Elachisina colellai, Cunha, Carlo M., Santos, Franklin N. & Lima, Silvio F. B., 2016

Cunha, Carlo M., Santos, Franklin N. & Lima, Silvio F. B., 2016, New species of the genus Elachisina (Gastropoda: Elachisinidae) from northeastern Brazil, Zootaxa 4139 (1), pp. 131-134 : 131-133

Elachisina colellai n. sp.

( Figure 1 )

Type material. Holotype MZSP 107714. Paratypes MZSP 107716, 2 shells. All from type locality.

Type locality. BRAZIL: Bahia, Itaparica Island, 1985, J. Colella coll.

Etymology. In honor to Julio Colella, an enthusiastic Brazilian conchologist who collected the material studied here. Diagnosis. Shell small, translucent, ovate-conical profile. Protoconch paucispiral, 1/2 whorl, smooth, separation from teleoconch sharp, with a narrow orthocline scar. Teleoconch globose, sculptured by rather equally spaced, weak slight spiral threads, crossed axially by irregular growth lines. Last whorl rounded. Columellar region arched. Umbilicus narrow, delimited by very slight, blunt rim.

Description. Shell small (SH 1.8–2.5 mm), thin, translucent, ovate-conical profile ( Figs 1 A, C); SW/SH 0.60–72; spire height (0.8–1.0 mm) about 2/3 SH, spire whorls rounded, suture distinct. Protoconch 1/2 whorl (sensu Verduin 1977), 0.34 mm wide, smooth, separation from teleoconch sharp (narrow orthocline scar) ( Fig. 1 B). Teleoconch globose, 3 roundly inflated whorls, which increase rapidly in size; sculptured by rather equally spaced, weak spiral threads, crossed axially by irregular faint growth lines ( Fig. 1 E). Penultimate and last whorls with about 10 and about 16 spiral threads, respectively. Suture well marked, channeled ( Fig. 1 D). Last whorl rounded, about 1/2 SH. Columellar region slightly arched; base ornamented with about 18 spiral threads. Aperture large, moderately narrow, anteriorly rounded, AW/AH 0.53–0.60, AH/SH 0.56–0.61; parietal region about 1/2 AH, with sharp angulation in highest part, slightly convex; columellar region slightly concave about 1/2 AH; inner lip smooth, thin, weakly deflected ( Fig. 1 A); outer lip smooth, thin, moderately curved ( Fig. 1 A). Umbilicus narrow, moderately deep, sculptured with few fine threads; axial thread may be present coming into the umbilicus through the middle; umbilical area delimited by very slight, blunt rim ( Fig. 1 A).

Measurements. Holotype: MZSP 107714 — SH = 1.8 mm, SW = 1.3 mm, AH = 1.0 mm, AW = 0.6 mm; paratypes (2): MZSP 107716—SH = 2.5 mm, SW = 1.5 mm, AH = 1.5 mm, AW = 0.8 mm; SH = 1.9 mm, SW = 1.5 mm, AH = 1.0 mm, AW = 0.7 mm.

Distribution. Known only from type locality.

Habitat. Unknown.

Material Examined. Types.

Remarks. This family was established by Ponder (1985) based on a unique combination of anatomical characters of the species Elachisina floridana . The anatomy of the family can be summarized as having a bilobed snout; foot with an anterior pedal gland, a metapodial tentacle arising from its bilobed posterior end; a pair of pallial tentacles; long, slender, ciliated, parallel-sided cephalic tentacles with the eyes on swellings at their outer bases; a large ctenidium with low triangular filaments; an oval osphradium; a well-developed hypobranchial gland and a bursa copulatrix located in the pallial roof ( Ponder 1985; Ponder & Keyzer 1998). Members of this family (e.g. Elachisina ) have shell morphology very similar to rissoellids (e.g. Rissoella ), differing in having usually numerous spiral grooves and threads on the teleoconch as observed in Rolán & Rubio (2001).

Elachisinids of the genera Elachisinia, Dolicrossea Iredale, 1924 and Pseudocirsope O. Boettger, 1907 † have a very similar combination of conchological characters. The presence of an umbilicus bordered by a slight keel/ridge/rim and sculptured inside with an axial thread are the striking features in species of Elachisina ( Rolán & Rubio 2001; Rolán & Gofas 2003). Dolicrossea and Pseudocirsope differ from Elachisina mainly in having a strong ridge/cord bordering the umbilicus ( Finlay 1930; Muller 2011). Furthermore, there is a strongly projecting, twisted cord bordering the umbilicus and a short siphonal canal in members of Dolicrossea ( Finlay 1930) . Laeviphitus van Aartsen, Bogi & Giusti, 1989 differs from these three genera of elachisinids mainly by the rissoiform shell, usually with a minutely granular surface and cancellate protoconch ( Warén & Bouchet 2001).

The general shell morphology of the new species resembles the Western Atlantic Elachisina floridana and Eastern Atlantic E. canaliculata Rolán & Rubio, 2001 , E. canarica , E. pelorcei Rolán & Gofas, 2003 and E. senegalensis Rolán & Gofas, 2003 . However, E. colellai n. sp. clearly differs from these congeners by its paucispiral protoconch with less than one whorl ( Fig. 1 B), whereas previously described Elachisina have protoconch with a little more than one up to two whorls (see Rolán & Rubio 2001; Rolán & Gofas 2003). Another important feature of the new species is the moderately narrow aperture measuring about 60% of the total length of shell and having a sharper angulation in the adapical part. The aperture of other Atlantic Elachisina is enlarged, ovate-pyriform, and about 50% of the total length of shell and with a greater adapical angulation (e.g. E. canaliculata , E. canarica , E. floridana , E. pelorcei and E. senegalensis ) ( Rolán & Rubio 2001; Rolán & Gofas 2003). Elachisina colellai n. sp. also differs in having the umbilical region delimited by a very slight, blunt rim, while E. canaliculata , E. canarica and E. floridana have a well-delineated umbilical rim (see Rolán & Rubio 2001; Rolán & Gofas 2003).

Elachisina colellai n. sp. and E. floridana live sympatrically in northeastern Brazil. The new species also differs from E. floridana in having slight spiral threads on the teleoconch and the antero-posteriorly elongated aperture with slightly curved inner and outer lip. Elachisina floridana has a dense and distinctive sculpture formed by regular spiral threads and grooves on the teleoconch whorls and a pyriform aperture with more broadly curved outer and inner lips ( Ponder 1985: fig. 6B–C; Rolán & Gofas 2003: figs 1–2, 4–5). Furthermore, the last whorl is largely rounded, and the upper part of the inner lip is not separated from the parietal wall and is expanded on the lower part in E. colellai n. sp. In contrast, E. floridana has a globose last whorl, and the upper part of the inner lip is slightly separated from the parietal wall ( Ponder 1985: fig. 6B–C; Rolán & Gofas 2003: figs 1–2, 4–5).

Figures

FIGURE 1. Elachisina colellai n. sp. A, C – E. Holotype (MZSP 107714). B. Paratype (MZSP 107716), apical view of protoconch (SEM). E. Detail of ornamentation on the last whorl (SEM). Scale bars: A, C. 500 µm. B, D. 200 µm. E. 100 µm.