Argeneuthria euthrioides ( Melvill & Standen, 1898 ) Melvill & Standen, 1898

Pastorino, Guido, 2016, Revision of the genera Pareuthria Strebel, 1905, Glypteuthria Strebel, 1905 and Meteuthria Thiele, 1912 (Gastropoda: Buccinulidae) with the description of three new genera and two new species from Southwestern Atlantic waters, Zootaxa 4179 (3), pp. 301-344 : 330-332

Argeneuthria euthrioides ( Melvill & Standen, 1898) new comb.

Figures 21 A–P, 22A–E

Lachesis euthrioides Melvill & Standen, 1898: 98 , pl. 1, fig. 9.

Meteuthria martensi Strebel. Castellanos, 1992: 20 , pl. 1, fig. 7 only.

Type material. 3 syntypes from Shallow Bay, Lively Island are deposited at the Manchester Museum. One of these specimens, EE.7750, illustrated here in Figs 21 A–C, is designated as lectotype in order to preserve stability of nomenclature in agreement with ICZN article 74; and 2 others are paralectotypes, EE.7751 ( Figs 21 D–F, G–I).

Description. Shell small, less than 10 mm in height, fusiform, red, brownish, bright, outside and inside, of 6 slightly convex, distinct whorls; protoconch of 2 1/2 convex whorls ( Figs 21 O, P), translucent, entirely smooth, transition to teleoconch only signalled by onset of spiral ornamentation; suture impressed, somewhat channelled; aperture oval, siphonal canal deep, oblique and short; parietal callus very thin; spiral ornamentation of thick threads, 3 in the second and third whorls, 4 in the others; axial sculpture of 12 to 13 varices that develop into nodes when crossing the spiral threads.

Operculum ( Fig. 22 D) thick, elliptical in shape, nucleus subterminal, attachment area with a thick rim. Radula ( Figs 22 A–C) as in A. paessleri ; lateral teeth have 3 cusps but the innermost less developed. Penis ( Fig. 22 E) as in the other species of the genus.

Material examined. 29 spms., Ushuaia, (MACN-In 40507).

Distribution. Known from Ushuaia, Beagle Canal, Tierra del Fuego and Lively Is.

Remarks. This species was included in Argeneuthria basically because of the close similarity with radula and penis of A. paessleri despite some minor proportional variations. The shell morphology most closely resembles that of F. kobelti ; however, the protoconch in F. kobelti is smaller (1.5 whorls in F. kobelti vs. 2.5 whorls in A. euthrioides ). Also, in A. euthrioides the ornamentation begins with axial varices and then the spiral cords appear, while in F. kobelti three cords develop initially on the first whorls over a smooth surface and then the axial varices rise (see figures 15I –K). In addition, A. euthrioides has a shorter siphonal canal, lower spire and the nodes are more globose and rounded that those of F. kobelti .

Figures

FIGURE 21. Argeneuthria euthrioides (Melvill & Standen, 1898). A – I. Lachesis euthrioides Melvill & Standen; A – C: Lectotype, Shallow Bay, Lively Island, EE. 7750; D – F and G – I: two paralectotypes, EE. 7751. J – K. MACN-In 40507, Ushuaia. L – M. MACN-In 40507, Ushuaia, Scale bar = 3 mm. O – P. Two views of the protoconch, scale bar = 500 µm,

FIGURE 22. Argeneuthria euthrioides (Melvill & Standen, 1898). A – C. three views of the radula, scale bars: A = 20 µm, B = 10 µm; C = 50 µm. D. external and internal view of the operculum, scale bar = 500 µm. E. critical point dry of the penis, scale bar = 200 µm.