Raphitoma aequalis ( Jeffreys, 1867 )

Høisaeter, Tore, 2016, A taxonomic review of the Norwegian species of Raphitoma (Gastropoda: Conoidea: Raphitomidae), Fauna norvegica 36, pp. 9-32 : 16-19

Raphitoma aequalis ( Jeffreys, 1867)

Figures 2B, C , 3B and 8 - 11

Defrancia linearis var. aequalis Jeffreys, 1867:369 Cordieria (Cirillia) aequalis, Jeffr. - Monterosato 1884 Clathurella aequalis, de MONTEROSATO - Locard 1892 Mangelia linearis var. intermedia Forbes & Hanley, 1853:472

Clathurella linearis var. intermedia F. and H. - Marshall 1912

Pleurotoma (Pleurotomoides) aequalis (Jeffreys) Monterosato - Dautzenberg & Fischer 1925 Cenodagreutes aethus E.H. Smith, 1967a:1

Philbertia linearis aequalis (Jeffreys) - Rodriguez Babio & Thiriot-Quiévreux 1974

Raphitoma aequalis ( Jeffreys, 1867) - Sabelli et al. 1990; Cachia et al. 2001; Høisaeter 2009

Defrancia linearis ( Montagu, 1803) [in part] - Friele 1874 Clathurella linearis - G.O. Sars 1878

Philbertia linearis ( Montagu, 1803) [in part] - Hubendick & Warén 1976; Høisaeter 1986

Raphitoma linearis ( Montagu, 1803) [in part] - van Aartsen et al. 1984 (?); Fretter & Graham 1985; Graham 1988; Smith & Heppell 1991; Olsen 1994 (?); Heppell et al. 1997

Type material. Types could not be found ( Warén 1980).

Holotype and one paratype of Cenodagreutes aethus E.H. Smith, 1967 , in California Academy of Sciences, Department of Invertebrate Zoology, Type number 320 (holotype) and 321, see Figure 10 below.

Type locality. Great Britain. Type locality for Cenodagreutes aethus E.H. Smith, 1967 , off Farland Point , Isle of Cumbrae, Firth of Clyde , Scotland (55°44’N, 04°57’W) on a bottom of stones and mud in 20 m.

Material examined. Around 245 specimens from 85 stations between 58° and 69°N on the coast of Norway .

Description. (Based mainly on specimens illustrated in Figures 8 and 11A). The size of the specimen in Figure 8, 10.1 mm, is the maximum recorded for the species. Shell moderately narrow (height rarely more than 2.25 times the diameter). Body whorl 53 to 70 % of total shell height. Shell subfusiform with convex whorls and with deeply incised sutures. Sculpture of moderately pronounced axial ribs (costae) crossed by narrow spiral cords, six cords on penultimate whorl. The space between spiral cords two to three times wider than the spiral cords. Where the cords cross the ribs, rather low, smooth and glossy tubercles are produced. Axial ribs disappear gradually towards the base. Yellowish white to golden yellow ground colour with reddish brown spiral cords. On penultimate whorl, the sixth (or seventh) spiral cord from top often white or much lighter than remaining cords. Every second or third rib pure white in some specimens. In specimens from deeper water, ground colour usually almost white and spiral cords with much less pigment than in those from shallower water ( Figures 11F and H ). Aperture an elongated oval drawn out into a siphonal canal of varying length, longer in juveniles than in adults, but never as long as in equally long R. maculosa n.sp. Shallow anal sinus in outer lip near suture. Spiral cords on the siphonal canal smooth, wider and closer together than on the whorls above the aperture. Teleoconch microsculpture of fine, well separated microscopic pustules ( Figures 2B, C and 8), best visible between spiral cords in upper parts or in juvenile shells. Protoconch of 3.5 to 4 (varies) light brown, convex whorls (Figures 3B and 8). Protoconch W/L: 0.97. Apical angle 50° to 54°. Apical whorl from 180 to 220 µm in diameter. Protoconch ending in a weak spiral keel.

A specimen observed alive in a petri-dish (Figure 9) turned out to be rather sedate. It crawled slowly along in its preferred direction, with the siphon extending only a fraction of a mm in front of the siphonal canal. The foot is wide, tapering to a narrow point posteriorly and has distinctly recurved anterolateral corners. The foot and siphon is uniformly white.

Variability. This is a variable species, both as regards colour and shape ( Figure 11 ). The Height to width ratio varies a lot as does the length and width of the siphonal canal. The colour may be light yellowish white with scattered light brown spiral cords, or darker yellow with reddish brown cords. However the colour is fading fast in preserved specimens and thus the colours in the descriptions may not be completely reliable. The colour pattern appears to vary geographically as well, as there is a much higher proportion of specimens with very light coloured spiral cords in the material from Skagerrak than in the material from further north on the coast. Fretter & Graham (1985) mention a row of nine small teeth on inside of outer lip (as R. linearis see below), but this is very rarely the case even for large specimens in my material. The most reliable characters are the microsculpture consisting of well separated small pustules and the light brown wide angled protoconch with delicate diamond-shaped decussate sculpture.

Distribution. By Jeffreys (1867) stated to be more common in the northern parts of British waters than in the south, but with a distribution overlapping the one of R. linearis . Recorded from Malta ( Cachia et al. 2001) and Italy ( Spada 2008) in the Mediterranean to Finnmark (as R. linearis in G.O. Sars 1878). The latter record is based on a single empty shell from Hammerfest (71°N). In addition G.O. Sars reports a single specimen (live caught) from Lofoten. Judging from his drawing and description (in latin), the 9.5 mm long specimen is certainly R. aequalis and not R. linearis (see also citation of Marshall 1912, below). In my material common along the whole coast at least as far north as Kvaefjord, 68°50’N, in Troms county, but especially frequent (105 of the c. 245 live caught specimens) from the area just north of Bodø, at 67°15’N (mainly due to very diligent collecting efforts of Per Wikander, thus not necessarily more common there than elsewhere in northern Norway).

Remarks. Described by Jeffreys (1867:369) as a variety of R. linearis : “Shell broader than the typical form, with the whorls more rounded; ribs more numerous, and not so prominent or rugged; spiral striae closer or finer; apex yellowish white; coloured lines regularly distributed, and of a paler hue; in some specimens these markings are very faint or altogether wanting. L. 0.5. B. 0.225.” In a general way these characters match my material, but the ‘apex’ is rarely yellowish white. Monterosato (1884) was the first to elevate the ‘variety’ to full specific status, followed by among others Locard (1892) and Dautzenberg & Fischer (1925), the latter based on material from the vicinity of Roscoff, Bretagne. Rodriguez Babio & Thiriot-Quiévreux (1974) reported the two forms from Roscoff, but retained aequalis as a variety of linearis primarily based on the similarity of the protoconchs. They noted that in the vicinity of Roscoff, linearis was four times as common as aequalis .

Forbes & Hanley (1853:471-472) described three ‘principal varieties’ of Mangelia linearis , the purple-tipped ( var. scabra ), the blunt-ribbed ( var. intermedia ) and the colourless form ( var. pallida ). Even from this brief sentence it is tempting to equate the three varieties with respectively R. linearis , R. aequalis and R. obesa n.sp. Jeffreys (1867:369) introduced another ’variety’, Var. aequalis , which he explicitly states is a new name for the two ‘varieties’ Mangelia linearis vars intermedia and pallida of Forbes & Hanley. Jeffreys thus merges the two varieties of Forbes & Hanley, as he regards the difference between the ‘blunt-ribbed’ form and the ‘colourless’ form as too small or vague to justify giving a name to the colourless (or pure white) form of the species: “…in some specimens (of Var. aequalis ) these markings are very faint or altogether wanting.” Jeffreys (1867:369).

Marshall (1912:299) disagreed with Jeffreys’ merging and renaming of the ‘varieties’, mentioning that R. linearis as well as the two ‘varieties’ intermedia and pallida described and figured by Forbes & Hanley (1853) were three validly described ‘varieties’. If this is accepted, R. aequalis is a junior synonym of R. intermedia , while R. obesa n.sp. is a junior synonym of R. pallida . Since R. aequalis has been generally accepted as a full species since it was adopted by Monterosato (1884), while R. intermedia and R. pallida have never been used as valid names after Marshall (1912), they are better regarded as nomina oblita according to Article 23.9.2 of ICZN.

In North European literature, R. aequalis , has long been treated as a synonym of R. linearis . As already noted by Marshall (1912:299), the records of R. linearis in G.O. Sars (1878) from northern Norway are of this species (… except Sars’ fig. 2 (t. 23), which well represents the var. intermedia ). Also Fretter & Graham (1985) described and illustrated (their figures 368 and 369) R. aequalis as R. linearis . Their SEM photograph of the transition zone between protoconch and teleoconch particularly clearly shows the microsculpture (fine pustules) found in R. aequalis but not in R. linearis . E.H. Smith (1967a) may have been the first (after Jeffreys 1867) to clearly distinguish between these two species in British waters (see Discussion below), although he did not realise that he dealt with already described taxa.

Figures

Figure 2. Details of microsculpture of six specimens of Raphitoma. A. R. linearis; B and C. R. aequalis; D. R. obesa n.sp.; E. R. maculosa n.sp.; and F. R. concinna. Scale bars = 200 µm, except F = 500 µm. Figure 3. Raphitoma spp, protoconchs. A. R. linearis; B. R. aequalis; C. R. maculosa n.sp. D. R. concinna. Scale bar = 200 µm.

Figure 11. Raphitoma aequalis, eight specimens showing variability of the species in Norway. Specimens to scale, the largest 6.5 mm. A. Grovfjord, 68°51’N, 16°30’E, 10 m; B. Bukkasundet, 60°15’N, 05°17’E, 8-15 m; C. Liholmsrennen, 60°18’N, 05°09’E, 70-90 m; D. Hillersholmen, 60°18’N, 05°15’E, 8 m (2007); E. Hillersholmen, 60°18’N, 05°15’E, 8 m (1967); F. Near Grimstad, 58°22’N, 08°48’E, 57 m; G. Bukkasundet, 60°15’N, 05°17’E, 8-15 m (2007); H. North Sea, 60°30’N, 02°00’E, 122 m.