The malacologicalsocietymalacological society of Japan

fima VENUS (Jap, Jour, Malac.) Vpl. 4S, No. 4 C19S9):25C-254

'2ljreeeOA i a= vi - de tF' 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 krypta is distinguished from other known Panamic 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