Praeaphanostoma foramivora, Hooge, Matthew D. & Tyler, Seth, 2008

Hooge, Matthew D. & Tyler, Seth, 2008, Acoela (Acoelomorpha) from Bocas del Toro, Panama, Zootaxa 1719, pp. 1-40 : 30-32

Praeaphanostoma foramivora sp. nov.

( Figs. 27–29 )

Type Material. Holotype. USNM 1096774, one set of 2-µm-thick serial sagittal sections of epoxy-embedded specimen stained with toluidine blue. Paratype. USNM 1096775, one set of 2-µm-thick sagittal sections of epoxy-embedded specimen stained with toluidine blue.

Type Locality. Islas Zapatillas (9°15’56.4” N, 82°02’75.0” W), from subtidal sediment located between the Islas Zapatillas.

Other Material Examined. Living specimens in squeeze preparations from Isla Bastimentos (920.898’ N, 82°9.959’ W), from subtidal, clean, coarse-grained, well-sorted sand surrounded by Thalassia ; 2 sets of serial sections of epoxy-embedded specimen stained with toluidine blue; whole mounts for fluorescence imaging of musculature.

Etymology. The species name refers to the foraminifera that were found in the digestive syncytium of this species.

Description. Living specimens 330–405 µm long and ~100 µm wide ( Fig. 27 A). Anterior and posterior ends rounded; body cylindrical. Body mostly colorless by transmitted light. Epidermis completely ciliated. Scattered rhabdoid glands present. Frontal organ present; frontal glands present from area shortly behind statocyst to frontal pore. Mouth opening on ventral surface, middle of body. Digestive syncytium of some specimens contains foraminiferans ( Fig. 27 A). Chordoid vacuoles present along periphery of body give body vacuolated appearance ( Figs. 27 A, 28A).

Ovaries paired; small diffuse strands of oocytes extend from level of frontal glands posteriorly to seminal bursa. Testes paired, lateral to ovaries; extend length of body from frontal glands to male copulatory organ.

Common gonopore ( Fig. 28 A), opens to unciliated atrium. Atrium opens anteriorly to vagina surrounded by thick circularly oriented musculature ( Figs 28 B, 29A, B). Distal end of vagina lined with ring of glandular secretions ( Figs. 27 B, 28B); most of vagina lined with thick microvilli ( Fig. 28 B). Vagina opens to a thin walled seminal bursa lacking a bursal nozzle or other bursal appendage ( Figs. 28 A, B).

Dorsal side of common atrium leads to male copulatory organ. Atrium opens to short, muscular, glandular penis invaginated into a spherical, muscular seminal vesicle. Musculature of penis composed of circular fibers and thin longitudinal fibers ( Fig. 29 B). Proximal end of penis capped with cluster of spherical glandular secretions, presumably a prostatic vesicle ( Fig. 28 B). Seminal vesicle largely empty except for penis and few scattered sperm ( Figs. 27 A, 28B). Posterio-lateral sides of seminal vesicle surrounded by gland cells ( Fig. 28 B).

Remarks. Of the eleven valid species of the genus Praeaphanostoma , our species most resembles P. m u s - culosum Ehlers and Dörjes, 1979, P. v i t re u m Ehlers and Dörjes, 1979, and P. wadsworthi Hooge and Tyler, 2003 . All four species have extensive chordoid tissue, sphincter muscles surrounding the vagina, and glands surrounding the distal end of the seminal vesicle. Separate male and female gonopores are present in two of the four species, P. vitreum and P. wadsworthi . Proaphanostoma foramivora is unique in having very thick sphincter muscles surrounding the vagina, microvilli lining the vagina, and granular gland cells lining the distal end of the vagina.

Figures

FIGURE 27. Praeaphanostoma foramivora sp. nov.; photomicrographs of a living specimen. A. Whole specimen. B. Copulatory organs.

FIGURE 28. Praeaphanostoma foramivora sp. nov.; photomicrographs of histological sections. A. Median sagittal section through whole animal. B. Sagittal section through copulatory organs.

FIGURE 29. Praeaphanostoma foramivora sp. nov.; photomicrographs of copulatory organs in whole-mount stained with Alexa- 488 - labeled phalloidin and viewed with confocal microscopy. A. Projection of male copulatory organ and vaginal musculature. B. Optical section through male copulatory organ and vagina.