Pseudaphanostoma herringi, Hooge, Matthew D. & Rocha, Carlos E. F., 2006

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 : 30-35

Pseudaphanostoma herringi sp. nov.

( Figs. 20–21 )

Type material. Holotype. MZUSP PL. 191, one set of 2-µm-thick serial sagittal sections of epoxy-embedded specimen stained with toluidine blue.

Type locality. Praia de Feiticeira, Ilhabela, São Paulo, Brazil, from subtidal coarsegrained and fine-grained sand (23°50’45.2”S, 45°24’33.8”W).

Other material examined. Living specimens in squeeze preparations from Praia de Pequeá, Ilhabela; 1 sets of 2-µm-thick serial sagittal sections of epoxy-embedded specimen stained with toluidine blue; whole mounts for fluorescence imaging of musculature.

Etymology. Species name in honor of Mr. Paul Herring of Scottsdale, Arizona.

Description. Living specimens ~575 µm long and ~150 µm wide ( Fig. 20 A). Anterior and posterior ends rounded. Chordoid tissue (large vacuolated cells) prominent, forming large clear areas around periphery of body ( Fig. 20 A). Epidermis completely ciliated. Scattered rhabdoid glands numerous ( Fig. 20 C). Body colorless in transmitted light.

Digestive syncytium and eggs with yellow-brown coloration. Frontal glands well developed, extend from frontal pore posteriorly to level behind statocyst. Mouth opening on ventral surface, middle of body. Digestive central syncytium positioned behind statocyst and anterior to testis ( Fig 20 A).

Body-wall musculature with circular muscles that encircle the body along entire length of animal; straight longitudinal muscles present between frontal organ and anterior edge of mouth; longitudinal muscles with a longitudinal orientation anteriorly that bend medially to cross diagonally over the body (longitudinal-cross-over fibers) present in dorsal and ventral body walls; longitudinal muscles in anterior half of the body that wrap around the posterior rim of the mouth (U-shaped muscles) present in ventral body wall.

Ovary and testis unpaired, positioned at body midline; ovary anterior to compact testis ( Figs. 20 A, B). Testis positioned immediately anterior to male copulatory organ. Female gonopore and seminal bursa absent.

Male gonopore opens ventrally or subterminally ( Figs. 21 A, B). Gonopore opens to ciliated male antrum. Wall of antrum with glands, the necks of which are visible in specimens stained with Alexa-488 phalloidin ( Figs. 20 B, 21A, B). Antrum opens to a long (~65 µm) caudad-directed penis, surrounded by sperm and invaginated into a nonglandular, strongly muscular seminal vesicle ( Figs. 20 B, 21A, B). Penis musculature composed of outer non-anastomosing longitudinal muscles and inner circular muscles ( Figs. 21 A, B). Proximal end of penis capped with prostatic vesicle (space of prostatic vesicle visible at tip of penis in Fig. 21 B).

Remarks. Of the seven currently known species of the genus Pseudaphanostoma , our species is similar to P. d i v a e Marcus, 1952 in having an unpaired testis positioned immediately behind an unpaired ovary; all other described species have paired ovaries and testes. P. d i v a e differs from our species in having a longer (~ 1.3 mm), more filiform body that is without extensive chordoid tissue, a shorter penis (~55 µm long), an antrum lacking glands, and conspicuous caudal glands.

Figures

FIGURE 20. Pseudaphanostoma herringi sp. nov.; photomicrographs of a living specimen. A. Dorsal view of squeezed specimen. B. Dorsal view of male copulatory organ. C. Rhabdoid glands.

FIGURE 21. Pseudaphanostoma herringi sp. nov.; projections of male copulatory organ in wholemounts stained with Alexa- 488 - labeled phalloidin and viewed with confocal microscopy. A. Projection showing lumen of male antrum. B. Projection showing entire length of penis. Arrowheads point to gland necks in wall of male antrum (zonulae adherentes joining necks to other cells of lumenal epithelium).