. B, pereopod 2. C, pereopod 3. D, pereopod 4. E, pereopod 5. F, pereopod 6. G, pereopod 7. Scale bars: A–G = 0.1 mm.

FIGURE 10. Limnoria nagatai Paratype male TOYA Cr-23343. A, pleopod 1. B, pleopod 2. C, pleopod 3. D, pleopod 4. E, pleopod 5. F, uropod. Scale bars: A–F = 0.1 mm. Outline of folliculinid protozoans attached to some setae also shown.