Apseudes nipponicus, Shiino, 1937

Kakui, Keiichi & Hiruta, Chizue, 2023, Differential masculinization of the chelipeds in two simultaneously hermaphroditic Apseudes tanaidaceans (Crustacea: Malacostraca), Zoologischer Anzeiger 305, pp. 23-27 : 24

3.1. Apseudes nipponicus

All individuals we observed bore a genital cone (a male trait) on the ventral surface of pereonite 6 ( Fig. 1A ). Ranges in CW were 1.55–2.33 mm (ln CW, 0.44–0.84) for oostegite-lacking individuals, 2.16–3.39 mm (ln CW, 0.77–1.22) for preparatory individuals, and 2.61–3.12 mm (ln CW, 0.96–1.14) for ovigerous individuals ( Fig. 2A–D ). Paired ovaries and testes were evident in an ovigerous individual (CW, 2.94 mm;

Fig. 1B and C ).

The growth of CarW and CheW relative to CW was diphasic. The breakpoint for CarW–CW was ln CW = 0.790 (standard error, 0.045) ( Fig. 2A, C ), with the regressions ln CarW = 1.522 (ln CW) – 2.103 before the breakpoint and ln CarW = 2.246 (ln CW) – 2.675 after the breakpoint (R 2 = 0.979). The breakpoint for CheW–CW was ln CW = 0.824 (standard error, 0.046) ( Fig. 2B, D ), with the regressions ln CheW =1.290 (ln CW) – 1.825 before the breakpoint and ln CheW =2.301 (ln CW) – 2.658 after the breakpoint (R 2 = 0.945).

Individuals in the CW range 1.55–2.23 mm (ln CW, 0.44–0.80) lacked a dorsal process on the fixed finger, whereas those in the range 2.06–3.39 mm (ln CW, 0.72–1.22) had a process ( Fig. 2C, D, F, H ); the process varied in size and was generally smaller in smaller individuals. Individuals of CW 2.61–3.39 mm (ln CW, 0.96–1.22) had four ventral processes on the carpus ( Fig. 2C, D, E, G ); in smaller individuals, the ventral margin of the carpus was smooth or bore one small process.

Figures

Fig. 1. Reproductive organs of Apseudes nipponicus. SEM image showing a developing oostegite (a female trait) on the left pereopod-4 coxa and a genital cone (a male trait) on pereonite 6 of a preparatory individual in ventral view; the pereopods and an oostegite on the right pereopod-4 coxa were detached (A). Light micrographs of an HE-stained transverse section of the body showing ovary and testis; the box in B indicates the region enlarged in C (B, C). a, anterior; d, dorsal; gc, genital cone; hp, hepatopancreas; in, intestine; oo, developing oostegite; ov, ovary; p, posterior; p4–6, pereonites 4–6; te, testis; v, ventral.

Fig. 2. Masculinization of chelipeds in A. nipponicus and Apseudes sp. A–H, A. nipponicus; I–P, Apseudes sp. Relationships between chelipedal carpus width and carapace width after log-transformation (A, C, I, K). Relationships between chela width and carapace width after log-transformation (B, D, J, L). Lateral views of chelipedal carpi and chelae in small individuals (E, F, M, N) and large individuals (G, H, O, P). Arrowheads, processes. Abbreviations: Ap, individual without processes on fixed finger and chelipedal carpus; CarW, chelipedal carpus width; CheW, chela width; CW, carapace width; OL, individual lacking oostegite; Ovi, ovigerous individual; Ppf, individual with process on fixed finger; Ppfc, individual with fixed finger and chelipedal carpus bearing one and four processes, respectively; Pr, preparatory individual.