Isopoda Latreille, 1816

Order: Isopoda Latreille, 1816

Superfamily: Cymothooidea Leach, 1814 Family: Cymothoidae Leach, 1814 Genus: Anilocra Leach, 1818

Anilocra prionuri Williams and Bunkley-Williams, 1986 View in CoL [Japanese name: Nizadai-no-ginka] ( Figs. 1–19 View Fig View Fig View Fig View Fig View Fig View Fig View Fig View Fig View Fig View Fig View Fig View Fig View Fig View Fig View Fig View Fig View Fig View Fig View Fig , SM 1)

Material examined: six aegathoid stages, SMBL-V 0772–0777, BL14.2, 14.4, 14.8, 15.5, 17.6, and 18.0 mm; two males, SMBL-V 0778 and V 0779. BL20.0 and 20.1 mm; one transitional, SMBL-V 0780, BL 24.7 mm; two ovigerous female, SMBL-V 0781 and V 0782, BL34.0 and 34.2 mm. All specimens from Okino-se, the East China Sea, off Oshima, Ushibuka-cho, Amakusa City, Kumamoto Prefecture, Japan ( 32°10'30.6"N 129°56'25.1"E), body surface of Prionurus scalprum Valenciennes, 1835 (SL: 304.5 mm, SMBL-V 0783), 2 January 2024, coll. T. Ohnaka.

Description of aegathoid stage ( Figs. 2 View Fig , 6 View Fig , 8 View Fig , 10 View Fig , 12 View Fig , 14 View Fig , 16 View Fig , 18 View Fig ): Body narrow, 4.0–5.1 times as long as greatest width, widest at pereonite 5 or pereonite 6, with smooth dorsal surfaces.

Cephalon 1.3–2.1 times wider than long, semi-oval, with well developed rostrum, not immersed in pereonite 1. Eyes oval, with distinct margins, with long axis of each eye 0.7–1.0 times length of cephalon, and short axis 0.1–0.3 times maximum width of cephalon. Anterior border of pereonite 1 straight. Coxae almost invisible in dorsal view, of pereonites 2–4 roundly, of pereonites 5–7 concave; pereon longest at pereonite 5 or pereonite 6, shortest at pereonite 7; posterior margins of pereonites 1–5 smooth and slightly curved laterally, that of pereonites 6 and 7 slightly recessed. Pleonites 1–5 0.2–0.3 times as long as total length, 0.7–0.8 times as wide as greatest body width, with all pleonites visible in dorsal view. Pleotelson 1.4–1.5 times as long as wide, 0.8–1.3 times as long as pleonites 1–5, with usually swimming setae posterior margins.

Antennula 8 articles, extending beyond mid-length of cephalon, article 3 enlargement or no enlargement. Antenna 10–11 articles, extending beyond anterior border of pereonite 1.

Pereopod 1 basis 1.7–2.0 times as long as greatest width; ischium 0.5–0.6 times as long as basis; merus 0.3–0.6 times as long as ischium, with 1 robust seta on superior distal angle; carpus 0.5–1.3 times as long as merus; propodus 2.8–4.5 times as long as carpus; dactylus 0.7–0.8 times as long as propodus. Pereopod 7 basis 2.4–2.7 times as long as greatest width; ischium 0.8 times as long as basis; merus 0.5–0.6 times as long as ischium, with 1–2 robust setae on superior distal angle, 0–1 robust seta on inferior margin; carpus 0.9–1.2 times as long as merus, with 0–3 robust setae on inferior margin; propodus 1.5–1.8 times as long as carpus, with 2–7 robust setae on inferior margin; dactylus 0.7–0.8 times as long as propodus.

A

Pleopods all lamellar with smooth surfaces. Pleopod 1 peduncle 0.6–1.0 times as wide as long, medial margin with 4–5 coupling hooks and 3–5 plumose setae; endopod rectangular, 1.6–1.9 times as long as wide; exopod elliptical, 1.7–2.2 times as long as wide, 0.9–1.1 times as long as endopod. Pleopod 2 peduncle 0.5–0.6 times as wide as long, medial margin with 4 coupling hooks and 0–5 plumose setae; endopod rectangular, 1.8–2.2 times as long as wide, with appendix masculina, without swimming seta; exopod elliptical, 1.7–1.9 times as long as endopod, 1.0–1.2 times as long as wide, lateral margin with or without swimming seta.

Uropodal peduncle triangular, 1.9–2.4 times as long as wide, 0.7–1.0 times as long as exopod, with distal corner with 2–26 setae; endopod rami 0.7–0.9 times as long as that of exopod; extending beyond posterior margin of pleotelson; endopod oval, 2.1–2.6 times as long as greatest width, with apical and distal half or less of medial and lateral margins with swimming setae; exopod triangular, 2.9–4.0 times as long as greatest width, with apical margins bearing swimming setae.

Description of male ( Figs. 3 View Fig AB, 7AB, 9AB, 11AB, 13AB, 15AB, 17AB, 19AB): Body narrow, 3.5–4.4 times as long as greatest width, widest at pereonite 5, with smooth dorsal surfaces.

Cephalon 1.6–2.1 times wider than long, semi-oval, with well-developed rostrum, not immersed in pereonite 1. Eyes oval, with distinct margins, with long axis of each eye 0.8–0.9 times length of cephalon, and short axis 0.2 times maximum width of cephalon. Anterior border of pereonite 1 straight. Coxae almost invisible in dorsal view, of pereonites 2–4 roundly, of pereonites 5–7 concave; pereon longest at pereonite 4 or pereonite 5, shortest at pereonite 2; posterior margins of pereonites 1–5 smooth and slightly curved laterally, that of pereonite 6 and 7 slightly recessed. Pleonites 1–5 0.1–0.2 times as long as total length, 0.7 times as wide as greatest body width, with all pleonites visible in dorsal view. Pleotelson 1.4–1.5 times as long as wide, 1.7–1.9 times as long as pleonites 1–5, with no seta.

Antennula 8 articles, extending beyond mid-length of cephalon, article 3 enlargement. Antenna 10 articles, extending beyond anterior border of pereonite 1.

Pereopod 1 basis 1.7–1.8 times as long as greatest width; ischium 0.5–0.7 times as long as basis; merus 0.5 times as long as ischium, with 1 robust seta on superior distal angle; carpus 0.7–0.8 times as long as merus; propodus 2.4–4.0 times as long as carpus; dactylus 0.8–1.0 times as long as propodus. Pereopod 7 basis 3.1–3.5 times as long as greatest width; ischium 0.7–0.8 times as long as basis; merus 0.5 times as long as ischium, with 1 robust seta on superior distal angle, no robust seta on inferior margin; carpus 1.1 times as long as merus, with 1–2 robust setae on inferior margin; propodus 1.7–1.8 times as long as carpus, with 3–5 robust setae on inferior margin; dactylus 0.8 times as long as propodus.

Pleopods all lamellar with smooth surfaces. Pleopod 1 peduncle 0.6–0.7 times as wide as long, medial margin with 4 coupling hooks and 0–3 plumose setae; endopod elliptical, 1.6–1.8 times as long as wide; exopod elliptical, 1.8–1.9 times as long as wide, 1.1 times as long as endopod. Pleopod 2 peduncle 0.4–0.5 times as wide as long, medial margin with no coupling hook and no plumose seta; endopod rectangular, 1.9– 2.0 times as long as wide, with appendix masculina, without swimming seta; exopod elliptical, 1.7 times as long as endopod, 1.1–1.2 times as long as wide, without swimming seta.

Uropodal peduncle triangular, 1.9–2.1 times as long as wide, 0.7 times as long as exopod, with distal corner with 9–11 setae; endopod rami 0.9–1.0 times as long as that of exopod; extending beyond posterior margin of pleotelson; endopod oval, 2.6–2.7 times as long as greatest width, without swimming seta; exopod triangular, 3.7–3.9 times as long as greatest width, without swimming seta.

Description of transitional ( Figs. 3C View Fig , 7C View Fig , 9C View Fig , 11C View Fig , 13C View Fig , 15C View Fig , 17C View Fig , 19C View Fig ): Body narrow, 3.7 times as long as greatest width, widest at pereonite 5, with smooth dorsal surfaces.

Cephalon 2.0 times wider than long, semi-oval, with well-developed rostrum, not immersed in pereonite 1. Eyes oval, with distinct margins, with long axis of each eye 0.8 times length of cephalon, and short axis 0.2 times maximum width of cephalon. Anterior border of pereonite 1 straight. Coxae almost invisible in dorsal view, of pereonites 2–4 roundly, of pereonite 5–7 concave; pereon longest at pereonite 5, shortest at pereonite 2; posterior margins of pereonites 1–5 smooth and slightly curved laterally, that of pereonite 6 and 7 slightly recessed. Pleonites 1–5 0.18 times as long as total length, 0.7 times as wide as greatest body width, with all pleonites visible in dorsal view. Pleotelson 1.4 times as long as wide, 1.2 times as long as pleonites 1–5, with no seta.

Antennula 8 articles, extending beyond mid-length of cephalon, article 3 enlargement. Antenna 10 articles, extending beyond anterior border of pereonite 1.

Pereopod 1 basis 1.8 times as long as greatest width; ischium 0.7 times as long as basis; merus 0.3 times as long as ischium, with 1 robust seta on superior distal angle; carpus 0.9 times as long as merus; propodus 3.3 times as long as carpus; dactylus 0.8 times as long as propodus. Pereopod 7 basis 3.3 times as long as greatest width; ischium 0.7 times as long as basis; merus 0.4 times as long as ischium, with 1 robust seta on superior distal angle, no robust seta on inferior margin; carpus 1.2 times as long as merus, with no robust seta on inferior margin; propodus 1.7 times as long as carpus, with 3 robust setae on inferior margin; dactylus 0.7 times as long as propodus.

Pleopods all lamellar with smooth surfaces. Pleopod 1 peduncle 0.4 times as wide as long, medial margin with no coupling hook and no plumose seta; endopod elliptical, 1.8 times as long as wide; exopod elliptical, 1.8 times as long as wide, as long as endopod. Pleopod 2 peduncle 0.4 times as wide as long, medial margin with no coupling hook and no plumose seta; endopod rectangular, 2 times as long as wide, without appendix masculina, without swimming seta; exopod elliptical, 1.8 times as long as endopod, as long as wide, without swimming seta.

Uropodal peduncle triangular, 1.9 times as long as wide, 0.7 times as long as exopod, with distal corner with 3 setae; endopod rami 0.9 times as long as that of exopod; extending beyond posterior margin of pleotelson; endopod oval, 2.8 times as long as greatest width, without swimming seta; exopod triangular, 4.2 times as long as greatest width, without swimming seta.

Description of ovigerous female ( Figs. 3 View Fig DE, 7DE, 9DE, 11DE, 13DE, 15DE, 17DE, 19DE): Body elliptical, 2.8–2.9 times as long as greatest width, widest at pereonite 6, with smooth dorsal surfaces.

Cephalon 1.3–1.4 times wider than long, semi-oval, with wide rostrum, not immersed in pereonite 1. Eyes oval, with distinct margins, with long axis of each eye 0.5 times length of cephalon, and short axis 0.2–0.3 times maximum width of cephalon. Anterior border of pereonite 1 medially protrudes forward. Coxae almost invisible in dorsal view, of pereonites 2–4 roundly, of pereonites 5–7 concave; pereon longest at pereonite 5 or pereonite 6, shortest at pereonite 2; posterior margins of pereonites 1–5 smooth and slightly curved laterally, that of pereonites 6 and 7 slightly recessed. Pleonites 1–5 0.2 times as long as total length, 0.6–0.7 times as wide as greatest body width, with all pleonites visible in dorsal view. Pleotelson 1.0–1.1 times as long as wide, 1.4 times as long as pleonites 1–5, with no seta.

Antennula 8 articles, extending beyond mid-length of cephalon, article 3 enlargement. Antenna 10 articles, extending beyond anterior border of pereonite 1.

Pereopod 1 basis 1.7–2.0 times as long as greatest width; ischium 0.5–0.6 times as long as basis; merus 0.3 times as long as ischium, with 1 robust seta on superior distal angle; carpus 0.9–1.2 times as long as merus; propodus 2.5–2.9 times as long as carpus; dactylus 1.0–1.1 times as long as propodus. Pereopod 7 basis 3.0–3.3 times as long as greatest width; ischium 0.8 times as long as basis; merus 0.4–0.5 times as long as ischium, without robust seta; carpus 1.0–1.1 times as long as merus, with 2–4 robust setae on inferior margin; propodus 1.7–1.8 times as long as carpus, with 3–4 robust setae on inferior margin; dactylus 0.8 times as long as propodus.

Pleopods all lamellar with smooth surfaces. Pleopod 1 peduncle 0.4–0.5 times as wide as long, medial margin with 0–3 coupling hooks and no plumose seta; endopod elliptical, 1.7 times as long as wide; exopod elliptical, 1.7–1.8 times as long as wide, as long as endopod. Pleopod 2 peduncle 0.4–0.5 times as wide as long, medial margin with no coupling hook and no plumose seta; endopod elliptical, 1.8 times as long as wide, without appendix masculina, without swimming seta; exopod elliptical, 1.7–1.8 times as long as endopod, as long as wide, without swimming seta.

Uropodal peduncle triangular, 1.7–2.0 times as long as wide, 0.6 times as long as exopod, with distal corner with 0–1 seta; endopod rami 1.0–1.1 times as long as that of exopod; extending beyond posterior margin of pleotelson; endopod oval, 3.0–3.2 times as long as greatest width, without swimming seta; exopod oval, 3.4–3.6 times as long as greatest width, without swimming seta.

Manca : Unknown.

Coloration: The color changed from pearl yellow to dark brown as the individual grew (in preserved ethanol).

Hosts: Anilocra prionuri had the highest record from P. scalprum ( Hata et al. 2017, Nagasawa and Fujimoto 2018). Anilocra prionuri was also recorded from the large-scale blackfish Girella punctata Gray, 1835 , and threadsail filefish Stephanolepis cirrhifer (Temminck and Schlegel, 1850) ( Williams and Bunkley-Williams 1986) .

Distribution: Anilocra prionuri has been reported on the Pacific Ocean and East China Sea coasts of southern Japan ( Williams and Bunkley-Williams 1986; Hata et al. 2017; Nagasawa and Fujimoto 2018). See Nagasawa and Fujimoto (2018).

DNA sequences accession numbers: SMBL-V 0772 ( COI: LC860812 View Materials ), SMBL-V 0778 ( COI: LC860813 View Materials , 16S rRNA: LC860815 View Materials ), SMBL-V 0780 (16S rRNA: LC860816 View Materials ), SMBL-V 0781 ( COI: LC860811 View Materials , 16S rRNA: LC860814 View Materials ).

Remarks: Females of A. prionuri are distinguished from the other two species recorded in Japan by having swelling-free pereopod 1–4 dactyls and a uropod slightly extending the posterior margin of the pleotelson. Of the three Anilocra species found in Japan, aegathoid stages have been described only for A. clupei ( Table 1). In the aegathoid stage of A. clupei and the smaller aegathoid stage of A. prionuri , antennular characteristics were underdeveloped. The swelling of dactyls in A. clupei is also underdeveloped in the aegathoid stage; therefore, these characteristics cannot be used for species identification of the aegathoid stages. The aegathoid stage of A. prionuri is distinguished from that of A. clupei by 1) 3–5 and 0–5 plumose setae of pleopod 1 and 2 (5 and 8 plumose setae in A. clupei ), 2) uropodal exopod longer than endopod (same length in A. clupei ), and 3) triangular uropodal exopod (oval in A. clupei ).

With growth, the morphology of A. prionuri changed: 1) body shape becomes rounder, 2) eye length becomes shorter, 3) shortest pereonite changes from 7 to 2, 4) antennula article 3 enlarged, 5) length of dactylus relative to propodus in pereopod 1 becomes longer, 6) pleopod peduncle becomes shorter, 7) decrease robust setae of pereopods, coupling hooks and plumose setae of pleopods, swimming setae of pleotelson, pleopod, and uropod, 8) appendix masculina on the pleopod 2 endopod shortens and disappears, 9) rami of pleopods and uropods become rounded, and 10) endopods of uropods become elongated.

The aegathoid stage was distinguished from the male by 1) pereon shortest at pereonite 7 (pereonite 2 in male), 2) longer pleotelson, 3) antennula article 3 enlargement or no enlargement (enlargement in male), 4) Pleopod 1 endopod rectangular (elliptical in male), 5) pleopod 2 peduncle with 4 coupling hooks (no coupling hook in male), 6) posterior margins of pleotelson, pleopods, and uropods having swimming setae. The male is distinguished from the traditional by 1) pleopod 1 peduncle with coupling hooks (no coupling hook in traditional), 2) pleopod 2 endopod with appendix masculina (without it in traditional), 3) uropodal peduncle distal corner with 9–11 setae (3 setae in traditional). The traditional is distinguished from the female by 1) body narrow (elliptical in the female), 2) widest at pereonite 5 (pereonite 6 in the female), 3) cephalon having narrower rostrum (wide rostrum in the female), 4) bigger eyes, 5) anterior border of pereonite 1 straight (medially protrudes forward in the female), 6) pereopod 7 merus with a robust seta on superior distal angle (without it in the female), 7) pleopod 2 endopod rectangular (elliptical in the female), 8) uropodal peduncle distal corner 3 setae (0–1 seta in the female), 9) uropodal exopod triangular (oval in the female).