Praeconvoluta bocasensis, Hooge, Matthew D. & Tyler, Seth, 2008

Hooge, Matthew D. & Tyler, Seth, 2008, Acoela (Acoelomorpha) from Bocas del Toro, Panama, Zootaxa 1719, pp. 1-40 : 33-35

Praeconvoluta bocasensis sp. nov.

( Figs. 30–32 )

Type Material. Holotype. USNM 1096776, one set of 2-µm-thick serial sagittal sections of epoxy-embedded specimen stained with toluidine blue. Paratype. USNM 1096777, one set of 2-µm-thick 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 .

Other Material Examined. Living specimens in squeeze preparations from; 5 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 type locality, Bocas del Toro, Panama.

Description. Living specimens 450–550 µm long and ~115 µm wide ( Fig. 30 A). Anterior and posterior ends rounded; body cylindrical. Body mostly colorless by transmitted light. Epidermis completely ciliated. Rhabdoid glands in irregular longitudinal rows present. Frontal organ present; frontal glands present from frontal pore to mouth. Mouth opening on ventral surface, anterior half of body. Digestive syncytium extends from frontal glands to level of seminal bursa. Chordoid vacuoles present, especially in posterior half of body, give body vacuolated appearance ( Figs. 30 A, 31A).

Ovaries paired; oocytes extend from level of mouth posteriorly to seminal bursa ( Fig. 31 A). Testes paired, lateral to ovaries; extend length of body from frontal glands to male copulatory organ.

Single gonopore present ( Fig. 31 B); connects to male copulatory organ; connection to female copulatory organ not discernible. Walled, sperm-filled seminal bursa filled with located anterior to male copulatory organ. Tissue of bursa extends posteriorly, over dorsal side of male copulatory organ and may wrap entirely around male copulatory organ to reach gonopore ( Fig. 31 B). Anterior wall of seminal bursa composed of thick cap of elongated cells ( Fig. 31 A) that extend posteriorly to surround sides of seminal bursa. Central area of bursal cap contains concentration of F-actin ( Figs. 32 A, B); no discernible opening between seminal bursa sperm and oocytes could be seen.

Gonopore opens directly to isodiametric, muscular, glandular penis; proximal end of penis curved caudally ( Figs. 30 B, 31B). Penis musculature composed of outer longitudinal and inner circular muscle fibers ( Fig. 32 B). Proximal one-third of penis with spherical glandular secretions, composing what is likely a prostatic vesicle ( Figs. 30 B, 31B). Penis invaginated into muscular seminal vesicle that has a diameter only slightly larger than penis, and which has same general shape as penis. Space between penis and seminal vesicle wall filled with sperm. Cluster of gland cells positioned outside of seminal vesicle at proximal end ( Fig. 31 B).

Remarks. Of the seven known valid species of Praeconvoluta , our species is most similar in appearance to P. k a r i n a e Dörjes, 1968, P. minor Faubel, 1974 , and P. tigrina Hooge and Tyler, 2003, all of which have numerous chordoid vacuoles along the edges of the body and similarly-shaped penes with their proximal ends directed posteriorly. Praeconvoluta bocasensis is without a ciliated genital atrium as found in P. k a r i n a e and P. m i n o r, and the glandular region of its penis that composes the prostatic vesicle is lengthier than in P. t i g r i n a. Except for P. stephania Faubel and Regier, 1983 , all of the presently known species of Praeconvoluta have a common gonopore that opens anteriorly to the vagina and dorso-posteriorly to the penis. Our species appears to have a different condition altogether. In P. bocasensis , the vagina extends from the seminal bursa dorsally over the male copulatory organ. It is unclear from our histological sections if the vagina continues this path to connect to the gonopore behind its connection with the penis. The configuration of the vagina positioned behind the male copulatory organ was historically recognized as the diagnostic character of the family Otocelididae ; however, recent studies have found this to be a common configuration that occurs in several acoel families (see Hooge & Rocha 2006).

Figures

FIGURE 30. Praeconvoluta bocasensis sp. nov.; photomicrographs of a living specimen. A. Whole specimen. B. Copulatory organs.

FIGURE 31. Praeconvoluta bocasensis sp. nov.; photomicrographs of sagittal histological sections of holotype. A. Median sagittal section through whole animal. B. Sagittal section through copulatory organs. Arrowhead points to location of common gonopore.

FIGURE 32. Praeconvoluta bocasensis sp. nov.; photomicrographs of copulatory organs in whole-mount stained with Alexa- 488 - labeled phalloidin and viewed with confocal microscopy. A. Optical section through male copulatory organ and seminal bursa. B. Projection of male copulatory organ and seminal bursa.