Allocoenia undetermined

Genus Allocoenia Etallon, 1859

SPECIES ORIGINALLY INCLUDED. — Astrea trochiformis Michelin, 1847, Allocoenia furcata Etallon, 1859.

TYPE SPECIES. — Allocoenia furcata Etallon, 1859, subsequent designation by Wells (1936: 100).

REMARKS

Alloiteau (1952) and several subsequent authors indicated erroneously A. trochiformis Michelin, 1847 as type species.

The differences between the genera Actinastrea d’Orbigny, 1849, Allocoenia Etallon, 1859, Stephanastrea Etallon, 1864, Stelidioseris Tomes, 1893 Allocoeniopsis Alloiteau, 1956 and Chondrocenia Roniewicz, 1989 remain very difficult and we propose here an assignment to the genus Allocoenia for the following reasons:

The genus Actinastrea being the most anciently described was defined in the Late Cretaceous and was used in the most lumping practices (see for instance Geyer 1955 who grouped in Actinastrea three species that are today considered as belonging to, at least, two different genera). Despite recent revisions (Löser 2012), the status of the genus remains nomenclaturally problematic in the sense that the currently admitted type species A. goldfussi d’Orbigny was not a part of the originally included nominal species (opposition to article 67-2 ICZN). On a taxonomic point of view, it seems that the lectotype of A. goldfussi (if, after all, we use it as a reference) and also the lectotype of Stelidioseris gibbosa (another probable species of Late Cretaceous) show septal strong granules near the wall. In Stelidioseris, these granules have been misinterpreted by Löser (2012) who considered these septal parts, trabecular in nature and dark in thin section, as lacunae. We cannot assign the Liassic samples to these taxa and prefer to place temporarily our samples within Allocoenia, a genus that would also deserve a revision.

The groupings proposed by Geyer (1955) that placed within Actinastrea the type species of Coenastrea Etallon, 1862 and Enallocoenia d’Orbigny, 1849 seem immoderate. The occurrence of S2 with paliform inner edge, with S3 tending to join on S2 (the septa are free in both latter genera), and globally smaller calices are characteristic for the forms named Allocoenia in the present work.

These forms are distinguished from Cyathocoenia Duncan, 1867 by the occurrence of a styliform columella.

In the end, the genus differs from Isastrea Milne Edward & Haime, 1851 by its straight septa with an often marked angle between confluent septa and the presence of a columella.