Dendrocoelum inexspectatum 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 : 10-12

Dendrocoelum inexspectatum Vila-Farré & Sluys , sp. nov.

( Table 1 , Figs. 3 , 7 A–D)

Material examined. ZMA V.Pl. 6867.1, River Bidasoa, Narbarte, Navarra, Spain, 11 November 2007, sagittal sections on five slides.

Etymology. The specific epithet is derived from the Latin adjective inexspectatus, unexpected, and alludes to the fact that the single specimen available was found by chance, after the locality had been sampled unfruitfully over several years.

Ecology. Although the area was sampled four times, the species was only collected on one occasion. The use of traps with beef liver was unsuccessful.

Diagnosis. Dendrocoelum inexspectatum sp. nov. can be distinguished anatomically from its congeners by the combination of the following features: presence of a caecum at the posterior end of the bursal canal, testes extending from the ovaries to the posterior end of the body, and an adenodactyl with a voluminous bulb and a free papilla that is located under the penis.

Description. When the single specimen was fixed in the field and later prepared for sectioning, it was considered to be morphologically similar to Ph. vitta . Therefore, we did not pay particular attention to its external features. The dorsal and the ventral surface are hyaline. The head is truncated. From the sections, it could be determined that the animal was about 6 mm long.

The cylindrical, horizontally oriented pharynx is inserted at about the middle of the body and measures about 1/7th (in sections) of the body length. The outer epithelium of the pharynx is underlain by a layer of longitudinal muscles, followed by a layer of circular muscles. The inner epithelium is underlain by a thick and intermingled layer of circular and longitudinal fibres. The mouth is situated in the posterior portion of the pharyngeal pocket, close to the hind wall of the pharyngeal pouch.

Numerous dorsal and ventral testes are irregularly distributed on either side of the body and extend posteriorly to the hind end. The oval-shaped to elongated follicles may occupy almost the entire dorsoventral diameter of the body, but they are usually smaller. At the posterior end of the pharyngeal pouch the vasa deferentia widen to form spermiducal vesicles, which narrow and ascend vertically and, subsequently, penetrate the ventral section of the penis bulb to open separately into an intrabulbar cavity. The ejaculatory duct runs centrally through the dorsally situated penis papilla ( Fig. 7 A). An extra fold projects from the lateral wall of the penis papilla into the distal expanded section of the ejaculatory duct.

The penis bulb is formed by intermingled circular and longitudinal muscle fibres. The penis papilla is covered with tall, nucleated epithelium, under which is a subepithelial layer of circular muscles that is thick at the base of the papilla. The male atrium is covered with circular muscle fibres, followed by longitudinal fibres. The epithelium is very thick in its tubular distal portion, close to the communication with the common atrium. The male atrium is surrounded by a very thick layer of circular muscle fibres, followed by a layer of longitudinal muscles.

Information on the position of the ovaries is not availabe because the front part of the animal was used for molecular analyses. The oviducts run backwards dorsally to the ventral nerve cords. Posterior to the gonopore, the oviducts fuse to form a short common oviduct, which opens into the common atrium. The distal section of the oviducts and the common oviduct receive the openings of the shell glands.

The bursal canal is lined with thin, nucleated epithelium that has distinct cilia. The canal is surrounded by a layer of circular muscle fibres, followed by a layer of longitudinal fibres. At its point of communication with the common atrium, the epithelium of the bursal canal thickens and is underlain by a very thick layer of circular muscles fibres ( Fig. 7 B). The distal, posterior end of the bursal canal forms an extension or caecum that projects posteriorly to the point of communication with the atrium ( Fig. 7 D). A ventrally situated adenodactyl is located to the right of the penis papilla and the common atrium. This adenodactyl consists of a bulb that is located within the mesenchyma, and a free papilla, which measures about half of the total length of the adenodactyl. The bulb is formed by abundant intermingled circular and longitudinal muscle fibres. The erythrophilic glands open into the adenodactyl duct.

Discussion. It was difficult to compare the anatomy of this specimen to that of species of the genus Dendrocoelum as only one specimen is available and many published descriptions of Dendrocoelum species only provide horizontal reconstructions of the copulatory apparatus. Modern descriptions, including ours, are based on sagittal reconstructions. Sagittal and horizontal reconstructions are complementary accounts of the same anatomical characters, albeit that it is more difficult to properly document all details of the anatomy in horizontal reconstructions. The most characteristic trait of Dendrocoelum inexspectatum is that the posterior end of the bursal canal forms a caecum. Consequently, in the discussion below, we omit species whose descriptions clearly show the absence of a caecum, and those in which the posterior end of the bursal canal is expanded, but does not form a caecum.

In D. albidum Kenk, 1978 , D. plesiophthalmum De Beauchamp, 1937 and D. prespense (Stankoviċ, 1969) , the gonopore is surrounded by glands. Such glands are absent in D. inexspectatum .

In D. brachyphallus ( De Beauchamp, 1929) and D. puteale , the penis papilla is reduced or absent, whereas it is well developed in D. inexspectatum .

In contrast to D. inexspectatum , the following species have a retractile tip of the penis papilla or a flagellumlike structure: D. bohemicum ; D. gineti De Beauchamp, 1954 ; D. hussoni Sauber, 1970 ; D. infernale , D. lipophallus ( De Beauchamp, 1929) ; D. parvioculatum De Beauchamp, 1932 ; D. romanodanubiale ; and D. tubuliferum . In some specimens of D. lipophallus , the penis papilla is absent due to (1) a preservation artefact or (2) the fact that the papilla has the capacity to invaginate ( De Beauchamp, 1932). D. clujanum also have a flagellum-like structure, although it has never been observed invaginated ( Codreanu, 1943). In contrast to D. inexspectatum , it has dorsal testes only.

D. agile has an extremely big bulb that is larger than that in D. inexspectatum . In D. hankoi , D. barbei and D. warnimonti Hoffmann, 1964 , the penis is much bigger than the adenodactyl, whereas in D. inexspectatum the adenodactyl and the penis papilla are of similar size. Moreover, the seminal vesicle in D. warnimonti is elongated and the shape of the intrabulbar cavity is different from that of D. inexspectatum .

In the following species, the sperm ducts fuse in a different anatomical region than in D. inexspectatum : D. atriostrictum , D. cavaticum , D. chappuisi De Beauchamp, 1932, D. kenki , D. racovitzai , D. regnardi , D. sollaudi De Beauchamp, 1931 , D. sphaerophallus , D. stenophallus , D. tuzetae Gourbault, 1965 and D. vaillanti De Beauchamp, 1954 .

The testes in D. italicum are dorsal and extend posteriorly to the level of the end of the pharynx only, whereas in D. inexspectatum they are dorsal and ventral and extend posteriorly to the hind end of the body.

The descriptions of D. alexandrinae and D. geticum are incomplete and it is therefore difficult to compare these species with D. inexspectatum .

We consider that the internal anatomy of our specimen is very different from that of other members of the genus Dendrocoelum , with the exception of D. minimum Kenk, 1978 from Lake Ohrid. However, in D. minimum the adenodactyl is larger, the penis papilla has a different shape, and its testes extend posteriorly to about the level of the gonopore (to the hind of the body in D. inexspectatum ).

Figures

FIGURE 3. Distributional records of twelve species of freshwater planarians in the Iberian Peninsula. Data from De Beauchamp, 1920; De Beauchamp, 1932; Baguñà et al. 1980, 81; Gourbault, 1981; Ribas, 1990; Sluys et al. 1995; Carranza & Giribet, 1997; unpublished records, this study.

FIGURE 7. Dendrocoelum inexspectatum. Holotype, V. Pl. 6867.1, (A – B) sagittal sections of the copulatory apparatus (anterior to the right), (C – D) sagittal reconstructions of the copulatory apparatus (anterior to the right).