Obrimoposthia wandeli (Hallez, 1906)

Yang, Hee-Min, Sluys, Ronald, Kawakatsu, Masaharu & Min, Gi-Sik, 2018, New molecular sequences for two genera of marine planarians facilitate determination of their position in the phylogenetic tree, with new records for two species (Platyhelminthes, Tricladida, Maricola), ZooKeys 781, pp. 1-17 : 1

Obrimoposthia wandeli (Hallez, 1906)

synonym: Procerodes sanderi [Hauser, 1987]

Material examined.

NIBRIV0000813547, King George Island, South Shetland Islands, 62°12'31"S - 58°47'42"W, 2 February 2017, coll. Hee-Min Yang, sagittal sections on 11 slides; ZMA V.Pl. 7280.1, ibid., sagittal sections on 14 slides. The animals were collected from a pebble beach; temperature of the sea surface water was 0~1°C; at a depth of 10m water temperature was 1~0°C. Many worms were observed to be attached to the seaweed Kelp.

ZMA V.Pl. 951.1, King George Island, South Shetland Islands, 1983, sagittal sections on 15 slides; V.Pl. 951.2, ibid., whole mount on 1 slide; V.Pl. 951.3, ibid., sagittal sections on 13 slides; V.Pl. 951.4, ibid., sagittal sections on 13 slides; V.Pl. 951.5, ibid., transverse sections on 19 slides; V.Pl. 951.6, ibid., horizontal sections on 8 slides.

Holotype Procerodes sanderi : MZU PL. 00290, sagittal sections on 48 slides (nos. A-140/A-188).

MZU PL. 00291, sagittal sections on 30 slides (nos. A788-821) of presumed specimen of Procerodes sanderi from the original collection of J. Hauser.

Comparative description.

Preserved specimens, collected in 2017, up to approx. 11 × 3.5 mm, thus being somewhat larger than reported for preserved animals of Obrimoposthia wandeli (Hallez, 1906), which measured 4-8 mm in length and 2.5-4 mm in width ( Sluys 1989). However, much of this variation in size may be due to different fixatives used in the field, resulting in different states of contraction of the animals. Nevertheless, preserved specimens of the sample ZMA V.Pl. 951 also were quite large, measuring 8-10 × 3-5 mm.

Dorsal surface of our animals from 2017 mottled blackish or dark brown, with a pale mid-dorsal stripe, which is only weakly developed on the middle portion of the body (Figure 7). At the front end of the body the dark pigmentation gives way to a broad, pale patch on either side of the body, extending from the eyes towards the antero-lateral body margins; further there is a pale patch on the mid-frontal body margin. In this way the dark pigmentation on the head forms a kind of V-shaped pattern; the same pattern was described for other specimens of O. wandeli ( Sluys 1989). The external appearance and colouration of our 2017 specimens fully agree with that of specimens of P. sanderi as originally described in 1987 (see figure in Anonymous 1987).

In the specimens from the 2017 sample the small, rounded testes are situated ventrally and extend from immediately behind the ovaries to somewhat posteriorly to the copulatory apparatus, as may be the case also in other specimens of O. wandeli ( Sluys 1989). The anatomy of the penis papilla of these specimens from the 2017 sample is precisely the same as that documented for O. wandeli (see Sluys and Ball 1988, Sluys and De Vries 1988, Sluys 1989) (Figure 8).

The several specimens available from the population of King George Island revealed the presence of intraspecific variability in the female reproductive system. Generally, O. wandeli has been described as having a bursal canal that shows a distinct T-junction, with the posterior branch of the T forming a kind of diverticulum that receives the opening of the common oviduct (see Sluys 1989, fig. 141). In some animals from King George Island such a T-junction is indeed present (ZMA V.Pl. 951.1, V.Pl. 951.4, V.Pl. 951.6). However, in others, the situation is different in that in these animals the common oviduct opens, via a constriction, into the bursal canal, which from there on runs antero-dorsad and then gently curves rather abruptly ventrad to open into the common atrium (Figs 9, 10). This portion of the bursal canal shows a clear, lateral bend during its course towards the common atrium (Figure 11), as reported earlier for O. wandeli ( Sluys 1989). From the side of this obliquely, antero-dorsally running part of the bursal canal arises a branch that runs more or less straight forward to communicate with the copulatory bursa (Figure 9). Precisely the same situation is present in the holotype of P. sanderi (Figure 12). In some presumed specimens of P. sanderi the branch that runs to the bursa may even originate very close to the point where the common oviduct communicates with the bursal canal (Figure 13).

The entire bursal canal, including its side branch, is lined with an infranucleated epithelium and is surrounded by a thick, subepithelial layer of circular muscle, bounded by a much thinner layer of longitudinal muscle. Oviducts and common oviduct are lined with a nucleated epithelium and are surrounded by a thin layer of circular muscles. The entire bursal canal is surrounded by a broad zone of unicellular glands, which discharge their erythrophilic secretion into the canal. Erythrophilic shell glands discharge their secretion into the ventral portion of the bursal canal, near its communication with the common atrium.

Discussion.

In an anonymous article in a bulletin, the late Josef Hauser described the presumed new species Procerodes sanderi [Hauser, 1987] ( Anonymous 1987). That Hauser was indeed the author of this article was apparent, for example, from the fact that in 1988 and 1989 he corresponded on this subject with both Masaharu Kawakatsu and Ronald Sluys and that he forwarded to these workers photocopies of the article. Furthermore, in the article the new species is attributed to Hauser. In his article Hauser claimed that the anatomy of P. sanderi was different from congeneric species, including species currently assigned to the genus Obrimoposthia . Unfortunately, the article did not provide a reconstruction drawing of the copulatory apparatus, while the short description of the reproductive apparatus in the Portuguese language neither did make clear the anatomical differences between the new species and its congeners. Furthermore, the material that Hauser made available to both Sluys and Kawakatsu, consisting of printed photographs, histological slides, and reconstruction drawings, at the time did not convince these two workers that indeed the specimens represented a new species. As a result, in his monograph Sluys (1989) synonymized Procerodes sanderi with Obrimoposthia wandeli . In their joint publication, Sluys and Kawakatsu (2005) reiterated their conclusion, as expressed also in correspondence with Hauser, that the species P. sanderi is synonymous with O. wandeli .

Nevertheless, examination of our new material collected in 2017, as well as re-examination of specimens from King George Island that were collected in 1983 and were part of Hauser’s samples, including a specimen that he had designated as the holotype specimen of P. sanderi , revealed that at least within this population there is clear intraspecific variation in the construction of the female copulatory apparatus.

In earlier studies (e.g., Sluys and Kawakatsu 2005) the deviant course of the bursal canal in some specimens of O. wandeli from King George Island, i.e. absence of the T-junction and origination of a duct from the side of the bursal canal, was not clearly observed as no reconstruction drawings were made of the various specimens. The present series of material that is available undeniably shows that the intraspecific variability of this population is exhibited by animals collected both in 1983 and 2017. Therefore, we do here consider this variability in the course of the bursal canal, as described above, to be a constant, stable feature of at least the population from King George Island and probably for other populations of O. wandeli as well.

One might contemplate an alternative explanation for the deviant course of the bursal canal. As the specimens from King George Island were somewhat larger than generally reported for O. wandeli (see above), one may view their copulatory apparatus as having reached the final stage of maturation. However, although we can envision structures becoming larger during maturation, we believe it to be unlikely for anatomical organs to become structurally different. In other words, we consider it unlikely that upon maturation a T-junction in the bursal canal will re-assemble in such a way that it develops into a duct with a distinct loop from which originates a side-branch that runs to the copulatory bursa. Therefore, we consider these different expressions of the course of the bursal canal and its connection with the copulatory bursa to be the result of intraspecific variation, independent of the stage of maturation.

In our phylogenetic tree (Figure 1) O. wandeli is the sister-group of the genus Procerodes Girard, 1850. This reflects the taxonomic history of the current members of the genus Obrimoposthia , most of which were formerly assigned to the genus Procerodes . However, it became increasingly clear that in the past the genus Procerodes constituted an unnatural assemblage of species that belonged to different natural groups ( Sluys 1986), one such group being formed by the present members of the genus Obrimoposthia ( Sluys and Ball 1988, Sluys 1989). This has resulted in the situation that in the most recent taxonomy of the Maricola the genera Procerodes and Obrimoposthia are even classified in different families, viz. Procerodidae Diesing, 1862 and Uteriporidae Böhmig, 1906, respectively ( Sluys 1989, Sluys et al. 2009). In the phylogenetic tree of the Uteriporidae based on morphological characters, the genus Obrimoposthia is closely related to Paucumara Sluys, 1989 and Ectoplana Kaburaki, 1917 ( Sluys 1989, fig. 302), both belonging to the subfamily Ectoplaninae Bresslau, 1933. It is clear that in our present tree (Figure 1) Obrimoposthia is rather far removed from Ectoplana and Paucumara .