Skeneimorph gastropods in Neomphalina and Vetigastropoda — A preliminary

Abstract

Until recently the systematics of the Skeneidae (type species Skenea serpuloides Montagu, 1808) has been solely based on shell characters, radula details and external morphology. However, methodological progress (e.g. SEM) and preliminary anatomical data suggest that this vetigastropod group represents a polyphyletic, “skeneimorph” assemblage. Serial semithin sectioning combined with computer-aided 3D-reconstruction permits the detailed anatomical investigation of such small (1–3 mm), helicoid gastropods. The taxa for which micro-anatomical data are available include six skeneimorph species from six genera: (1) True Skeneidae, exemplifi ed by the type species, Skenea serpuloides (Montagu, 1808), doubtlessly belongs to Vetigastropoda and probably rests within the Trochoidea/Turbinoidea. Apomorphies of Skenea and related genera include a penis formed by the right propodium. (2) Bathyxylophila excelsa Marshall, 1988, Ventsia tricarinata Warén & Bouchet, 1993 and an undetermined “skeneimorph vetigastropod” have papillate cephalic and epipodial tentacles, a single monopectinate ctenidium with skeletal rods and bursicles, a papillary left and a right excretory organ, and statocysts with several statoconia. All these characters are indicative for a position of these species inside Vetigastropoda. Distinct appearance of epipodial tentacles and the lack of a combined epipodial sense organ argue against an inclusion into Trochoidea/Turbinoidea and thus Skeneidae s.s. (being defi ned by the characteristics of Skenea serpuloides). At present, these species cannot be classifi ed in any known vetigastropod subclade. (3) Leptogyra constricta Marshall, 1988 and Leptogyropsis kalinovoae Marshall, 1988 both are characterized by smooth cephalic and epipodial tentacles, a single, left excretory organ and statocysts with one statolith. These anatomical data strongly suggest a systematic position in the likewise rhipidoglossate Neomphalina, which might be considered as an independent rhipidoglossate clade outside the Vetigastropoda. Although we are still at the very beginning in our investigation of skeneimorph anatomies, it is clear that this polyphyletic assemblage needs to receive much more attention for a complete understanding of vetigastropod and neomphalinan phylogeny.

Morphological, ecological and molecular characterization of the enigmatic planispiral snail genus Adeuomphalus (Vetigastropoda: Seguenzioidea)

“…Semi-internal fertilization in the female mantle cavity is strongly suspected in all seguenziids and also in many, if not all, skeneimorph seguenzioids ( previously exemplified in Microcarina and Ventsia; see Kano, 2008;Kunze et al, 2008). Interestingly, Seguenziidae and three included skeneimorphs constituted a clade in the present H3 and 18S gene trees as well as in those from the small 16S data set (PP ¼ 99% in the 18S data).…”

Denser mitogenomic sampling improves resolution of the phylogeny of the superfamily Trochoidea (Gastropoda: Vetigastropoda)

“…However, major changes to the systematics of Trochoidea were based on recent molecular phylogenies (Geiger & Thacker, 2005;Williams & Ozawa, 2006;Kano, 2008;Williams et al, 2008;Williams, 2012), which challenged the monophyly of the superfamily as well as of several of the internal groups as defined by Hickman & McLean (1990), and prompted for important changes to the taxon composition and arrangement of families (Williams, 2012). For instance, some taxa were transferred to the superfamily Seguenzioidea (Verrill, 1884), newly redefined by Kano (2008), and a number of minute skeneimorph genera were variously relocated either to Seguenzoidea (Kano, Chikyu & Warén, 2009;Haszprunar et al, 2016), Neomphalina (Kunze et al, 2008), or to the new family Crosseolidae of uncertain taxonomic position (Hickman, 2013).…”