Murukkumpuzha retting zone, Thiruvananthapuram coast, Kerala, India, 8°36'57.47"N, 76°49'8.914"E (Fig. 1; site 2).

Holotype AQJ1 (ZSI/WGRC/IR/IV 2330), adult specimen collected from muddy sediment in Murukkumpuzha retting zone, 8°36'57.47"N, 76°49'8.914"E (Fig. 1; site 2) by M. Magesh on 31 March, 2009. Paratypes, four specimens: AQJ2–4 (ZSI/WGRC/IR/IV 2331, 2332 and 2337) collected in Kadinamkulam estuary, Thiruvananthapuram coast, Kerala, India, 8°37'33.34"N, 76°48'7.827"E (Fig. 1; Site 1); and AQPE1 (ZSI/WGRC/IR/IV 2191), collected in muddy sediment from Kadinamkulam estuary, Thiruvananthapuram coast, Kerala, India, 8°36'27.21"N, 76°49'9.474"E (Fig. 1; site 3). All paratypes collected by M. Magesh on 21 January, 2010.

Holotype with body widest mid-anteriorly, tapering gradually anteriorly and posteriorly. Antennae small, distally subacute, aligned over mid-palps. Brown epidermal pigmentation present anterodorsally and posterodorsally.Prostomium triangular, deeply cleaved anteriorly. Longitudinal groove extending from tip to posterior part of prostomium,slightly indented laterally. Eyes 2 pairs, black, arranged obliquely, posterior pair considerably smaller. Posterodorsal tentacular cirri extending posteriorly to chaetiger 2. Jaws with 8 teeth, 4 subterminal and 4 ensheathed proximally.Acicular neuropodial ligule bilobed, superior lobe larger than inferior lobe. Dorsal cirri increasing in length posteriorly. Typically less than 4 sesquigomph spinigers in neuropodial supra-acicular fascicle in midbody. Notochaetae absent in all parapodia. Heterogomph chaetae with boss not lengthened. Supra-neuroacicular falcigers in chaetiger 10 with finely serrated blades, 9–12 teeth, approximately uniform in length. Sub-neuroacicular falcigers in chaetiger 10 with roughly serrated blades, about 20 teeth. Sub-neuroacicular spinigers in anterior region (up to segment 50) with blades finely serrated. Sub-neuroacicular spinigers in mid and posterior region (from about segment 70) with blades coarsely serrated proximally. Supra-neuroacicular spinigers in mid and posterior region with blades finely serrated. Pygidium with multi-incised rim, black with two lateral anal cirri.

Named in honour of Dr. Jayalalithaa Jayaram (born 1948), the current Chief Minister of Tamil Nadu State of India, in recognition of her contributions to the field of education (especially for impoverished people) and scientific research. The specific epithet is considered to be a noun in apposition.

Known only from the Thiruvananthapuram coast of southwest India (but see note below).

Namalycastis jaya sp. n. resembles Namalycastis elobeyensis Glasby, 1999 and Namalycastis hawaiiensis Johnson, 1903 by virtue of lacking notochaetae. However, our new species differs from Namalycastis elobeyensis as the latterhas long antenna, equal size eyes, comparatively longer posterodorsal tentacular cirri, subconical acicular neuropodial ligule, tripartite pygidium and no epidermal pigmentation. Namalycastis jaya sp. n. also differs from Namalycastis hawaiiensis, by the latter possessing 35 to 70 teeth on the blades of the sub-neuroacicular falcigers in parapodia of chaetiger 10, mid-posterior falcigers with proximally coarsely serrated blades from chaetiger 120 (chaetiger 30 in smaller specimens) and by the absence of epidermal pigmentation. The lack of notochaetae sets Namalycastis jaya sp. n. apart from other Indian species, including Namalycastis indica Southern, 1921, the Namalycastis abiuma species group, Namalycastis fauveli Nageswara Rao, 1981 and the recently described species Namalycastis glasbyi Fernando and Rajasekaran, 2007. These other species typically have 1–3 notochaetae in at least some parapodia, except those in the anterior-most and posterior-most body. Namalycastis jaya sp. n. most closely resembles Namalycastis abiuma, but differs from the holotype of that species in having very short tentacular cirri (posterodorsal one only extending to chaetiger 2 as compared to chaetiger 5 in Namalycastis abiuma), in the very short, distally sub-acute antennae (antennae pointed and extending to end of palps in Namalycastis abiuma) and in lacking notochaetae (present from chaetiger 12 in Namalycastis abiuma). A key for taxonomic differentiation between species recorded from the Indian region is provided below.

Based on the above comparative account of the features used for identifying the species of the family Nereididae, the present species can be distinguished as a new species by the following combination of characters: (1) smooth and small antennae, (2) absence of notochaetae in all chaetigerous segments, (3) sub and supra-neuroacicular falcigers of parapodia 10 with finely serrated blades, (4) coarsely serrated teeth in sub-neuroacicular spinigers in mid-posterior region, (5) brown pygidium with multi incised rim and two lateral anal cirri, (6) jaws with 8 teeth, and (7) eye capsule protruded above the dorsal alignment of the head. In all of these features, the new species resembles Namalycastis meraukensis (var. zeylancia), described from Dondra, southern Sri Lanka by de Silva (1961). This taxon was considered to be a junior synonym of the Namalycastis abiuma species group by Glasby (1999). However, de Silva’s (1961) variety name is not an available name under the ICZN (1999; Article 15.2), and so the name zeylanica cannot technically be considered a synonym or elevated to a species to represent the present specimens. The name Namalycastis jayasp. n. is therefore likely attributable to the Dondra population and the species more widely distributed throughout southern India and Sri Lanka. Interestingly, the Dondra specimens also live in the retting zone (C. Glasby, pers. obs. 1987).

This species is able to sustain in polluted (sulphide rich and odorous) sediments and is especially associated with decaying materials such as bark and retting coir; the salinity at the collection localities ranged from 5–22 psu.