Epitonium fabrizioi Pastorino & Penchaszadeh, 1998

Zelaya, Diego G. & Güller, Marina, 2017, Undercover speciation of wentletraps (Caenogastropoda: Epitoniidae) in the Southwestern Atlantic, Zootaxa 4286 (1), pp. 41-69 : 46-49

Epitonium fabrizioi Pastorino & Penchaszadeh, 1998

( Figures 3 , 4 )

Scala aff. orbignyi: Carcelles, 1944: 248 (in part)

Epitonium albidum: Clench & Turner, 1951 , pl. 114, fig. 3 (only) (non d’Orbigny, 1842) Epitonium georgettina: Scarabino, 1977: 183 , pl. 2, fig. 8 (non Kiener, 1839) Epitonium georgettinae: Pastorino, 1995: 8 , pl. 2, fig. 10 (non Kiener, 1839) Epitonium fabrizioi Pastorino & Penchaszadeh, 1998: 63 –68

Type locality. 42°34’S 64°17’W, Puerto Pirámides , Chubut Province, Argentina.

Type material. Holotype (MLP-Ma 5402), 10 paratypes from the type locality (USNM 880252).

Additional material examined. Buenos Aires Province: [36°21’S 56°43’W], San Clemente del Tuyú (MLP- Ma 3951: 1 sh.); [38°33’20’’S 58°42’58’’W], Puerto Quequén (MACN-In 25697: 7 sh.) ; 38°34’28.7’’S 58°42’42.1’’W, Puerto Quequén (MACN-In 18676-2: 1 sh.); off Buenos Aires (MACN-In 30331: 2 sh.) . Río Negro Province: [40°49’00’’S 64°45’00’’W], Baliza Plata, Puerto San Antonio Este (MACN-In 14828: 1 sh.) ; 40°52’30’’S 65°07’31’’W, intertidal (MACN-In 40367: 1 spm.); 40°54’00.0’’S 65°06’43.1’’W, 6 m (MACN-In 40368: 1 sh.); 40°54’08.3’’S 65°06’28.0’’W, 9 m (MACN-In 40369: 7 sh.); 40°55’17.4’’S 65°08’07.6’’W, 7-8 m (MACN-In 40370: 1 sh.); 41°38’02.6’’S 65°01’13.3’’W, Playas Doradas, intertidal (MACN-In 40371: 1 spm.); 41°38’06.6’’S 65°00’55.9’’W, Playas Doradas, 7 m (MACN-In 40372: 3 sh.); [42°00’00’’S 65°04’19’’W], Puerto Lobos (MACN- In 40373: 2 sh.; MACN-In 40374: 1 sh.). Chubut Province: [42°34’S 64°17’W], Puerto Pirámides (MLP-Ma 5171: 1 sh.); [42°46’S 65°03’W], Puerto Madryn (MACN-In 10954: 3 sh.; MACN-In 37236: 1 sh.; MACN-In 9171-22: 27 spm.; MACN-In 9673: 13 spm., +50 sh.; MLP-Ma 12197: 4 spm.); [42°46’50’’S 64°59’58’’W], Punta Cuevas, Puerto Madryn, intertidal (MACN-In 40375: 10 spm.; MLP-Ma 6739: 3 sh.); [42°49’00’’S 64°53’00’’W], Punta Loma, Puerto Madryn (MACN-In 37516: 3 sh.); [42°37’S 64°16’W], Punta Pardelas (MLP-Ma: 1 sh.).

Known distribution. San Clemente del Tuyú (36°21’S) , Buenos Aires Province to Puerto Madryn (42°49’S) , Chubut Province, Argentina; living specimens only found in the intertidal zone.

Description. Shell medium sized (maximum L observed = 15 mm, protoconch broken), broadly conical, solid, white, dull ( Fig. 3 A–C, E, F, I). Protoconch of 4¼ convex whorls, of 485 µm in length and 390 µm in maximum diameter ( Pastorino & Penchaszadeh 1998); usually partially or completely lost in larger specimens; smooth (?). Teleoconch with up to 8 inflated whorls ( Fig. 3 A–C, E, F, I); suture deep, fenestrated by axial sculpture ( Fig. 3 J). Last whorl evenly curved at the base. Aperture subovate; peristome somewhat expanded at the base; outer margin thick. Umbilicus indistinct. Fasciole moderate to wide ( Fig. 3 A–C, F, I).

Teleoconch sculptured with markedly-prosocline axial ribs, formed by fusion of several layers; ribs constant in number along the shell, usually 13 to 15 per whorl, but up to 18, separated by wide interspaces ( Fig. 3 A–F, H–J). Ribs on the first whorl are low, slightly increasing in height on subsequent whorls, where they remain either erect or somewhat recurved ( Fig. 3 D, H). Ribs of adjoining whorls obliquely aligned and greatly overlapping (“connected”) ( Fig. 3 J). Ribs on the last whorl regularly arched at base, extending to umbilical area ( Fig. 3 A–C, F, I). Interspaces between ribs smooth.

Operculum: Thin, oval; paucispiral, with eccentric, slightly-sunken nucleus ( Fig. 3 G). Outside surface sculptured with about 40 wide bars per 0.1 mm ( Fig. 3 K). Colour: yellowish-brown; translucent.

Jaw ( Fig. 4 D, E): Anterior margin with a row of blunt, “mushroom-like” denticles. Each denticle composed of an elongate, densely-pitted, solid base (“buttress”) that distally expands forming a disc, with a marginal reinforcement (“inner plate”). Adjacent surface irregular, pitted.

Radula: With numerous teeth per row, all of them with a minute basal denticle and slender blades ( Fig. 4 A). Teeth of the central field small, widely separated ( Fig. 4 A); subsequent teeth larger, with longer blades, closely set ( Fig. 4 A, B). Cusps composed of an acute, narrow apical denticle, followed by a large, wide, secondary denticle, which is rounded at the tip, directed towards the apical denticle ( Fig. 4 C). An additional, secondary denticle present, varying from a small, conical structure in the central field, to a knob in the outer teeth.

Remarks. Epitonium fabrizioi is most similar to E. georgettinum , particularly those specimens having erect axial sculpture. However, in contrast to these specimens, in E. fabrizioi ribs are evenly arcuate throughout the whorls (i.e., lacking the straight slope near apical suture that appears in E. georgettinum ), and the ribs of adjoining whorls are more widely overlapping. Furthermore, E. fabrizioi has a higher incremental rate of whorls, which results in a broad shell profile. Other differences arise from the number of protoconch whorls (4¼ in E. fabrizioi vs. 2½ in E. georgettinum ), the morphology of the operculum (multispiral in E. georgettinum vs. paucispiral in E. fabrizioi ), the jaw (with the denticles of the anterior margin “mushroom-like” in E. fabrizioi vs. flat, ovate, distally blunt in E. georgettinum ), and radula (see discussion below). Pastorino & Penchaszadeh (1998) also mentioned that E. fabrizioi has smaller egg capsules, each one containing a lower number of eggs. Epitonium fabrizioi was previously confused with E. albidum . A comparison with the syntypes of that species shows that E. fabrizioi has a higher incremental rate of whorls and the ribs of adjoining whorls more widely overlapping, thus making the separation of the whorls less evident and its outline less convex. Furthermore, E. fabrizioi has a dull shell surface, while in E. albidum it is shiny.

The shell and opercular characters here recognized as diagnostic for E. fabrizioi are consistent with those previously described by Pastorino & Penchaszadeh (1998); however, the morphology of the radula does not agree with their observations. According to the authors, E. fabrizioi shows “… tricuspid marginal teeth, identical in shape. Outermost cusps large and hook-like, central and inner cusps similar in size and shorter”. In the same paper, the authors included information on the radula of a specimen of Epitonium georgettinum that they described as having “… one sharp terminal cusp… and two blunt cusps, one almost obsolete”. Our study of the radulae of these two species consistently reveal for E. fabrizioi the morphology showed in figures 15 and 16 of Pastorino & Penchaszadeh’s (1998) paper (i.e., the morphology they attributed to E. georgettinum ), and for E. georgettinum a morphology which corresponds to their description and figures for E. fabrizioi . These results suggest that at the time that E. fabrizioi was described, the two species’ radulae were confused.

Among the specimens reported by Carcelles (1944) as “ Scala aff. orbignyi ” from Quequén, Buenos Aires Province, one specimen of E. fabrizioi (currently MACN-In 18676-2) was found mixed in.

Figures

FIGURE 3. Epitonium fabrizioi Pastorino & Penchaszadeh, 1998, shell and operculum. A. Holotype (MLP-Ma 5402). B. Specimen from Puerto Madryn (MACN-In 9171 - 22). C, D, G, H, K. Specimens from Punta Cuevas (MACN-In 40375). K. Detail of operculum sculpture. E, F. Specimen from Las Grutas (MACN-In 40367). I, J. Specimen from Puerto Lobos (MACN- In 40374). J. Detail of teleoconch sculpture at last whorl. Scale bars: A – C, E, F, I = 5 mm; D, H = 2 mm; G, J = 500 µm; K = 20 µm.

FIGURE 4. Epitonium fabrizioi, radula and jaw. A, D, E. Specimens from Punta Cuevas (A same specimen as Fig. 3 C) (MACN-In 40375). B, C. Specimen from Las Grutas (same specimen as Fig. 3 E, F: MACN-In 40367). A – C. Radula. A. Detail of half field of radula. B. Intermediate teeth. C. Detail of cusps. D, E. Jaw. D. Anterior margin. E. Detail of marginal denticles. Scale bars: A = 100 µm; B = 20 µm; C, D = 10 µm; E = 2 µm.