Cochlostoma Jan, 1830

Gofas, Serge, 2001, The systematics of Pyrenean and Cantabrian Cochlostoma (Gastropoda, Cyclophoroidea) revisited, Journal of Natural History 35 (9), pp. 1277-1369 : 1283-1288

Genus Cochlostoma Jan, 1830

Type species (subsequent designation by Wenz, 1923): Cyclostoma maculatum Draparnaud, 1805 (5 Helix septemspirale Razoumowsky, 1789 ).

Cochlostoma was introduced by Jan (1830: 6) in a species list, as a subgenus of Cyclostoma Draparnaud , with six species included. The name was ignored during the nineteenth century, even by de Cristofori and Jan (1832), and authors then used the name Pomatias Studer, 1789 following Hartmann (1821: 204 ±214) who understood Pomatias according to one of the originally included species ( Cyclostoma maculatum ) but did not formally designate it as type species. Newton (1891) designated the other originally included species, namely Nerita elegans MuÈller, 1774 , as type species of Pomatias , thus installing the modern usage. He proposed the genus Hartmannia for Pomatias sensu Hartmann and later authors, but this was seldom used. Kobelt (1902) revived the use of the valid name Cochlostoma which today has general acceptance.

Many subgenera or sections were proposed in the nineteenth century, and some also in recent years. Those relevant for the Pyrenean species are:

Obscurella Clessin, 1889 . Type species (subsequent designation by Wenz, 1923): Cyclostoma apricum Mousson, 1847 (from IseÁre, French Alps). Raven (1990) argued that the type species should be C. obscurum by`virtual tautonymy’. This is not recognized by ICZN and Wenz’s designation is valid, although it may be regrettable.

Rhabdotakra Wagner, 1897. This genus included most of the species currently considered as belonging to Obscurella , and was proposed independently of Clessin’s work. I hereby designate as type species the ®rst included species, Pomatias insubricus Pini, 1877 (5 P. canestrinii Adami, 1876; from Presolana, Italian Alps), which makes it available as a replacement name for Canestrinia Raven, 1990 (see below).

Raven (1990) raised Obscurella to genus rank and introduced the subgenera Cantabrica (type species by original designation: Pomatias hidalgoi Crosse, 1864 ) and Canestrinia (type species by original designation: Pomatias canestrinii Adami, 1876 ). The latter name is preoccupied by Canestrinia Berlese, 1881 , Canestrinia Megnin and Trouessard, 1884 and Canestrinia Mello-LeitaÄo, 1931, all arachnids.

Morphology and anatomy

External morphology and anatomy are very conservative among all the species considered, and this is in part the cause of taxonomic confusion in the genus. Some characters which are homogeneous are here described globally for all the species considered, so as to leave only the species-diagnostic features under the species headings. The most useful characters for species recognition are found on the shell.

The young Cochlostoma already have a shell when they hatch. This stage of growth is marked usually by a change in sculpture but not by a clearcut limit. There are generally three diOEerent types of sculpture, on the embryonic half whorl, on the next one and one half whorls formed before hatching, and on the next spire whorls. The size and shape of the larval shell is quite homogeneous among the species studied, but some morphological traits are species-speci®c.

The shell of Cochlostoma (®gure 2) is dextrally coiled, high-spired with 7 to 9.5 convex whorls. Abnormal sinistrorsity was observed in the order of magnitude of 1:10 000 shells. The juvenile shells have a thin outer lip and are usually subcarinate on the body whorl, this keel surrounding a rather ¯at zone of the abapical end. The suture of the following whorl may follow that keel exactly and conceal it, or run just below so as to leave it apparent. On the body whorl, the keel disappears or is so attenuated that the shell cannot be said to be subcarinate: there is just a slight discontinuity of the pro®le, sometimes enhanced by elements of the sculpture. The body whorl (without the outer lip) may be constricted, i.e. more narrow than expected if it were the geometrical continuation of the spire whorls.

The peristome of adult shells of Cochlostoma is always thickened and ¯aring, and details of this morphology are important taxonomic characters. Two signi®cant features to be observed in the peristome are:

the shape of the thickening inside, whether a regular thickening of the whole inner surface, leaving a funnel-shaped aperture, or a distinct rim around which there is a ¯aring collar.

the shape of anterior (columellar) and posterior (parietal) insertions of the outer lip, which may be simple or more or less auriculated.

Another important character is whether the narrowing of the collar towards the columella is gradual, or abrupt (®gure 2: ac), and then forming a projecting lobe.

When the aperture has an inner rim (this is called`peÂristome bilabieÂ’ by Germain, 1931), it is functionnally more narrow and thus is an adaptive character in dry environments. The outer lip develops so as to ®rst take its ®nal shape and extension, and later become thickened from its inner side only. The shell will not grow further once the thickened outer lip has been formed, and there is never any resorption or later growth leaving a varix behind.

The shell is generally ornamented with ribs, which are made of an appressed undulated layer and are hollow inside. The spacing of ribs (expressed as number of ribs/mm) is an important feature, which varies on the same shell with ontogeny. The pattern of spacing is usually quite homogeneous within a single population, but can show important geographical variations. The ribs are roughly parallel to the growth lines, usually with an angle ca. 20±22 ss against the axis, and may be either straight or more or less ¯exuous. It is important to note whether the ribs terminate with a bulge or thickening where they meet the suture, or not.

The colour patterns on the shell are informative. There are two kinds of pattern, which may be combined on the same shell: those originated by brown or reddish pigments forming bands, blotches or ¯ames, and those formed by white ribs or coordinate white segments on the ribs. Juvenile shells may have misleading colour patterns.

External characters of the soft parts (®gure 3) are rather homogeneous in the group, except for variations in the intensity of the pigmentation. The head-foot is massive, moderately elongate; the foot truncated anteriorly and tapering posteriorly, with a peripheral groove slightly above the edge of the sole. The operculum of all the studied species is thin, horny, paucispiral, bordered by a ¯eshy rim on the dosal part of the metapodium. The snout is slightly bilobed, a little larger than the anterior part of the foot and lies over it. The cephalic tentacles are slender and tapering, usually darker than the body, situated well apart on the sides of the head. Each tentacle bears a small eye in a bulge next to its basal outer part. The mouth is armed with a pair of jaws, appressed to the roof of the buccal cavity, and bearing small uncini in a rhomboidal pattern. The jaws show up rhythmically when the animal is browsing. The radula (®gure 4) is c. 100 Mm broad and several millimetres long. Each row consists of a central, one pair of laterals and one pair of marginal teeth, all similar in size and shaped as a bent, parallel-sided spatula; in addition to this there is a second pair of very reduced outer marginals.

The internal body plan is typical of a coiled prosobranch (®gure 5). The body whorl contains the pallial cavity, along which are situated the rectum and the distal part of the genital apparatus. The edge of the mantle reaches the edge of the aperture when the animal is crawling. The middle part of the spire contains a diOEuse digestive gland, through which the digestive tract runs straight up to the stomach and then with irregular loops down to the rectum, and also the pericardial cavity and the nephridium.

All Cochlostoma have separate sexes. The female genital tract (®gure 6) is composed of an ovary in the apical spire whorls, connected by a narrow duct to the uterus/bursa copulatrix complex which lies along the pallial cavity in the body whorl. The part of the oviduct preceding the uterus is slightly swollen and packed in a tight, irregular coil, then two branches reach the bursa copulatrix and the uterus, respectively. There is some variation in the coiling of this part of the oviduct, but this was not found to be meaningful for species recognition. The bursa copulatrix is tightly appressed to the proximal end of the uterus, so that the separation may be inconspicuous. This structure is a site for the storage of sperm and takes a yellowish colour when full. The branch of the oviduct reaches it in a rather distal position (i.e. next to the uterus) in all the species studied here, contrary to C. septemspirale where its insertion is rather at the proximal end, further up the spire ( Prince, 1967; Varga, 1984).

The male genital tract (®gure 7) is composed of a testis, usually bright orange in colour, in the apical spire whorls, a narrow spermiduct running down along the columella, and entering a prostatic gland situated along the dorsal wall of the pallial FIG. 5. External view of a preserved Cochlostoma obscurum (female, from Arcy s/Cure, Burgundy), shell removed. dg: digestive gland, fg: foot groove, kd: kidney, lo: opercular lobe, ma: mantle, me: mentum, oe: internal tract of oesophagus (seen when dissected), ov: ovary, re: rectum, sn: snout, st: stomach, tc: tentacles, ut: uterus. Scale bar 1 mm. cavity. The prostatic gland is elongate, ¯attened, rounded at the proximal end, and opens distally at its tapering end at some distance from the mantle edge, to the right of the animal’s head. The opening of the prostatic gland faces a groove which runs into a closed duct and thence into the base of the penis. The penis is well developed and contains an internal duct running quite straight to the very tip in all the species observed. This contrasts with the sinuous trajectory of the duct in C. septemspirale ( Giusti, 1971; Varga, 1984) and with the open groove on the penis of ToOEolettia (see Giusti, 1971). Juveniles of C. obscurum with an incompletely formed penis have an open groove instead of a duct.

There is a sexual dimorphism which is reēcted in the shells, males being smaller and stouter, sometimes also darker. It is usually possible to roughly sort males and females by the shell in a given locality, but geographic variation will obscure the pattern at a larger scale.