Setia alexandrae Avila & Cordeiro

Cordeiro, Ricardo & Avila, Sergio P., 2015, New species of Rissoidae (Mollusca, Gastropoda) from the Archipelago of the Azores (northeast Atlantic) with an updated regional checklist for the family, ZooKeys 480, pp. 1-19 : 3

Taxon classification Animalia Littorinimorpha Rissoidae

Setia alexandrae Avila & Cordeiro sp. n. Figure 1

Setia sp.: Ávila et al. (1998: 496) - DBUA 449, 478, 496, 662.

Setia sp.: Ávila et al. (2000: 147) - DBUA 787.

Setia sp.: Costa and Ávila (2001: 126) - DBUA 898 (as ATA 1).

Setia sp.: Ávila (2003: 32) - DBUA 704/A, 787.

Type material.

Holotype, DBUA 1051 (spc., 1.17 × 0.70 mm); paratype 1, DBUA 1070 (spc., 0.99 × 0.65 mm); paratype 2, DBUA 1071 (spc., 1.09 × 0.73 mm); paratype 3, DBUA 1072 (spc., 1.08 × 0.66 mm); paratype 4, DBUA 1073 (spc., 1.04 × 0.65 mm), Graciosa Island (Santa Cruz, intertidal, 01/08/2010); paratype 5, DBUA 1074 (sh., 0.95 × 0.65 mm); paratype 6, DBUA 1075 (sh., 1.02 × 0.61 mm); paratype 7, DBUA 1076 (sh., 1.07 × 0.68 mm), Pico Island (Lajes do Pico, intertidal, 07/1989); paratype 8, DBUA 1077 (spc., 0.91 × 0.62 mm); paratype 9, DBUA 1078 (spc., 1.10 × 0.65 mm), São Miguel Island (Caloura, 5-15 m depth, 21/05/1999).

Type locality.

Santa Cruz, Graciosa Island, Azores.

Additional material examined.

Graciosa Island: DBUA 35 (Fonte da Areia, intertidal, 3 spc., 10/06/1988); DBUA 37 (Porto Afonso, intertidal, 14 spc., 06/1988); DBUA 40 (Santa Cruz, intertidal, 1 sh., 06/1988); DBUA 48 ( Baía da Folga, infralittoral, 1 sh., 06/1988); DBUA 50 ( Baía da Folga, 8 m depth, 1 spc., 10/06/1988). Pico Island: DBUA 449 (Lajes do Pico, intertidal, 5 spc., 07/1989); DBUA 468 (Lajes do Pico, intertidal, 11 spc., 07/1989); DBUA 471 (Lajes do Pico, intertidal, 1 spc., 07/1989); DBUA 478 (Lajes do Pico, intertidal, 7 spc., 07/1989), DBUA 496 (Lajes do Pico, intertidal, 31 spc., 28/06/1991); and DBUA 662 (Lajes do Pico, 0-3 m depth, 1 sh., 19/08/1995). São Miguel Island: DBUA 704/A ( São Vicente, 12 m depth, 1 spc., 18/07/1996); DBUA 787 ( São Vicente, 15.1 m depth, 2 spc., 11/07/1997), DBUA 898 (Atalhada, 11.2 m depth, 4 spc., 10/10/1996), DBUA 901 ( Ilhéu de Vila Franca do Campo, 15 m depth, 1 spc., 15/07/1996), DBUA 920 (Caloura, 10 m depth, 1 spc., 12/07/1997), DBUA 963 (Porto de Vila Franca do Campo, 6 m depth, 2 spc., 22/07/1997). Formigas Islets: DBUA 336 (intertidal, 2 spc., 07/1990); and DBUA 355 (15 m depth, 22 spc., 03/07/1991). Santa Maria Island: DBUA 1018 ( Ilhéu da Vila, 17 m depth, 6 spc., 5 sh., 26/08/2004); and DBUA 1019 ( Ilhéu da Vila, 17 m depth, 2 spc., 26/08/2004).

Etymology.

Named after Alexandra Castela, the wife of Sérgio Ávila.

Description.

Shell fragile, minute, translucent, oval-conical, up to 1.2 × 0.7 mm (Fig. 1A). Protoconch smooth, dome-shaped (typical of the genus), whorls 1.25, diameter 280 µm, separated from the teleoconch by a clearly visible line (Fig. 1D and E). Teleoconch with 2.5 to 3 inflated, rounded, strongly convex whorls; whorls with regular contour and conspicuous increase in width (Fig. 1 B–D). Spire moderately high. Sculpture absent, except for very fine, inconspicuous growth lines (Fig. 1 B–D). Suture deep, constricted (Fig. 1 B–D). Last whorl large, globose, 70-75% of shell length (Fig. 1B and C). Base large, rounded. Aperture oval, oblique with continuous peristome, adapical angle somewhat acute (Fig. 1B and C). Parietal region thin, very slightly convex (Fig. 1B and C). Outer lip with very thin edge (Fig. 1B and C). Inner lip thin, very slightly recurved over umbilicus (Fig. 1B and C). Umbilicus a very narrow fissure (Fig. 1B and C). Animal light-yellow with dark-brown blotches visible at transparency (Fig. 1A). Operculum simple, thin, nucleus eccentric, yellowish at transparency (Fig. 1A and B).

Habitat.

On rocky shores covered by algae, from the intertidal down to 20 m depth.

Geographical distribution.

Pico, Graciosa, São Miguel and Santa Maria Islands, and Formigas Islets. Probably endemic to the Azores.

Remarks.

Setia alexandrae sp. n. is distinguished from the other Azorean congeners by its smooth, transparent to translucent shell, and yellowish animal having light to dark-brown blotches over the entire body. Setia alexandrae sp. n. lacks any colour decoration/pattern on the shell. Colour is a distinctive feature of most of the known Setia (e.g., variably coloured flames, spots or vertical lines, sometimes interrupted medially), which are so abundant on the Azorean Setia subvaricosa Gofas, 1990, Setia amabilis (Locard, 1886), Setia ambigua (Brugnone, 1873) and Setia scillae (Aradas & Benoit, 1876). Setia lacourti (Verduin, 1984) is similar in size (up to 1.2 mm in length) and also lacks any coloured pattern on the shell; this species was reported from the Azores by Segers (2002: 89) as Setia cf. lacourti . Setia alexandrae sp. n. clearly differs from Setia lacourti in shell shape (more elongated on the first, flattened on the latter). Setia ambigua was also reported from the Azores (Hoenselaar and Goud in litt. 2002, Ávila et al. 2012), from Terceira Island (Praia da Vitória, 38°43'N, 27°04'W, sandy beach). Setia alexandrae sp. n. differs from Setia ambigua by being about 50% smaller and by lacking any coloured decoration on the shell. A very similar specimen to Setia alexandrae sp. n. was recently found in the Pleistocene record of Santa Maria Island, Azores (Prainha outcrop, bed B1 of Ávila et al. (2009a); latitude 36°57'3.05"N, longitude 25°6'44.20"W). This well-preserved juvenile shell is herein reported as Setia cf. alexandrae DBUA-F 137/151-4 (0.61 × 0.40 mm). The protoconch and teleoconch shape and sculpture are identical to Setia alexandrae sp. n., as is the shape of the aperture. However, as it is a juvenile specimen we prefer to treat it as Setia cf. alexandrae until adult material is examined.