Novomitchellia bursaelongata, 2016

Harrath, Abdel Halim, Mansour, Lamjed, Moissou, Lagnika, Sluys, Ronald, Boutin, Claude, Alwasel, Saleh, Poch, Arnau & Riutort, Marta, 2016, A molecular analysis of the phylogenetic position of the suborder Cavernicola within the Tricladida (Platyhelminthes), with the description of a new species of stygobiont flatworm from Benin, Zoological Journal of the Linnean Society 178 (3), pp. 482-491 : 486

NOVOMITCHELLIA BURSAELONGATA HARRATH, SLUYS & RIUTORT SP. NOV

Material examined

Holotype: ZMA V.Pl. 7225.1, well A1, about 11.6 km south-west of Parakou (9°16 ′ 22.7 ″ N, 2°34 ′ 54.7 ″ E), Republic of Benin, 14. X.2014, collection Mo €ıssou Lagnika and Claude Boutin, sagittal sections on 49 slides.

Paratypes: ZMA V.Pl. 7225.2, ibid., horizontal sections on 50 slides ; V.Pl. 7225.3, ibid., sagittal sections on 57 slides (not fully mature specimen) .

Diagnosis

Novomitchellia bursaelongata is characterized by (1) a truncated head with small protuberances and absence of eyes; (2) numerous, dorsal testicular follicles arranged in 2 – 3 irregular rows, extending from behind the ovaries to the posterior end of the body; (3) vasa deferentia that separately penetrate the penis bulb and the seminal vesicle; (4) a long and narrow copulatory bursa, situated posterior to the gonopore and connected to the atrium through a short bursal canal; (5) a common oviduct orientated perpendicularly to the horizontal bursal canal.

Etymology

The specific epithet is derived from the Latin word bursa, meaning ‘sac’, and the Latin adjective elongatus, meaning ‘elongated’, and refers to the presence of the long and narrow copulatory bursa.

Ecology

The water of well A1 contains a rate concentration of more than 220 coliform bacteria (including 38 Escherichia coli ), 66 faecal Streptococcus and 8.4 anaerobic sulpho-reducing bacteria per ml. Hence, by comparison with many other wells studied in the region ( Lagnika, 2015), A1 contains water that is significantly more contaminated by various kinds of bacteria, probably coming with strings and buckets used by inhabitants of the region. This is somewhat surprising as the water is protected against pollution because the well is closed off by a thick ring of cement where it opens onto the surface, and the actual cylindrical, cemented well in the middle of this ring is closed off by iron covers when not in use.

As to the physicochemical characteristics of the water of well A1, see Lagnika et al. (2014). We here only point out that well A1 belongs to a small group of wells (five to 18) with a better water quality than other stations, with a lower level of mineralization, and a relatively low level of pollution by nitrogenous ions or sulphates and other chemical pollutants.

Possibly for this reason, the aquatic fauna of well A1 is one of the two richest assemblages amongst the 18 wells regularly studied in Parakou. The faunistic assemblage of well A1 includes eight epigean species and four stygobiont species, living in groundwaters close to the well. Thus, N. bursaelongata probably occurs not only in the well but also in the groundwaters of the region.

Description

Preserved animals up to 10 mm long and 1.4 mm wide. Dorsal surface white. Head truncate with some small protuberances on the dorsal surface. Eyes absent ( Fig. 1A, B ). An adhesive organ was not found.

Pharynx cylindrical, located in the posterior third of the body ( Fig. 2 ). The pharyngeal lumen is lined with a ciliated epithelium, underlain by the inner pharyngeal musculature, which is composed of a thick subepithelial layer of circular fibres, followed by a layer of longitudinal fibres ( Fig. 3A ). The outer musculature of the pharynx consists of a subepithelial layer of circular muscle.

Numerous testes arranged in approximately 2 – 3 irregular rows lateral to the intestinal diverticula, near the body margins ( Fig. 3B ). The follicles occur only dorsally and extend from the level of the ovaries to the posterior end of the body. The two vasa deferentia run ventrally, but after extending posteriorly a little beyond the pharynx, they curve mediodorsally and separately penetrate the penis bulb, after which the sperm ducts open into a broad duct, or seminal vesicle, or bulbar lumen ( Fig. 4 ). The latter is ovoid in shape and is lined with a nucleated epithelium and surrounded by a layer of circular muscle. It expands in the distal section of the penis papilla, after which it opens at the tip of a very short and blunt papilla. Many glands are present throughout the penis bulb and papilla, discharging their secretions into the penial lumen. The musculature of the penis bulb is loose, mainly composed of intermingled circular and longitudinal muscles.

Two small ovaries are situated dorsally to the nerve cords, at some distance behind the brain ( Fig. 3C ). The oviducts arise from the posteroventral side of the ovaries and run backwards medially to the ventral nerve cords. At the level of the bursal canal, i.e. slightly posterior to the gonopore, the oviducts turn dorsomedially and, subsequently, unite to form a common oviduct dorsally to the bursal canal. This common oviduct receives the secretion of some glands, possibly shell glands, before perpendicularly opening into the horizontally orientated bursal canal. The latter is short and runs more or less parallel to the body surfaces; it is lined with a nucleated epithelium and surrounded by a layer of circular muscles. The bursal canal connects the atrium with the copulatory bursa, which is remarkably long and narrow and is orientated parallel to the dorsal and ventral body surfaces. The bursa is lined with a nucleated, vacuolated epithelium and is surrounded by a layer of circular muscle.

Figures

Figure 1. Bayesian tree inferred from the 18S rDNA sequences showing the relationship of the new Novomitchellia species to other Tricladida species included in this analysis. Maximum likelihood (ML) yielded the same topology. Asterisks at nodes indicate posterior probabilities = 1/bootstrap values> 75% obtained respectively in the ML and Bayesian inference analyses. Scale bar: number of substitutions per nucleotide position.

Figure 2. Novomitchellia bursaelongata Harrath, Sluys & Riutort, sp. nov. Holotype. A, photograph of preserved specimen in dorsal view; some protuberances are seen on the head (arrowheads); arrow indicates the tail (T). B, photograph of preserved specimen in ventral view; arrow indicates the pharynx (PH). Scale bars not available.

Figure 3. Novomitchellia bursaelongata Harrath, Sluys & Riutort, sp. nov. A, holotype. Microphotograph of sagittal section of the pharynx; musculature composed of subepithelial layer of circular fibres, followed by a layer of longitudinal fibres (arrowhead), and outer subepithelial layer of circular muscle (arrow). B, paratype V.Pl. 7225.3. Sagittal section showing the numerous, dorsal testes (arrowheads). C, holotype. Sagittal section showing ventral position of ovary and oviduct, above the ventral nerve cord. D, photomicrograph of the copulatory apparatus of the holotype in sagittal section; large arrow indicates direction of head. E, sagittal section of the copulatory apparatus of the holotype showing connection between common oviduct and bursal canal; large arrow indicates direction of head. Abbreviations: A, atrium; BC, bursal canal; CB, copulatory bursa; CM, circular muscle; COD, common oviduct; DS, dorsal side; ED, ejaculatory duct; G, gonopore; L, lumen; OD, oviduct; OV, oviduct; PP, penis papilla; SV, seminal vesicle; VD, vas deferens; VNC, ventral nerve cord; VS, ventral side. Scale bars = 200 µm.

Figure 4. Novomitchellia bursaelongata Harrath, Sluys & Riutort, sp. nov. Sagittal reconstruction of the copulatory apparatus of the holotype. Abbreviations: A, atrium; BC, bursal canal; CB, copulatory bursa; COD, common oviduct; G, gonopore; GL, glands; M, mouth; OD, oviduct; PB, penis bulb; PH, pharynx; PP, penis papilla; VD, vas deferens. Scale bar = 150 µm.