Haplocelis dichona (Marcus, 1954)

(Fig. 24)

Otocelis dichona: Marcus 1954 (p 429).

Haplocelis dichone: Dörjes 1968 (p 102).

Haplocelis dichona: Dörjes and Karling 1975 (p 180); Ehlers and Dörjes 1979 (p 34).

Material. MZUSP PL. 192, one set of 1.5-µm-thick serial sagittal sections of epoxyembedded specimen stained with toluidine blue; living specimens in squeeze preparation; whole mounts for fluorescence imaging of musculature.

Locality. Praia São Francisco, São Sebastião, São Paulo, Brazil, from intertidal coarse sand (23°45’45.1”S, 45°24’27.1”W).

Description. Living specimens ~ 950 m long and ~ 250 m wide (Fig. 24 A). Body without coloration in transmitted light. Rhabdoids scattered across body. Mouth opening on ventral surface, middle of body.

Ovaries and testes paired. Common gonopore terminal at posterior end; opens dorsally to vagina and ventrally to male copulatory organ. Vagina leads to bursa with one or two winding bursal nozzles (Fig. 24 B). Long, coiled, muscular, glandular penis invaginated into muscular seminal vesicle containing sperm (Fig. 24 B).

Remarks. This species can be distinguished from all other species of acoels by its winding curlicue bursal nozzle and penis. Marcus (1954) described his specimens of H. dichona, collected from Ilhabela, as having two bursal nozzles; however, all of our specimens possessed only a single nozzle.