Acoela (Acoelomorpha) from the northern beaches of the state of São Paulo, Brazil, and a systematic revision of the family Otocelididae Author Hooge, Matthew D. Author Rocha, Carlos E. F. text Zootaxa 2006 1335 1 50 journal article 10.5281/zenodo.174287 26ac73b9-1c53-4f82-bc02-78a055ba31e9 1175-5326 174287 Avagina marci Dörjes and Karling, 1975 ( Fig. 15 ) Mecynostomum tenuissimum : Marcus 1950 (p 102). Avagina marci : Dörjes and Karling 1975 (p 178); Hooge and Tyler 2005 (p 102). Not Avagina tenuissima ( Westblad, 1946 ) : Dörjes 1968 (p 86). Not Proaphanostoma tenuissima ( Westblad, 1946 ) : Dörjes 1972 (p 189). Material . Living specimens in squeeze preparation; whole mounts for fluorescence imaging of musculature. FIGURE 14. Archaphanostoma marcusi sp. nov. ; A. Sagittal histological section of posterior end of body. B, C. Projections of whole-mount stained with Alexa-488-labeled phalloidin and viewed with confocal microscopy. B. Ventral view of posterior portion of specimen. C. Ventral view of bursal nozzle. FIGURE 15. Avagina marci ; photomicrographs of a living specimen. A. Dorsal view of squeezed specimen. B. Dorsal view of male copulatory organ. Localities . Itaçucê Island, São Sebastião Channel, from coarse shelly sand with silt taken from 5 m water depth ( 23°49’S , 45°20’W ); Praia Barreiros, Ilhabela, from subtidal coarse-grained sand with silt ( 23°45’52.2”S , 45°20’56.6”W ); Praia do Araçá, São Sebastião, from intertidal mud ( 23°49’01.9”S , 45°24’23.2”W ). Description . Mature specimen ~ 620 m in length and ~ 150 m wide ( Fig. 15 A). Anterior and posterior ends rounded; posterior club-shaped ( Fig. 15 A). Body mostly without coloration in transmitted light except for gold coloration of diatoms in digestive syncytium. Rhabdoid glands not present. Mouth opening on ventral surface, anterior half of body. Ovaries and testes paired. Female gonopore and accessory organs absent. Male gonopore on ventral surface, middle of body; opens to short, muscular penis invaginated into a muscular seminal vesicle ( Fig. 15 B). Remarks . Marcus (1950) found this species in gray mud at 5 m water depth along the coast of Ilhabela and identified it as Proaphanostoma tenuissima ( Westblad, 1946 ) despite the fact that his specimens lacked a seminal bursa, which is present in P. t e n u i s s i m a . Due to this morphological difference, Dõrjes and Karling (1975) erected a new species, Avagina marci , for the Brazilian specimens. In spite of the differences of the female reproductive organs, P. tenuissima and A. marci are quite similar to each other and are likely to be sibling species.