Mothocya parvostis Bruce, 1986

Fujita, Hiroki, Aneesh, Panakkool Thamban, Kawai, Kentaro, Kitamura, Shin-Ichi, Shimomura, Michitaka, Umino, Tetsuya & Ohtsuka, Susumu, 2023, Redescription and molecular characterization of Mothocya parvostis Bruce, 1986 (Crustacea: Isopoda: Cymothoidae) parasitic on Japanese halfbeak, Hyporhamphus sajori (Temminck & Schlegel, 1846) (Hemiramphidae) with Mothocya sajori Bruce, 1986 placed into synonymy, Zootaxa 5277 (2), pp. 259-286 : 265-276

Mothocya parvostis Bruce, 1986

[Standard Japanese name: Sayori-yadori-mushi]

( Figs. 3 – 14 )

Mothocya parvostis Bruce, 1986: 1005–1008 , figs.6–7; Yamauchi & Nunomura, 2010: 73, figs. 9–11; Kawanishi, Sogabe, Nishimoto & Hata, 2016: 13; Yamauchi & Kashio, 2018: 56; Hata, Sogabe, Tada, Nishimoto, Nakano, Kohya, Takeshima & Kawanishi, 2017: 104; Fujita, Kawai, Taniguchi Tomano, Sanchez, Kuramochi & Umino, 2020: 6, figs. 7–8; Nagasawa, 2020a: 52, figs, 6–7; Nagasawa & Uenoyama, 2022: 138–141, figs. 2–5; Fujita, Kawai, Deville & Umino, 2023a: fig. 3; 2023b: fig. 2–3.

Irona melanosticta Schioedte & Meinert, 1884: 388 (part); Thielemann, 1910: 45, figs 28, 29; Hiraiwa, 1934: 382, fig. 2; Gurjanova, 1936: 94, fig. 50; Inouye, 1941: 219, figs 1-14, pis 1–3; Shiino, 1951: 87, fig. IE, IF; 1965; Nunomura, 1981: 55; Hattori & Seki, 1956: 442; Kussakin, 1979: 308, figs 174, 175; Hatai & Yasumotu, 1980: 87 figs 1–4; 1981: 77; 1982a: 75; 1982b: 147.

Irona sp. Nunomura, 1981: 55 , fig. 10.

Mothocya sajori Bruce, 1986: 1143–1145 , fig. 30; Yamauchi & Kashio, 2018: 57; Nagasawa & Tawa, 2020: 68, figs. 1–2 [new synonymy].

Material examined: 370 females; 163 males; 52 transitionals.

Type material: Paratypes of M.parvostis- TOYA-Cr4102, 9.1 mm, transitional, host S. quinqueradiata , collected in Nagasaki by K. Hatai; TOYA-Cr4122, 11.5 mm, host H. sajori , collected in Imizu City, Toyama Prefecture by H. Kuroda. Paratypes of M. sajori- female, TOYA-Cr4082, 27.0 mm, female, host H. sajori .

Additional materials: TOYA-Cr4101, 9.5 mm, transitional, host S. quinqueradiata , collected in Nagasaki by K. Hatai; female, TOYA-Cr4123, 12.2 mm, host H. sajori , collected in Imizu City , Toyama Prefecture by H. Kuroda. HUM-Iso-00001, 26.3 mm, host H. sajori collected in the Shikokuchuo City , Ehime Prefecture by H. Fujita; HUM-Iso-00002, 13.5 mm, host H. sajori collected off Tokyo by H. Fujita; HUM-Iso-00003, 14.7 mm, host H. sajori collected in Nagayo City , Nagasaki Prefecture by H. Fujita ( HUM: Hiroshima University Museum , Hiroshima, Japan) .

Redescription of female ( Figs 3 , 4A–B , 5–12 ): Body 2.0 – 2.2 times as long as greatest width, dorsal surfaces convex, widest at pereonite 4, most narrow at pereonite 1. Cephalon 2.1–2.5 times wider than long, anterior margin evenly rounded or slightly pointed, moderately immersed in pereonite 1. Frontal margin with weakly produced rostrum. Eyes oval with distinct margins, one eye 0.3 times width of cephalon; 0.7 times length of cephalon. Pereonite 1 anterior margin medially straight, slightly curved laterally; anterolateral angles produced. Coxae 2–7 visible in dorsal view; coxae posterior margins rounded, lateral margins straight or weakly convex; coxae of pereonite 6 equal, 7 extending slightly beyond posterior of segment. Pereonites 1–7, gradually decreasing length; posterior margins smooth, slightly curved laterally; pereonites 7 with recessed posterior margin, extending pleonite 1 lateral margin. Pleon short, 12% (body length) BL or less, pleonites all visible in dorsal view, pleon wide, 0.9–1.0 times as wide as pereon max. width; pleonite 1 largely concealed by pereonite 7. Pleotelson with indistinct longitudinal median ridge; posterior margin broadly rounded; 0.8 times as long as pereonite 7, 0.6–0.7 times as long as anterior width.

Antennula with 8 articles; article 1 widest; articles 1–3 more robust than 4–8; articles 1, 1.2 times as wide as long; article 2, 1.6 times as wide as long; article 3, 1.4 times as long as wide; 5–8 gradually decreasing the length and width; article 8 with few terminal setae. Antenna with 8 articles; article 1 widest; articles 2–8, subequal in length and width; terminal article shortest, with few terminal setae. Mandibular with molar process; palp article 1 longest, 1.4 times as long as wide; article 2, 0.7 times as long as article 1, 1.5 times as long as wide; article 3 shortest, narrow, 0.7 times as long as article 2, 1.3 times as long as wide, 0.5 times as wide as article 1. Maxillula simple with 4 terminal robust setae (RS). Maxilla mesial lobe and lateral lobe each with 2 RS. Maxilliped without oostegite lobe; article 2 without setae, article 3 with three large terminal RS, and two RS on proximal posterior surface.

Pereopod 1 basis 1.1 times as long as greatest width; ischium 0.7 times as long as basis; merus 0.3 times as long as wide, 0.2 times as long as ischium; carpus 0.5 times as long as wide; propodus 1.2 times as long as wide; dactylus 1.2 times as long as propodus, 2.1 times as long as proximal width. Pereopod 2 basis 1.2 times as long as greatest width; ischium 0.9 times as long as basis, 1.7 times as long as wide; propodus 1.5 times as long as wide, 0.8 times as long as ischium; dactylus 1.8 times as long as propodus, 3.0 times as long as proximal width. Pereopod 3 basis 1.2 times as long as greatest width, ischium as long as basis, 1.6 times as long as greatest width; carpus 0.7 times as long as wide; propodus 1.8 times as long as wide, as long as ischium; dactylus as long as propodus, 2.9 times as long as greatest width. Pereopod 4 similar to 3. Pereopod 5 basis 2.0 times as long as greatest width, ischium 0.7 times as long as basis, 1.9 times as long as greatest width; merus 0.4 times as long as wide, 0.2 times as long as ischium; propodus 1.1 times as long as wide; dactylus 1.7 times as long as propodus, 2.7 times as long as greatest width. Pereopod 6 basis 1.4 times as long as greatest width, ischium 0.9 times as long as basis, 1.9 times as long as greatest width; merus 0.6 times as long as wide, 0.4 times as long as ischium; carpus 0.6 times as long as wide; propodus 1.3 times as long as wide; dactylus 1.5 times as long as propodus, 2.9 times as long as greatest width. Pereopod 7 basis 1.3 times as long as greatest width; ischium as long as basis, 2.3 times as long as wide; merus 0.6 as long as wide, 0.3 times as long as ischium; carpus 0.7 times as long as wide, 0.3 times as long as ischium; propodus 1.6 times as long as wide, 0.7 times as long as ischium; dactylus 1.2 times as long as propodus, 3.2 times as long as basal width. Brood pouch typical of the genus.

Pleopod peduncles narrow; pleopods 3–5 endopod proximomedial lobes moderately developed, 5 slightly larger than that of pleopod 4. Pleopod 1 exopod 0.9 times as long as wide, distally rounded, mesial margin convex; endopod as long as exopod, 1.1 times as long as wide, lateral margin weakly convex; peduncle 2.6 times as wide as long. Pleopod 2 exopod as long as wide, lateral margin convex, distally rounded, mesial margin convex; endopod as long as exopod, 1.2 times as long as wide, lateral margin weakly convex, distally broadly rounded; peduncle 3.8 times as wide as long. Pleopod 4 exopod 0.9 times as long as wide; endopod 1.1 times as long as exopod, 1.1 times as long as wide. Pleopod 5 exopod 1.2 times as long as wide, lateral margin convex, distally rounded, mesial margin convex; endopod 0.9 times as long as exopod, 1.3 times as long as wide, lateral margin weakly convex, distally broadly rounded.

Uropod rami broad, bluntly rounded, as long as or just beyond posterior margin of pleotelson; uropod, peduncle 0.6 times as long as exopod, as long as wide. Endopod 2.7 times as long as greatest width, 0.6 as long as exopod. Exopod 3.6 times as long as greatest width, 1.7 times as long as peduncle.

Male ( Figs 4C , 13A–D ): Body 2.4 times as long as greatest width, widest at pereonite 3. Cephalon 1.8 times wider than long, broadly rounded, not immersed in pereonite 1. Eyes oval with distinct margins, one eye 0.4 times width of cephalon. Pereonite 1 longest, 7 shortest; pereonite gradually decreasing the length and width from 3–7. Coxae 2–7 visible in dorsal view; shorter than pereonites. Pleon short, 12% BL or less, pleonites all visible in dorsal view, pleon wide, 0.7 as wide as pereon max. width; pleonite 5 longest. Pleotelson apical margin rounded, nearly as wide as pereonite 7; 0.8 times as long as anterior width. Uropod 1.4 times as long as pleotelson; uropods, equal in size. Uropod rami, endopod, 0.6 times as long as exopod, lateral margin convex. Exopod apically rounded, 2.2 times as long as peduncle, 1.6 times as long as endopod. Pleopod 2 with appendix masculina, longer 1.1 times as long as endopod. Penis well developed.

Transitional ( Figs 13E–F , 14 ): Body 2 times as long as wide; straight. Eyes distinct, one eye 0.4 times as wide as cephalon. Cephalon 2.0–2.2 times wider than long, anterior margin evenly rounded, moderately immersed in pereonite 1. Pereonites, pleonites, in between male and female. Antennula, antenna similar to those of the female. Pleotelson 0.8 times as long as anterior width. Pereopods in between female and male. Pleopod 2, similar to male; Uropods slightly longer than pleotelson posterior margin, in between male and female; rami similar to male. Penis, not distinct.

Coloration: Body coloration varies from pale yellow to grey in preservation ethanol.

Hosts: Cage-cultured Seriola quinqueradiata and Girella punctata , wild Hyporhamphus sajori , and juveniles of Acanthopagrus schlegelii , Acanthopagrus latus , and Hypoatherina tsurugae ( Bruce 1986; Saito & Yoneji 2000; Fujita et al. 2020, 2023b).

Distribution: Known from Japanese waters (Yamagata, Miyagi, Toyama, Osaka and Kagoshima Prefectures, Tokyo Bay and the Seto Inland Sea) ( Bruce 1986; Kawanishi et al. 2016; Yamauchi & Kashio 2018) and Korean waters (Yeosu City) ( Inoue 1941).

Remarks: Mothocya parvostis can be separated from other congeners by the following combinations of characters: 1) body slightly to moderately twisted to one side; 2) pereonite 7 posterior margin moderately to deeply recessed; 3) uropod uropodal rami extending to pleotelson posterior margin; 4) uropod rami bluntly rounded; 5) exopod 1.5 times as long as peduncle.

The present study re-described Mothocya parvostis based on the type specimens and fresh materials collected from the type locality.We also thoroughly examined and compared the type specimens of M. sajori .All morphological characters of Mothocya parvostis and the type material of M. sajori showed substantial similarity. Only variation in body twisting was found; the smaller individuals less twisted than larger individuals. According to Aneesh et al. (2016, 2018, 2020), body hunching of cymothoids depends on the site of attachment and in which branchial cavity the cymothoid is attached. If the cymothoid is attached in the right branchial cavity, the body will be twisted towards the left side and verse visa. Furthermore, the degree of twisting in branchial cymothoids is dependant on the size of the animal; to safely settle in the branchial cavity, the larger animal needs more twisting than the smaller one.

The present morphological study clearly states that M.sajori should be treated as a junior synonym of M. parvostis .

Figures

FIGURE 3. Type specimens. A, dorsal view of Mothocya sajori Bruce, 1986, paratype ovigerous female (27 mm, partially molted) (Cr4082); B, dorsal view of Mothocya parvostis Bruce, 1986, paratype (Cr4122) ovigerous female (11. 5 mm).

FIGURE 4. Paratype specimens of Mothocya parvostis Bruce, 1986 dorsal view. A, ovigerous female (12.2 mm) (Cr4123); B, ovigerous female (11.5 mm) (Cr4122); C, male (9.0 mm) (Cr4124).

FIGURE 5. Mothocya parvostis Bruce, 1986, large ovigerous female (26 mm) collected from Shikokuchuo, Japan. A, dorsal view; B, ventral view; C, lateral view.

FIGURE 6. Mothocya parvostis Bruce, 1986 collected from Shikokuchuo, Japan.A–B, dorsal and lateral view of large ovigerous female (27 mm); C–D, dorsal view and ventral view of female (20 mm) on partial oostegition moult.

FIGURE 7. Mothocya parvostis Bruce, 1986, A–B, dorsal and ventral view of small ovigerous female (12 mm) collected from Etajima, Japan.

FIGURE 8. Mothocya parvostis Bruce, 1986, A–D, dorsal, ventral and lateral view (of both sides) of ovigerous female (23 mm) collected from Shikokuchuo, Japan.

FIGURE 9. Mothocya parvostis Bruce, 1986.A, ovigerous female (26 mm) collected from Shikokuchuo, Japan; B–C, ovigerous female (12 mm) collected from Etajima, Japan.A–B, dorsal view; C, dorsal view of cephalon.

FIGURE 10. Mothocya parvostis Bruce, 1986, ovigerous female (23 mm) collected from Shikokuchuo, Japan. A, cephalon dorsal view; B, cephalon ventral view; C, antennula; D, antennae; E, mandible; F, maxilla; G. maxilliped.

FIGURE 11. Mothocya parvostis Bruce, 1986, ovigerous female (23 mm) collected from Shikokuchuo, Japan.A–G, pereopods 1–8 respectively; H, brood pouch.

FIGURE 12. Mothocya parvostis Bruce, 1986, ovigerous female (23 mm) collected from Shikokuchuo, Japan. A–B, pleopods 1–2 respectively; C–D, pleopods 4–5 respectively; E, uropod; F, pleotelson and uropods.

FIGURE 13. Mothocya parvostis Bruce, 1986 collected from Etajima, Japan. A–B, dorsal and ventral view of early male (7 mm); C–D, dorsal view and ventral view male (12 mm); E–F, dorsal and ventral view of very early transitional (14 mm).

FIGURE 14. Mothocya parvostis Bruce, 1986. A–B, dorsal and ventral view of mid transitional (11 mm) collected from Etajima, Japan; C–D, dorsal view and ventral view of late transitional (19 mm) collected from Sendai, Japan.