Epitonium georgettinum ( Kiener, 1838 )

Zelaya, Diego G. & Güller, Marina, 2017, Undercover speciation of wentletraps (Caenogastropoda: Epitoniidae) in the Southwestern Atlantic, Zootaxa 4286 (1), pp. 41-69 : 43-46

Epitonium georgettinum ( Kiener, 1838)

( Figures 1 , 2 )

Scalaria georgettina Kiener, 1838: 14 , pl. 5, fig. 15

Scalaria elegans d'Orbigny, 1839: 389 –390, pl. 54, figs. 1–3

Scalaria orbignyi Nyst, 1871: 124 –125 (nomen novum for Scalaria elegans d’Orbigny non Risso, 1826); Mörch, 1876: 197 –198; Boury, 1911: 36 –37

Scala aff. orbignyi: Carcelles, 1944: 248 , pl. 2, fig. 29 (in part)

Epitonium (Epitonium) georgettina: Clench & Turner, 1951: 265 –266, pl. 116, figs. 1, 2; pl. 117, fig. 1; Castellanos, 1970: 62 –63, pl. 4, fig. 5; Rios, 1994: 97, pl. 32, fig. 386

Type localities. “ Océan Atlantique ” ( Scalaria georgettina ); “baie de San Blas ”, “baie Blanche ” and “embouchure du Rio Negro ” [Buenos Aires Province, Argentina] ( Scalaria elegans ).

Type material. 8 syntypes of Scalaria georgettina (NHMG Inve 75290); 15 syntypes of Scalaria elegans , only one of them examined herein (NHMUK 1854.12.4.358).

Additional material examined. Uruguay: Rocha: [33°54’00’’S 53°31’00’’W], La Coronilla (MACN-In 19215: 16 sh.); [34°39’00’’S 54°10’00’’W], La Paloma (MACN-In 28773: 7 sh.; MACN-In 17547: 11 sh.) ; 34°40’00’’S 53°59’30’’W, off La Paloma, 27 m (MACN-In 15352: 2 sh.). Maldonado: [34°58’00’’S 54°57’00’’W], Punta del Este (MACN-In 15204: 2 sh.; USNM 180870 : 4 sh.). Argentina : Buenos Aires Province: [36°17’23’’S 56°46’53’’W], Punta Rasa , Bahía San Borombón (MACN-In 28770: +50 sh.); [36°17’35’’S 56°46’37’’W], Cabo San Antonio (MACN-In 1248: 25 sh.; MACN-In 16304: 14 sh.) ; 36°53’S; 53°54’W, 61.9 m (MACN-In 23443: 1 spm.); [37°09’00’’S 56°52’49’’W], Ostende (MACN-In 20101: 4 sh.); 37°35’03’’S 54°55’03’’W, 175.5 m (MACN- In 25169-1: 1 sh.); 37°59’49.96’’S 57°34’35.69’’W, Mar del Plata (MACN-In 25362: 12 sh.); [38°00’S 57°33’W], Mar del Plata, 42 m (MACN-In 8890: 1 sh.); [38°00’S 57°33’W], off Mar del Plata (MACN-In 14331: 4 sh.); [38°16′13″S, 57°50′W], Miramar (MLP-Ma 1449: 1 sh.; MLP-Ma 1472-1: 1 sh.; MLP-Ma 3245: 1 sh.); 38°25’18.50’’S 56°30’37.07’’W, off Mar del Plata (MACN-In 10245, 2 sh.; MACN-In 10741: 4 sh.; MACN-In 10322: 1 sh.; MACN-In 10296: 1 sh.; MACN-In 12211: 1 spm.); 38°34’28.7’’S 58°42’42.1’’W, Puerto Quequén (MACN-In 18676: 4 sh.; MLP-Ma 2403-1: 1 sh.); 38°59’05.25’’S 61°17’58.68’’W, Monte Hermoso (MACN-In 9209-24: 8 sh.; MACN-In 6619-44: 1 sh.; MACN-In 11214: 1 sh.; MLP-Ma 1407-1: 2 sh.; MLP-Ma 2024 in part: 3 sh.; MLP-Ma 3213: 12 sh.; MLP-Ma 3214: 4 sh.); [39°35’18.6’’S 62°06’10.2’’W], Bahía Brigman (MACN-In 16138: 4 sh.); [38°52’00’’S 62°04’00’’W], Arroyo Pareja , Bahía Blanca (MACN-In 11213: 5 sh.); [38°53’13’’S 62°05’52’’W], Base Naval Puerto Belgrano, Punta Alta (MACN-In 11212: 1 sh.); [39°08’34’’S 61°58’08’’W], Isla Trinidad , Bahía Blanca (MACN-In 19668: 2 sh.); [39°42’S 62°07’W], mouth of Río Colorado (MLP-Ma 1369: 10 sh.; MLP-Ma 1372: 16 sh.; MLP-Ma 1377: 8 sh.) ; 40°18’29.79’’S 62°14’15.66’’W, Bahía San Blas (MACN-In 20265: 3 spm., +100 sh.; MACN-In 20267-1: 1 sh.); [40°47’S 62°58’W], Carmen de Patagones (MLP-Ma 2608: 1 sh.); off Buenos Aires (MACN-In 10421: 1 sh.; MACN-In 11724: 2 sh.) . Río Negro Province: Golfo San Matías (MACN-In 30809: 1 sh.); [41°00’S 64°07’W], Aguada de los Loros, San Antonio Este (MACN-In 13339: +300 sh.); [40°49’S 64°54’W], Punta Villarino, San Antonio Este (MACN-In 9379-44: 1 sh.; MACN-In 13150: 2 sh.; MACN-In 13364: 9 sh.); [40°44’00’’S 64°57’00’’W], Puerto San Antonio Oeste (MACN-In 9379-43: 2 sh.) ; 41°02’S; 62°24’W, 20 m (MACN-In 20667: 1 sh.); 40°25’47.4’’S 65°25’14.1’’W, 8 m (MACN-In 40359: 1 sh.); 40°45’18.7’’S 64°56’31.8’’W, La Mar Grande, intertidal (MACN-In 40360: 18 sh.); 40°54’08.3’’S 65°06’28.0’’W, 9 m (MACN-In 40361: 1 sh.); 40°55’17.4’’S 65°08’07.6’’W, 7-8 m (MACN-In 40362: 1 sh.); 40°56’27.2’’S 65°07’58.2’’W, 10-11 m (MACN-In 40363: 1 sh.); 41°16’S 65°12’W, 45.7 m (MACN-In 23742: 1 sh.); 41°38’06.6’’S 65°00’55.9’’W, Playas Doradas, 7 m (MACN-In 40364: 3 sh.); 41°38’49’’S 65°01’25.9’’W, Playas Doradas, intertidal (MACN-In 40365: 1 spm.); 42°15’24.6’’S 62°54’52.8’’W, 60 m (MACN-In 40366: 2 sh.).

Chubut Province: [42°25’49’’S 64°08’26’’W] , Puerto San José (MACN-In 11479: 3 sh.); [42°34’S 64°17’W], Puerto Pirámides , Chubut (MLP-Ma 5404: 2 spm.); 42°45’26.91’’S 65°02’33.13’’W, Puerto Madryn (MACN-In 22478: 4 sh.).

Known distribution. Santa Catarina (27°16’S), Brazil ( Rios 1994) to Puerto Madryn (42°45’S) , Chubut Province, Argentina. Living specimens: intertidal to 61.9 m ; dead shells up to 175.5 m.

Cárdenas et al. (2008) identified as Epitonium georgettinum specimens from the Chilean Fjords Region, in the Southeastern Pacific Ocean. The study of these specimens (housed at the MZUC and MNHN-Cl) reveals that they do not actually correspond to this species. The identity of this material will be discussed elsewhere.

Description. Shell large (maximum L observed = 37.3 mm, protoconch missing), narrowly elongated, moderately solid, white, porcelainous ( Fig. 1 A–C, F, H, I). Protoconch elongated, about 500 µm long and 350 µm in maximum diameter; composed of 2½, evenly-rounded whorls ( Fig. 1 E); usually lost in larger specimens; sculptured with faint axial threads ( Fig. 1 G). Transition between protoconch and teleoconch well-defined. Teleoconch with up to 10½ whorls, markedly convex in outline; suture deep, fenestrate ( Fig. 1 K). Last whorl evenly curved at the base. Aperture subovate, slightly expanded at its base. Outer margin thick; inner margin completely attached to last whorl ( Fig. 1 A–C, F, H, I). Umbilicus usually absent, narrow when present. Fasciole small to large.

Teleoconch only sculptured with slightly prosocline, widely-separated axial ribs, formed by fusion of several layers ( Fig. 1 K). Number of ribs constant throughout the whorls: usually 12 to 15, but as few as 10 ( Fig. 1 D). Ribs on the first whorl are low and rounded, increasing in height in subsequent whorls, where they may remain either as narrow, erected elements or, more frequently, as strongly recurved elements that give the appearance of rounded cords ( Fig. 1 A–D, F, H, I). In the first case, a flattened, sloping part of the ribs is evident near the suture ( Fig. 1 A, C, I); in the second case, the flattening is less noticeable ( Fig. 1 F, H). Ribs of adjoining whorls obliquely aligned and in contact at their bases ( Fig. 1 K). Axial ribs extending to the umbilical area ( Fig. 1 A–C, F, H, I). Interspaces between ribs smooth.

Operculum: Moderately solid, subcircular, multispiral, with subcentrally-located nucleus ( Fig. 1 J); whorls without raised edges. Outside surface sculptured with 35–43 fine threads per 0.1 mm, obliquely oriented with respect to growth lines ( Fig. 1 L). Colour: light-brown, translucent.

Jaw ( Fig. 2 E, F): Anterior margin with a row of flat, ovate, distally-blunt denticles, pitted along their entire surface; followed by two to four rows of polygonal, densely-pitted plates; remaining surface granulate to smooth in appearance.

Radula: With numerous teeth per row, each with a well-developed basal denticle ( Fig. 2 A). Teeth of the central field with short and stout blades ( Fig. 2 D); subsequent teeth with elongate, strong blades, reducing in size near the outer margin ( Fig. 2 A–C). Cusps similar along all radular field, comprising an acute apical denticle and two somewhat shorter secondary denticles ( Fig. 2 C).

Remarks. The sculpture of this species was usually previously described as wide, rounded axial ribs (e.g., Clench & Turner 1951; Castellanos 1970). In fact, d’Orbigny (1839) when describing Scalaria elegans (here regarded as a synonym of E. georgettinum ) pointed out that this species differs from Epitonium albidum by lacking the lamellate ribs that are present in the latter. However, Weil et al. (1999) described for the species the presence of “narrow” ribs. This apparent contradiction disappears when considering that both alternatives are present in specimens with the same radular, jaw and opercular morphologies. These observations indicate that erect and markedly recurved axial ribs are part of the intraspecific variability of this species. Clench & Turner (1951) described the protoconch of E. georgettinum as being smooth. However, a relatively well-preserved specimen allows us to confirm (herein) that it actually shows faint axial threads when examined under high magnification. Concerning discrepancies with the previous description of the radula of this species, see remarks under Epitonium fabrizioi .

D’Orbigny (1839) reported “baie de San Blas”, “baie Blanche” and “embouchure du Rio Negro ” as the provenance of Scalaria elegans . Clench & Turner (1951) limited the type locality of this species to the first locality alone; but taking into account that there has been no formal designation of a lectotype for the species, all the material reported by d’Orbigny (1839) should be regarded as syntypes, and consequently the type localities of the species correspond to all the sites mentioned by the author (ICZN arts. 73.2.3 and 76.1). The syntypes of Scalaria georgettina , currently labelled as NHMG Inve 75290, have been previously divided into “probable syntypes ” (previously numbered as 989.11.1 to 989.11.3) and “possible syntypes ” (previously numbered as 989.11.4 to 989.11.8). In this case, there has not been a formal designation of a lectotype either.

Figures

FIGURE 1. Epitonium georgettinum (Kiener, 1838), shell and operculum. A. Syntype of Scalaria georgettina (NHMG Inve 75290). B. Syntype of Scalaria elegans (NHMUK 1854.12.4.358). C, H. Specimens from La Mar Grande (MACN-In 40360). D – E. Specimens from Bahía San Blas (MACN-In 20265). F, G, K. Specimen from Puerto Quequén (MACN-In 18676). G. Detail of protoconch sculpture, K. Detail of teleoconch sculpture at last whorl. I, J, L. Specimen from Playas Doradas (MACN- In 40365). L. Detail of operculum sculpture. Scale bars: A – C, H, I = 10 mm; D, K = 500 µm; E = 200 µm; F = 2 mm; G = 50 µm; J = 1 mm; L = 20 µm.

FIGURE 2. Epitonium georgettinum, radula and jaw. A, B, E. Specimen from off Mar del Plata, with “ blade-like ” ribs (MACN-In 12211). C, D, F. Specimen from Playas Doradas with “ cord-like ” ribs (same specimen as Fig. 1 I: MACN-In 40365). A – D. Radula. A. Half radular field. B, C. Intermediate teeth. D. Detail of teeth of central field. E, F. Jaw. E. Anterior margin. F. Detail of marginal denticles. Scale bars: A = 100 µm; B, C, E = 20 µm; D = 50 µm; F = 10 µm.