Raphitoma linearis ( Montagu, 1803 )

Raphitoma linearis ( Montagu, 1803) View in CoL

Figures 1A View Figure 1 , 2A View Figure 2 , 3A and 14 - 17

Murex linearis Montagu, 1803:261 , Tab. 9, f. 4

Defrancia linearis ( Montagu, 1803) View in CoL - Jeffreys 1867; Friele 1874; Norman 1879 [in part]

Clathurella linearis, Mont. [in part] - G.O. Sars 1878 Cirillia linearis, Mtg. - Monterosato 1884 View in CoL

Philbertia linearis ( Montagu, 1803) View in CoL - Rodriguez Babio & Thiriot-Quiévreux 1974; Hubendick & Warén 1976 [in part]; Høisaeter 1986 [in part]

Raphitoma linearis ( Montagu, 1803) View in CoL - Rolán 1983 [in part?]; Fretter & Graham 1985 [in part]; Graham 1988 [in part]; Sabelli et al. 1990; Rolán et al. 1998; Cachia et al. 2001; Öztürk et al. 2004; Høisaeter 2009

Raphitoma (R.) linearis ( Montagu, 1803) View in CoL - van Aartsen et al. 1984 [in part?]; Smith & Heppell 1991 [in part]; Heppell et al. 1997 [in part]

Cenodagreutes coccyginus E.H. Smith, 1967a:3 View in CoL

Type material. Lectotype designated by Rolán et al. (1998),

BMNH 1995090 (one of several syntypes). Holotype and one paratype of Cenodagreutes coccyginus E.H. Smith, 1967 , in California Academy of Sciences, Department of Invertebrate Zoology, Type number 322 (holotype) and 323. Photographs of both types shown in Figure 17 View Figure 17 below.

Type locality. Falmouth Harbour , Cornwall, England . Type locality for Cenodagreutes coccyginus E.H. Smith, 1967 , off Tan Buoy between Great Cumbrae and Little Cumbrae Islands, Firth of Clyde, Scotland (55°44’N, 04°57’W) on a sandy shell bottom in 17 m. GoogleMaps

Material examined. Ninety-seven specimens from 36 stations from c. 58° to 61°N on the coast of Norway .

Description. Based mainly on a specimen from Bukkasundet (1966), 7.4 x 3.5 mm, ( Figure 16A View Figure 16 ), and another from Bukkasundet (2007), 5.9 x 2.8 mm, ( Figure 14 View Figure 14 ). Shell fairly thick and opaque; moderately narrow. Shells longer than 4.9 mm with height 2.10 to 2.32 times the diameter, and body whorl 64–70 % of total shell height. Shell colour varies, but always with a comparatively light ground colour and dark brown nodules on the axial ribs, alternating with scattered ribs with white nodules. Spiral cords nos 5 and 7 from above on penultimate whorl, with uninterrupted dark brown colour, while the spiral cord between these two is pure white ( Figures 14 View Figure 14 and 15). Ground colour darker on adapical teleoconch whorl and below periphery on body whorl. Five teleoconch whorls (on 7.4 mm long shell) convex (but varying a lot, see below) with a deep and distinct suture. Adapical teleoconch whorl 625–925 µm in diameter. Sculpture of axial ribs crossed by spiral cords, five or six narrow cords, the uppermost distinctly less prominent than the rest, on the penultimate whorl. The interspaces are around three times the width of the cords. Tubercles where cords cross axial ribs form rather sharp ‘points’. Aperture elongated oval drawn out into moderately long siphonal canal. Sculpture on siphonal canal of wide spiral cords crossed by equally wide ribs. A shallow anal sinus in outer lip near suture. Microsculpture ( Figures 1A View Figure 1 , 2A View Figure 2 and 14 View Figure 14 ) of contiguous, irregular granules, not separate pustules as in R. aequalis and R. obesa n.sp. Protoconch (Figures 3A and 14) 3.5 to 4 whorls, narrow, W/L: 0.96, apical angle 43.5°–46.3°, with a coarse decussate grid and a distinct keel at transition to teleoconch. Protoconch colour usually dark purplish brown closest to the teleoconch and opaque yellowish white at the apex, rarely much lighter throughout.

Variability. Specimens from the Mediterranean apparently have pure white ground colour with fine brown spiral lines (see Remarks below). One of my specimens approach this colour, viz. the one illustrated in Figure 14 View Figure 14 and 16C View Figure 16 . This specimen with most contrast (yellowish white against dark brown) was the most recently caught, having been kept in ethanol for only a week, others have been stored in ethanol for some 40 years before being photographed. The colour variation is partly due to the effect of ethanol. In some of the stored specimens, however, both the ground colour and the spiral cords (yellowish brown) are much lighter than the majority. Usually the brown spiral cords are darker than in R. aequalis (e.g. Figure 16E View Figure 16 also photographed alive, Figure 15) but with a large overlap.

The specimen studied alive (Figure 15) had foot and siphon uniformly white. The specimen was rather lively, frequently and swiftly changing directions while crawling. The siphon in front of the siphonal canal is long, tubular and slightly narrower in front. The foot is deeply embayed in the mid line, and has recurved anterolateral corners. As seen in Figure 15, the foot is very flexible and aids the animal to rapidly turn around if placed upside down on the substrate.

Distribution. Recorded from Morocco and the Canary Islands to northern Norway, including the entire Mediterranean ( Cachia et al. 2001, Öztürk et al. 2004, Giannuzzi-Savelli, pers. comm, and G.O. Sars 1878). The North European records in the literature ( Friele 1874, G.O. Sars 1878, Norman 1879, Fretter & Graham 1985, Høisaeter 1986, Smith & Heppel 1991) are just as likely to be the more common R. aequalis than R. linearis (see above). The material I have seen, is from the Grimstad area on the Skagerrak coast and north to Raunefjorden south of Bergen (60°15’ N). There are no verified records north of Sognefjorden, except for a single doubtful shell from 67°N.

Remarks. Norwegian specimens of R. linearis are morphologically similar to R. aequalis , and the two are often hard to tell apart. The best way to separate R. linearis from R. aequalis is the microsculpture (see above), the slightly more ‘spiky’ macrosculpture, and the knobby spirals on the outer siphonal canal as opposed to the smooth spirals in R. aequalis . Most specimens have a very dark purplish colour in the transition whorls between protoconch and teleoconch. A further argument for the specific separation of R. aequalis and R. linearis is the observation of E.H. Smith (1967a, b) that there are several differences in the internal organs (alimentary tract and reproductive system) between Cenodagreutes aethus and C. coccyginus , here regarded as synoms for R. aequalis and R. linearis respectively. The morphological data indicate that R. linearis and R. aequalis are closely related. The fact that both species lack radula, as opposed to several other species of Raphitoma s.l., e.g. R. purpurea and R. concinna , supports the hypothesis of a closer relationship between these two species than of any of them to either R. purpurea or R. concinna .