No. 2] Proc. Japan Acad., 58, Ser. B (1982) 29

8. A New Bivalved Gastropod, Julia mishimaensis n. sp.

By Siro KAWAGUTI*) and Teruf umi YAMAsU * * )

(Communicated by Kiyoshi TAKEWAxl, M. J. A., Feb. 12, 1982)

Among several hundred beach shells of Julia japonica which were collected at Mishima, Hagi-shi, from 1960 to 1962, we found about twenty shells showing quite different characteristics from those of the others. These shells bore green or brownish-green stripes radiat- ing from the umbo to the ventral margin. They were distinctly smaller and thinner than the other shells. At the end of August 1965 we found three living shellfish of this type in Tsunoshima, together with many Julia japonica.5> By the end of 1969 we collected ten more living specimens of the new type from the same place. Some of them were cultured in the laboratory. Un- fortunately, however, our study was suspended for a long while. In the spring of 1980 the senior author collected about twenty living shells of this type (Fig. 1) at Ishigaki Island, and resumed the study of the shells on both the new and the previous materials. These materials could be divided into two groups. One group have valves bearing green bands, and the other brownish green valves with radiat- ing brown lines in their anterior portions. This paper deals with the first group. Classification : Order: Suborder: Tamanovalvida Kawaguti & Baba 19596) Family: Tamanovalvidae Kawaguti & Baba 19594) Genus : Julia Gould 18623) (=Prasina Deshayes 18632) ) Species: Julia mishima,ensis n, sp. Description : Shell small and thin, about 3 mm, 2 mm and 1.5 mm in length, height and breadth, respectively (Fig. 2) and about 5.0 mg in weight in a full-grown adult.***) Oval in shape, anterior margin rounded and posterior margin deeply excavated at the umbo, posterior peripheral margin strongly pointed ; dorsal margin acutely convex and ventral margin slightly convex or nearly even. Protoconch measures about 150 p with about 12 whorls on the left . *' Kawasaki Paramedical School , Matsushima, Kurashiki-shi. **' General Education Division , University of the Ryukyus, Nakagusuku, Okinawa. * * *' There appears to be some local variations in dimensions and textures in the valves. Samples from Ishigaki Island are smaller and thinner than those from Tsunoshima. 30 S. KAWAGUTI and T. YAMASU [Vol. 58(B),

Shell has a heavy hinge at posterior excavation with cardinal tooth at the top of hinge column on the right valve ; cardinal f ossa surrounded by hinge column and para-tooth on the left valve (Fig. 3) ; thin but long ligament along the antero-dorsal margin : translucent or almost transparent especially in water, with about 12 radiating brilliant green bands*) of varying breadths from umbo to peripheral margin over the whole shell surface, between green bands, small non- translucent white dots distributed in a line. The shell surface glitters especially on the interior. In old dry shells the umbonal area is frequently frosted.

Figs. 1-4. Julia mishimaensis n. sp. 1: Living state. 2: Outer side view of the left valve showing 12 green radiating bands, x16. 3: Inside view of the left valve showing the hinge column and the para-tooth, X 16. 4: Complete series of radular teeth, x170. Dark green or brownish green pigmentations appear at the proximal portion and peripheral corner of hinge columns of both valves. These pigmentations, however, are frequently subject to local and individual variations.**) Moreover, they fade in time in weathered *' The number of green hands is variable because some bands show dicho- tomous branching with a non-pigmented line of various breadth and length be- tween. There are also local and individual variations in the number and form of green bands. **' Specimens from Tsunoshima is usually faint purple in color on peri- pheral margins. In laboratory conditions the color of the green stripes is greatly reduced, resulting in pale green in the newly grown area. No. 2] New Bivalved Gastropod 31

beach shells. Even in specimens preserved direct from living in the laboratory they became almost bleached after 16 years. This fact may have given rise to confusion in the description of some previous species. The general features of the soft part of J. mishimaensis closely resemble those of J. japonica5~ except for their dimensions and color- ations as is shown in Fig. 1. The body may extend almost as long as the shell length but is very thin especially in its elongated state. It is rather dull green as a whole, and is ornamented with white and brown patches or bands. As mentioned above, shells are almost trans- parent in water and the body colors inside the shell are seen through the shell. Bright and dull green bands radiating from the umbo to the ven- tral margin are seen in the living shell. The most conspicuous mark- ing is seen in the top or umbonal area; a milky white gourd-shaped form fringed with a chocolate brown band. The radulal row and radulae show different features from those of Julia japonica and J. burni.9> The number of radulae is 21 in a full grown adult, 7 ascending and 14 descending (Fig. 4). Radulae are small but wide, and faintly denticulated on both sides of the blade with a small notch at the tip. Locality: Beach shells of this were first found in Mi- shima, Hagi-Shi. The living specimens were collected in Tsunoshima, Yamaguchi-Ken from 1965 to 1969 and at Ishigaki Island, Okinawa- Ken in 1980 and 1981. Julia mishimaensis differs markedly from some recent species of Julia, such as J. japonica Kuroda and Habe,7> J. borbortica (Deshayes),2> J. cornuta (de Folin & Perier),1~ J. exquisita Gould,3> and J. burni Sarma.9~ It may come close to J. equatorialis Pilsbury and Olsson.8~ But, it differs distinctly from J. equatorialis in its shell size, form and coloration. Detailed comparisons with these species will be given elsewhere.

References

1) De Folin, L., and Perier, L. (1868) : Les Fonds de la Mer, 1, 83-84. 2) Deshayes, M. G. P. (1863) : Catalogue des Mollusques de l'Ille de la Reunion (Bourbon), p.29. 3) Gould, A. A. (1862) : Otia conchologica, p. 241. 4) Kawaguti, S., and Baba, K. (1959) : Biol. Jour. Okayama Univ., 5, 177-184. 5) Kawaguti, S., and Yamasu, T. (1962) : Pron. Japan Acad., 38, 284-287. 6) Keen, A. M., and Smith, A. G. (1961) : Proc. Calif. Acad. Sci., 30, 47-66. 7) Kuroda, T., and Habe., T. (1951) : Illust. Catal. Japanese Shells, 1, 13. 8) Pilsbury, H. A., and Olsson, A. A. (1944) : Nautilus, 57, 86-87. 9) Sarma, A. L. N. (1975) : Jap. Jour. Malac., 34, 11-25.