Recurva postrema, 2013

Sluys, Ronald, Solà, Eduard, Gritzalis, Konstantinos, Vila-Farré, Miquel, Mateos, Eduardo & Riutort, Marta, 2013, Integrative delineation of species of Mediterranean freshwater planarians (Platyhelminthes: Tricladida: Dugesiidae), Zoological Journal of the Linnean Society 169 (3), pp. 523-547 : 539-541

RECURVA POSTREMA SLUYS & SOLÀ SP. NOV.

( FIGS 14–16 )

Material examined: Holotype: ZMA V.Pl. 7122.1, NE Laerma, Rhodes , Greece, 36°10′6.76″N, 27°57′34.55″E, alt. 135 m, 5 April 2009, coll. Eduardo Mateos and Eduard Solà, sagittal sections on six slides.

Paratypes: ZMA V.Pl. 7122.2, ibid., sagittal sections on four slides (not fully mature specimen) ; V.Pl. 7122.3, ibid., sagittal sections on six slides ; V.Pl.7122.4, ibid., sagittal sections on four slides ; V.Pl. 7122.5, ibid., sagittal sections on seven slides ; V.Pl. 7122.6, ibid., horizontal sections on four slides ; V.Pl. 7122.7, ibid., sagittal sections on six slides ; V.Pl. 7122.8, ibid., sagittal sections on eight slides ; V.Pl. 7122.9, ibid., sagittal sections on six slides .

Etymology: The specific epithet is derived from the Latin adjective postremus, located posteriorly, and alludes to the far posteriorly located position of the copulatory apparatus.

Diagnosis: Animals slender, with rotund head. Pharynx and copulatory apparatus situated in the far posterior end of the body. Dorsal testes, distributed throughout the body length but anteriormost testes located at a considerable distance behind the brain. Vasa deferentia open asymmetrically into intrabulbar seminal vesicle. Penis papilla asymmetrical, with more or less vertical orientation in the male atrium. Ejaculatory duct opening at the anterior or ventroanterior side of the penis papilla. Ventral or ventroanterior, muscular penial fold present at the point of insertion of the penis papilla. Ovaries located at about 1/4th the distance between the brain and the root of the pharynx. Distal, posterior parts of the oviducts increase in diameter before communicating with an equally wide common oviduct. Bursal canal is surrounded by a well-developed coat of circular muscle.

Ecology and distribution: The species is known only from the type locality, where it was collected from stagnant water in a rather dry creek. Specimens were found in high numbers, gliding on the substrate, together with other small, white flatworms of an unknown species.

Description: Preserved specimens measure up to 9.5 mm in length and 2.25 mm in width. Notably live specimens are very slender ( Fig. 14 ), with a rotund head that is provided with a pair of close-set eyes, situated in pigment-free patches. Each eye cup houses numerous retinal cells. Behind the eyes, along the lateral margins of the body, there is an auricular streak on either side, at the level of which the head narrows so that there is a more slender neck region. The dorsal surface is finely pigmented pale brown, with notable accumulations of pigment around the pharyngeal pocket. Ventral surface pale.

The pharynx measures between 1/6th and 1/8th of the body length and is positioned far into the posterior part of the body. The musculature of the pharynx conforms to the planariid type. This highly posterior location of the pharynx means that the copulatory apparatus is pushed far into the tail end of the animal. The mouth opening is located at the posterior end of the pharyngeal pocket.

The testes are located dorsally, extending from directly behind the ovaries to almost the posterior margin of the body. After having penetrated the penis bulb, the vasa deferentia open separately into the intrabulbar seminal vesicle. The openings of the seminal ducts are asymmetrical in that one vas deferens opens into the ventral section and the other in a more dorsal section of the seminal vesicle ( Figs 15, 16 ). The latter, lined with a nucleated epithelium and surrounded by a coat of intermingled muscle, communicates with the ejaculatory duct, which in most of the specimens examined exhibits an S-shaped loop before curving downwards to follow its central course through the penis papilla. The papilla is more or less cylindrical in shape and has a more or less vertical orientation in the male atrium. The penis papilla is highly asymmetrical in the sense that in its distal, ventral section the ejaculatory duct shows a sharp, anteriorly directed, knee-shaped bend, after which it opens at the anterior or ventroanterior side of the penis papilla ( Figs 15, 16 ). This course of the ejaculatory duct results in the situation that the anterior portion or lip of the penis papilla is shorter and smaller, in some specimens much shorter and smaller, than the posterior section. At the base of this anterior or ventro-anterior lip of the penis papilla, at its point of insertion, a penial fold is present. This fold is characterized by a more or less developed outbulging and is provided with its own musculature. It is a penial fold, in contrast to an atrial fold, because it is located entally to the point of attachment of the musculature of the penis bulb. The penis papilla is covered with a thin, nucleated epithelium.

The ovaries are located at about 1/4th the distance between the brain and the root of the pharynx. This implies that also the row of testes starts at a considerable distance posterior to the brain, as may be observed even in living specimens ( Fig. 14 ).

Directly posterior to the gonopore the oviducts turn dorso-medially, while their diameter increases

sv cb considerably. Subsequently, the oviducts fuse to form a common oviduct, with an equally wide diameter, that opens into the ventral section of the bursal canal. The latter starts at the copulatory bursa as a rather narrow duct that gradually widens and posterior to the gonopore makes a sharp anteriorly directed bend before opening into the rather dorsal section of the atrium. The more or less horizontally running and widened part of the bursal canal receives the openings of the shell glands anteriorly to the opening of the common oviduct. The nucleated bursal canal is surrounded by a well-developed coat of circular muscle. The copulatory bursa sits immediately anterior to the penis bulb.

Figures

Figure 14. Recurva postrema Sluys & Solà sp. nov. Photograph of external features (scale bar not available).

Figures 15, 16. Recurva postrema Sluys & Solà sp. nov. 15. ZMA V.Pl. 7122.4. Sagittal reconstruction of the copulatory apparatus. 16. ZMA V.Pl. 7122.1. Sagittal reconstruction of the copulatory apparatus.