Limnoria aspera Yoshino & Ohsawa, 2021

Yoshino, Hiroki, Kambara, Yuriko, Kajiwara, Shota & Ohsawa, Takeshi A., 2021, New species of Sargassum-boring Limnoria Leach, 1814 (Crustacea, Isopoda Limnoriidae) from Japan, Zootaxa 4970 (1), pp. 119-130 : 120-124

publication ID	https://doi.org/ 10.11646/zootaxa.4970.1.4
publication LSID	lsid:zoobank.org:pub:3F7A60FB-7206-441E-94C6-AF718B9A5E56
DOI	https://doi.org/10.5281/zenodo.4814248
persistent identifier	https://treatment.plazi.org/id/039587CB-3555-6933-FF25-F9BBFE69F826
treatment provided by	Plazi
scientific name	Limnoria aspera Yoshino & Ohsawa
status	sp. nov.

Treatment

Limnoria aspera Yoshino & Ohsawa , sp. nov.

Figs 1–8 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 View FIGURE 8

Material examined. Holotype: male 2.6 mm, Kamogawa-shi , Chiba prefecture, Japan, 35°07’N, 140°10’E, subtidal zone (0–1 m in depth), Sargassum ringgoldianum holdfasts, Takeshi A. Ohsawa and Hiroki Yoshino, 9 September 2020 (CBM-ZC 16564). GoogleMaps

Paratypes: male 2.8 mm, Kamogawa-shi, Chiba prefecture, Japan, 35°07’N, 140°10’E, subtidal zone (0–1 m in depth), Sargassum ringgoldianum holdfasts, Yuriko Kambara, 14 July 2014 (CBM-ZC 16565). male 2.7 mm, Kamogawa-shi, Chiba prefecture, Japan, 35°07’N, 140°10’E, subtidal zone (0–1 m in depth), Sargassum siliquastrum holdfasts, Takeshi A. Ohsawa and Hiroki Yoshino, 9 September 2020 (CBM-ZC 16566). male 3.2 mm, Kamogawa-shi, Chiba prefecture, Japan, 35°07’N, 140°10’E, subtidal zone (0–1 m in depth), Sargassum siliquastrum holdfasts, Takeshi A. Ohsawa and Hiroki Yoshino, 9 September 2020 (CBM-ZC 16567).

Type locality. Kamogawa-shi, Chiba Prefecture, Japan.

Description. Body oblong, dark yellow to light brown in 70% ethanol ( Figs. 1 View FIGURE 1 , 2A View FIGURE 2 ). Head almost globular. Eyes black in color, each with 8 ommatidia. Pleonite composed of 5 distinct segments. Pereonal segment 1 longest, approximately 1.5–1.7 times longer than segment 2 ( Fig. 1 View FIGURE 1 ), with 1 thinly V-shaped groove. 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 approximately 0.6 times as long as pleotelson ( Figs 2 View FIGURE 2 , 3A View FIGURE 3 ). Pleonite 5 dorsomedially with Y- or Ishaped indistinct longitudinal carina on which few scale spikes form line ( Figs 2B View FIGURE 2 , 3A View FIGURE 3 ). Pleonite 5 covered with fused scales, which make tile mosaics ( Fig. 2C View FIGURE 2 ).

Pleotelson 0.6–0.8 times as long as wide, medially with 1 tubercle on which few scale spikes follow its line ( Figs 2 View FIGURE 2 , 3A View FIGURE 3 ). Pleotelson covered with fused scales, which present tiled pattern on surface ( Fig. 2C View FIGURE 2 ). Lateral crests and posterior margin of pleotelson margined with sets of about 2–5 directed upward scale spikes. Posterior edge of pleotelson with fringe of long sheathed setae and many short setae ( Fig. 3B View FIGURE 3 ).

Antenna 1 with 4 flagellar articles; second article with 7 aesthetascs ( Fig. 3D View FIGURE 3 ). Flagellum of antenna 2 with 4 articles ( Fig. 3E View FIGURE 3 ).

Mandibular palp lacking, replaced by single long stout seta ( Figs 4A, B View FIGURE 4 ). Mandibular incisors lack rasp and file ( Figs 4A–B View FIGURE 4 , 8A View FIGURE 8 ). Lacinia mobilis of right mandible branched at intermediate point, branches gradually curving 90-degrees and serrated on anterior side ( Fig. 4B View FIGURE 4 ). Posterior branch almost same length as anterior branch. Lacinia mobilis of left mandible with 1 serrated seta.

Epipod of maxilliped, clavate, approximately 3 times as long as wide, reaching articulation of palp, with simple true setae ( Fig. 4E View FIGURE 4 ).

Secondary unguis on pereopod 1 undivided, without spinule or with 1–7 spinules ( Fig. 5A View FIGURE 5 ). Secondary unguis on pereopods 2–6 undivided ( Figs 5B, D View FIGURE 5 , 6A–B View FIGURE 6 ) or slightly bifid ( Fig. 5C View FIGURE 5 ). Secondary unguis on pereopod 7 undivided with 4–7 spinules ( Fig. 6C View FIGURE 6 ). Ventral comb seta absent on merus and present on carpus of pereopods 6 and 7. Propodus of pereopods 3–5 with prominent barbed projection opposing secondary unguis, projection reduced on pereopod 2 ( Figs 5 View FIGURE 5 , 6 View FIGURE 6 , 8B View FIGURE 8 ).

Pleopod 2 with plumose setae up to 0.9 times length of exopod ( Fig. 7B View FIGURE 7 ). Appendix masculina long, reaching beyond endopod tip, articulating near midlength of endopod. Endopod of pleopod 5, oval ( Fig. 7C View FIGURE 7 ). Peduncle of pleopod 5 with simple seta laterally. Peduncles with coupling hook sequence 32220.

Uropod exopod with laterally recurved apical claw ( Figs 3C View FIGURE 3 , 8C View FIGURE 8 ). Row of simple long setae on endopod placed apically. Uropod peduncle about 1.1 times as long as endopod, with many short simple setae and row of plumose setae. Exopod about 0.4–0.5 times as long as peduncle.

Molecular data. We deposited the nucleotide sequences of COI region of mitochondrial genes (Acc. no. LC610781 View Materials , LC610782 View Materials ) and 28S rRNA of nuclear genes (Acc. no. LC612562 View Materials , LC612563 View Materials ) obtained from the holotype and paratype in GenBank .

Substrate. Sargassum ringgoldianum , S. siliquastrum holdfasts.

Distribution. Known only from the type locality.

Etymology. From the Latin aspera (= rough; Gender feminine), referring to the rough exoskeleton on pleonite 5 and pleotelson.

Remarks. Mandibular palp of Limnoria aspera sp. nov. is reduced to a seta. This feature is also found in 7 species: L. bacescui , L. bituberculata , L. furca , L. nagatai , L. segnoides , L. uncapedis and L. zinovae ( Cookson 1991; Pillai 1957; Kussakin 1963; Menzies 1957; Nunomura 2012; Ortiz & Lalana 1988; Yoshino & Ohsawa 2019). Cookson 1991 stated that “ L. uncapedis , L. segnoides and L. bituberculata all share the following features: broad maxillipedal epipod, loss of mandibular palp, similar shape of the lacinia mobilis of the right mandible, and modification of the secondary unguis on pereopod 1”, and Yoshino & Ohsawa (2019) said that the species of non- mandibular-palp group are algal-feeding and shared the broad epipod of maxilliped, except seagrass-feeding L. zinovae , the shape of epipod of maxilliped of which is unknown. L. aspera sp. nov. fits into this group, as an algalfeeding species that also has the broad epipod of maxilliped ( Table 1 View TABLE 1 ).

L. bacescui , L. segnoides , and L. zinovae differ from L. aspera sp. nov. by the number of flagellar articles of antenna 2, the secondary unguis on the pereopods, lacinia mobilis of right mandible, and the sculpturing of pleonite 5 and pleotelson.

L. aspera sp. nov. is similar to L. uncapedis in the number of flagellar articles of antennae 1 and 2, secondary unguis of pereopod 1, lacinia mobilis of right and left mandible, and pereopods 2–5 with barbed projection on the propodus. However, L. uncapedis is pale yellow and has no carinae on pleonite 5 and pleotelson, while L. aspera sp. nov. is dark yellow and has Y- or I-shaped carina on pleonite 5 and 1 tubercle on pleotelson.

Similarly to L. aspera sp. nov., L. bituberculata has 4 flagellar articles of antenna 1, spinules on the secondary unguis of pereopod 1, and a dorsomedial longitudinal carina between 2 longitudinal grooves on pleonite 5. However, L. bituberculata is pale yellow and has 2 prominent tubercles on the pleotelson, while L. aspera sp. nov. is dark yellow and has 1 medial tubercle on the pleotelson.

L. aspera sp. nov. seems to be most similar to L. furca , and L. nagatai . L. aspera sp. nov. is distinguished from L. furca , and L. nagatai by dark yellow body color ( L. furca , and L. nagatai pale yellow), undivided or slightly bifid secondary unguis of pereopods ( L. furca bifid or trifid, L. nagatai bifid), and the medial tubercle on the pleotelson lacks the attachment of two inverted V-shaped carinae ( L. furca , and L. nagatai with medial tubercle followed by a pair of subparallel carinae).