Timbellus sixi Merle, Pacaud, Ledon & Goret, 2024, n. sp.
Creators: name: Merle, Didier
name: Pacaud, Jean-Michel
name: Ledon, Daniel
name: Goret, Bernard
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Neogastropoda
Muricidae
Timbellus
Timbellus sixi

description: Timbellus sixi n. sp.
(Figs 13; 26M)
urn:lsid:zoobank.org:act: 98875389-52BE-40D1-920C-5D8E4BB7B580
TYPE MATERIAL. — Holotype. France • Paris Basin, Oise, Trosly-Breuil (Fond Couturier); Sables de Cuise, (biozone NP12); early Eocene (Ypresian, lower Cuisian); MNHN.F.A90544 (Six coll.), H: 14 mm (Figs 13; 26M).
ETYMOLOGY. — Dedicated to Didier Six who collected this rare species.
TYPE HORIZON. — Sables de Cuise, (biozone NP12), see Gély & Lorenz (1991: pl. 1), early Eocene (Ypresian, lower Cuisian).
TYPE LOCALITY. — France, Paris Basin, Oise, Trosly-Breuil (Fond Couturier).
DISTRIBUTION. — Only known from the type locality.
DESCRIPTION
Unknow protoconch. Teleoconch up to 14 mm in height, up to 7.6 mm in width, biconic in profile, composed of five whorls. Moderately high spire. Last whorl 74% of total length. Apical angle 74° including spines, 66° excluding spines. Spiral sculpture with fine, narrow, well developed primary cords. First whorl, no spiral sculpture. Second whorl, appearance of weak P1 and P2. Third whorl, P1 and P2 well marked, appearance of s1. Fourth whorl, appearance of threads on infrasutural ramp. Fifth whorl: P1 to P6, s1 to s3; primary and secondary cords almost same relief; ADP to ABP on siphonal canal. On first whorl, nine protovarices. On second whorl, appearance of varices with two intervarices intercalated. On third whorl: three varices and three intervarices intercalated. From fourth to fifth whorl, three varices and two or three intervarices intercalated. Intevarices low. Higher relief of the intervarices on P2. Varices sublamellose on early whorls, rather thick on last whorls. Appearance of short P1 spine on second whorl. On last whorl, short P1 spine oriented adapically; no other cord spines. Ovate aperture up to 34% of diameter and up to 68% of length of last whorl (including the siphonal canal). Columellar lip smooth, narrow, slightly erect anteriorly, forming flat curved inductura at base. Parietal lip adherent. Outer lip with well developed denticles including ID, D1 to D3 (D4-D5 probably not formed); all denticles simple. Siphonal canal open, slightly dorsally recurved, up to 43% of apertural length. Pseudoumbilicus narrow.
COMPARISONS
This shell represents the oldest known Timbellus from the Paris Basin, as no Timbellus has been recorded from the Early Cuisian (biozone NP12, Ypresian) despite intensive fieldwork. It is easily distinguishable from the middle Eocene Paris Basin Timbellus species: T. tripteroides (Lamarck, 1822), T. crenulatus tricarinatus (Lamarck, 1803), T. micropterus (Deshayes, 1835) and T. capitaneus Pacaud, Ledon & Goret, 2017. Juveniles of T. tripteroides and T. capitaneus have weak spiral sculpture; Timbellus crenulatus tricarinatus lacks internal denticles, and juveniles of T. micropterus have coarser spiral sculpture. Timbellus sixi n. sp. resembles juveniles of T. magnei n. name from Bos d’Arros and Gan (Fig. 12C, D) in sharing a similar shape of its cords (fine, narrow, but well marked) and by having flat intervarices between the varices. However, T. sixi n. sp. differs from T. magnei n. name in having less foliated varices, having less numerous intervarices (usually 2-3 instead 4-5 in T. magnei n. name), and by having MP and ABP on the siphonal canal.
SPECIES GROUP OF T. CRENULATUS (RÖDING, 1798)
In this species group, the last whorl is generally broader than in the species group of T. tripteroides and the shoulder spine (P1) is more strongly developed. The spiral sculpture corresponds to fine primary cords, as in the T. tripteroides species group.Two species have an acute open shoulder spine, similar to that seen in the genus Pterochelus Jousseaume, 1880: the Eocene species T. crenulatus (Röding, 1798) and the Miocene species T. valdintortus (Cossmann & Peyrot, 1924). In the T. crenulatus species group the rounded aperture bears poorly developed denticles or lirae within the outer lip, except in the oldest known member (T. palensis [Magne, 1941]) from the early Eocene of Aquitaine Basin of Gan (Fig. 12 G-I). However, according Cossmann & O’Gorman (1923), the short shape and the rounded aperture of shells of this species resemble more closely T. crenulatus tricarinatus (Lamarck, 1803) than T. tripteroides. Probably, the presence of internal denticles in T. palensis represents a plesiomorphic character state and its loss in younger species of this group (e.g., T. crenulatus tricarinatus and T. crenulatus crenulatus) represents a derived state. For this group, we describe a new species: T. curvispina n. sp. from the Lutetian of the Paris Basin. As for T. tripteroides, the type material of Murex tricarinatus Lamarck, 1803 is lost, as it is also missing in the collections of Geneva and Paris. In order to avoid future taxonomic mistakes, we designate a neotype herein (MNHN.F.A90547, Fig. 14B, C) from the original type locality of Grignon (precisely Falunière of Grignon; Calcaire à Orbitolites complanatus Formation, biozone NP15, see Gély & Lorenz [1991: pl. 1], middle Lutetian).
description: Published as part of Merle, Didier, Pacaud, Jean-Michel, Ledon, Daniel & Goret, Bernard, 2024, New Cenozoic Muricidae (Mollusca: Gastropoda) from Europe, pp. 495-551 in Geodiversitas 46 (15) on page 518, DOI: 10.5252/geodiversitas2024v46a15, http://zenodo.org/record/13985760