Loxolenichnus Breton and Wisshak

Breton, Gérard, Wisshak, Max, Néraudeau, Didier & Morel, Nicolas, 2017, Parasitic gastropod bioerosion trace fossil on Cenomanian oysters from Le Mans, France and its ichnologic and taphonomic context, Acta Palaeontologica Polonica 62 (1), pp. 45-57 : 51

Ichnogenus Loxolenichnus Breton and Wisshak nov.

Type ichnospecies: Loxolenichnus stellatocinctus Breton and Wisshak isp. nov.; see below.

Included ichnospecies: The type ichnospecies, Loxolenichnus halo ( Neumann and Wisshak, 2009) comb. nov., and Loxolenichnus taddei ( Ruggiero and Raia, 2014) comb. nov.

Figs. 5 , 6 .

Etymology: Contraction of the ancient Greek words loxós (λοξός), oblique, and solen (σωλήν), canal, pipe; allusion to the central oblique penetration hole in the holotype of the type ichnospecies. Ichnus is a common ending for trace fossils names, referring to ancient Greek ichnos, track. Gender masculine.

Diagnosis.—A single or rarely several cylindrical holes, completely cutting through calcareous shelly substrates, surrounded by a circular to elliptical depression with concentrical grooves.

Remarks.—The ichnogenus Oichnus Bromley, 1981 , except the ichnospecies Oichnus halo Neumann and Wisshak, 2009 and Oichnus taddei Ruggiero and Raia, 2014 which are herein transferred to Loxolenichnus , lack the attachment scar and peripheral groove. The ichnogenera Anellusichnus Santos, Mayoral, and Muñiz, 2005 , Lacrimichnus Santos, Mayoral, and Muñiz, 2003 and Centrichnus Bromley and Martinell, 1991 in turn are pure attachment scars and lack the penetration hole(s) passing through the substrate. Kardopomorphos , with its sole ichnospecies Kardopomorphos polydioryx Beuck, López Correa, and Freiwald, 2008 is a rounded or spiral-shaped pit, from which many whip-shaped, branched canals including sometimes one or few central larger canals penetrate deeply in the substrate. By including two former Oichnus ichnospecies, Oichnus is now constrained to pure predation traces (Praedichnia). The new ichnogenus, in contrast, comprises three ichnospecies that are all combinations of complete penetrations (parasitic in nature and thus unlike Praedichnia sensu stricto) and an attachment scar (Fixichnia), and this combination of two different modes of bioerosion is characteristic of the new ichnogenus.

Figures

Fig. 5. Parasitic gastropod bioerosion and perforation trace Loxolenichnus stellatocinctus igen. et isp. nov., MHNLM 2015.2.244, holotype, Marnes à Pycnodonte biauriculata Formation, Upper Cenomanian, Lycée Bellevue earthmoving works, Le Mans, Sarthe Department, France; on LV of Rhynchostreon suborbiculatum (Lamarck, 1801). A. Entire LV shell with the arrow showing the perforation. B. LV (viewed from inside), the arrow shows the opening of the perforation on the inner side of the shell, diascopic illumination. Outer (C) and inner (D) sides of the shell, close-ups of the perforation, the dashed line delimitates approximately the course of the perforation through the shell, diascopic illumination. E. Positive X-ray print of the perforation.

Fig. 6. Parasitic gastropod bioerosion trace Loxolenichnus stellatocinctus igen. et isp. nov., MHNLM 2015.2.346 and MHNLM 2015.2.347, paratypes; lower Campanian Inoceramus lingua–Goniotheuthis quadrata Zone, quarry near Höver, Germany. A. Outer side of an oyster valve, accommodating two specimens of L. stellatocinctus (arrows). B. Close-up of the two specimens and the multiple perforations. C. Inner side of the oyster valve showing two of the perforations reaching the adductor muscle pad. Outer (D) and inner (E) sides of an oyster valve with a marginal L. stellatocinctus. F. Close-up of D, note the two concentric stellate rims and the marginal notch.