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

Abstract

Adeuomphalus Seguenza, 1876 is a little known genus among the skeneimorph vetigastropods, with very few specimens previously reported alive from the deep sea. We examined newly collected and museum-stored specimens from upper to lower bathyal depths in the Atlantic, Mediterranean, Pacific and Indian Oceans and recognize seven recent species in the genus: A. ammoniformis Seguenza, 1876, A. densicostatus (Jeffreys, 1884), A. trochanter Ware´n & Bouchet, 2001, A. sinuosus (Sykes, 1925 n. comb., A. guillei n. sp., A. elegans n. sp. and A. collinsi n. sp., along with a fossil species, A. bandeli (Schro¨der, 1995) from the Lower Cretaceous, Poland. These species are characterized by a minute and colourless shell with almost perfectly planispiral whorls, an orthocline aperture, distinct radial ribs and a deeply concave apex and base. At least three species are confirmed to be radula-less, while A. guillei n. sp. has a simplified (3 -2-1-2-3) rhipidoglossate radula. Anatomical investigations of A. collinsi n. sp. and A. trochanter revealed the following traits: a monopectinate ctenidium, blunt and tapering cephalic tentacles with sensory papillae, a cylindrical snout, a simple right neck lobe, a large foot with the anterior corners drawn out into finger-like projections, a smooth ESO-tentacle and a single, micropapillate epipodial tentacle on each side of the foot; absence of pigmented eyes, eye lobes, cephalic lappets and subocular peduncles. Three species collected by submersibles in the vicinity of hydrothermal vents co-occurred with carnivorous sponges of the family Cladorhizidae; a parasitic mode of life is suggested based on the lack of the radula and the peculiar, tube-like shape of the snout. Separate and combined phylogenetic analyses of mitochondrial (COI and 16S rRNA) and nuclear (histone H3 and 18S rRNA) gene sequences revealed six monophyletic groups in Seguenzioidea: Seguenziidae, Chilodontidae, Calliotropidae, Cataegidae, Spinicalliotropis and skeneimorph seguenzioids. Three included skeneimorphs (A. elegans n. sp., Xyloskenea sp. and Ventsia tricarinata) were ambiguously grouped together with long branches and low statistical supports, possibly suggesting a vast, undiscovered phylogenetic diversity of the group. Taxonomic composition, morphological characteristics and evolutionary history are discussed for the skeneimorphs and five other groups in the superfamily.

Relationships of the Triassic Eucycloidea Koken, 1897 (Mollusca, Gastropoda) to modern genera such as Pagodatrochus, Calliotropis and Euchelus, based on morphology of the early shell

“…Apparently Trochoidea and Eucycloidea have lived side-by-side since at least the Triassic that is since about 220 Ma. A similar derivation in time was also speculated by Kano et al (2009) based on molecular studies of living species considered to belong to the Seguenzioidea.…”

“…Another possible position is Danilia, which it resembles in shape but differs from it in some characters of the ornament. Kano et al (2009) classified most genera of Eucyclinae sensu Hickman & McLean (1990) in Chilodontidae and Calliotropidae. The two were interpreted as sister tribes or as two subfamilies in Chilodontidae (Bouchet et al 2005, Williams et al 2008.…”

“…One of them that have been in existence for a long time is seen in the Seguenzioidea, into which also the Calliotropis and Turcica relation had been included (Kano 2008, Kano et al 2009). Previously both genera had been interpreted to belong to the Trochoidea by Hickman & McLean (1990) including almost all Vetigastropoda without a slit-bearing shell, and families and groups within them had been distinguished by anatomical characters, predominantly the morphology and arrangement of the teeth of their radula.…”

“…When it comes to the interpretation of fossil species neither molecular data nor the morphology of the teeth of the radula can be applied. Hickman & McLean (1990) included in their interpretation earlier suggestions based on general shell shape, summarized by Knight et al (1960) and this is also the basis on which, for example, Kano et al (2009) elaborate on the fossil species. Knight et al (1960) collected existing earlier data especially from the compilation of Wenz (1938) based on the studies of former authors who compared shell shape of fossils with Recent species.…”

“…Other genera based on living species such as Pagodatrochus and Perrinia also have characters of the general morphological relationship of Calliotropidae. Kano et al (2009) summarized that Vetigastropoda are an archaic and diverse group of Gastropoda, comprising several thousand living species. Their systematic interpretation has changed former classification schemes and reconstruction of phylogeny considerably due to the molecular analysis and by including data presented by Warén et al (2003), Geiger & Thacker (2005), Williams & Ozawa (2006), Kano (2008) and Williams et al (2008Williams et al ( , 2010.…”