Ancylocirrus, KOZLOFF, 2000 AND

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 : 750

SYNONYMIZATION OF ANCYLOCIRRUS KOZLOFF, 2000 AND PRAEAPHANOSTOMA DÖRJES, 1968

Kozloff (2000) proposed the genus Ancylocirrus after finding secretory granules in the lumen of the cirrus and in the vagina of its one species, A. ornatus Kozloff, 2000 . The only details presented about these granules were that they were colourless, ~3–5 µm in diameter and likely secreted by the male system, since they were associated with sperm masses and present in the female system only after insemination. Kozloff (2000) stated that such secreted granules had not been reported in any other genera at the time and was thus sufficient for the establishment of a new genus.

Sequence data is not available for Ancylocirrus ornatus at this time. However, while secretory granules such as those described by Kozloff (2000) may not be a character that has typically been assessed in the past (although, see e.g. Aphanostoma album Dörjes, 1968 ; Baltalimania histobursalium ; Diatomovora amoena Kozloff, 1965 ), we can confirm that it is present across multiple species of Acoela ( Fig. 8 ), including in at least one species of Praeaphanostoma ( P. rubrum ; Fig. 8D ). Further, based on our own personal observations, we hypothesize that far from being unique to one species, such secretions are probably common, especially in species with larger and more glandular male copulatory organs, such as can be found in species of, for example, Baltalimania ( Fig. 8B, C ).

Ancylocirrus is further characterized by the morphology of the reproductive system: a long, curved cirrus invaginated into a seminal vesicle; a small, unciliated antrum masculinum; a long, muscular vagina; and, finally, a conspicuous seminal bursa without adornment. This morphology, along with the general body shape and pigmentation, fits in its entirety with species of Praeaphanostoma . While Ancylocirrus ornatus does differ in that it has pigmented eyespots, genera with species both with and without eyespots are widespread throughout Acoela (e.g. Amphiscolops Graff, 1904; Isodiametra ; Nadina Ulajnin, 1870; Otocelis ; Proporus Schmidt, 1848) and the character is unlikely to be of much taxonomic importance. Thereby, Ancylocirrus is designated a junior synonym of Praeaphanostoma .

Figures

Figure 8. Micropictographs of the male copulatory organ of various species of Acoela depicting widespread presence of secretory granules (arrow). A, Aphanostoma finkei. B, Baltalimania ylvae. C, Baltalimania macrospiriferum. D, Praeaphanostoma rubrum, E, Otocelis rubropunctata.