Arachnocorallium stilla

Taxonomy

Catalog entries: Arachnocorallium stilla

Original description:

Description. Shell consists only of an apically elongated tear- shaped cephalis. Pores are circular to elliptical, generally large, irregularly arranged. Shell wall is rough and numerous spine-like thorns arise from bar nodes. Spines A and V (Pl. 5, fig. 3) are incorporated in the shell wall but do not seem to protrude as horns (or they are not distinguishable from the numerous thorns). Spines D, Ll and Lr are fairly long, conical and can bifurcate close to their base (Pl. 5, fig. 5). Ax is not noticeable.

Remarks. It differs from Peridium infundibuliforme (Funakawa, 1995b) in its upper cephalis bearing numerous spines, being crested, with a smaller number of pores. This new species also differs in spines D, Ll and Lr being more robust and longer than in P. infundibuliforme. It is also distinguished from Plectacantha oikiskos Jørgensen, 1905, Arachnocorys dubius Dogiel in Dogiel & Reshetnyak, 1952, Plectacantha cresmatoplegma Nigrini, 1968 and Plagiacantha panarium Dumitrica, 1973 primarily by those species’ cephalic wall being only a thin meshwork spread between a series of spines connected to MB and directed upwards and not a proper eucephalic chamber as in A. stilla. It differs from Peridium longispinum Jørgensen, 1900 (see also Bjørklund 1976a, pl. 7, figs 9–15) in its elongated cephalis, thicker bars, shorter spines and in being much larger (c. 80 μm v. c. 45 μm); and from Peridium piriforme Popofsky, 1908 also in its larger size (P. piriforme is c. 60 μm) and, more importantly, in its basal spines (D, Ll and Lr) being shorter and lacking the many distal branches that Popofsky described and illustrated for P. piriforme. It is finally distinguished from Arachnocorallium calvata (Haeckel, 1887) by its numerous thorns/spines and in its elon- gated cephalis.

The specimen illustrated on Plate 5, fig. 5A–B possesses a thin, unfinished thoracic wall, connected to spines D, Ll and Lr but also to some thorns on the lower third of the cephalic wall (i.e. where the cephalis outline starts to narrow). This growth stage is reminiscent of what has been shown for Arachnocorallium calvata in Petrushevskaya, (1971, pl. 70, figs 1–8); however, in A. calvata, some branchings seem to connect the thorax wall to the upper third of the cephalic wall as well, in an early stage of the thorax development (Petrushevskaya, 1971, pl. 70, fig. 7), whereas here there is no trace of such connections in our specimens of A. stilla.

Description

Biogeography and Palaeobiology

Biostratigraphic distribution

Geological Range:
Last occurrence (top): within Piacenzian Stage (2.59-3.60Ma, top in Piacenzian stage). Data source:
First occurrence (base): within Tortonian Stage (7.25-11.62Ma, base in Tortonian stage). Data source:

Plot of occurrence data:

• Range-bar - range as quoted above, pink interval top occurs in, green interval base occurs in.
• Triangles indicate an event for which a precise placement has been suggested.
• (NB There is no histogram as there are no occurrence records for the taxon in the Neptune database) Parent: Arachnocorallium

Arachnocorallium stilla compiled by the radiolaria@mikrotax project team viewed: 20-8-2026 Taxon Search: Advanced Search Short stable page link: https://mikrotax.org/radiolaria/index.php?id=206227 Go to Archive.is to create a permanent copy of this page - citation notes

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