Philocelis robrochai, 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 : 41-45

Philocelis robrochai sp. nov.

( Figs. 27–29 )

Type Material. Holotype. MZUSP PL. 196, one set of 2-µm-thick serial sagittal sections of epoxy-embedded specimen stained with toluidine blue. Paratype. MZUSP PL. 197, one set of 2-µm-thick oblique sections of epoxy-embedded specimen stained with toluidine blue.

Type locality. Praia da Vila, Ilhabela, São Paulo, Brazil, from subtidal coarse-grained sand (23°46’44.6”S, 45°21’32.6”W).

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

Etymology. Species name in honor of Mr. Roberto Rocha of San Jose, CA.

Description. Living specimens ~500 µm long and ~140 µm wide ( Figs. 27 A, B). Anterior and posterior ends rounded. Body cylindrical. Epidermis completely ciliated. Rhabdoid glands in distinct rows ( Fig. 27 A, C). Mucoid glands present mostly in ventral body wall ( Fig. 28 A). Body colorless in transmitted light, but digestive syncytium has orange coloration. Frontal organ well developed. Cell bodies of frontal glands positioned 70 µm behind frontal pore ( Figs. 27 B, 28A). Mouth opening on ventral surface, middle of body. Digestive central syncytium extends from frontal glands posteriorly to male copulatory apparatus.

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 the anterior half of the body that wrap around the posterior rim of the mouth (U-shaped muscles) present in ventral body wall.

Ovaries paired, ventral; extend from frontal glands posteriorly to bursal nozzle ( Figs. 27 B, D, 28A). Testes paired, dorsal; separate from ovary. Testes extend from frontal gland posteriorly to seminal vesicles ( Fig. 28 B).

Common gonopore positioned ventrally at posterior end of body; opens directly to male copulatory organ anteriorly, and to vagina caudally ( Figs. 28 A, B).

Male copulatory organ composed of a long (~120 µm), curved, conical sclerotized stylet surrounded by a weakly muscular penis sac ( Figs. 27 B, D, 28B, 29A, B). Penis flanked laterally by muscular seminal vesicles with long muscular ducts that connect to proximal end of penis.

Vagina with thick wall; positioned dorsal to male copulatory organ; extends anteriorly to well-developed seminal bursa ( Figs. 27 D, 28A). Bursa with bursal nozzle directed ventrally and slightly posteriorly ( Figs. 27 D, 28A).

Remarks. Species of the genus Philocelis are united in having the vagina positioned posterior to the male copulatory organ, a seminal bursa with attached bursal nozzle, and a male copulatory organ composed of a muscular penis-sac surrounding sclerotized stylets. Although the penis stylet of P. robrochai is more compact than that of P. brueggemanni Hooge and Tyler, 2003 , P. cellata Dörjes, 1968 , and P. karlingi ( Westblad, 1946) , which have widely spaced stylet needles, the overall organization of the male copulatory organ appears to be homologous. Preliminary analysis of both cytochrome oxidase I and 18S rDNA molecular sequence data support a strong relationship between P. robrochai and P. brueggemanni (unpublished data). Interestingly, 18S sequence data also supports a close relationship between Philocelis species and Philactinoposthia saliens (Graff, 1882) (Actinoposthiidae) —a relationship that is further supported by similarities in sperm ultrastructure ( Petrov et al. 2004). Several species of Philactinoposthia appear to have male copulatory organs with a similar composition to that of Philocelis , and given that the Otocelididae has been shown to be non-monophyletic ( Hooge & Tyler 2005), any future revision of the Otocelididae should include an examination of the relationship of these two genera.

Figures

FIGURE 27. Philocelis robrochai sp. nov.; photomicrographs of living specimens. A. Dorsal view of unsqueezed specimen. B. Dorsal view of squeezed specimen. C. Rhabdoid glands within epidermis. D. Dorsal view of copulatory organs.

FIGURE 28. Philocelis robrochai sp. nov.; reconstructions to show arrangement of organs. A. Sagittal reconstruction showing arrangement of female copulatory organ. B. Sagittal reconstruction showing arrangement of male copulatory organ.

FIGURE 29. Philocelis robrochai sp. nov.; whole-mounts stained with Alexa- 488 - labeled phalloidin and viewed with confocal microscopy. A. Ventral projection of posterior end of animal. B. Projection of male copulatory organ.