Orientomysis rotundicauda ( Liu and Wang, 1980 ) Fukuoka & Murano, 2005

Fukuoka, Kouki & Murano, Masaaki, 2005, A revision of East Asian Acanthomysis (Crustacea: Mysida: Mysidae) and redefinition of Orientomysis, with description of a new species, Journal of Natural History 39 (9), pp. 657-708 : 685-687

Orientomysis rotundicauda ( Liu and Wang, 1980) comb. nov.

( Figure 7 )

Acanthomysis rotundicauda Liu and Wang 1980: 326–327 , Figure 4 (1–7); 1986: 195; Müller 1993: 197 (list); Liu and Wang 2000: 249–250, Figure 93. Acanthomysis longicauda Murano 1991: 86–89 , Figures 3 , 4 (type locality: Tateyama Bay, Chiba, Japan); Müller 1993: 194 (list).

Type locality

18 ° 309N, 108 ° 309E, Gulf of Tongking, southern China.

Material examined

One male (damaged) and one female (4.9 mm), 19 ° 009N, 111 ° 309E, off eastern Hainan, the South China Sea, 23 m, sand bottom, 18 May 1960, on loan from Liu and Wang. Forty-seven males (6.1–7.9 mm) and 114 females (6.2–9.0 mm), Tateyama Bay , Chiba, central Japan, 1–2 m, 19 June 1978, NSMT-Cr 11079. Thirty-one males (5.0–8.0 mm), 10 immature males (3.6–5.0 mm), 11 females (5.2–6.4 mm), 31 immature females (3.5–5.7 mm) and 56 juveniles (2.5–3.7 mm), Kyoto, central Japan, 6–8 m, sledge net, 2 November 1983, NSMT-Cr 11081. Sixty-nine males (4.9–7.0 mm), 76 immature males (3.7–4.3 mm), 47 females (5.8–6.5 mm), 103 immature females (3.4–5.3 mm) and 70 juveniles (2.3–3.2 mm), Yura , Kyoto, central Japan, sledge net, 13 July 1988, NSMT-Cr 15590. One male (6.9 mm) and one female (damaged), between Jusan-ko and Ajigasawa, Japan Sea side of Aomori, northern Japan, 5–10 m, date unknown, NSMT-Cr 11080 .

Remarks

When Acanthomysis longicauda was established, Murano (1991) mentioned three points distinguishing this species from a similar species, O. rotundicauda : the length of the rostrum, the size of the eye, and the length-breadth ratio of the telson. The rostrum of the present specimens collected from the South China Sea extends to the proximal fourth to middle of the first segment of the antennular peduncle, as seen in the original description by Liu and Wang (1980) ( Figure 7A ). On the other hand, in the majority of Japanese specimens the rostrum does not overreach the base of the antennular peduncle as described by Murano (1991) ( Figure 7G ), but in some individuals it extends to the proximal fourth of the first antennular peduncle segment ( Figure 7J ). As to the eyes, Murano (1991) noted that those of A. longicauda were large and far extending laterally beyond the lateral margin of the carapace, whereas those of O. rotundicauda were rather small and barely extending beyond the lateral margin of the carapace. In the present specimens from the South China Sea, the eyes were observed to be an intermediate form between the two species ( Figure 7A ). The telson also is not distinctly different; 2.3 times as long as broad in the female from the South China Sea ( Figure 7F ), whereas 2.3–2.6 times as long as broad in those from Japanese waters ( Figure 7I ).

Other differences between O. rotundicauda and A. longicauda are also observed in the original descriptions and illustrations. The plumose seta at the inner distal angle of the proximal exopodal segment of the fourth male pleopod is slightly longer than the distal segment in O. rotundicauda ( Liu and Wang 1980, Figure 4 (4)), whereas it is twice as long as the distal segment in A. longicauda ( Murano 1991, Figure 3I, J ). In the present specimen from the South China Sea, however, it is nearly twice as long as the distal segment ( Figure 7E ). The larger apical spines of the telson are subequal in size to the larger spines on the lateral margin in O. rotundicauda ( Liu and Wang 1980, Figure 4 (6)), while these are shorter than the larger spines on the lateral margin in A. longicauda ( Murano 1991, Figure 4A–D ) and the present specimens from the South China Sea ( Figure 7F ).

Differences between these two species are small and considered to fall within the range of intraspecific variation. Consequently, A. longicauda is declared to be a junior synonym of O. rotundicauda .

Distribution

China: the South China Sea off Hainan and Guangdong ( Liu and Wang 1980) . Japan: Tateyama Bay , Chiba; between Jusan-ko and Ajigasawa , Japan Sea side of Aomori; Kyoto ( Murano 1991).

This species was collected from depths of 6–31 m in the South China Sea ( Liu and Wang 1980) and from depths of 1–10 m in Japanese waters ( Murano 1991).

Figures

Figure 3. Orientomysis japonica Marukawa, 1928. (A) First to sixth abdominal somites, lateral; (B–E) telson, dorsal. (A) Male (11.0 mm), Tateyama Bay, Pacific, NSMT-Cr 15562; (B) male (11.0 mm), Tateyama Bay, NSMT-Cr 15562; (C) male (14.2 mm), Uchiura Bay, Pacific, NSMT-Cr 15560; (D) female (17.0 mm), Kashima, Pacific, NSMT-Cr 15570; (E) male (10.6 mm), Japan Sea side of Aomori, NSMT-Cr 15571.

Figure 4. Orientomysis japonica Marukawa, 1928. Distal end of telson, dorsal. (A) Female (13.9 mm), Kashima, Pacific, NSMT-Cr 15569; (B) male (10.2 mm), Uchiura Bay, Pacific, NSMT-Cr 15560; (C) female (broken), Uchiura Bay, Pacific, NSMT-Cr 15560; (D) male (11.8 mm), type of Acanthomysis nakazatoi, Iwai, Pacific; (E) male (11.7 mm), type of A. nakazatoi, Iwai, Pacific; (F) female (10.2 mm), Tateyama Bay, Pacific, NSMT-Cr 15562; (G) female (11.5 mm), Japan Sea side of Aomori, NSMT-Cr 15571; (H) female (11.4 mm), Japan Sea side of Aomori, NSMT-Cr 15571; (I) female (13.0 mm), Tottori, Japan Sea, NSMT-Cr 15572; (J) female (15.8 mm), Tottori, Japan Sea, NSMT-Cr 15572.

Figure 7. Orientomysis rotundicauda (Liu and Wang, 1980) comb. nov. (A, B, F) Female (4.9 mm), South China Sea; (C–E) male (damaged), South China Sea; (G, H), male (7.3 mm), Tateyama Bay, Pacific, NSMT-Cr 15590; (J), male (6.9 mm), Japan Sea side of Aomori, NSMT-Cr 11080. (A, G, J) Anterior part of body, dorsal; (B) maxilla, posterior; (C) penis, lateral; (D) fourth pleopod, anterior; (E) distal part of fourth pleopod, anterior; (F) uropod and telson, dorsal; (H) distal part of fourth pleopod, posterior; (I) telson, dorsal.