Alluna, FAUBEL & REGIER, 1983 TO THE

Atherton, Sarah & Jondelius, Ulf, 2022, Phylogenetic assessment and systematic revision of the acoel family Isodiametridae, Zoological Journal of the Linnean Society 194, pp. 736-760 : 745

REASSIGNMENT OF ALLUNA FAUBEL & REGIER, 1983 TO THE FAMILY ACTINOPOSTHIIDAE HOOGE, 2001

There were several inconsistencies in Faubel & Regier’s (1983) original description of Alluna . First, they stated in the genus diagnosis that A. sublittoralis Faubel & Regier, 1983 was the type and only species, but entitled Alluna vulgaris as the caption of their illustrations. Since no other species description occurred apart from that of A. sublitoralis , and no illustration of A. sublitoralis was provided, Alluna vulgaris can be considered a synonym of Alluna sublitoralis . More importantly, Faubel & Regier (1983) stated in the diagnosis of Alluna that a true seminal vesicle is absent, but they described paired false seminal vesicles attached to a (true) seminal vesicle in the subsequent description of A. sublitoralis , a feature that was also clearly present in the following illustrations.

If the genus diagnosis is thus emended to fit its type and only species, its morphology becomes more consistent with species of Actinoposthiidae than with Isodiametridae . Following the family diagnosis of Hooge (2001), Actinoposthiidae includes those species of Acoela with a penis built of either sclerotized or muscular elements that is never invaginated into a seminal vesicle. Alternately and according to the diagnosis of Hooge & Tyler (2005), Isodiametridae includes those species of Acoela with a muscular, isodiametric penis that is partially or completely invaginated into a muscular seminal vesicle, if present. The penis of Alluna sublitoralis is highly muscular, not isodiametric (following the original illustrations, the proximal part of the penis swells to form a bulb), and – different to all other species of Isodiametridae – lies entirely outside of the seminal vesicle. Unfortunately, sequences of Alluna sublitoralis are currently not available for analysis, so the position of the species could not be tested using molecular techniques. However, in consideration of its morphology, the species and genus must be transferred to Actinoposthiidae .