Planocera graffi Lang, 1879

Marquina, Daniel, Osca, David, Rodríguez, Jorge, Fernández-Despiau, Estrella & Noreña, Carolina, 2014, State of knowledge of the Acotylea (Polycladida, Platyhelminthes) from the Mediterranean coasts of Spain: new records and new species, Zootaxa 3780 (1), pp. 108-134 : 119-120

Planocera graffi Lang, 1879

Figs. 1 (5), 9, 10

Type locality. Gulf of Naples, associated with other invertebrates such as Balanus, Halichondria, Penares and Lithodomus ( Lang 1879, 1884, Tyler et al. 2012).

Type material. not available.

Material examined. One mature specimen from Cabo de Palos (Murcia, Spain) and two mature specimens from littoral areas near Calpe (Alicante, Spain) were studied. One mature specimen from Calpe was sectioned sagittally and mounted on 50 slides ( MNCN 4.01/130 - MNCN 4.01/180). The specimen from Cabo de Palos and the second specimen from Calpe were stored in alcohol 70%.

Localities: Cala Racó, Calpe, Alicante (38º38.07’N, 0º04.46’E) Spain; Cabo Palos, Murcia, Spain (37º37.39’N, 0º42.25’W); Fig. 1 (5).

Other material. Planocera pellucida (Mertens, 1833) Oersted, 1844 Zoologisches Institut und Zoologisches Museum der Universität Hamburg, slides: V 13167 / 1- V 13167/18 (Atlantic Ocean, pelagic); V 131171 / 1- V 13171/ 15 (Atlantic Ocean, pelagic); V 13169 / 1- V 13169/37 (Atlantic Ocean); V 13177 / 1- V 13177/11 (Atlantic Ocean) and 5 specimens in alcohol: V13131 ( Cape Verde Islands).

Description. The specimen ( Fig. 9 A–D) has a broadly oval, almost round, form with slightly ruffled margins, 20 mm long by 15 mm wide (measurements from fixed specimen). The ground colour is yellow-orange, with a reddish net-like accumulation of pigment granules at the body midline along the intestine branches. The terminal ramifications on the dorsal side and the margin of the body sometimes reflect a white colour. The body appearance is fleshy, but very transparent and frail in appearance. Two conspicuous conical tentacles located near the brain, but far from the margins. Numerous tentacular eyes at the base of each tentacle. Several small cerebral eyes present anterior as well as posterior to the tentacles, being more abundant behind the tentacles. A broad ruffled pharynx occupies the central region of the body ( Fig. 9 E).

In general, the organisation of the copulatory complex ( Fig. 9 F) agrees with the detailed descriptions of Lang (1884). Nevertheless, some additional details can be discerned in our specimens. For example, the vasa deferentia dilate and become the spermiducal bulbs before entering proximally into the muscular cirrus bulb. The prostatic vesicle opens together with the spermiducal bulbs at the distal end of the male bulb. The prostatic vesicle is lined with a glandular epithelium forming the characteristic tubular chambers. The ejaculatory duct is wide and short. The cirrus is composed of distal spines and teeth that progressively increase in size towards the genital atrium. The rather short male genital atrium is bottle-shaped. The entire male complex is surrounded by thick muscle layers. The female apparatus does not show remarkable differences from Lang's (1884) description of the species. Briefly, it consist of a muscular external vagina or vagina bulbosa, surrounded by muscle layers, which is lined with a delicate cuboidal, glandular epithelium at the distal end; in some sections, this epithelium shows fringe-like extensions. The internal vagina first runs anteriorly and then posteriorly. Numerous cement glands open in the distal section of the internal vagina. Proximally, the two oviducts join the internal vagina and Lang’s vesicle is either entirely lacking or only present as a vestigial vesicle.

Discussion. The genus Planocera Blainville, 1828 shows a wide, almost cosmopolitan, distribution ( Fig. 8 ). From the Mediterranean basin, three species have been reported: Planocera folia Grube, 1840 , Planocera graffi Lang, 1879 and Planocera ceratommata ( Palombi, 1936) .

Planocera graffi was first described for the Gulf of Naples ( Lang 1879, 1884), and also reported for the islands of Sao Vicente ( Cape Verde) ( Laidlaw 1903) and the Catalan coast ( Novell 2003).

Planocera folia was originally described for Palermo by Grube (1840), and later cited for Barwick Bay, USA (Apalachee Bay?) by Johnston (1865). Unfortunately, the internal anatomy of P. folia is unknown, thus making it impossible to compare with other species of the genus. Ludwig von Graff (1904) last cited P. folia , merely as the record of Grube (1840); therefore, the last real record of P. folia appears to be in 1865 by George Johnston. For the Mediterranean, the only record is the original description of Grube (1840).

Planocera ceratommata was originally described by Palombi (1936) for Cape Town ( South Africa), but more recently has been cited by Novell (2003) for the Catalan coast.

Although Lang (1879, 1884) could not compare Planocera graffi with P. pellucida (Mertens, 1833) as the description of P. pellucida does not include internal anatomical features, he did comment on the great similarity between P. g r a f f i and P. pelagica (Moseley, 1877) , which only differ in the shape of the ejaculatory duct (tortuous in P. pelagica ). Years later, Faubel (1983) synonymised P. pelagica with P. pellucida (Mertens, 1833) .

Bock (1913) and Faubel (1983) described P. pellucida as oval, tapering posteriorly and P. graffi as rounded, sometimes broader than long. However, Prudhoe (1985) reported that P. pellucida could show both body shapes, slightly elongated or rounded. This variation in body shape is, in our opinion and after a careful reading of the original description, the only reported difference between both species. An anatomical comparison between both species was necessary. Therefore, specimens of P. pellucida from the invertebrate collection if the Zoological Museum of Hamburg, captured in the Atlantic shores, were compared with our specimens from the Mediterranean coasts. The results of this comparative study ( Fig. 10 ) are the following: the cirrus of the male copulatory organ shows the same shape and type of spines in all specimens, the disposition and localisation of the prostatic and seminal vesicle is the same and the vasa deferentia show identical trajectories. It is evident that there are no significant morphological differences between the two species and a synonymization is justified. Therefore, we propose that P. graffi is synonymous with P. pellucida with the consequent expansion of the distribution of P. pellucida within the Mediterranean Sea.

With respect to the third Planocera species cited for the Mediterranean shores, P. ceratommata ( Palombi, 1936) , this species is actually the most cited species of the genus Planocera within the Mediterranean Sea, although it was originally described for Still Bay, Cape Town ( South Africa) ( Palombi 1936).

Unfortunately, the original material of P. ceratommata is missing, but numerous similarities between this species and P. pellucida suggest a possible case of synonymy; although, some differences must also be considered, that not allow a synomization. The most significant variation between P. ceratomata from South Africa and our material lies in the arrangement of the eyes. In P. pellucida , the tentacular eyes surround the tentacles in an orderly (stereotypical) manner, whereas in P. ceratommata the arrangement of the eyes is irregular ( Palombi, 1936; fig. 17). A similar pattern is also observed for the cerebral eyes. Another difference concerns the organisation of the prostatic vesicle. According to Palombi (1936), the copulatory organ “É formato de una grossa vescicola glandulare granulosa avvolta di una rica fascci muscolare costituita di fibri longitudinale e circolari” (“It is formed by a large glandular prostatic vesicle involved by well developed bundles of muscles formed by longitudinal and circular fibers"); this description, together with the figure ( Palombi 1936, fig. 18), illustrate a prostatic vesicle that is different from the vesicle in P. pellucida described by Bock (1913). Nevertheless, we assume that many of the records of P. ceratommata for the Mediterranean in fact concern P. pellucida .

Figures

FIGURE 1. Distribution map of examined specimens. General views of A the eastern coast of the Iberian Peninsula, B Mar Menor (Murcia). Numbers: Notoplanella inarmata (1), Notoplanella estelae sp. nov. (2), Trigonoporus cephalophtalmus (3), Leptoplana mediterranea (4), Planocera graffi (5), Imogine mediterranea (6), Imogine stellae sp. nov. (7), Stylochus neapolitanus (8), Stylochus pilidium (9).

FIGURE 8. Map of known localities of Planocera pellucida (black dots), Planocera ceratommata (white squares) and Planocera graffi (red dots).

FIGURE 9. Planocera graffi (Lang, 1879). A Dorsal and B ventral views of fixed specimen; C dorsal view of a cleared animal; D dorsal view of a live animal; E sagittal reconstruction of the whole animal (anterior to the left); F sagittal reconstruction of male and female genital systems (anterior to the left). Abbreviations: e, eyes; ed, ejaculatory duct; fp, female pore; m, mouth; mp, male pore; o, ovary; ph, pharynx; pv, prostatic vesicle; spb, spermiducal bulb; t, tentacle; ts, testes; tee, teeth; v, vagina; vb, vagina bulbosa; vd, vas deferens. Scale bars: A, B, C, D 7 mm, E 500 µm, F 500 µm.

FIGURE 10. Planocera pellucida (Mertens, 1833) of the Atlantic coast. A – B specimen V 13167 / 1 - V 13167 / 18 (Ironhematoxylin-eosin stain), A male copulatory organ, B detail of cirrus and teeth; C – D specimen V 13171 / 1 - V 13171 / 15 (Pasini staining), C male copulatory organ, D detail of cirrus; E – F specimen V 13169 / 1 - V 13169 / 37 (Pasini staining), E male copulatory organ, F detail of cirrus; G – H specimen of the Mediterranean coast (Azan staining), G male copulatory organ, H detail of cirrus. Anterior to the left in all figures. Scale bars: A, C, E, G 500 µm, B, D 200 µm, F, H 100 µm.