Ondina perezi (Dautzenberg & Fischer, 1925)

Figure 81

Odontostomia (Auristomia) Perezi Dautzenberg & Fischer, 1925:81

Ondina perezi (Dautzenberg & Fischer) - van Aartsen 1987; Smith & Heppell 1991; Schander 1995; Schander et al. 2003; Høisaeter 2009

Odostomia (Brachystomia) perezi (Dautzenberg & Fischer) - Winckworth 1932

Odostomia diaphana (Jeffreys) - Warén 1980

Menestho (Evalea) diaphana (Jeffreys) - Hylleberg Kristensen 1970; Høisaeter 1986

Evalea diaphana (Jeffreys) - Fretter et al. 1986; Graham 1988

Ondina diaphana (Jeffreys) - Warén 1991

Type material: Syntypes USNM 471508 and in coll. Dautzenberg, Inst. Royal de Sciences Naturelles, Bruxelles.

Type locality: Bisayeres and Goulet de Brest in western France, found in shells inhabited by Phascolion strombus.

Material seen: None.

Diagnosis: Shell: Much like O. diaphana but with a dull shell surface, larger, to 2.5 mm (van Aartsen 1987) or 2.9 mm (Warén 1991) and flatter, less convex whorls. (From van Aartsen 1987 and Schander 1995). Soft parts: Not known.

Operculum: Not known.

Biology: By most authors (e.g. Hylleberg Kristensen 1970) considered to be host specific on Phascolion strombus. This is followed up by both Warén (1991) and Schander (1995).

Distribution: Not yet reported from Norway, but as this species is far more common than O. diaphana in western Sweden, it should certainly occur together with Phascolion strombus in the Norwegian part of Skagerrak. The distribution outside Norway is impossible to specify because of the confusion with O. diaphana. It is confirmed from the Faroes, the Swedish west coast, the Atlantic coast of France and the British Isles (Schander 1995).

Remarks: As discussed under Ondina diaphana, authorities disagree as to whether O. perezi is a good species or only a synonym of O. diaphana (Ankel 1959, Hylleberg Kristensen 1970, Gibbs 1978, Warén 1980, 1991 and Fretter et al. 1986, argues for synonymy. Van Aartsen 1987, Schander 1995 and Schander et al. 2003 prefer to classify it is a separate species.) As I have not seen any specimens that unambiguously could be referred to O. perezi, the following discussion is based solely on literature data.

Van Aartsen et al. (1984) note that the European Ondina species may be divided into two distinct groups, those without spiral sculpture and those with such sculpture. The subdivision of the former of these groups is exceedingly difficult, as is illustrated by the O. diaphana / O. perezi dispute. The third north European member of this group, O. normani, was not mentioned at all by van Aartsen (1987), and was not compared directly with O. diaphana (= O. perezi) by Warén. In my opinion O. normani is a fairly common member of the Norwegian pyramidellid fauna (see below). This opinion is based on my interpretation of O. diaphana, as illustrated in Figure 80, an opinion shared by Schander (1995: Figure 1 E). The SEM photo in Warén (1991: Figure 34B), said to be of O. diaphana is most likely of O. perezi, as both the locality and size indicate (Roscoff, France and 2.9 mm). If my interpretation is correct, the size difference between the two presumed species is not as large as claimed by van Aartsen (1987) (2.5 against 1.6 mm). Drawings of the two in Fretter et al. (1986) are of shells respectively 3.0 and 2.4 mm long, and my specimen shown above (Figure 80) is of a 2.6 mm long specimen.

Schander et al. (2003) included specimens of both O. diaphana and O. perezi as well as O. divisa in their molecular study of various pyramidellids. Their comparison of the mitochondrial 16S gene showed that O. diaphana and O. perezi differed in only a single character. This was based, however, on a very reduced dataset only those 200 characters that could be unambiguously aligned for the total set of 32 species. When only the three Ondina species were included, all 483 characters could be unambiguously aligned, and then O. diaphana and O. perezi differed in a total of 16 characters. This as opposed to a similar comparison between Pyrgiscus rufus and P. fulvocinctus which differed in seven characters.

If a specimen of an Ondina species is found within the aperture of a shell inhabited by Phascolion strombus, this has been taken as a strong indication that the species in question is actually O. perezi. In my material a single specimen from Grimseidpollen (c. 60°16’N, 13-15 m, coll. and leg. S. Bakke 1964) was found within the aperture of a Littorina shell inhabited by Phascolion strombus. Unfortunately, today it is partly broken and rather corroded by acidic conditions, and not any longer easily identifiable. A camera lucida drawing of the undamaged shell presented in Figure 82, is more like O. normani than O. perezi. I therefore suspect that more than one species of Ondina might live together with Phascolion strombus.