Cryptostylochus koreensis, Bulnes & Faubel & Park, 2005

Bulnes, V. N., Faubel, A. & Park, J. - K., 2005, Two new marine species from South Korea with remarks on the family Stylochidae (Acotylea, Polycladida, Plathelminthes), Journal of Natural History (J. Nat. Hist.) 39 (23), pp. 2089-2107 : 2102-2104

Cryptostylochus koreensis sp. nov.

( Figures 3A–C , 4 , 5 )

Material examined

Holotype: one specimen from tidepool of the intertidal zone from Geomundo Island , Jeollanamdo Province, Korea, 127 ° 179410E, 34 ° 19450N; leg. Dr Hyun Soo Rho, 16 October 2001; one specimen in sagittal serial section, deposited in ZMUH, V 13242 .

Habitat. Eulittoral benthal, muddy sand, marine.

Etymology

The specific epithet refers to Korea where the species was found.

Description

Length of fixed, sexually mature specimen 47.2 mm by 42.7 mm width. Body squareshaped, oval, with numerous marginal folds. Colour of dorsal surface presumably brown or brownish red, visible by incident light, ventral surface pale, without any pigments. Nuchal tentacles anterior to bilobed brain. Tentacular, cerebral, and scattered frontal eyes present ( Figure 4A ); marginal eyes encircling the entire body. Epidermis completely ciliated, cellular, with intra-epithelial nuclei and rhabdites. Dorsal epidermis about 69 mm high, underlain by basal membrane, about 5 mm thick. Layer of granular pigmentation present between basal membrane and body muscle wall. Dorsal body muscle wall consists of an outer circular layer, followed inwards by longitudinal, diagonal and inner longitudinal muscle layers. Ventral body muscle wall reaches 95 mm thick, consisting of outer circular muscle layer followed inwards by thick longitudinal, intermixed with diagonal muscular fibres, forming a loose, longitudinal cross-over texture. The transversal muscle fibres are numerous and well differentiated.

Ruffled pharynx mid-ventral, 15 mm long; mouth ventrally in the posterior half of the pharyngeal cavity ( Figure 4B ).

Reproductive system. Bilateral testes follicles ventral, and oogonia of bilateral ovaries extending from dorsal side ventrad between intestinal branches. The male copulatory apparatus ( Figure 4C ) consists of seminal vesicle, prostatic vesicle, and distal penis papilla housed in a ciliated atrium. The vasa deferentia, their distal courses displaying some loopings, enter the seminal vesicle from anterior via a single pore. Voluminous seminal vesicle, elongate, with thin muscular wall, ventrally of prostatic vesicle.

Prostatic vesicle 1.5 mm long, 0.68 mm diameter, the muscular wall of which well developed. The interior lining of the prostatic vesicle is tubular; it consists of numerous short tubes radially arranged close to each other along the inner border of the muscle wall. Each tube represents the distal ending of the ducts of the extra-vesicular glands which are closely attached to the outer edge of the muscle wall. The number of tubes, therefore, is identical with the number of extra-vesicular glands. Each tube seems to be unicellular with a monoglandular pore. The evidence, however, is only based on light microscopic observations. The distal ends of the tubes do not display a solid, firm lining, apparently, indicating an apocrine-secreting nature of the distal ending of the tubes ( Figures 3A, B , 5 ).

The prostatic duct distally joins the ejaculatory duct at the base of the penis papilla. The ejaculatory duct opens at the tip of the penis papilla. The male copulatory organs are embedded within a reticulated network of muscular fibre but they do not form a compact, muscular, copulatory bulb.

The female system lacks a Lang’s vesicle. The oviducts enter the vagina separately from antero-dorsal. The vagina continues backwards a short way, then turns ventrad, and opens ventrally via the female atrium and gonopore to the exterior. The vagina is developed as a vagina bulbosa surrounded by circular muscles, showing folds in the inner epithelium of the female channel, pierced by the ducts of the cement glands. The epithelium covering the inner walls of the female ducts is completely ciliated.

Male and female gonopore separate.

Discussion

In 1921, Frieda Meyer described a specimen of Stylochus from the Red Sea, noting that the species could be synonymous with Stylochus reticulatus Meixner, 1907 . Meyer did not describe the male organ very meticulously and reproduced a detailed section of only a single tube of the prostatic vesicle ( Figure 2A ). Bock (1925) discussed this species according to the rules of nomenclature and created the new name Stylochus coseirensis . In the revision of 1983, Faubel transferred Stylochus coseirensis to the new, monotypic genus Cryptostylochus Faubel, 1983 , Pseudostylochidae , mainly based on the apparently tubular-chambered interior of the prostatic vesicle. The true nature of the interior lining of the prostatic vesicle was not discerned. In 1996, Faubel and Gollasch described a second species, Cryptostylochus hullensis . Re-investigation of the holotype of C. hullensis confirms that the tubular glandular lining of the prostatic vesicle represents a prostatic vesicle of monoglandular type. The tubes arise proximally in the prostatic vesicle and extend distad. The same situation is evidently developed in C. coseirensis Bock. Therefore , the monoglandular type of prostatic vesicle warrants the transfer of the genus Cryptostylochus from the family Pseudostylochidae to the family Stylochidae .

The genus Cryptostylochus is now characterized by the monoglandular type of prostatic vesicle, unarmed penis papilla, and absence of Lang’s vesicle. The presence of an unarmed penis papilla and a non-tripartite seminal vesicle, and the absence of Lang’s vesicle are in common with the genus Stylochus . Cryptostylochus differs distinctly from Stylochus in the presence of the monoglandular type of prostatic vesicle.

The new species, Cryptostylochus koreensis sp. nov., is characterized by the monoglandular type of the interior lining of the prostatic vesicle. Based on this character C. koreensis represents a member of the genus Cryptostylochus Faubel. The genus now contains C. coseirensis , C. hullensis , and C. koreensis sp. nov. Both C. coseirensis and C. hullensis differ distinctly from C. koreensis . The latter species is distinctly characterized by the autapomorphic feature of an interior lining of the prostatic vesicle, consisting of numerous short tubes arranged radially along the inner border of the prostatic vesicle in contrast to the few, long, interior tubes directed distad of the prostatic vesicles in C. coseirensis and C. hullensis . Additionally, the establishment of the new species Cryptostylochus koreensis is marked by the presence of a vagina bulbosa, the arrangement of tentacular, cerebral, frontal eyes, and marginal eyes encircling the whole body.

Figures

Figure 2. Diagrammatic reconstruction of prostatic vesicles of Stylochidae. (A) Cryptostylochus coseirensis (Bock) after Meyer, 1921; (B) Imogine nebulosa (Girard); (C) Imogine oculifera Girard; (D) Stylochus alexandrinus Steinböck; (E) Stylochus frontalis Verrill; (F) Stylochus ellipticus (Verrill).

Figure 3. Diagrammatic reconstruction of prostatic vesicles of Stylochidae. Monoglandular types: (A–C) Cryptostylochus koreensis sp. nov.: (A) medio-sagittal section through the prostatic vesicle, (B) peripheral section through the prostatic vesicle, (C) diagrammatic reconstruction of the prostatic vesicle; (D) Cryptostylochus hullensis Faubel and Gollasch. Polyglandular types: (E) Stylochus neapolitanus (Delle Chiaje); (F) Distylochus pusillus Bock. Scale bars: 70 mm.

Figure 4. Cryptostylochus koreensis sp. nov. (A) Dorsal view of fixed specimen; (B) sagittal reconstruction of whole organism; (C) sagittal reconstruction of male and female apparatus. Scale bars: 20 mm (A); 8 mm (B); 4 mm (C).

Figure 5. Photomicrographs of the prostatic vesicle of Cryptostylochus koreensis sp. nov. (A) Medio-sagittal section; (B) peripheral section. Scale bars: 70 mm.