Orthoplana lunae, Meini, Gianluca, 2015

Meini, Gianluca, 2015, Two new Otoplanid species (Platyhelminthes: Rhabditophora: Proseriata) of the genera Orthoplana Steinböck, 1932 and Postbursoplana Ax, 1956 from the Tuscan coast (Italy), Zootaxa 3947 (3), pp. 425-439 : 427-433

Orthoplana lunae sp. nov.

( Figs 1–10 )

Holotype. A sagittally-sectioned specimen (EMLC-UP 160) deposited in the Electron Microscopy Laboratory Collection of the Dipartimento di Biologia, Unità di Etologia (Università di Pisa).

Type locality. Italy, Tuscany, Ligurian Sea: loc. Partaccia ( Marina di Massa, Massa) (44°01’24’’N, 10°04’16’’ E). Surf-zone characterized by fine sand. Coll. September 2008.

Additional material. At least 30 specimens were studied in vivo, including drawings and photographs, all from the type locality. Paratypes (EMLC-UP 160-A,B,C,D): four specimens from the type locality, sagittally sectioned. Three whole mounts (EMLC-UP 160-E,F) from the type locality.

Description. The length of sexually mature animals, alive and in extension, reaches 1.4–1.6 mm. The body is fusiform, dorsally convex, ventrally flat, colourless and transparent ( Figs 1 , 2). The anterior end is characterized by a ‘Köpfchen’ ( Ax 1956) or cephalic swelling with numerous tactile hairs (th) and followed by two lateral couples of ‘Tastborsten’ ( Ax 1956) or tactile bristles (tb) retractable into the respective wide pockets ( Figs 1 , 2, 3, 4 ). The anterior pair of these bristles is thinner and shorter than the posterior pair, which is characterized by a greater length and thickness. The rhabdites (r), a variety of secretions in epidermal cells or in sub-epidermal glands, are present grouped in longitudinal lines along the body areas without cilia, with the exception of the anterior end, where they are scattered with a low concentration ( Fig. 1 ). The anterior restricted intestine protuberance, called cephalic intestine (ci), with the statocyst (sta) and the ovoid brain (b) are located behind the cephalic swelling. The ovoid brain (b) is lengthened and provided with two - three pairs of lateral rounded protuberances ( Figs 1 , 2, 3, 4 ).

The testes (te), situated behind the brain and anterior to the pharynx, consist of two close series of medium-size follicles arranged along the longitudinal axis, 11–13 per side, in a single line.

Two longitudinal rows of small vitellaries (vi) stretch externally to the testes from just behind the brain to the penis papilla opening, uniformly distributed in single units ( Figs 1 , 2, 3 ).

Two globoid germaries (ge), at some distance from each other, lie in front of the pharynx, posterior to the last testis follicles; they have small dimensions and contain numerous egg cells ( Fig. 1 ).

The pharynx (ph), situated in the rear half of the body, exhibits the so-called bell-shaped organization or ‘Glöckchen’ ( Ax, 1956), typical of the genus. The sacciform intestine (i) is a caecum at both ends and the anterior restricted protuberance or cephalic intestine (ci) is constituted by turgid cells ( Fig. 1 ).

The accessory male pore (amp) is clearly visible laterally to the penis papilla and can be observed in living and semi-squashed specimens ( Figs 1 , 7 ). The caudal end appears sharpened and narrow, provided with numerous adhesive papillae (ap) ( Figs 1 , 2, 5 ). In the post-pharyngeal zone, the sacciform vesicula seminalis (vs) is connected distally with a well developed vesicula granulorum (vg). The male sclerotic apparatus (s) consists of a median stylet and 19 spines of variable shape and length ( Figs 8, 9, 10 ):

• a “Trichterrohr” (T) (according to Ax, 1956) or median stylet, 48–49 Μm long, centrally located in the sclerotized complex, club-shaped with pointed tip at both ends;

• 1 pair of straight spines, 44 Μm long, arranged at both sides of the median stylet, with a very slight subterminal prominence and a pointed tip.

• 17 spines, placed on both sides of the previous ones, practically straight, with pointed tips weakly bent outwards and small subterminal cuneiform prominence. Their length becomes progressively reduced starting from a maximum of 40 Μm, to a minimum of 17 Μm. The proximal end is narrow and blunt.

Remarks. Orthoplana lunae sp. nov., is of a similar body length to that observed in O.borealis (1.5 mm), shorter than in O. bregazzii (4–5 mm), O. mediterranea (3–5 mm) and O. sewardensis (1.5–3 mm), and larger than in O. kohni (1.2–1.4 mm).

Starting from the upper end of the testis rows, the body of the new species shows a constant width until the level of germaries, located in front of the pharynx in the initial part of the caudal body half, as in O. sewardensis and O. mediterranea . The shape of the small cephalic swelling differs from previously described species of the genus: in O. lunae the ‘Köpfchen’ is ovoid and slightly rounded, while in the other species of the genus the small head is clearly flattened.

The distribution and the conspicuous size of the tactile bristles correspond to that described in O. mediterranea and O. kohni , while in O. sewardensis only one pair is visible on the sides of the cephalic swelling. Unlike any other species of the genus, the brain of the new species shows lateral rounded protuberances. The yolk follicle path, arranged in a single longitudinal row from the anterior end to the penis papilla opening on each side of the body, as well as the medium-small follicle dimensions, are similar to that observed in O. mediterranea . In O. sewardensis , the vitellaries are generally similar to those of the new species, but they are different in their distribution and the presence of gaps between every single follicle. The localization of the testes is generally comparable to that observed in two of the species of the genus, but there is a dissimilarity in their distribution: in O. mediterranea there are many more follicles, that reach the level of the upper vitellaries; they are smaller and have gaps between the follicles. In O. sewardensis , the testes have larger dimensions and the presence of gaps between each follicle; which are rounded and few in number. The position of the paired germaries is similar to that observed in O. mediterranea and O. sewardensis , although their dimensions are smaller. In O. kohni , the germaries are much more anterior than the pharynx, and they have a larger dimensions.

The sacciform intestine with cephalic protuberance, the pharynx, the position of vesicula seminalis, vesicula granulorum and penis papilla coincide with the other species of the genus.

The spines of the sclerotic apparatus of the new species show a different organization compared to that of all the other species described in this genus. They are constituted by a median stylet pointed at both ends, 48–49 Μm long, encircled by 19 bristles, with variable shape and length (17–44 Μm). In O. mediterranea , the median stylet has a relatively similar but variable length (49–85 Μm) and is funnel-shaped, with a sharp narrowing toward the distal pointed end. The new species O. lunae , O. mediterranea and O. kohni have a tube-shaped median stylet with a continuous, uninterrupted wall. O. sewardensis and O. bregazzii are particularly similar regarding their sclerotic apparatus as both species have a groove-shaped stylet. In O. lunae and O. mediterranea , the spines are arranged around the median stylet to form a crown, similar in shape and numbers of spines in each species. In fact, in the former species there are 19 spines, while in the latter 17–22 spines are present. They show an elongated and thin body, with a sub-terminal prominence and a bent tip. The different peculiarities between the spines in both species are in their length, 55–65 Μm in O. mediterranea and 18–44 Μm in O. lunae , and also in their peculiar structures of the distal ends: O. mediterranea has a sub-terminal cuneiform protrusion well distinguishable with an outwards small tip, and the distal extremity is sharply curved to form a hooked tip; the new species displays a poorly developed sub-terminal cuneiform prominence, and the distal end of each spine appears with straight tip upward.

On the base of the data presented, O. lunae differs from the previously described species in body dimensions, size and distribution of testes and vitellaries, and, above all, the characteristics of the sclerotic apparatus.

The new species has many homologies with O. mediterranea , but it constitutes a valid new otoplanid species.

Etymology. The name lunae refers to the type locality where this species has been collected. The site of sampling is on the coast of the territory called Lunigiana, corresponding to the basin of the Magra River located between Liguria, Emilia-Romagna and Tuscany (Ligurian Sea, Italy), and lunae means “coming from the territory of the ancient Etruscan town of Luna”.

Habitat. Surf zone.

Distribution. Known only from type locality.

Figures

FIGURE 1. General organi z ation of Orthoplana lunae sp. nov. (a) and superficial dorsal view with the general arrangement of the rhabdites on the body surface (b).

FIGURES 3 – 5. Photographs of Orthoplana lunae sp. nov., in vivo: anterior end (3, 4) and posterior end (5).

FIGURES 6 – 7. Photographs of Orthoplana lunae sp. nov., in vivo: pharyngeal zone (6) and post-pharyngeal zone (7).

FIGURES 9 – 10. Reconstruction from camera-lucida drawings of the morphology (9) and spatial distribution (10) of the spines of the male sclerotic apparatus of Orthoplana lunae sp. nov.