Solen Linnaeus, 1758

Giacomino, Sebastián & Signorelli, Javier H., 2021, Systematic redescription of Solen (Ensisolen) tehuelchus and Ensis macha (Bivalvia: Solenoidea) from Argentina, southwestern Atlantic Ocean, Zootaxa 4964 (3), pp. 541-558 : 544

Genus Solen Linnaeus, 1758

For synonymies see Myra Keen (1969, p. 610, 611).

Type species: Solen vagina Linnaeus, 1758: 672 . Subsequent designation by Schumacher (1817, p. 124).

Diagnosis: Shell up to 88 mm, elongated, sub-quadrangular, with ventral and dorsal sides much longer than anterior and posterior sides, gapes anterior and posterior; anterior end truncated; umbo on or very close to anterior-dorsal corner; outer surface smooth, periostracum shiny, thin, light yellow to brownish, usually eroded on the anteriordorsal area.

Remarks: The genus includes around 70 species grouped in S. ( Solen ) and S. (Ensisolen) (Coan & Valentich- Scott 2012; Cosel 1990). According to Keen (1969) the genera Vagina Megerle von Mühlfeld, 1811, Listera Gray, 1852 , and Fistula Mörch, 1853 , are synonyms of Solen ; Solenia Oken, 1823 , is a nomen nudum. The name was taken from the Greek word solen, a pipe, the gender is masculine ( Valentich-Scott et al. 2020).

Comparison: Besides the number of teeth, the genus Solen can be differentiated from Ensis by the position and shape of both adductor muscles. In Solen the anterior adductor is elliptical to elongate-elliptical extending parallel to the dorsal margin, internal of the mantle line and dorsally coincident with the mantle line ( Figs. 1A–B ); in Ensis the anterior adductor is roughly club-shaped, with the anterior end pointed and coincident with the pallial line below the ligament and the thick end pointing posteroventrally and thus detached from the dorsal pallial line ( Figs. 1E–F ). In addition, there is a small retractor muscle scar between the thicker end of the adductor scar and the dorsal pallial line which is not distinguishable in Solen , probably fused with the adductor. The posterior adductor muscle of Solen is obliquely oval and placed dorso-anteriorly of the pallial sinus ( Figs. 1A–B ); in Ensis this muscle lies posterodorsally, not in touch with the pallial sinus ( Figs. 1E–F ).

Furthermore, the foot of Solen is more cylindrical and posteriorly elongated but slightly laterally compressed in Ensis ; and the siphons are fused with transversal constrictions but smooth and variable in morphology in Ensis ( Cosel 1990; Owen 1959). According to Atkins (1936), both genera have long and narrow gills, almost free along their length and with the dorsal edges of the ascending lamellae of the outer demibranchs fused with the mantle. However, the longitudinal muscles related to the ctenidia are more developed in Ensis than in Solen .

Distribution: Species of the genus Solen are mainly distributed in the Indo-Pacific region with some exceptions occurring along the Atlantic coasts of Europe, northern Pacific Ocean, and southwestern Atlantic Ocean from southern Brazil to Argentina ( Guerra et al. 2011; Huber 2010; Saeedi et al. 2016, 2017).

Figures

FIGURE 1. A–D: Solen (Ensisolen) tehuelchus MLP 3623. A–B: schematic drawings of the inside of valves. C–D: close-up view of hinge teeth. E–H: Ensis macha, MLP 6829. E–F: schematic drawings of the inside of valves. G–H: close-up view of hinge teeth. Scale bars: A–F = 2 cm; G–H = 1 cm.