The malacologicalsocietymalacological society of Japan fima VENUS (Jap, Jour, Malac.) Vpl. 4S, No. 4 C19S9):25C-254 '2ljreeeOA - i a= vi detF'h"t FFO 1 ;efpt S.M, h'- F't- A New Vermetid from the West Coast of Mexico (Gastropoda: Vermetidae) Sandra M. GARDNER (Research Associate, Department of Biological Sciences, San Jose State University, San Jose, California 95192, U.S.A.) Abstract,: Dendropo?na kTypta n. sp. is described from Isla Isabela, off the west eoast of Mexieo. This vermetid is readily differentiated from other described eastern Pacific forms by a ealeified operculum and lack of sculptural pattern. It is related to an Indo-Pacific form, De?zdropo7na meroclista Hadfield & Kay, 1972, whieh also has a calcified operculum. Vermetids with a calcified operculum may more properly be aceorded separate subgeneric or generic status; this deeision awaits a review of the genus Dendropoma. Introduction Marine snails of the Family Vermetidae occur intertidally and subtidally in tropical alld temperate seas around the world. They are mesogastropods characterized by extremely variable coiling, permanent attachment to a sub- strate during adult life, and a tendency toward gregarious living. They are aMxed to varieus biotic and abiotic substrates and constitute primary and seeondary components of reef Toek The Panamic marine faunal provinee extends from the central part of the Pacific coast of Baja California, throughout the Gulf of California, to northern Peru. In the Panamic provinee, where the operculum of vermetid species is known, it is ehitinous. Vermetids which have a caleified operculum have been found on shells of the patellacean limpet Ancistromesus mexicanus (Broderip & Sewerby, 1829) from Isla Isabela, off the west coast of Mexico. The host limpets are in the eollection of the California Aeademy of Sciences in San 'trait Francisco (CAS). These vermetids Iack seulptural pattern, an unusual in the family. The distinetion ef a ealcified opereulum in conjunction with this eonchological character readily distinguishes the newly discovered form from other known Panamic province vermetids. NII-Electronic Library Service The malacologicalsocietymalacological society of Japan Gardner: New Verrnetid from w. Mexico 251 Systematics Family VERMETIDAE Rafinesque, 1815 Genus Dendropoma M6rch, 1861 Type species: Dendropoma Lituelta MOreh, 1861 (Lectotype selected by Keen, 1961), Frem Ca]ifornia to La Paz, Baja Califgrnia Sur, Dendeopama krgpta n. sp. (Figs. 1-4> Descriptio?z: Shell light honey brown er sometimes white with mottled brown exteriorly; light brown or darker brown within, Sculpture wanting er seen as occasional very weak incremental ribs; shell surface irregular (Fig. 1). Coiling habit regular, semetimes planorboid, or irregular, Terminal portion of tube nestled against final whorL Aperture diameter 1 mm when not constricted by overgrewing algae. When under algal erust, aperture often severely eon- stricted to tiny round or elliptical pinhole perforating the algal crust (Fig. 2). Shell sometimes deeply entrenching in substrate; sometimes merely cemented on top of substrate. Proteconeh glossy brown, two whorls. Operculum calcified, Figs. 1-4. Dendropoma krst,ta n. sp. 1. Holotype (CAS e65114); 2. Constricted apertures of D. kr)ipta perforating algal.crust; 3. Exterior surface of the operculum (CAS e65115); 4. Interior surface of the opercuulrn (CAS 065115). NII-Electronic Library Service The malacologicalsocietymalacological society of Japan 252 VENUS: VoL 48, No.4(1989) opaque white, eonvex exteriorly, thiekened at center with central mamilla on interior side (Figs. 3 and 4); mamilla varies from flat, thiekened area to distinct tiny plug. Opereulum at least as large in diameter as foot. Since aperture may be reduced to pinhole size, operculum may be larger than aperture. Foot diameter 1 mm. Type tocality: Isla Isabe]a, Nayarit, Mexico (21051'N, 105055'W). Type material: The holotype has been deposited in the California Academy ef Seiences, Department of Invertebrate Biology, Type Series 065114. The holotype is one specimen clearly marked on the host limpet. Paratypes: CAS 065116. 0percula of paratypes: CAS 065115. The type sample oecurs on two specimens of the large Mexican limpet Anci$tromesus mexicanus, which ranges from Mazatlan, Mexico to Paita, Peru (Keen, 1971). This sample comprises about 1000 individuals on one limpet and about 300 individuals on a second limpet; both limpets were collected during a CAS expeditien in 1925. The host limpet shells measure 150-170 mm long by 110-140 mm wide by 75-85 mm high. The vermetids are settled gregariously on the exterior surface of the limpet shell, their shells frequently abutting. The type sample is completely over- grown, except for the apertures, by the alga Lithophyllum lichenare Mason. The existence of the vermetids apparently went undetected because no part of the shell was visible. Their presenee is indicated only by minute black heles in the overlying algal crust. Careful removal of the crust was necessary to expose the vermetids. The relationship between the alga and the vermetid in this population is not clear. It appears that the vermetids keep just one step ahead of the alga in growth, managing to keep their apertures open flush with the crustose surface. As a result, the upper surface of the limpet appears to be covered by a crust perforated throughout by tiny holes. Distribution: Known at present only from the type material. It is possible that the new species will be found on other substrates in the intertidal zone of rocky, surf-beaten coasts in the tropical eastern Pacific. Etymology: The name comes from the Greek, meaning hidden, covered, concealed, in reference te this anirnal's appearance in the field. Discussion Dendropoma is distinguished from known Panamic krypta other province vermetid taxa on the basis of its calcified operculum and its lack of sculptural pattern. Dendropoma krypta may be eompared to the one other congener reeognized in this biogeographic prevince, D. tituelta. Dendropoma lituelta is a larger organism, attaining an apertural diameter of about 3mm, and it has a chitinous operculum. Its sculpture ranges from a highly ornate fiuted surface to one completely flattened by wave abrasion, NII-Electronic Library Service The malacologicalsocietymalacological society of Japan Gardner: New Vermetid {rorn w. Mexico 253 'te Dendropoma krypta is related, on the basis of its calcified operculum, the only other described vermetid which has a calcified operculum: D. meroclista Hadfield & Kay, 1972. The latter species occurs in the Hawaiian Islands and the Marshall Islands. It is also a small erganism, with a maximum apertural diameter of 1.5mm. The opereulum of D. meroctista has a fragile, thinned nucleus, often resulting in a eentral hole, in contrast to the solid opereulum of D. lerypta. Dendropomct meroclista coils its shell in a fairly regular pattern but D. krypta exhibits no consistent coiling pattern at any stage of growth. Whereas D. meroelista is eolored dark purple exteriorly and white or green interior!y, D. ler･ypta is brown or white with brown mottling exteriorly and always brown within. Dendropomct meroclista is seulptured wifh axial ribs and concentrie striae en expesed shell parts while D. kr･upta has a very irregular shell surface, lacking any sculptural pattern and enly occasionally bearing very weak incremental ribs. Hadfield et al. (1972) were not concerned with the ealcified operculum of D. meroclista but noted that D. meroclista is dendropomatid on the basis of its operculum and shell characters, and in its body organization, and found no cause to separate the species generically. Keen (1961) characterizes Dendropoma (s.s.) as a form with a ehitinous operculum and sculpture ranging from weak transverse lines to well developed longitudinal scales. Keen (1961) lists subgenera of Dendropoma: Novastoa Finlay, 1927 and Eltiptovermetus Cossrnan & Peyrot, 1922, Novastoa species, of which D. Iamellosum (Hutton, 1873) is the type speeies, are colonial, usually oceurring as sheet-like masses on rock, The teleoeonch is tightly coiled, the coils angular and grewing outward from the substrate. The opereulum is bright reddish brown and eorneus. Elliptovermetus, of whieh D. breigneti (Cossman & Peyrot, 1922) is the type species, is known only from the Oligocene ef France and occurs deeply embedded in coral. It is sculptured with lamellar striae and longitudinal ribs. The eperculum of this group is apparently unknown, Neither of these subgenera are, therefore, appropriate for species with a calcified operculum and lack of sculptural pattern. While Dendropoma krypta and D. meroclista might best be placed in a new taxon at the subgeneric or generic level based on the calcified opereulum, I have allocated D. lerypta to Dendropoma provisionally until the genus can be fully reviewed. Acknowledgements :-I thank Dr. Vida C. Kenk fer her eneouragement and her counsel, Dr, Miehael G. Hadfield for topotypical speeimens of Dendropoma meroclista, and Dr. James B. Jensen for identifying the alga associated with the type specimens of D. lerypta, Dr. Eugene V. Coan gave helpful comments on an earlier draft of the manuscript. San Jese State University kindly made facilities available during the cour$e of this work, NII-Electronic Library Service The malaoologioalmalacological societysooiety of Japan 254 VENUS ： Vo1 ．48， No ．4 （1989） 要 約 − DendroPoma leryPtan ．sp ．（Figs，1 4）。殻 は 時 に 平巻 きだ が，通常 不 規 則 。 胎 殻 は 褐 色 で 2 巻 き 。 殻 表 は 淡 褐 色 又 は 白 色 に 褐 斑 。殻 内 は 暗 褐 色 。彫 刻 は な くあ っ て も 微 弱 な 成 長 線 の み 。殻 口 径 1mm ス へ で ， 石 灰藻 に 包 ま れ た 時 に は 僅 か に リ ッ ト 状。蓋 は 石 灰 質 で 白色，外 凸 ，内 に 乳状 突 起 が あ る 。 コ ベ メ キ シ 西岸 の イ サ ラ 島 。 References Hadfield M G ． Kay A ， ． ， ， E ． ．， Gillette，M ．U ．，Lloyd，M ．C ． 1972． The Vermetidae − （Mollusea ： Gastropoda ） of the Hawaiian Islands． M α rine Biology，12 （1｝： 81 98． 1（een ， A ． M ．1961 ． A proposed reclassification of the gastropod family Vermetidae ． Bull ・B γ it・Mus ． ・Hist ・ 7 3 ： 181 −213 ． （Nat ），Zoolog！ノ， （ ） 1（een ， A ． M ．1971 ． Seα shelts o ／tropical west Americ α ． Stanford， California． Stanford Univ ． Press ．1064 pp ． Received ： July 20 1989 ［ ， ］ 一 NII-ElectronicN 工 工 Eleotronio Library Service.