Neoleptonidae Thiele, 1934

Neoleptonidae Thiele, 1934 View in CoL

The position of this family has been controversial. Some authors included it in Cyamioidea (e.g. Thiele, 1934; Chavan, 1969; Powell, 1979; Sabelli et al., 1990; Morton, 2015), whereas others regarded it as a (possible) Veneroidea (Ockelmann in Bowden & Heppell, 1968; Salas & Gofas, 1998). Mikkelsen et al. (2006) pointed out that this family joined Veneridae in the traditional morphology tree, but fell outside Veneroidea in their all-morphology analysis. The cardinal teeth in Neolepton appear translocated with respect to the condition present in Cyamiocardium , Cyamiomactra , Cyamium , Heteromactra and Jukesena (compare Figs 1A, C, D, F, G, I, J, L, 2A, C of the present study with Salas & Gofas, 1998: figs 1, 2 or Zelaya & Ituarte, 2004: fig. 2). In addition, none of the teeth in Neolepton is grooved, and Neolepton has strong posterior lateral teeth in both valves, which are not discernible in Cyamiidae . Another difference arises in the degree of development of the external ligament, which is small in Neolepton and is equally projected at both sides of the umbones ( Salas & Gofas, 1998; D. Zelaya, personal observation), in contrast to the large ligament present in Cyamiidae , which is longer posteriorly. Regarding the anatomy, adult specimens of Neolepton (unlike cyamiid species) lack the byssus groove and functional byssus glands. In addition, Neolepton lacks tentacles at the posterior part of the mantle margin and lacks the peculiar follicular epithelium characteristic of Cyamioidea ( Ituarte & Presta, 2017; D. Zelaya, personal observation). All this evidence pleads for the exclusion of Neolepton (and, consequently, the Neoleptonidae ) from Cyamioidea . The additional molecular information obtained as part of the present study also supports this hypothesis, at the same time confirming its placement in Veneroidea.