The relationships of the enigmatic neogastropodLoxotaphrus(Cancellariidae)

Abstract

The relationships of Loxotaphrus Harris, 1897 within Neogastropoda are discussed based on anatomical and DNA data. Sequences from 12S and 16S rDNA confirm Beu & Maxwell's placement of Loxotaphrus in the Cancellariidae, closer to Plesiotritoninae than to Cancellariinae. The nematoglossan radula of Loxotaphrus deshayesii and L. rosadoi and the elongated and spirally convoluted valve of Leiblein observed in L. deshayesii support a plesiotritonine affinity. Peculiar anatomical features include acinous rather than tubular salivary glands, accessory salivary glands fused along their posterior third and a mid-oesophageal gland placed anteriorly to the nerve ring.

The first anatomical description of two trigonostomatine Cancellariidae,Scalptia androyensisandScalptia foveolata(Mollusca: Gastropoda: Neogastropoda: Cancellarioidea)

“…The present results seem to indicate that in Cancellariidae, conchologically similar species (as Scalptia foveolata and S. androyensis appear to be) may display a remarkable degree of anatomical differentiation, allowing a better definition of species boundaries and highlighting the high levels of homoplasy of shell characters traditionally used in cancellariid systematics, as reported elsewhere (Modica et al 2011). More anatomical data on other species of Cancellariidae could help to evaluate the levels of anatomical differentiation in this insufficiently known gastropod group and may provide informative characters useful for phylogenetic and evolutionary studies.…”

“…Bouchet & Rocroi 2005) include Trigonostoma and allies in the subfamily Cancellariinae Forbes and Hanley, 1851, and recognised two additional subfamilies: Admetinae Troschel, 1865 andPlesiotritoninae Beu &Maxwell, 1987. The genus Scalptia Jousseaume, 1887 includes about 20 recognised species (Hemmen 2007), similar to Trigonostoma species in their shell characters, namely a strong shoulder, an open umbilicus and 2-3 columellar plaits. Noteworthy, a close affinity between Scalptia and Trigonostoma is also supported by molecular data, defining a monophyletic "trigonostomatine" clade inside the Cancellariinae (Modica et al 2011).…”

“…The salivary glands in S. foveolata are much shorter and more globular than in S. androyensis, and not connected at their posterior ends. A posterior connection of the salivary glands was reported, with different degrees, in two plesiotritonine cancellariids: in Tritonoharpa antiquata (Modica et al 2009) showing a situation similar to S. androyensis, and in Loxotaphrus deshayesii (Modica et al 2011), in which salivary glands are fused for the posterior third. This characteristic seems to be rather common and scattered in different cancellariid groups, and thus is probably not informative at high taxonomic levels.…”

“…The few anatomical works on cancellariid anatomy (Graham 1966;Ponder 1973;Harasewych & Petit 1982, 1984Strong 2003;Modica et al 2009Modica et al , 2011 did not focus on the comparison of closely related species. The present results seem to indicate that in Cancellariidae, conchologically similar species (as Scalptia foveolata and S. androyensis appear to be) may display a remarkable degree of anatomical differentiation, allowing a better definition of species boundaries and highlighting the high levels of homoplasy of shell characters traditionally used in cancellariid systematics, as reported elsewhere (Modica et al 2011).…”

“…A general issue when dealing with Cancellariidae is the relative scarcity of anatomical data: living cancellariid specimens are infrequently found and, consequently, anatomical literature is remarkably scant, with a low number of published papers on both internal anatomy (Graham 1966;Harasewych & Petit 1982, 1984Strong 2003;Modica et al 2009Modica et al , 2011 and radular structure (e.g. Troschel 1865;Barnard 1958;Olsson 1970;Oliver 1982;Schremp & Richmond 1983;Verhecken & Prelle 2014).…”