Diskussion:Eodiscina

Cephalopyge Geyer, 1988 is jr. homonym

Cephalopyge Geyer, 1988 is a jr. homonym of the nudibranch Cephalopyge Hanel, 1905. The new name for the eodiscid is Marocconus Özdikmen, 2009. See en:Marocconus Dwergenpaartje (Diskussion) 10:28, 5. Feb. 2013 (CET)

Not always 3 thorax segments

The information under Merkmale could be improved.

• Eodiscina are limited to the late Lower Cambrian and the Middle Cambrian. Perhaps wikicommons file "Cladogram Eodiscina.jpg" helps here.
• If they have eyes (many are blind, such as all Weymouthiidae), these are of a unique type called abatochroal.
• Also there are eodiscids with 2 and with 3 thorax segments.
• Eodiscids may or may not have free cheeks (librigenae).
• Pygidia may be effaced, with a rachis that may or may not show between 4 and 12 rings and the pleural regions that may or may not show furrows.
• Eodiscids have an undivided occipital ring (at the very back of the glabella) except for a few Weymouthiid genera (such as Tannudiscus, the probable ancestor of the Agnostina).

Agnostina are always blind, never possess free cheeks, always have 2 thorax segments, never have furrowed pleurae on the pygidia, always have a split occipital ring (left and right part).

There is one unique distinction between Agnostina and Eodiscina, but it can seldomly be observed: Eodiscina always have an articulating half-ring. This seals the opening in the axis between cephalon and the anterior thorax segment that is created when the animal was enrolled. Agnostida do not have an articulating half-ring, resulting in an opening between the thorax and the cephalon when enrolled, called cephalothoracic aperture.

To make it a bit more difficult: Agnostina and Eodiscina are often found or are even only known from disarticulate cephalons and pygidia (so no thorax segments to be counted) and both groups have species that are very much effaced, leaving hardly any feature that would help assign it to either group. Dwergenpaartje (Diskussion) 11:05, 5. Feb. 2013 (CET)