Seraphs olivaceus ( Cossmann, 1889 )

Caze, Bruno, Merle, Didier, Pacaud, Jean-Michel & Saint Martin, Jean-Paul, 2010, First Systematic Study using the Variability of the Residual Colour Patterns: The Case of the Paleogene Seraphsidae (Mollusca, Gastropoda, Stromboidea), Geodiversitas 32 (3), pp. 417-477 : 430-432

Seraphs olivaceus ( Cossmann, 1889) ( Figs 6 H-J; 10)

Terebellum (Seraphs) olivaceum Cossmann, 1889: 97 , 98, pl. 3, figs 1, 2.

Terebellum (Seraphs) olivaceus – Cossmann 1904: 46. — Cossmann & Pissarro 1911: pl. 31, fig. 158-4.

Seraphs olivaceus – Jung 1974: 21, pl. 5, fig. 5-11, textfig. 15. — Le Renard 1992: 6. — Le Renard & Pacaud 1995: 112. — Pacaud & Le Renard 1995: 162.

TYPE LOCALITY. — Chaussy (Val d’Oise, France), Lutetian (Middle Eocene).

TYPE MATERIAL. — The illustrated syntype of Cossmann (1889) has been selected unambiguously by Jung (1974:

21) as lectotype, using wrongly the term holotype: “Cossmann’s figure […]. Th is specimen is the holotype ”. According to article 74.5 of the ICZN (1999), this mention, made before 2000, constitutes a valid lectotype designation. Unfortunately, the type material of this species has not been found in the Bourdot collection, deposited at University of Lyon 1 ( UCBL). A neotype designation is needed to clarify the taxonomic status of this species. A neotype from the type locality ( MNHN A28885 , leg. Pacaud, Fig. 10 F-H) is accordingly chosen here. Th is initiative is in conformity with the rules specified by the ICZN (1999: art. 75), as regards the designation of a neotype.

OTHER MATERIAL EXAMINED. — See Appendix 1.

DESCRIPTION

Shell

Shell up to 28 mm in height and 7 mm in diameter, moderately slender with elongated and pointed apex ( Fig. 6H). Aperture long and narrow. Callus of the inner lip very thin, inconspicuous and rarely preserved. Straight columella near the base. Outer lip not thickened, reaching the apex and sinuous for the whole height in labral view, i.e. outer lip prosocyrt on the anterior part and opisthocyrt on the posterior part of the shell ( Fig. 6J). Siphonal notch moderately deep on the dorsal side of the shell. No sculpture on the surface of the shell.

Colour pattern

The shells show small and irregular dots on a lighter background. Th ese dots are composed of two levels of residual pigmentation ( Fig.10E, H). The first one consists of triangular spots,darker than the background. These small triangles are pointed towards the growing edge. The second one consists of white fluorescent fuzzy-bordered spots directed towards the inner lip. They are adjacent to the base of the dark triangles. White fluorescent spots are generally narrower than the dark spots ( Fig.10E, H). Th ese two components form the dots. Th ese dots, variable in size and sometimes coalescent ( Fig.10H),form sinuous axial nearly collabral rows ( Fig.10C,D, F, G). Th e space between these rows is narrow on the apex and broader on the median and basal parts of the shell.

VARIABILITY OF THE COLOUR PATTERN

The background is generally uniform and can bear large and diffuse darker areas ( Fig. 10 F-H). The density of the dots varies.When the density is high the axial rows are clearly defined, whereas they are less clearly or not defined when it decreases.

COMPARISONS OF THE THREE SPECIES OF SERAPHS : S. VOLUTATUS , S. SOPITUS AND S. OLIVACEUS

Shell

Among the representatives of Seraphs , the adult shell shape of S. volutatus , S. sopitus and S. olivaceus is very similar ( Fig. 6). Moreover, these shells share a lack of sculpture. Seraphs volutatus generally has a straight columella, while it is bent in the two other species. Jung (1974) regarded Bulla volutata as a synonym of Bulla sopitus . However, according to Le Renard (1992), S. sopitus differs from S. volutatus by its short and blunt apex. For Jung (1974), S. olivaceus is distinguished from S. volutatus (= S. volutatus + S. sopitus sensu Jung [1974] ) by an elongated and acute apical part ( Fig. 6H). According to Jung (1974), S. volutatus shows a gradual change in the shell shape during ontogeny, and we observed some very large specimens similar to S. olivaceus and some small specimens similar to S. sopitus .

Residual colour pattern

Dots on a light background are common to S. volutatus ( Fig. 8), S. sopitus ( Fig. 9) and S. olivaceus ( Fig. 10). These species show the same type of dots with two levels of residual pigmentation: 1) dark triangular spots orientated towards the growing edge; and 2) white fluorescent spots towards the inner lip. Furthermore, they have sinuous rows, almost parallel to the line of growth. In the studied material (22 ex.) of S. olivaceus , the dots are always small and less numerous than in the two other species.

DISCUSSION

After study of 15 specimens of S. sopitus , 22 of S. olivaceus , 562 of S. volutatus , the colour patterns of each species appear variable, but very similar and no distinction can be made. According to Jung (1974) and Le Renard (1992), the main differences result from shell characters (the morphology of the apex and the columella).However, these differential characters, which vary during ontogeny and even in adulthood, were not defined considering variability. In conclusion, our personal opinion is that, following the colour patterns, the discrimination of these three species is not justified. In order to know if it is necessary to continue to distinguish them, it would be rewarding to study the shell using modern morphometric methods.