Eurylepta alicula, Pitale & Apte, 2021

Pitale, Reshma & Apte, Deepak, 2021, Further addition to the Indian fauna of Euryleptidae (Polycladida: Cotylea) with description of a new Cycloporus Lang, 1884 and Eurylepta Ehrenberg, 1831, Zootaxa 5052 (4), pp. 486-500 : 492-495

Eurylepta alicula sp. nov.

( Figure 4 , 5 )

Etymology: Named derived from the Latin word alicula meaning light coat or cloak, referring to the coat or covering of papillae over the dorsal surface of the species.

Material examined: Holotype: One specimen (BNHS-Pclad 320, 4.99 mm x 6.01 mm) in ethanol 80% and serial sagittal sections of the reproductive structures (97 slides). Collected 27-3-2019 at type locality Craggy Island (13.22421° N, 93.057941° E), Andaman Islands.

Paratypes: One specimen (BNHS-Pclad 321, 4.76 mm x 3.95 mm), collected on 27-3-2019 from Craggy Island ; one specimen (BNHS-Pclad 322, 4.98 mm x 3.25 mm) collected on 27-3-2019 from Craggy Island .

A five specimens were also found during surveys spanning 2012–2019 from Mandvi , Mirya and Alawa in Ratnagiri, but they were distorted during preservation .

Distribution: Craggy Island, Andaman and Alawa and Mirya in Ratnagiri, Maharashtra.

Diagnosis: Background colour white with pointed tentacles. Translucent papillae with white tip, present across the dorsal surface. Black maculae present dorsally in the unspecified pattern except for the medial longitudinal raised portion where they form one anterior and one mid-length cluster.

Description:

Colour: Translucent white dorsal surface bears raised acuminate translucent papillae with white tip. These papillae continue over the narrow translucent margin. Small black coloured maculae are present dorsally, in a random arrangement. Medial longitudinal raised portion bears three distinct clusters of these maculae across its length. Group of five (three-five in paratypes) maculae are present between the anterior region of the pharynx and cerebral eyespots. The second cluster approximately at mid-length and the third cluster found aligned over the distal portion of the median longitudinal line ( Figures 4A–F ). Ventral surface smooth and whitish pale.

Form: Body elongated and margin slightly ruffled.

Pseudotentacles: Well-developed, Conical, 0.55 mm in length.

Eyespots: Cerebral eyespots are arranged as two distinct elongate clusters (12–18 in each cluster), 1.03 mm away from the anterior margin ( Figure 4C, F ). Dorsal tentacular eyespots are at the base and some spread over the tentacles. Few ocelli are also present between the tentacles separated from the margin. Ventrally, eyespots arranged over the tentacles in a dense cluster and a few eyespots found at the base of the tentacles.

Digestive system: Pharynx, short tubular 0.83 mm long ( Figures 4C, G ). The intestinal ramification is clearly visible through the dorsal surface and these anastomosing branches assumes more intricacies as it approaches the peripheral region.

Gonopores: One male gonopore present immediately behind the pharynx at a distance of 2.26 mm from the anterior margin, measuring 0.14 mm. One female gonopore 0.571 mm behind the male gonopore and at 2.88 mm distance from the anterior margin, measuring 0.154 mm ( Figure 4G ).

Male reproductive system:

The male reproductive system found disposed parallel to the sagittal body plane. Oblong seminal vesicle measures 0.21mm x 0.193 mm. Prostatic vesicle oval measuring 0.233 mm x 0.157 mm, placed in front of the seminal vesicle oriented dorso-ventrally ( Figures 5A, B and E ). Seminal vesicle empties into the penis through narrow duct. Prostatic vesicle enters the penis through the prostatic duct and assembles with the ejaculatory duct at the distal end of the penis ( Figure 5D ). The pointed stylet measuring 0.202 mm enters the roughly triangular male atrium ( Figure 5B ).

Female reproductive system: Female atrium small (0.027 mm), opens into vagina with lateral invagination (0.066 mm) of cement pouch. Cement glands radiating from the female gonopore, densely disposed ( Figures 4G , 5A ). Vagina short (0.100 mm), ascends dorsally and slightly curved posteriorly to enter uteri ( Figure 5A ). One pair of uterine vesicles is observed in the serial sections and one vesicle (0.256 mm x 0.210 mm) is presented in the Figures 5A, C . Uteri filled with oocytes appear on either side of the median line and is visible through the ventral surface ( Figure 4G , 5C, 5E ).

Taxonomic Remarks: The presence of conical-pointed tentacles, short tubular pharynx, one pair of uterine vesicles, absence of a frontal extension of intestinal branch places this specimen in the genus Eurylepta Ehrenberg, 1831 .

The present species can be easily distinguished from its colour pattern, especially the prominent arrangement of black maculae and papillate dorsal appearance. Until now Eurylepta rugosa is the only known species of the genus bearing papillae ( Hyman, 1959a). The present species is distinct from E. rugosa in that the latter has an orangered dorsal surface, smaller tentacles, fusiform seminal vesicle, short, truncated penis stylet, and a small number of cerebral eyespots.

Furthermore, among the present assemblage of the genus Eurylepta , two species namely Eurylepta multicelis and E. piscatoria possess white ground colour and black pigmentation over the dorsal surface ( Hyman, 1955b; Marcus, 1947). E. multicelis have short tubular pharynx and long penis stylet similar to E. alicula sp. nov. but the former possesses wedge shaped cerebral eye cluster and higher number of ocelli (range 32–45) in contrasting to newly described species. E. piscatoria have bell-shaped pharynx, short stylet and irregular arrangement of cerebral eyespots unlike the E. alicula sp. nov. The arrangement of black maculae, pseudotentacular shape and shape of cerebral eye cluster of present specimen resembles with the Eurylepta sp. 1 ZRC.PLA.0150, ZRC.PLA.0151, ZRC. PLA.0152.— Fig 1E , of Ong and Tong (2018).

However, the specimens studied herein do not fit any of the valid Eurylepta species and therefore described as new to the science.

The specimen from Ratnagiri shows brownish-grey colouration of the intestinal content whereas specimens from the Andaman appears whitish. The variation can be attributed to the type of food ingested by the species, available at the site. At the type locality, although no evidence about the feeding habits of these worms were obtained but all the specimens were found around the compound ascidian Ecteinascidia sp.

Figures

FIGURE 1. Map showing study area and geographical position of sampling sites (yellow dots) A: Mumbai—Haji Ali Bay; B: Ratnagiri—Mandvi; C: Andaman Island—Craggy Island, North Andaman. (A & N Island—Andaman and Nicobar Islands).

FIGURE 4. Eurylepta alicula sp. nov A. in situ (BNHS-Pclad 321); B. in situ (Ratnagiri-December 2020); C. in vivo; D. in vivo dorsal view of a specimen from Ratnagiri on 1.11.2012; E. diagram of dorsal colour pattern; F. holotype in dorsal view (preserved specimen); G. holotype in ventral view (preserved specimen). Abbreviations—ce: cerebral eyespots; cg: cement glands; cp: cement pouch; fp: female gonopore; mp: male gonopore; ph: pharynx; su: sucker; ut: uteri.A–G, anterior to the top.

FIGURE 5. Eurylepta alicula sp. nov. A. and B. male and female reproductive structures (holotype); C. uterus; D. penis receiving prostatic and ejaculatory duct; E. sagittal reconstruction of the reproductive system.Abbreviations—cg: cement glands; cp: cement pouch; ed: ejaculatory duct; fa: female antrum; fp: female gonopore; it: intestine; ma: male antrum; pe: penis; pd: prostatic duct; pv: prostatic vesicles; st: stylet; su: sucker; sv: seminal vesicle; vd: vas deferens; vg: vagina; ut: uterus; uv: uterine vesicle. A–E, anterior to the left.