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Prosobranchia:Neogastropoda The malacologicalsocietymalacological society ofJapanof Japan Nrc Jap. Jour. Malac. (VENUS) Vol. 36, No. 2 (1977):81 88 -v -( tT * v- l/ rf F v Jif -r tre -)b Mtwa ngE (ru･[･1rt*mp\sustuRe?tfag) Notes on Genkaimurex varicosa (KURODA, 1953) (Prosobranchia:Neogastropoda) Akihiko MATsuKuMA (Department of Geology, Faeulty of Science, Kyushu University) Ten living specirnens of Genka-imurea: varicoso (KuRoDA) weTe eollected from a sand bottom in 94m of water in the Sea of Japan, off Yamaguchi Prefecture. They were found attaehed to the left valve of Pecten (Notovola> albica"s (ScHR6TER) in which they had drilled holes. G. vam"cosa sometimes impre･sses a faint attachment scar upon the scal]op shells and apparently does not damage the soft paTts of the scallops. This species may suek juiees from the scallops. The boreholes made by G. varicosa are often repaired interiorly by the hosts. Some of the living speeimens have been kept in a tank during November, 1976 May, to 1977, to observe their feeding behavior. G. varicosa･ has a raehi- glossate radula and is a hole-boring inactive predator, namely, parasite or commensal on molluscs, preferably on P. (N.) albdeans. I advocate varieosa should that G. be plaeed in the Murieidae, although it shows some' features similar to the Coralliophilidae, in whieh the original authoT placed this speeies. Introduetion Genhaimurex va･rioosa was originally described by KuRoDA (1953) on the basis of the specimens from the Genkai off Sea, Fukueka, west Japan. The original material was collected by the dredging nets of scallop-fishing boats from sand bottoms of about 45m depth. In general features this species closely resembles some species belonging to the Ocenebrinae of the Muricidae, but G. varz'cesQ, according to KuRoDA C1953), lacks a radula and its shell is ornamented with spiral eords which are made up uf microscopie seales. Henee KuRoDA (1953) plaeed this speeies in the Rapidae (=Coralliophilidae). Several examples of this un ¢ ommon species were eolleeted by one dredge during haul a marine survey carried out by Tsugio SHuTo and others on board the Researeh Vessel Tanseh-MaTu of the Ocean Researeh Institute, University ef NII-Electronic Library Service The malacologicalsocietymalacological society of Japan 82 VENUS: VoL 36, No.2(1977) Tokyo, in the southwest extremity of the Sea of Japan in November 20-27, 1976. Some specimens were kept in a tank during November 24, 1976 to May 19, 1977, to observe their feeding behavior. This study deals with the feeding behavior and systematic position of G. vaTicosa. Radular morphology of this species is originally deseribed herein. Acknotvledgements-I wish to express my gratitude to Drs. Tsugio SHuTo, Yasuhiko KAMADA, Koichiro MAsuDA, Shozo HAyAsAKA, Kazuo OKAMoTg, Hiroshi NoDA, and Kenshiro OGAsAwARA, for their fruitful co-operation in the field work and for helpful criticism of the manuscript. Appreeiation is extended to Drs, Melbourne R. CARRIKER, Emily H. VoKEs and Norman F. SoHL for their eritical reading and helpful eomments. I am grateful to Mr. Katsuyeshi SATo fQr his many suggestions and diseussion on the subject. Material fTom bottoms of Then living specimen (GK-M 10007-16) were collected sand about 94 m depth by one haul of a dredge operated around St. II-4, off Yuya Bay, Yamaguchi Phefeeture Clat. 34e28.5'N; long. 130"50.4'E). Geetkai?n･zarex va･ricosa (GK-M 10007-9 and 10011-16) were found attached to living speeimens of Pecten (Notovola) atbicans (ScHR6TER), GK-M 10017-18. 0xyperas bernaTdi (PILsBRy), Polinices vestitus KuRoDA, and several speeimens of starfishes were also collected by the same net. These eollections of G. va･ricosth and P. (N.) albicans are deposited in the Department of Geology, Kyushu University. Observations The specimens of G. varicoso in hand are rather young and characterized by ovately pyriform, sma.11, and yellowish brown shell with a moderately long canal, large body whorl and rather small spire. The pretoconch is smooth, paucigyrate consisting of about one and three-quarter volutions. The teleoeonch eonsists of about four and a quarter rapid]y inereasing whorls, of which the earliest one is coarsely caneellated. The suture is deep. The whorls are ornamented with massive, spiral eords which are made up of crowded axial folds and variously sized dense number about or eleven on body whorl. microscopic scales. The axial folds ten the a tint of within. The inner lip is The aperture is evate and white with purple enamel-white. The outer lip is weakly and finely denticulate inside. The anterior eanal is not closed in young specimens and curves slightly to the right and away from the aperture. The smallest speeimen, GK-M 10013, has a thin yellowish brown periostracum with sparse hair. The epereulum, with a nucleus on the lateral margin, is chitinous and yellowish brown in color. Measurements.- specimen height(mm) width(mm) GK-M NII-Electronic Library Service The malacologicalsocietymalacological society of Japan MATsuKuMA : Notes on Genkaiwturex varicosa 83 1000710008100091001010011100121001310014100151001624.6 14.6 7.117.820.4 3.910.913.0 6.6 3.3 8.7 4.8 3.2 2.0 5.7 3.0 9.4 4.9 8.3 4.7 Radula The radula of G. vaTicosa is rachiglossate in form with three teeth in each row. The radula of a specimen (GK-M 10009) is about 3.5mm in length and the number of tooth-rows is about 220. Width of the rachidian tooth is 24"m in cc LT c A RT A - I B- c cc tc B H mc Text-fig. 1 Text-fig. 2 Text-fig. 1. Some morphological features of Genkaimurex varicosa (KuRoDA), GK-M leo7. A : Operculum with a nucleus on the lateral margin. B : Protoconch and cancellated earlier whorls. C : Spiral cords with dense microscopic scales. Unite bars indicate respectively 2mm for A, 1mm for B and O, 85 rnm for C. Text-fig. 2. Radular teeth of Genfeaimurex varicosa (KuRoDA), GK-M 10009. A :Dorsal view of rachidian (RT) and lateral tooth (LT). B : Left lateral view of rachidian teeth, cc, central cusp; lc, lateral cusp; mc, marginal cusp. bar and Unite indicates20 Am for A B. NII-Electronic LibraryMbrary Service The malacologicalsocietymalacological society of Japan 84 VENUS: Vol. 36, No.2<1977) GK-M 10008 and 54"m in GK-M 10009. The rachidian has 5 cusps of which the central one is long, curved posteriorly, sharply pointed and situated at the midd]e. Eaeh lateral cusp is moderately long and sharply pointed. A small denticle protrudes from the base of the lateral cusp between the central cusp and the lateral one. Each marginal eusp is rather short, Two weak denticles/ protrude from the basal plate between the marginal cusp and the lateral one. The sickle- shaped laterals with the broad base are long, narrow, eurved inwards and sharply pointed, and are devoid of any cusp and denticle. Behayior The speeimens of G. var"icosa in hand were found attached to the left valve of P. (N.) albicthn6. Drilled holes and faint attachment scars made by these snails were observed. G. varicosa also drilled holes while maintained in the laboratory. The borehole is a nearly circular with a steep cylindrical wall and a completely bevelled outer edge. The outer diameter of boreholes varies from O.25 to 1.19 mm. Bottoms of ineomplete boreholes are eoneave, In general features boreholes made by G. varicosa closely resemble those drilled by small-sized murieids, e.g. Bedevina biriteX7i (LIscHKE), The boreholes are often repaired interiorly by host scal]ops and G. varicosa apparently does not damage the mant]e and other soft parts of the host. An interiorly repaired borehole attributed to muricid predation has been reported from the Gosport FormatiQn (Middle Eocene) of North America (SILER, 1965). The faint and nearly eircular attachment scar is made of calcareous material which is secreted by G. varic'osa. Some attachment scars･ of G. varicosa are shallowly hollowed. Some capu]id speeies, sueh as Caputus dilata･tus ADAMs, Copueus spendiyeieola HABE, and Capullus da･nieli (CRossE), have been known to impress somewhat faint or definite scars upon their host bivalve shells. These eapulid impressions are a hollowed-out sear without･ any ealcareous deposits. A non-sculptured eapulid species, Hyalorisia tosae7tsis OTuKA, leaves an attach- ment scar which is made of caleareous deposits, but this species is always a eommensal on Lute(zmzessium sibogai (DAUTZENBERG & BAvAy) and notches the edge of the shell just below the anterior auriele of the host. Preferred orientation of boreholes is characteristic of some boring snails (natieid: ANsELL, 1960; MATsuKuMA, 1976; muricid: KINosHITA & NAKAGAwA, 1934; MATsuKuMA, in preparation; capulid: ORR, 1962; KOsuGE & HAyASHI, 1967; MATSuKuMA, in preparation). The position of boreholes made by G. varicosa in shells of P. (N.) albictzns is not limited to any preferred region of the shell surface, During November, 1976, to May, 1977, G. v'aricosa in a tank drilled holes in the shells of Ruditapes phizapmnarum (ADAMs & REEvE), Caeceelca chinensis DEsHAyEs, Siphonalia sp., and G. varicosua. The bored bivalves died a few days after the dril]ing, but bered Siphonalia and Genkai･murex continued to live more than six months. During this period the borer was observed once to leave the host NII-Electronic Library Service The malacologicalsocietymalacological society of Japan MATsuKuMA : Notes on Genhaimttrex varicosa 85 and sit en a shell fragment on the bottom or wall of the tank. After several days of resting the borer again climbed on the host shell to the borehole which it had drilled. These observations and the partially or eornpletely repaired boreholes with attachment sears in the shells of P. (N.) albicans verify that G.
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