Rimicola glacilis Böhmig, 1908

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 : 756-757

• Rimicola glacilis Böhmig, 1908

Notes

Rimicola can be distinguished from most of the other genera of Isodiametridae by the absence of rhabdoid glands, a muscular seminal vesicle a n d f e m a l e a c c e s s o r y o r g a n s. I t i s c l o s e s t i n morphology to Pseudoposthia , which also lacks a true seminal vesicle and bursa, but Pseudoposthia can be differentiated through the absence of an antrum masculinum and the presence of rhabdoids and a glandular organ associated with the male copulatory organ.

KEY TO ISODIAMTETRIDAE 1a. Seminal bursa absent ................................................................................................................................... 2

1b. Seminal bursa present.................................................................................................................................. 7

2a. Pharynx absent .............................................................................................................................................3

2b. Pharynx present............................................................................................................................ Pharyngia

3a. Penis distinct. True seminal vesicle absent .................................................................................................4

3b. Penis at least partially invaginated into muscular seminal vesicle...........................................................5

4a. Rhabdoid glands absent. Male system includes false seminal vesicle, short antrum masculinum and muscular penis ................................................................................................................................. Rimicola

4b. Rhabdoid glands present. Male system includes muscular penis associated with a separate glandular organ and a separate false seminal vesicle............................................................................ Pseudoposthia

5a. Rhabdoids absent.............................................................................................................................. Avagina

5b. Rhabdoids present, usually in longitudinal rows........................................................................................ 6

6a. Penis well developed and distinctly curved, only partially invaginated into seminal vesicle ................................................................. Baltalimania ( B. fontaneti , B. occulta , B. sublitoralis , B. ylvae )

6b. Penis straight or nearly so, fully invaginated into seminal vesicle.............................. Pseudaphanostoma

7a. Bursa with distinct muscular walls ............................................................................................................. 8

7b. Bursa tissue only.................... Baltalimania ( B. agile , B. histobursalim, B. macrospiriferum , B. marcusi )

8a. Common gonopore terminal; vagina dorsal to male copulatory organ; bursa with one or two large, coiled nozzles ............................................................................................................................................ Haplocelis

8b. Gonopore usually ventral or subterminal. If terminal, gonopores separate, with female pore anterior (ventral) to male pore (terminal). Vagina never dorsal to male copulatory organ ....................................9

9a. One or two bursas present, each with multiple sclerotized nozzles....................................... Diatomovora

9b. Only a single bursa present, always without multiple sclerotized nozzles..............................................10

10a. Rhabdoids absent. Antrum masculinum absent. Penis an inpocketing of the epidermis.......................... ........................................................................................................................................... Proaphanostoma

10b. Rhabdoids present, scattered or in longitudinal rows...............................................................................11

11a. Vaginal sphincter weak or absent .......................................................................................... Praeconvoluta

11b. Vaginal sphincter muscles well developed .................................................................................................12

12a. Frontal glands prominent. Penis curved. Bursal appendage present as nozzle or cap ........ Aphanostoma

12b. Frontal glands weak. Penis straight. Bursa always simple without appendage ........... Praeaphanostoma

Rimicola is also similar in morphology to other species of Faerlea (Mecynostomidae) . Species of both lack rhabdoids and a seminal bursa and have a small antrum masculinum. Unlike Rimicola , species of Faerlea are characterized, among other things, by a short penis with associated glands and a muscular seminal vesicle. Further investigation, including obtaining DNA sequences, is needed to assess the position of the genus within Isodiametridae and Acoela .