Procerodella asahinai ( Kato, 1943 )

Sluys, Ronald & Kawakatsu, Masaharu, 2005, Biodiversity of marine planarians revisited (Platyhelminthes, Tricladida, Maricola), Journal of Natural History 39 (6), pp. 445-467 : 456-459

Procerodella asahinai ( Kato, 1943)

( Figures 13 , 16–21 )

Material examined

ZMA V. PL. 952.1, Ryûjin-ike Pond, Hegura-jima Island (37 ° 529N, 136 ° 569E), Wajima City , Ishikawa Prefecture, Chûbu Region, Honshû, Japan, sagittal sections on two slides ; V. Pl. 952.2, ibid., sagittal sections on three slides ; ZMA V. PL. 952.3, ibid., sagittal sections on one slide ; V. Pl. 952.4, ibid., sagittal sections on two slides ; V. Pl. 952.5, ibid., sagittal sections on two slides ; V. Pl. 952.6–16, ibid., sagittal sections of 11 specimens, each on one slide ; V. Pl. 952.17, ibid., sagittal sections on one slide ; V. Pl. 952.18, ibid., one whole mount on one slide ; V. Pl. 952.19, ibid., one whole mount on one slide ; V. Pl. 952.20, ibid., one whole mount on one slide ; V. Pl. 952, ibid., preserved specimens .

Ecology and distribution

The specimens examined were collected from a pond on Hegura-jima (also spelled as Hekura-jima) Island, a small island approximately 48 km NW of the Suzu-zaki Cape of the Noto Peninsula, Japan ( Figure 9 ). The pond measured about 26.4× 5.6 m, with a maximum depth of 0.5 m; sandy bottom; salinity 1556.5 mg l 21 ( Figure 13 ).

Description

Preserved specimens about 2.8×1.0 mm; front end rounded, posterior end pointed ( Figure 17 ). Dorsal body surface yellowish; ventrally pale. Each eye cup contains three retinal cells and is provided with a lens ( Figure 18 ). Behind the copulatory apparatus the two posterior gut trunks fuse to form a common branch ( Figure 19 ). The pharynx measures between one-quarter and one-fifth of the body length. The mouth opening is located at the posterior end of the pharyngeal pocket.

The rounded testes are situated ventrally between the ovaries and the root of the pharynx. Ovaries well developed, located at a short distance behind the brain.

The vasa deferentia separately penetrate the dorsal section of the penis bulb, but thereafter immediately fuse to form a common vas deferens; the point of fusion of the two ducts may also be located within the well-developed coat of intermingled muscles that make up the penis bulb. The common vas deferens is lined with a nucleate epithelium and is surrounded by a thin layer of mostly circular muscle fibres; the duct makes a characteristic anteriorly directed bend before communicating with the broad proximal section of the penial lumen. In general, the penial lumen is wide and of an elongate triangular shape; it is lined with an infranucleate epithelium that receives the numerous openings of erythrophilic penial glands. The lumen opens at the tip of the broadly coneshaped penial papilla. The distal end of the penial lumen forms a constriction, after which it widens again and subsequently opens to the exterior at the tip of the papilla ( Figure 20 ). This transition between penial lumen and tip of the papilla is such that the very tip appears as a club-shaped structure, at least in histological sections. It may well be the case that in much more extended penial papillae this club-shaped appearance can no longer be traced.

Posterior to the male copulatory apparatus lies a sac-shaped copulatory bursa, connected with the common atrium through a highly muscularized bursal canal. The canal is lined with an infranucleated epithelium and is surrounded by a thick, subepithelial layer of circular muscle, followed by a much thinner layer of longitudinal muscle fibres. Numerous unicellular glands are located just outside of the muscle coat, discharging their secretion into the bursal canal. The distal, or ventral, portion of the bursal canal shows an expanded section that narrows again slightly before communicating with the common atrium. Just ventrally to this expansion the bursal canal receives the openings of the oviducts. The ducts separately penetrate the posterior wall of the bursal canal but in some specimens (e.g. V.Pl. 952.2; Figure 21 ) the openings are so closely together that there is a suggestion of a very short common oviduct. The bursal canal receives the openings of shell glands, just ectally to the openings of the oviducts.

Discussion

The gross morphology of the reproductive system immediately suggested that the specimens examined are representatives of the species P. asahinai , albeit that in anatomical details there are differences between the material examined and Kato’s (1943) account of the species, collected from Lake Yûdô-numa, the estuary of the Tokachi River, near Tokachi, Hokkaidô ( Figure 13 ).

Kato (1943) described a broad, cone-shaped penial papilla with a sinuous common vas deferens communicating with a wide, funnel-shaped penis lumen, the latter receiving the abundant secretion of numerous glands (cf. Sluys 1989). Furthermore, he described the fusion of the two vasa deferentia at the dorsal side of the penis bulb. The only differences between Kato’s account of the male copulatory apparatus and our observations are that we did not observe cyanophilic glands opening into the common vas deferens and that Kato did not report the club-shaped tip of the penial papilla.

According to Kato (1943), the oviducts unite to form a very short common oviduct that opens through the posterior wall of the widened ventral section of the bursal canal, the vestibulum. The latter receives the secretion of shell glands ectally to the opening of the common oviduct. In our specimens there is an expanded section in the bursal canal just dorsally to the separate openings of the oviducts. On the other hand, it is also the case that in our specimens the ventral section of the bursal canal, receiving the openings of the oviducts and the secretion of shell glands, is wider than the more dorsal section of the bursal canal and therefore may be considered to represent the vestibulum. That Kato (1943) reported a very short common oviduct agrees with our observations that certain specimens indeed give the impression that the oviducts unite very shortly before opening into the bursal canal. In all, we consider the differences between our observations on the female copulatory apparatus and Kato’s account to result from differences in preservation artifacts. Kato (1943) did not report histological details on eye structure, but the presence of eye lenses in the species is not unexpected since it belongs to a clade for which lenses are postulated as an apomorphy ( Sluys 1989).

The material examined represents the first series of specimens that has become available to science since the destruction of the type specimens.

Figures

Figure 13. Geographic distribution of M. trifasciata, M. trifasciata?, P. asahinai and P. cervix in the Far East.

Figure 20. Procerodella asahinai, V.Pl. 952.5, sagittal reconstruction of the copulatory apparatus.

Figure 21. Procerodella asahinai, V.Pl. 952.2, sagittal reconstruction of the copulatory apparatus.

Figures 14–16. Obrimoposthia wandeli and Procerodella asahinai. (14) O. wandeli, V.Pl. 951.2, photomicrograph of whole mount. (15) O. wandeli, V.Pl. 951.3, photomicrograph of sagittal section through the copulatory apparatus. (16) P. asahinai, photograph of the pond on Hegura-jima Island.

Figures 17–19. Procerodella asahinai. (17) Photograph of preserved specimen. (18) V.Pl. 952.2, photomicrograph of eye cup with lens. (19) V.Pl. 952.17, photomicrograph of whole mounted specimen.

Figures 9–12. Miroplana trifasciata? (9) Freehand sketch of preserved specimen. (10) Specimen from the Tamagawa River. (11) V.Pl. 950.1, sagittal section. (12) V.Pl. 950.1, sagittal reconstruction of the copulatory apparatus.