Miroplana trifasciata? Kato, 1931

Sluys, Ronald & Kawakatsu, Masaharu, 2005, Biodiversity of marine planarians revisited (Platyhelminthes, Tricladida, Maricola), Journal of Natural History 39 (6), pp. 445-467 : 450-453

Miroplana trifasciata? Kato, 1931

( Figures 9–13 )

Material examined

ZMA V. Pl. 950.1, narrow stream near Kimpo Airport , Seoul, South Korea, 14 June 1975, sagittal sections on one slide .

Description Preserved specimens oblong, 3× 1 mm, with truncated anterior body margin and slight constriction anterior to the eyes; posterior end rounded. Dorsal surface with three transverse bands, one directly behind the eyes, one over the pharynx region and a third band across the tail end ( Figure 9 ).

With a pair of relatively large eyes (largest diameter of pigment cup 50 Mm) that each houses three retinal cells and are devoid of a lens.

The pharynx is situated in the middle of the body and measures about one-quarter of the body length; the mouth opening is at the posterior end of the pharyngeal pocket.

The reproductive system is not yet fully developed. Two pairs of large, albeit not fully matured, testes could be distinguished, one pair located between the brain and the root of the pharynx and the other pair at the level of the posterior end of the pharyngeal pocket; the follicles occupy most of the dorso-ventral space. The paired ovaries are situated posteromedially to the anterior testis follicles ( Figure 10 ).

The copulatory apparatus in statu nascendi consists of a penial papilla and penis bulb, a presumably female genital canal or bursal canal, provided with an anterior outgrowth ( Figure 11 ).

Comparative discussion

Although the animal evidently is not fully mature there is much similarity with the type species, M. trifasciata . The transverse bands are precisely in the same position as those described for M. trifasciata , as holds true also for the two pairs of testes. Furthermore, the outgrowth of the presumed bursal canal suggests that this is the beginning of the communicating duct between bursal canal and male atrium, as present in M. trifasciata . It is also striking that the present specimen was collected from a narrow stream at approximately 5 km distance from the shore of the Yellow Sea and that consequently its habitat most likely corresponds with that of M. trifasciata .

The species M. trifasciata so far has been reported only from its type locality: Tokyo, on the border of the Arakawa River, 20 miles inland from its estuary, but still within the limits of tidal action ( Kato 1931, 1965). The presumed present record from Seoul does not strike us as a remarkable range extension of this South-East Asian species ( Figure 13 ).

Sasaki (2000) reported the finding of M. trifasciata ? from a brackish pond located in the riverbed of the lower part of the Tamagawa River system, in the south-west of Tokyo ( Figure 10 ). The animal was found relatively close to the type locality of M. trifasciata and also relatively close to the upper part of the Sumida-gawa River, from which Kato (1965) also reported M. trifasciata from the vicinities of Shimura and Akabane, these lastmentioned localities more or less coinciding with the type locality ( Sudzuki 1981). Over land, the distance between Sasaki’s sampling locality and the Shimura-Akabana area is approximately 22 km.

Sluys (1989) concluded that the type locality of M. trifasciata was a freshwater habitat. However, in the upper parts of the Arakawa River, at 20–25 km from Tokyo Bay, both freshwater and brackish water fishes are found. The salinity of the pond from which Sasaki (2000) reported M. trifasciata ? was about one-quarter of usual seawater, and the pond houses animals such as bryozoans and the barnacle Balanus improvisus . Thus, we must conclude that the habitat of M. trifasciata is brackish water and not pure freshwater. Kimpo International Airport in Seoul is located at about 5 km from the sea; consequently, the locality from which M. trifasciata ? was obtained may well be brackish.

Figures

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

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.