Pseudoceros galatheensis Dixit, Raghunathan & Chandra, 2017, sp. nov.

Pseudoceros galatheensis sp. nov.

Figure 2, 3 & 4

Type material. Holotype: One specimen (6.6 × 3.6 mm) as serial sections (7 Slides). Collected on 17.2.2016, underneath rubble in intertidal area, Galathea Wildlife Sanctuary (06 0 40.051′′N 93 0 51.583′′E), Great Nicobar Island, India (ZSI/ANRC-14849).

Paratype: One specimen (6 × 4 mm) in 70% ethanol. Same as holotype (ZSI/ANRC-14850).

Distribution. Great Nicobar Island, India. Additional photographic record from Micronesia (Newman & Cannon, 2003 & 2005) and Indonesia (Newman & Cannon, 2005).

Diagnosis. Body colour light blue, darker at rim. One thin bright yellowish-orange median stripe with darker outline, ends without touching posterior margin. Pseudotentacles small and dark blue in colour in continuation with margins.

Etymology. Species name refers to Galathea Wildlife Sanctuary in Great Nicobar Island of India, where type specimens were collected (Fig. 1 D)

Synonyms. It is likely that it corresponds to Pseudoceros sp. 6 Newman & Cannon (2003, pg. 78) and Pseudoceros sp. 6 Newman & Cannon (2005), CD-ROM; see taxonomic remarks below.

Description. Live. Small, smooth, light blue in colour and terminally rounded. Margin dark blue without any ruffles. Thin, bright yellowish-orange median line starting from behind cerebral eyes and ending before posterior margin without touching it. Pseudotentacles small, formed by simple folds of the anterior margin and dark blue with presence of 12-14 scattered eyespots on each pseudotentacle on either side. Cerebral eyespots cluster with 25- 28 eyes. Ventrally light blue in colour.

Preserved. Specimen 6.6 mm long and 3.6 mm wide at central portion. Translucent due to loss of colour on fixation. Median stripe faint but visible. Body wall thickness is 30-37 µm for dorsal and ventral epidermis. Total distance between pharyngeal mouth and sucker is 1.6 mm. Male and female gonopores 0.4 mm apart from one another. Pharynx small and ruffled with 8 folds. Male pore 0.87 mm from pharyngeal mouth. Few white spots (blue spots when live) are also visible in the preserved paratype specimen on the dorsal side.

Reproductive characters. Measurements refer to length in a 6.6 mm long worm, the holotype. Seminal vesicle (Fig.3.A) elongated and oval (353×236 µm), thick walled, tapering towards anterior side and parallel to longitudinal body axis. Thickness of the wall varies from 33–108 µm. Its lumen is lined by ciliated epithelium with nucleus at periphery. Prostatic vesicle (Fig.3.B) small and round (177×126 µm), located slightly left from median line near base of penis papillae and anterior to seminal vesicle. Lumen is walled by muscular layer which is 24–27 µm dense surrounded by 17–19 µm thick distinct epithelium layer. Male atrium deep with many folds housing a stylet 197 µm (Fig.3.B) long and opening ventrally by a wide male gonopore. Some cement glands are visible very near to posterior end of seminal vesicle but no female gonopore was observed in the sections. This may be due to immaturity of female reproductive structures of the specimen sectioned.

Taxonomic remarks. Presence of ruffled pharynx, male copulatory apparatus just behind pharyngeal cavity and free prostatic vesicle (Faubel, 1984) place Pseudoceros galatheensis sp. nov in the family Pseudocerotidae while presence of characters such as one male pore; simple folds forming pseudotentacles; ruffled, round and oval pharynx (butterfly shape); equal distance between sucker and gonopores; and arrangement of eyes on pseudotentacles (Faubel, 1984; Newman & Cannon, 1998) place this newly described species in the genus Pseudoceros. Newman & Cannon (1994) determined that due to intraspecific homogeneity of the reproductive structures in the genus Pseudoceros, the colour patterns can be used to separate species. They separated 39 species under the genus Pseudoceros in 6 groups according to colour pattern. Later in 1998, Newman and Cannon modified the arrangement with 8 groups comprising 56 species. Pseudoceros galatheensis sp. nov. is likely to fall under group 3 comprising 12 species with plain background and longitudinal stripes. However, there are at least 5 species with similar blue or purple background body colour. P. galatheensis sp. nov. differs from all having a distinct yellowish-orange median stripe (Table.1). The species P. perviolaceous Hyman, 1959 is similar in terms of body colour but no median stripe is present. P. gravieri Meixner, 1907 and P. tristriatus Hyman, 1959 also have blue-purple background colour but have multiple yellow orange stripes on dorsal surface. P. bifurcus Prudhoe, 1989 is most similar to P. galatheensis in terms of body colour and margin but it differs having an elongate orange spot posterior to cerebral eyespot which continues to form a white median stripe outlined with dark burgundy (Newman & Cannon, 1994, 2003 & 2005). Sreeraj and Raghunathan (2011) reported P. bifurcus from same geographical area (Andaman and Nicobar Islands) which also contains a dark bordered median stripe and a red spot right behind cerebral eyes which gradually continues in a median stripe. The newly described species differs from P. bifurcus reported from Andaman and Nicobar Islands by having a brighter orange median stripe without any dark colour border and without having any red spot behind cerebral eye cluster. P. violaceus (Schmarda, 1859) is another species resembling our species with a yellow median stripe but it has a yellow marginal band which is not present in the newly described species. Newman & Cannon (2003 & 2005) reported this species as undescribed and rare.

TABLE. 1. Comparison of Pseudoceros galatheensis sp. nov. characters with similarly coloured species.

Characters Pseudoceros Pseudoceros Pseudoceros Pseudoceros Pseudoceros Pseudoceros gravieri Meixner, tristriatus bifurcus perviolaceous violaceus galatheensis sp. 1907 Hyman, 1959 Prudhoe, 1989 Hyman, 1959 (Schmarda, nov. 1859)

Colour Background Background Body solid blue Body colour Body colour Body colour

pattern blue-purple, blue-purple with to light mauve, purple or blue purple-blue blue

darker medially, three orange sometimes with no stripes. with a yellow intensifying to intensifying to longitudinal cream median stripe dark blue at purple at margin. stripes bordered intensifying to and a yellow margins. One Numerous by purple purple at marginal band. bright orange discontin-uous margin. Orange median stripe yellow stripes on elongate spot

dorsal surface after cerebral

eyes fading into

a burgundy

bordered white

median stripe.

Type locality Djibouti Ella Islet, Ifaluk Benthedi, Palau Islands Ceylon Galathea

Atoll, Western Mayotte, Wildlife

Carolines Comoro Sanctuary Islands, Great Nicobar Madagascar. Island, India

Distribution Australia; Australia; Africa; Ceylon and Red So far only India;

Djibouti; Gulf of Indonesia; Australia; Sea known from Micronesia and Oman; Miconesia; Indonesia; type locality. Indonesia Indonesia; Mozambi-que; Japan; (Photograp-hic Micronesia; Papua New Madagascar; record) Papua New Guinea Papua New

Guinea and Guinea;

Philippines Philippines and

Thailand.