Imogine stellae, Marquina, Daniel, Osca, David, Rodríguez, Jorge, Fernández-Despiau, Estrella & Noreña, Carolina, 2014

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 : 124-128

Imogine stellae sp. nov.

Figs. 1 (7), 11, 12; Table 2

Type locality. Mar Menor (Murcia, Spain) (37º46.16’N, 0º45.02’W); Fig. 1 (7).

Type material. Holotype one mature specimen sectioned sagittally. MNCN 4.01/181 - MNCN 4.01/199 (18 slides).

Material examined. 14 live specimens from the eastern seashore of Mar Menor (Murcia, Spain) were studied; of these, four mature specimens were sectioned sagittally and mounted on slides. The material is deposited in the invertebrate collection of Museo Nacional de Ciencias Naturales de Madrid ( Spain).

Etymology. The specific epithet is dedicated to Estrella Fernandez-Despiau, who collected the species.

Diagnosis. Imogine with elongated body, without marked undulations; pigmentation brownish with dark brown spots, less dense at the margins and midline; nuchal tentacles present; tentacular, marginal and cerebral eyes present; anchor-shaped seminal vesicle opens at the base of the prostatic vesicle; prostatic vesicle “ djiboutiensis” type; male and female atrium not ciliated; male and female gonopore close together, but clearly separated.

Description. Body elongated with rounded anterior and posterior ends, 12 mm long and 5.5 mm wide, tapering slightly posteriorly. Body margins without marked undulations. Nuchal tentacles located in the anterior one-fifth of the animal. Dorsal pigmentation brownish with dark brown spots, turning pale and less dense towards the margins and midline ( Fig. 11 A). Tentacular, marginal and cerebral eyes present. Tentacular eyes denser at the inner margins of the nuchal tentacles ( Fig. 12 A). Cerebral eyes form two elongated clusters. Marginal eyes small, arranged around the anterior end of the body margin. Ventral surface light yellow. Pharynx located in the anterior half of the body. Oral pore located at one-third of the body length. Main digestive trunk extends forwards and backwards of the pharyngeal cavity ( Fig. 11 B).

Reproductive system ( Figs. 11 C, 12B): The male system is located in the posterior part of the animal and consists of well developed spermiducal bulbs, a true anchor-shaped seminal vesicle, a musculo-glandular ovoid prostatic vesicle, a penis papilla, crossed by a straight ejaculatory duct and an atrium. The conspicuous spermiducal bulbs are located behind the anchor-shaped seminal vesicle. The vasa deferentia ducts are wide, becoming even wider towards the seminal vesicle, finally entering laterally into the vesicle. The characteristic seminal vesicle opens through a curved duct directly at the base of the prostatic vesicle. This duct subsequently becomes the ejaculatory duct. The prostatic vesicle shows, according to Faubel 1983, the characteristic shape of the “ djiboutiensis” type: a small lumen with an external muscle layer and internal glandular lining, and surrounded by numerous prostatic glands. The conspicuous muscle layer at the distal end of the ejaculatory duct forms the penis papilla. The male atrium is narrow and not ciliated.

The female system is located close to the male copulatory organ. Female and male gonopores are in close proximity, but clearly separated. The paired oviducts enter separately at the proximal end of the internal vagina. In preserved specimens, the vagina runs from the dorso-lateral side of the body to the medial axis, then bends anteriorly and runs ventrally towards the female pore; this last portion is known as the external vagina. The female atrium is narrow, conical and not ciliated. Numerous cement glands are located along the entire female system, but are open mainly in the external vagina. Lang's vesicle is absent.

Discussion. Due to the presence of an anchor-shaped seminal vesicle and a strong muscular penis papilla, Imogine stellae sp. nov. belongs to the genus Imogine . However, with a comparative study of highly characteristic features of the 34 known Imogine species ( Jennings & Newman 1996; Bulnes 2010; and Table 2 of this study), we can distinguish three major groups based on four main features; viz. the location of the male and female gonopores, the junction of the sperm duct with the prostatic duct, the shape and size of the penis papilla, and the distal shape of the female external vagina.

The first group (Table 2) contains species characterised by the presence of two separate, yet physically close, gonopores: Imogine stellae sp. nov.; I. hamanensis (Kato, 1944) ; I. hyalina ( Bock, 1913) ; I. ceylanica (Laidlaw, 1904) ; I. izuensis (Kato, 1944) ; I. meganae Jennings & Newman, 1996 ; I. sixteni ( Bock, 1931) ; I. megalops (Schmarda, 1859) ; I. minima (Palombi, 1940) ; I. nebulosa (Girard, 1853) ; I. rutilis (Yeri & Kaburaki, 1918) (Table 2). However, I. stellae sp. nov. can be differentiated from the other species of the group by its proximal junction of the prostatic and sperm ducts, a character also shared with I. minima ; the other species of this group show either medial or distal junctions. Other differences are found in the male and female systems. The female gonopore and distal region of the external vagina of I. stellae sp. nov. present a remarkable dilatation, while the penis papilla appears longer than in other species. These characters distinguish I. stellae sp. nov. from I. minima , in which the distal external vagina lacks dilatations and the penis papilla is very short in comparison. Nevertheless, these characters must be carefully treated as their size may be influenced by the state of relaxation or contraction of the animal during fixation ( Meixner 1907).

The second group comprises Imogine miyadii Kato, 1944 ; I. necopinata Sluys, 2005 ; I. tripartitus (Hyman, 1953) ; I. uniporus (Kato, 1944) ; and I. catus (Bois-Reymond Marcus, 1958) . This group is characterised by a common gonopore and an external vagina without dilatations. Differences between species concern the location of the fusion of the prostatic and sperm duct and the shape of the penis papilla.

The third group contains the largest number of species (Table 2) and is mainly characterised by the marked separation of the female and male gonopores. Species of this group show different types of prostatic and sperm ducts junctions, as well as varying sizes and shapes of penis papillae and external vaginas. Species of this group include Imogine aomori (Kato, 1937) ; I. arenosa Willey, 1897 ; I. exigua (Hyman, 1953) ; I. ijima (Yeri & Kaburaki, 1918) ; I. kimae Jennings & Newman, 1996 ; I. lateotentare Lee, Beal & Johnston, 2005 ; I. lesteri Jennings & Newman, 1996 ; I. marmorea (Bock, 1925) ; I. mcgrathi Jennings & Newman, 1996 ; I. mediterranea ( Galleni, 1976) ; I. melihertani Bulnes, 2010 ; I. oculifera Girard, 1853 ; I. orientalis ( Bock, 1913) ; I. pardalotus ( Jennings & Newman, 1996) ; I. pulcher (Hyman, 1940) ; I. referta (Bois-Reymond Marcus, 1965) ; I. speciosa (Kato, 1937) ; I. tica (Marcus, 1952) ; and I. zebra (Verrill, 1882) . Species of this group can be differentiated by the pattern of pigmentation, size of the tentacles, disposition of the tentacular, cerebral and marginal eyes and distribution of the cement glands around the female canal ( Jennings & Newman 1996, Bulnes 2010).

In relation to the Mediterranean basin, aim of our research, only two other Imogine species have been previously described from the Mediterranean basin: I. mediterranea ( Galleni, 1976) and I. melihertani Bulnes, 2010 (both members of the third group). Imogine mediterranea ( Galleni, 1976) is known from the Italian and Tunisian coasts ( Galleni 1976, Gammoudi et al. 2009), while I. melihertani has been reported from the western coast of the Aegean Sea ( Bulnes 2010). Imogine stellae sp. nov. differs from I. mediterranea in the location of the two gonopores, which are clearly separated in I. mediterranea and close together in I. stellae sp. nov. Another conspicuous difference in I. stellae sp. nov. is the opening of the seminal vesicle at the caudal base of the prostatic vesicle, whereas in I. mediterranea and I. melihertani , the ejaculatory duct receives the prostatic duct at a medial region. Furthermore, the vasa deferentia and spermiducal bulbs are more prominent and well developed in I. stellae sp. nov. compared to I. mediterranea , although this may be due to differences in developmental states.

The shape of the female system also shows clear differences between these three Mediterranean species. In I.stellae sp. nov., the female pore is wide, while the atrium is pyramid-like and lacks cilia, whereas in I. mediterranea and I. melihertani , the female pore is small, and the atrium is ciliated in I. melihertani . The location of the cement glands along the internal and external vagina is similar in I. stellae sp. nov. and I. mediterranea , but differs in I. melihertani , in which the cement glands extend along the entire female canal.

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 11. Imogine stellae sp. nov. A Habitus; B sagittal reconstruction of the whole animal anterior to the right); C sagittal reconstruction of male and female genital systems (anterior to the right). Anterior to the left in all figures. Abbreviations: b, brain; ce, cerebral eyes; cg, cement glands; ed, ejaculatory duct; fa, female atrium; fp, female pore; i, intestine; m, mouth; ma, male atrium; me; marginal eyes; mp, male pore; ov; oviduct; ph; pharynx; pv, prostatic vesicle; spb, spermiducal bulbs; t, tentacle; te; tentacular eyes; sv, seminal vesicle; vd, vas deferens. Scale bars: A, B 6 mm, C 200 µm.

FIGURE 12. Histological sections of Imogine stellae sp. nov. A tentacles region and B male copulatory organ (anterior to the left). Abbreviations: ce, cerebral eyes; ed, ejaculatory duct; fp, female pore; mp, male pore; pp, penis papilla; pv, prostatic vesicle; spb, spermiducal bulb; t, tentacle; te, tentacular eyes. Scale bars: A 100 µm, B 200 µm.