Isodiametra divae ( Marcus, 1950 )

Hooge, Matthew D. & Rocha, Carlos E. F., 2006, Acoela (Acoelomorpha) from the northern beaches of the state of São Paulo, Brazil, and a systematic revision of the family Otocelididae, Zootaxa 1335, pp. 1-50 : 26

Isodiametra divae ( Marcus, 1950)

( Fig. 16 )

Convoluta divae: Marcus 1950 (p 103); Marcus 1952 (p 12); Dörjes 1968 (p 84). Conaperta divae: Antonius 1968 (p 309); Dörjes and Karling 1975 (p 178); Hooge and Tyler 2005 (p 102). Isodiametra divae: Hooge and Tyler 2005 (p 112); Hooge and Eppinger 2005 (p 8).

Material. Topotype. MZUSP PL. 189, one set of 1.5-µm-thick serial sagittal sections of epoxy-embedded specimen stained with toluidine blue; living specimens in squeeze preparation; whole mounts for fluorescence imaging of musculature.

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, silty flocculent layer on sand (23°45’52.2”S, 45°20’56.6”W).

Description. Mature specimen ~ 500 m in length and ~ 200 m wide ( Fig. 16 A). Anterior and posterior ends rounded. Body mostly without coloration in transmitted light except yellow and green coloration in digestive syncytium. Sperm in seminal vesicle light orange in color. Rhabdoid glands arranged in distinct rows. Mouth opening on ventral surface, middle of body.

Ovaries and testes paired. Common genital pore opens caudally into male copulatory organ and rostrally into vagina. Vagina surrounded by weakly muscular sphincter; opens anteriorly to walled bursa that leads to short bursal nozzle ~ 5 m in length. Cells composing bursal nozzle wrap posteriorly around sides of bursa ( Fig. 16 B). Long, curved, muscular, glandular penis contains numerous spherical glandular secretions within lumen ( Fig. 16 B). Penis invaginated into muscular seminal vesicle containing sperm and a cluster of glandular secretions.

Remarks. This species can be distinguished from other species of Isodiametra known from Brazil by its long, curved penis containing large, spherical glandular secretions and by the lateral extensions of the bursal nozzle that enwrap the sides of the bursa.

Figures

FIGURE 16. Isodiametra divae; photomicrographs of living specimen. A. Dorsal view of squeezed specimen. B. Dorsal view of copulatory organs.