Phagocata hellenica Vila-Farré & Sluys, 2011

Vila-Farré, Miquel, Sluys, Ronald, Almagro, Ío, Handberg-Thorsager, Mette & Romero, Rafael, 2011, Freshwater planarians (Platyhelminthes, Tricladida) from the Iberian Peninsula and Greece: diversity and notes on ecology, Zootaxa 2779, pp. 1-38 : 24-27

Phagocata hellenica Vila-Farré & Sluys , sp. nov.

( Table 1 , Fig. 15 A–C)

Material examined. HOLOTYPE. ZMA V.Pl. 6878.4, Canal of Argos, near Argos and Néa Kíos, Peloponnese, Greece, 0 8 August 2008, sagittal sections on seven slides.

PARATYPES. ZMA V.Pl. 6878.1, ibid., horizontal sections on three slides; V.Pl. 6878.2, ibid., sagittal sections on five slides; V.Pl. 6878.3, ibid., sagittal sections on four slides; V.Pl. 6878.4, ibid., sagittal sections on four slides; V.Pl. 6878.5, ibid., horizontal sections on two slides.

Etymology. The specific epithet is based on the Greek hellenikos, meaning Greek.

Diagnosis. With respect to anatomical features, Phagocata hellenica can be distinguished from its congeners by the combined presence of (1) a short common vas deferens opening at the tip of a short projection into the very proximal part of the ejaculatory duct and (2) a plump plug of cells projecting into a slightly more distal part of the ejaculatory duct.

Description. Preserved specimens measure up to 7.1 x 2.2 mm. The dorsal surface is transparent and therefore the intestinal branches can be seen ( Fig. 15 A). The ventral surface is also devoid of pigment. A small narrowing of the body width is present at the level of the eyes; the tail is rounded or bluntly pointed.

The eyes (maximum eye cup diameter 58 µm) are located relatively far from the frontal margin. The number of retinal cells in each pigment cup could not be determined with certainty.

The end of the anterior intestinal branch forms an extension that reaches anterior to the eyes. The cylindrical pharynx is situated in the middle of the body and measures about 1/6th of the body length. The outer epithelium of the pharynx is underlain by a layer of longitudinal muscle fibres, followed by a layer of circular muscles. The inner epithelium is underlain by a thick layer of circular muscles, followed by a layer of longitudinal muscle fibres. The mouth is situated in the posterior portion of the pharyngeal pocket and opens to the exterior underneath the copulatory bursa. In specimen V.Pl. 6878.4, the mouth is situated 3.28 mm from the anterior end of the body and 106 μm from the gonopore (the total body length of this specimen is 5.68 mm).

The oval-shaped testes follicles occupy approximately one-half of the dorsoventral diameter of the body and extend from a short distance behind the ovaries into the posterior end of the body. The testes are mainly ventral but some are dorsal. At the level of the penis papilla, the vasa deferentia curve dorsally and, subsequently, recurve before penetrating the wall of the penis bulb. Once they have penetrated the penis bulb, the vasa deferentia open separately into the ejaculatory duct. Within the penis papilla, each vas deferens is surrounded by a thick layer of circular muscles fibres. The ducts fuse to form a very short common vas deferens, which opens at the tip of a small projection into the proximal part of the ejaculatory duct. The ejaculatory duct runs centrally through the penis and opens at the tip of the papilla. The ejaculatory duct is divided histologically into two sections ( Fig. 15 B, C). A short proximal, anterior portion is lined with very tall cells, forming a plug that fills almost the entire lumen of the canal. The second, distal section is lined by the usual epithelium, which is pierced by abundant erythrophilic glands.

The epithelium of the large conical penis papilla is underlain with a layer of thick circular muscle fibres; the epithelium is thinner at the basal wall of the papilla. The weak penis bulb is formed by intermingled longitudinal and circular muscle layers. The dorsal section of the male atrium is lined with thick nucleated epithelium, underlain by a thin layer of circular muscle fibres, followed by a layer of longitudinal fibres.

The paired, globular ovaries occupy about 1/3rd of the dorsoventral diameter of the body and are located a short distance behind the brain. The oviducts curve mediodorsally at the level of the penis papilla, where they unite to form a common oviduct ( Fig. 15 C). This opens into the posterodorsal section of the male atrium. Shell glands discharge into the common oviduct and also into the distal portion of the oviducts. The large copulatory bursa lies between the hind wall of the pharyngeal pocket and the copulatory apparatus and is lined with tall, vacuolated cells. The long bursal canal curves dorsally to the male atrium. The lining epithelium of the wide bursal canal bears distinct cilia and consists of nucleated cells. The canal is surrounded by a subepithelial layer of circular muscle fibres, followed by a thin layer of longitudinal muscle fibres.

Discussion. The most characteristic anatomical traits of these specimens is a plug of cells in the ejaculatory duct and the short common vas deferens that opens at the tip of a short projection into the most anterior part of the ejaculatory duct. Therefore, we will restrict our comparative discussion to species that have such a plug (cf. Sluys et al. 1995): Ph. albissima (Vejdoský, 1883) , Ph. armeniaca , Ph. undulata , Ph. bosniaca (Stankoviċ, 1926) , Ph. illyrica (Komárek, 1919) , Ph. macedonica (Stankoviċ, 1926) , Ph. maculata , Ph. dalmatica ( Stankoviċ & Komárek, 1927) , Ph. ochridana , Ph. stankovici (Reisinger, 1960) .

In Ph. albissima and Ph. armeniaca , the presumed plug of cells merely consists of an elevated, papillated epithelium. Thus, the plug is very reduced, if present at all. The body margin is folded in Ph. undulata , but not in Ph. hellenica . In Ph. bosniaca the vasa deferentia run through a very long intrapenial papilla-like structure. In contrast, the projection into the lumen of the penis papilla is very short in Greek Ph. hellenica specimens. The penis papilla is very elongated in Ph. illyrica and Ph. macedonica , in contrast to the shorter papilla in the Greek animals. Phagocata maculata is a pigmented species, whereas the Ph. hellenica animals are devoid of pigment.

The organization and histology of the reproductive organs of our specimens of Ph. hellenica corresponds closely to the scheme of the copulatory apparatuses of Ph. dalmatica , Ph. ochridana and Ph. stankovici . In his monograph on Lake Ohrid planarians, Kenk (1978) noted that the taxonomic position of these three nominal species is still an open question. After a brief summary of the opinions of various authors, Kenk (1978) concluded that: “It seems to me quite probable that all three will ultimately prove to be one species, Phagocata dalmatica (Stankoviċ & Komárec) .” The size, shape and body colouration of our specimens is similar to that of Ph. ochridana and Ph. stankovici from Lake Ohrid. The size of the pharynx, arrangement of the testes, and shape and structure of the penis papilla and the common oviduct are also similar. In our specimens, the anterior intestinal branch forms an extension that reaches anterior to the eyes. This is a characteristic feature of Ph. stankovici that is absent from Ph. ochridana . Recent electrophoretic results ( Krstanovski et al. 2004) have been interpreted to favour a separate taxonomic status for Ph. stankovici , which is frequently considered a synonym of Ph. ochridana .

The penis bulb is small in the Ph. dalmatica group. Its musculature is rather weak and found mainly near its periphery. In our specimens, we found reticulated mesenchymal tissue in the penis bulb that was not described in the former species. This tissue may well be present in these species, but may not have been adequately described in the literature, due to its small size or inconspicuousness.

In addition to these differences, some specimens of Ph. ochridana have a characteristic infranucleated ephitelium in the posterior section of the atrium and bursal. This does not appear to be present in the fully nucleated epithelium of the atrium and bursal canal of the new material of Ph. hellenica from Greece. After careful examination of the description of Ph. ochridana and of a specimen of this species from lake Ohrid in the Zoological Museum Amsterdam collection we noted that our Greek animals differ from Ph. ochridana and from any other currently known species of the genus Phagocata in two features: the combined presence of (1) a short common vas deferens opening at the tip of a short projection into the very proximal part of the ejaculatory duct and (2) a plump plug of cells that project into a slightly more distal part of the ejaculatory duct. In Ph. ochridana , the short projection of the common vas deferens is absent, while the plug of cells in the ejaculatory duct of this species is always elongated and pointed. Therefore, our Greek specimens represent a new species and do not belong to Ph. ochridana , even though this species has been reported in mainland Greece.

Figures

FIGURE 15. Phagocata hellenica, specimens from the Canal of Argos, near Argos and Néa Kíos, Greece. (A) living animal, (B – C) holotype, V. Pl. 6878.4, (B) sagittal section of the copulatory apparatus (anterior to the right), (C) sagittal reconstruction of the copulatory apparatus (anterior to the right).