Pseudoceros nigropunctatus, Dixit, Sudhanshu, Raghunathan, C. & Chandra, Kailash, 2017

Dixit, Sudhanshu, Raghunathan, C. & Chandra, Kailash, 2017, Two new marine flatworms (Polycladida: Pseudocerotidae) from Andaman & Nicobar Islands, India, Zootaxa 4221 (1), pp. 111-122 : 117-119

Pseudoceros nigropunctatus sp. nov.

Figures: 5, 6 & 7

Type material. Holotype: One specimen (26× 15 mm) as serial sections (7 slides), remainder of animal in 70% ethanol. Collected 21.11.2015, subtidally from 15 m depth, Hut Bay , Little Andaman (10°37.340’N 92°33.419’E), Andaman and Nicobar Islands, India (ZSI/ANRC-14851).

Distribution. Little Andaman Island, India. Additional photographic record from Maldives ( Newman & Cannon, 2003 & 2005) and Kenya (http://www.nudipixel.net/pictures/flatworms/24/)

Diagnosis. Background body colour mix of light brown and orange shades, margin cream colour interrupted with light brown. A very thin fluorescent yellow rim outlining the body. Numerous black coloured spots of variable sizes present all over body without reaching the margin. These spots are surrounded by cream colour like the margin giving a halo appearance. Ventral surface light orange in colour.

Etymology. From the Latin niger —black, punctatus —spotted; for presence of black spots on the body.

Synonyms. It is likely that it corresponds to Pseudoceros sp. 15 Newman & Cannon (2003, pg. 80) and Pseudoceros sp. 15 Newman and Cannon (2005), CD-ROM.

Description. Live: Body large, smooth, light brown to orange dorsally and light orange ventrally. Margin cream interrupted with light brown shades with a thin fluorescent yellow rim without any ruffles. Numerous black coloured equally spaced spots of variable sizes present all over body without touching the margin ( Fig.5.A ). These spots are surrounded by cream colour giving a halo appearance. Pseudotentacles small, formed by simple folds of the anterior margin with same colour pattern as that of margin with tentacular eyes present at the tips. Cerebral eyespots cluster horseshoe shaped with 80–85 eyes ( Fig.5 .D).

Preserved: Specimen 26 mm long and 15 mm wide at central portion. Yellow marginal rim not visible after fixation, but black spots and a clear cream margin without any interruptions remains easily visible. Body wall thickness 25-35 µm for ventral epidermis while dorsal epidermis was not clearly visible in the sections. The total distance between pharyngeal mouth and sucker is 7.53 mm. Male and female gonopores 1.7 mm apart ( Fig.5 .B). Pharynx small and ruffled with 7 folds. Male pore 2.8 mm from pharyngeal mouth. Female gonopore star shaped ( Fig.5 .C) with numerous easily visible cement glands. A paired vas deferens running towards male gonopore is recognisable. Sucker 40 µm in length and conspicuous.

Reproductive characters: Measurements refer to length in a 26 mm long worm, the holotype. Seminal vesicle ( Fig.7 .A) oval (481×516 µm), muscular wall thickness surrounding the lumen variable (48–114 µm), tapering towards the anterior side and slightly downwards at posterior side. Lumen lined by heavily ciliated epithelium with nucleus at periphery. Prostatic vesicle round (327×220 µm), located anterior to seminal vesicle above last fold of pharynx. Lumen not visible instead numerous glandular fibres are visible ( Fig.7 .B). Male atrium deep and ciliated, housing a stylet 81 µm long and opening ventrally by a small male gonopore. Some dense cement glands and a highly nucleus populated region is visible but no female gonopore was observed.

Taxonomic remarks. With 87 species (Tyler et al. 2006–2015), Pseudocero s is the largest genus in the family Pseudocerotidae . Members of this genus can be differentiated at specific level solely on the basis of colours and patterns ( Prudhoe, 1989; Newman & Cannon 1994, 1996, 1997, 1998) because of the similarity in their reproductive structures. This colour based species level identification was further validated by Litvaitis & Newman (2001), supported by a nucleotide sequences based study of Pseudocerotidae . The newly described species Pseudoceros nigropunctatus sp. nov. presented here is very distinctive and unmatched in terms of its colour and pattern within this genus, with the exception of P. nipponicus Kato, 1944 which also possesses a similar background and black spots on the dorsum but differs from the former in having a russet brown sub-marginal band with a black rim and a light coloured median stripe. However, there are a few more species with spots on their body, namely P. lindae Newman & Cannon, 1994 ; P. laingensis Newman & Cannon, 1998 and P. scintillatus Newman & Cannon, 1994 ( Table.2). Both P. lindae and P. laingensis are characterised by small spots but the appearance and colour of spots are very different from P. nigropunctatus sp. nov. P. lindae is characterised by golden yellow spots on the dorsum and elongate spots at the margin while P. laingensis is characterised by the presence of smaller purple dots scattered all over the dorsum. P. scintillatus is another species with spots but these are very big, clearly outlined and touching the margin. Newman & Cannon (2003, 2005) mentioned this species as rare and undescribed.

Figures

FIGURE 5. A. Pseudoceros nigropunctatus sp. nov. ex situ; B. Ventral surface details; C. Star shaped female gonopore; D. Dorsal region showing arrangement of eyes. ce: cerebral eyes; fp: female gonopore; mp: male gonopore; p: pharynx; pm: pharyngeal mouth; su: sucker; te: tentacular eyes; vd: vas deferens.

FIGURE 7. Diagrammatic representation of male genital system. cg: cement glands; ed: ejaculatory duct; ma: male atrium; mp: male gonopore; pd: prostatic duct; pv: prostatic vesicle; sv: seminal vesicle; st: stylet.