Diatomovora jacki, Hooge, Matthew D. & Tyler, Seth, 2008

Hooge, Matthew D. & Tyler, Seth, 2008, Acoela (Acoelomorpha) from Bocas del Toro, Panama, Zootaxa 1719, pp. 1-40 : 20-23

Diatomovora jacki sp. nov.

( Figs. 17–19 )

Type Material. Holotype. USNM 1096770, one set of 2-µm-thick serial sagittal sections of epoxy-embedded specimen stained with toluidine blue.

Type Locality. Isla Bastimentos (9°20.898’ N, 82°9.959’ W), from subtidal, clean, coarse-grained, wellsorted sand surrounded by Thalassia sp.

Other Material Examined. Living specimens in squeeze preparations; whole mount for fluorescence imaging of musculature; one set of serial sections of epoxy-embedded specimen stained with toluidine blue.

Etymology. The species name in honor of Jack Mitchell-Hooge of Ashland, Oregon.

Description. Living specimens up to 610 µm long and ~250 µm wide ( Fig. 17 A). Broad, flattened body with rounded anterior and posterior ends. Body mostly colorless by transmitted light. Epidermis completely ciliated. Numerous scattered rhabdoid glands throughout epidermis. Well-developed frontal organ present; frontal glands present in area between mouth and frontal pore ( Fig. 18 A). Mouth opening on ventral surface, middle of body.

Ovary unpaired, ventral; extends from middle of body posteriorly to seminal bursa ( Fig. 18 A). Testes paired, lateral to ovaries; extend from frontal glands to male copulatory organ ( Fig. 17 A).

Common gonopore ventral ( Figs. 18 A–C). Antrum absent; gonopore opens directly to both vagina and male copulatory organ ( Figs. 18 B, C). Vagina, possibly syncytial, positioned anterior to male copulatory organ; leads to walled seminal bursa ( Figs. 17 B, 18A–C). Distal one-third of seminal bursa cap-shaped due to constriction in bursal wall. Distal wall of bursal cap with ~6 bursal nozzles, each ~3 µm long and ~4 µm wide. Nozzles not discernible in squeeze preparations ( Fig. 17 B), but visible in histological sections and clearly seen in actin-stained whole-mounts viewed with fluorescence microscopy ( Figs. 18 C, 19A, B).

Posterior end of gonopore opens directly to lumen of large, muscular, glandular penis ( Figs. 17 B, 18B). Proximal end of penis bent caudally; capped with glandular prostatic vesicle. Mass of sperm present at proximal end of penis. Penis invaginated into muscular seminal vesicle. Penis surrounded by circular muscle fibers that are especially dense at proximal end of penis. Seminal vesicle musculature especially dense at proximal end of penis where circularly-oriented fibers surround penis ( Figs. 18 B, C, 19A).

Remarks. The monotypic genus Diatomovora was erected by Kozloff (1965) for D. amoena , a species of Isodiametridae that is unique in having more than one bursal nozzle. Kozloff (1965) reported that his specimens had a single seminal bursa and two bursal nozzles. Mamkaev (1971) found other specimens with one or two bursae and 1–3 bursal nozzles, and Dörjes and Karling (1975) found similar configurations in specimens deposited in the Swedish Musuem of Natural History by Kozloff.

Our specimens of Diatomovora jacki all had a single seminal bursa with as many as 6 distinct nozzles. The number of nozzles was easily seen in our actin-stained wholemount, but more difficult to discern in our histological sections; the nozzles were not recognizable in squeeze preparations of living specimens. Diatomovora jacki is similar to D. amoena in having a robust muscular and glandular penis with a dense mass of musculature at its distal end (see Figure 34 in Dörjes & Karling 1975), but is without the ciliated genital atrium and muscular vaginal sphincter present in D. amoena .

Figures

FIGURE 17. Diatomovora jacki sp. nov.; photomicrographs of a living specimen. A. Whole specimen. B. Copulatory organs. Arrowhead points to bursal cap containing bursal nozzles.

FIGURE 18. Diatomovora jacki sp. nov.; photomicrographs of sagittal histological sections of holotype. A. Whole animal. B, C. Copulatory organs. Arrowheads point to bursal nozzles in bursal cap of seminal bursa.

FIGURE 19. Diatomovora jacki sp. nov.; photomicrographs of copulatory organs in whole-mount stained with Alexa- 488 - labeled phalloidin and viewed with confocal microscopy. A. Male copulatory organ and bursal nozzles. B. Bursal nozzles.