Calcideletrix fastigata ( Radtke, 1991 ) Wisshak, 2017

Wisshak, Max, 2017, Taming an ichnotaxonomical Pandora’s box: revision of dendritic and rosetted microborings (ichnofamily: Dendrinidae), European Journal of Taxonomy 390, pp. 1-99 : 41-43

Calcideletrix fastigata ( Radtke, 1991) comb. nov.

Fig. 14

Polyactina fastigata Radtke, 1991: 89 , pl. 12, figs 3–4.

Algal form B – (?) Budd & Perkins 1980: 887, fig. 7B.

Morfotipo B 2 – Mayoral 1988 (partim?): 303, fig. 1.3, pl. 1, figs 2, 4.

Morfotipo B 3 – (?) Mayoral 1988: 303, fig. 1.4, pl. 1, fig. 5.

Polyactina fastigata – Wisshak 2008: 43, fig. 9A–B.

Original diagnosis

Von einem Hauptast oder einem sehr kleinen zentralen Hohlraum zweigen strahlenartig in einer Ebene Gänge auf, die sich zum distalen Ende hin verjüngen und in dünnen, z. T. sehr langen, verzweigten, rhizoidalen Ausläufern enden. Auf der der Schalenoberfläche zugewandten Seite stehen Rhizoide mit der Oberfläche in Verbindung. [Translation: From a main gallery or a very small central cavity, tunnels radiate and ramify in one plane, and taper along partly very long rhizoidal galleries towards their distal termination. Facing the substrate surface, rhizoids connect the galleries with the surface]

Original description

The general shape of the trace varies, but follows a dendritic growth pattern. Either from a very small central cavity dichotomously branching galleries radiate, or the central cavity is developed more as an elongated main branch, from which further partly bent galleries emerge. The galleries measure 8 to 15 µm in diameter (entire trace: 100 to 1150 µm) and branching points are mostly swollen (Ø 11 to 25 µm). They bifurcate in acute angles (ca 30° to 50°). The transitions to the side branches often show web-like widenings. All traces show the characteristic tapering terminations that lead into bifurcating and partly very long rhizoids (Ø 0.5 to 4 µm). The latter are not restricted to the terminations but occur in the entire gallery system, facing the substrate surface (Ø then mostly 0.5 to 1.5 µm). They partly act as small pillars below the main galleries. In the mostly chaotically arranged rhizoids occasionally spindleshaped swellings (Ø 2 to 5 µm) can be seen. [Translated from German]

Type material, locality and horizon

The type material consists of a cast with many specimens, collectively addressed as “ holotype ” in the original publication, in a resin cast of a shell of Pecten O.F. Müller, 1776 from the Sophia Jakoba

8 II locality, Niederrheinische Bucht, Germany; Grafenberger Sand Member, Upper Oligocene. Numerous further specimens collectively addressed as “ paratypes ” in several casts of another Pecten shell from the same locality, and in casts of an Ostrea shell from the Sophia Jakoba 6 locality, Lower Rhine Embayment; Germany, Ratheimer Beds, Lower Oligocene. Hereby, the specimen originally illustrated by Radtke (1991: pl. 12, figs 3–4) is designated as the lectotype ( Fig. 14 A–C), rendering all other specimens in the type material paralectotypes (e.g., Fig. 14 D–F). It is deposited at the Institut für Geowissenschaften, Goethe Universität, Frankfurt, Germany (inventory numbers: Bo 7/161 for the lectotype and paralectotypes; Bo 7/147 and Bo 7/160 for further paralectotypes).

Remarks

In the centre of one of the paralectotypes (on Bo 7/147), several framboidal pyrite aggregates were found (confirmed via EDX detection of Fe and S in stoichiometric correct proportions), possibly representing pyritised fungal spores ( Fig. 14D, F ). They were surrounded by calcite spar that was dissolved by the hydrochloric acid during the sample preparation procedure, explaining why the centre of the trace was not reached by the epoxy resin impregnation. In the case of the lectotype, several of these framboidal pyrite aggregates are embedded within the resin at points of slight swellings along the main gallery, as evidenced by a differential SEM signal when using a backscatter electron (BSE) detector ( Fig. 14C ).

This ichnospecies is the smallest representative of Calcideletrix . It often shows a rather rapid tapering from the generally constant diameter of the central main galleries towards the rhizoidal appendages as well as the extensive peripheral galleries. The latter often show a strict alternating bifurcation pattern, distinguishing it from the other taxa within this ichnogenus.

Originally established within the ichnogenus Polyactina, but clearly distinguished from its former sister ichnospecies Polyactina araneola (= type ichnospecies) by being a non-colonial and prostrate trace, the presence of the rhizoidal connections to the substrate surface, and the alternating bifurcation pattern of the peripheral galleries.

Figures

Fig. 14. Calcideletrix fastigata (Radtke, 1991) comb. nov. A–C. SEM of the lectotype (together with fungal trace Saccomorpha clava Radtke, 1991) in an epoxy cast of an Oligocene Pecten bivalve shell from the Niederrheinische Bucht, Germany. Close-up in B illustrates the fine rhizoidal connections to the substrate surface. Close-up in C shows framboidal pyrite spheres (fossil fungal spores?) embedded within the resin. D–F. Large paralectotype in a cast of an Oligocene Ostrea bivalve shell from the same locality. Close-up in E exhibits the alternating bifurcation pattern of very fine peripheral galleries. Closeup in F shows the centre of the trace with further framboidal pyrite aggregates; epoxy resin was hindered in penetrating the cavity due to calcite spar (now dissolved).