Notoplana alcinoi (Schmidt, 1861) Bock, 1913

Fig. 11

Leptoplana alcinoi Schmidt, 1861.

Opisthoporus tergestinus Minot, 1877.

Material examined.

• MNCN 4.01/3476 to 3492, Station 11, 29 April 2014, 23 mm long, sagittal sectioned into 17 slides. All of the measurements from the description refer to the following specimens: • MNCN 4.01/3984, Station 11, 19 February 2015, 9 mm long; • MNCN 4.01/3985 to 4007, Station 11, 10 May 2015, 10 mm long, transversally sectioned into 22 slides; • MNCN 4.01/4008, Station 11, 10 May 2015, 22 mm long; • MNCN 4.01/4083, Station 11, 19 May 2016, 23 mm long; • MNCN 4.01/4084, Station 11, 19 May 2016, 16 mm long; • MNCN 4.01/3955, Station 11, 22 March 2019, 16 mm long; • MNCN 4.01/4009 to 4045, Station 12, 21 March 2015, 21 mm long, transversally sectioned into 37 slides; • MNCN 4.01/4046 to 4070, Station 12, 21 March 2015, 16 mm long, sagittally sectioned into 25 slides; and • MNCN 4.01/4071 to 4082, Station 12, 18 April 2015, 11 mm long, sagittally sectioned into 12 slides.

Description.

Notoplanidae with elongated and narrow body, very delicate and fragile appearance. Maximum length alive approximately 23 mm (mean 16.7 ± 5.41). Without tentacles. Transparent, whitish background colour, sometimes with a yellowish spot in the pharynx area (Fig. 11 A). Visible intestinal branches colouring the dorsal surface with brownish or dark green shades. Paired tentacular and cerebral eye clusters present, with 9 tentacular and 17 cerebral eyes in each cluster (Fig. 11 B). Pharynx ruffled, located between the first and second thirds of the body. Mouth opening in the last third of the pharynx. Gonopores separated but very close together (at 0.1 mm distance) behind the pharyngeal cavity (Fig. 11 D, E).

Reproductive system.

Male copulatory apparatus is composed of a true seminal vesicle, an interpolated prostatic vesicle, and a deep atrium that hosts a stylet (Fig. 11 E). Vas deferens enter the seminal vesicle separately. Seminal vesicle elongated, bent in two sections. Prostatic vesicle rounded and large (0.54 mm long and 0.4 mm wide) with five tubular chambers joined to the ejaculatory duct (Fig. 11 C, E). One specimen with 8 chambers instead of 5 (see Fig. 11 F). Muscular wall of the prostatic vesicle (0.12 mm wide) crossed by numerous extravesicular glands. Penis stylet long (0.6 mm), slender and pointed, and housed in a deep atrium (0.42 mm).

Female copulatory apparatus consists of a smooth external vagina, a narrow internal vagina, and an elongated Lang’s vesicle (Fig. 11 D, E). Numerous cement glands surround the whole female organs. The external vagina curves dorsally to the posterior end. The common oviduct enters the internal vagina ventrally. Lang’s vesicle is large (0.5 mm) and wavy, extending backwards (Fig. 11 E).

Remarks.

Notoplana is one of the most species-rich genera within Polycladida, with 36 accepted species (Tyler et al. 2006–2024). Regarding the Mediterranean Sea and the Atlantic coasts of the Iberian Peninsula, the recorded species of this genus are N. atomata (Müller OF, 1776) Bock 1913 and N. vitrea (Lang, 1884) Bock 1913 (Novell 2001 Marquina et al. 2014 b), which are species from northern and southern Europe, respectively. More recently, N. alcinoi was recorded in Tunisia (Gammoudi et al. 2017).

Our identification of N. alcinoi was based on the description and the drawings provided by Lang (1884), because the original description (Schmidt 1861) is too brief for comparison. The specimens of N. alcinoi from Cádiz and those described by Lang hardly differ, except for the folded external vagina and the large Lang’s vesicle in comparison to the smooth external vagina and short Lang’s vesicle described by Lang. However, these female features depend on the state of maturation (Litvaitis et al. 2019).

Biology.

Collected from rocky substrates in the intertidal zone. The original description mentioned the presence of this species in the algae Ellisolandia and Chondria (Rhodophyta) environments.

Distribution.

This species was reported for the first time in Corfu, Greece (Schmidt 1861) and later in Trieste, Italy (Minot 1876; Micoletzky 1910), Naples, Italy (Lang 1884), Cape Verde (Laidlaw 1906), and Tunisia (Gammoudi et al. 2017). The presence of this species in the Iberian Peninsula is reported for the first time.