Prostheceraeus fuscolineatus, Dixit, Sudhanshu, Raghunathan, C. & Chandra, Kailash, 2017

Dixit, Sudhanshu, Raghunathan, C. & Chandra, Kailash, 2017, Two new Pseudoceros (Polycladida: Pseudocerotidae) and a Prostheceraeus (Polycladida: Euryleptidae) from Andaman and Nicobar Islands, India, Zootaxa 4269 (4), pp. 495-512 : 505-510

Prostheceraeus fuscolineatus sp. nov.

Figures: 10–12; Table. 2

Type material. Holotype: One specimen (7 × 4 mm) as serial sections (3 Slides), collected on 14.10.2015, subtidally at 10 m depth; Mayabunder (Lat: 12°58.926' N, Long: 092°57.211' E) Andaman and Nicobar Islands, India (ZSI/ANRC-16845)

Paratypes: One specimen (12 × 7 mm), collected on 20.01.2017, subtidally at 10 m depth; Paget Island (Lat: 13°25.144' N, Long: 092°49.288' E) Andaman and Nicobar Islands, India (ZSI/ANRC-16846).

One specimen (21 × 8 mm), collected on 23.01.2017, subtidally at 15 m depth; Point Island (Lat: 13°24.090' N, Long: 092°49.018' E) Andaman and Nicobar Islands, India (ZSI/ANRC-16847).

Etymology. Named from Latin; fuscus (adj.) = brown, linea = line, because of presence of brown lines on dorsum.

Diagnosis. Body elongate and leaf like with white background colour. Dorsum is covered with brown continuous longitudinal stripes with two black stripes on both sides and all stripes joining at posterior end giving a conical appearance. Tentacles erected, pointed and black with a white area in between. Ventral surface white ( Fig. 10.A , B).

Description. Live. Body elongate, slightly tapering at posterior side and smooth at margins with no ruffles. Background body color white with brown continuous longitudinal feebly undulate stripes with two black stripes on both sides. All stripes joining at posterior end at one point. No stripes at extremities leaving a white rim around the body. Tentacles black, pointed and erected with a patch of white in the area between the two tentacles ( Fig. 10.A , B); numerous eyespots present on ventral side of tentacles. Cerebral eyespots present in two close elongate but slightly curved rows with a total of around 70 eyes (paratype) ( Fig. 10 C). Ventrally white in colour.

Preserved. Preserved specimen was cream coloured due to loss of pigments during fixation. The distance between pharyngeal mouth and male pore is 0.4 mm while male pore and sucker are 0.86 mm apart. The total distance between pharyngeal mouth and sucker is 1.2 mm. Body wall composed of ciliated epithelium that surrounds the entire body. A distinct but very thin basement membrane separates epithelial cells from underlying muscular layers, thickness of epithelium dorsally as well as ventrally varies from 0.02–0.03 mm. A large bell shaped tubular pharynx, 702 µm long with an area of 217 µm2 is oriented frontally. Details of ventral surface of a paratype specimen are provided in Fig. 10 D.

Reproductive characters. Male copulatory apparatus posterior to male gonopore. A small, spherical and thick layered seminal vesicle (138 × 97 µm) is present and its epithelial thickness varied from 11 to 14 µm ( Fig. 11 D). Very close to seminal vesicle, a prostatic vesicle roughly of same size of seminal vesicle but slightly elongate in shape is present (155 × 58 µm). Penis papilla rounded in shape and 90 µm long with a small stylet. Male atrium ciliated and in shape of half moon. Female reproductive system was not visible possibly due to immaturity of specimen.

Taxonomic remarks. Presence of characters like tubular pharynx, conspicuous tentacles, arrangement of eyes in two rows and smooth glandular epithelium of true prostatic vesicle place this newly described species under the Family Euryleptidae while presence of longitudinal stripes on dorsum, elongate leaf like body, smooth dorsal surface agrees to the characters of the genus Prostheceraeus . The newly described species was compared to all other members of genus Prostheceraeus exhibiting longitudinal stripes on dorsum namely Prostheceraeus panamensis Woodworth, 1894 ; Prostheceraeus vittatus ( Montagu, 1815) ; Prostheceraeus roseus Lang, 1884 ; Prostheceraeus pseudolimax Lang, 1884 and Prostheceraeus giesbrechtii Lang, 1884 but was found unmatched with any of the above mentioned species. Detailed comparison is given in Table. 2. This will be the first description of any species under the Genus Prostheceraeus from Indian Ocean region as majority of previously described valid species are from Mediterranean region and one species from West Panama coast. Therefore, this newly described species will be second species after Prostheceraeus panamensis Woodworth, 1894 (described from Panama), which is being described from tropical sea area and will result in increment of habitat range of the genus Prostheceraeus from temperate to eastern tropical sea. Based on above mentioned characters, Prostheceraeus fuscolineatus sp. nov. is considered as a new species and seems to be rare with no photographic record elsewhere.

Figures

FIGURE 10. A. Prostheceraeus fuscolineatus sp. nov. in situ from Mayabunder; B. Prostheceraeus fuscolineatus sp. nov. ex situ; C. Dorsal surface of a paratype showing cerebral eyes (ce) and marginal eyes (me); D. details of ventral surface, fp: female pore; mp: male pore; p: pharynx; su: sucker; vd: vas deferens.

FIGURE 11. Prostheceraeus fuscolineatus sp. nov A. Dorsal surface after preservation B. Tentacular and cerebral eyes; C & D Histological sections of reproductive structures. ce: cerebral eyes; in: intestine; ma: male atrium; mp: male gonopore; p: pharynx; pp: penis papilla; pv: prostatic vesicle; sv: seminal vesicle; st: stylet; t: tentacle; te: tentacular eyes. Scale bars: A, 2 mm; B – D, 200 µm.