Turbonilla pusilla (Philippi, 1844)

Figure 107

Chemnitzia pusilla Philippi, 1844:124

Turbonilla pusilla (Philippi) - van Aartsen 1981; van Aartsen & al. 1984; Fretter et al. 1986; Graham 1988; Smith & Heppell 1991; Peñas et al. 1996; Öztürk & Bakir 2013

Turbonilla cf. pusilla (Philippi) - Høisaeter 2009

Turbonilla innovata Monterosato, 1884 - Winckworth 1932

Turbonilla acuta (Donovan, 1804) - sensu Fretter et al. 1986; Graham 1988

Type material: Not known

Type locality: Palermo, Sicily.

Material seen: Norway - Skagerrak, 2 spms, 40 shs (around 58°17’N, 8°35’E).

Diagnosis: Shell: Turbonilla with fairly elongate shell.

Total shell length rarely exceeding 5 mm. Number of whorls 10 or less. Sculpture consisting of up to 25 slightly opisthocline, close set ribs. No spiral sculpture. Columellar fold very slight and retracted. Protoconch helicoid of 2.5 to 3 whorls at an angle of about 95° to the teleoconch, its base completely exposed. Soft parts: Not known. Operculum: Not known.

Biology: Not known.

Distribution: Here reported from Norway for the first time, restricted to the Norwegian part of Skagerrak. Two specimens and 40 empty shells, all from localities close to Grimstad on the Skagerrak coast. All collected by Wikander 1970-1975. Outside Norway: “This is a southern species reaching its northern limits on the southern and western shores of the British Isles. Not found in the North Sea nor in Scandinavia” (Fretter et al. 1986:637). Possibly found in the Koster area in the Swedish part of Skagerrak (Warén in Hansson 1998). Otherwise reported from the Mediterranean where it is common (Peñas et al. 1996, Öztürk & Bakir 2013).

Remarks: This member of Turbonilla s.s. has turned out to be not uncommon in the Skagerrak region. The correct name of the species is not easily determined. In the British Isles, at least four species names are, or have been, in use for members of this genus (see e.g. Smith & Heppell 1991): T. lactea (L., 1758) (= T. elegantissima Montagu, 1803), T. acuta (Donovan, 1804), T. pusilla (Philippi, 1844), and T. pumila (G. Seguenza, 1876) (= T. innovata Monterosato, 1884). As most recent authors rely heavily on van Aartsen’s (1981) opinion concerning this group, I compare my specimens to his detailed description. He distinguishes first of all between T. pusilla and T. lactea, of which the former has a protoconch like the specimens from Skagerrak (type A, helicoid, 90° angle to the axis). T. lactea on the other hand, has a planorboid protoconch (type B, 135° angle to the axis), which clearly distinguish it from his T. pusilla. T. pumila is a scarce shell in the Channel, and its protoconch is of the same type as T. lactea, and is thus out of the question. The interpretation of T. acuta he finds difficult, but following the description of various recent British authors T. acuta should be a sister species to the purely Mediterranean T. delicata, with a type A protoconch, but with 3-5 of the uppermost turns in the first teleoconch whorls smooth, i.e. no axial ribs. On the remaining whorls, the ribs are broad and close together. Our Norwegian shells do not fit this description, neither do the drawings of T. acuta in Fretter et al. (1986, their figure 433). These are almost certainly conspecific with our Norwegian form (compare with Figure 107, right). I conclude that if I choose to follow van Aartsen (1981), T. pusilla is the most likely candidate, if I prefer Fretter et al. (1986), T. acuta is the correct name for our species. Unless the material from Skagerrak represent an undescribed species, T. pusilla (Philippi) (= T. acuta sensu Fretter et al. 1886) is by far the most likely name. Van Aartsen (1981) claims that T. pusilla is the commonest and most variable species of Turbonilla in Europe.