Ancistrosyllis matlaensis, Mandal & Deb, 2018

Mandal, Sumit & Deb, Soumya, 2018, Ancistrosyllis matlaensis n. sp. (Polychaeta: Pilargidae) from the Sundarban Estuarine System, India, Zootaxa 4531 (3), pp. 419-429 : 422-423

Ancistrosyllis matlaensis n. sp.

( Figs 2–4 )

Material examined. Holotype- PUZ-323, (Length 48 mm; width 0.6 mm; 80 chaetigers): collected from Station 3 (21°50'16.9" N, 88°39'31.7" E) in Matla river in Sundarban Estuarine System, India from 2 m depth, silty-sand, during September 2016.

Paratypes- 2 specimens PUZ-357 and PUZ-358 from station number 4 (21°47'34.37" N, 88°39'1.02" E) collected December 2016, 1 PUZ-359, collected February 2017.

Diagnosis. Ancistrosyllis matlaensis n. sp. is characterized by the absence of eyes, presence of two lateral antennae and absence of median antennae. Dorsal cirri from 1 st chaetiger and ventral cirri from 2 nd chaetiger. Notopodial hook from 7 th chaetiger; notopodia reduced and neuropodia truncate and straight.

Description (based on Holotype). Specimen complete, with 80 segments and 48 mm long and 0.6 mm wide. Body creamy white, depressed, tapered anteriorly ( Figs 2a , 3a ). Prostomium broad, with two lateral antennae, median antennae absent. Eyes absent. Palps biarticulate, divergent; palpophores comparatively larger than palpostyles ( Fig. 2b ). Pharynx globular, soft, unarmed, with denticles ( Fig. 2c ) and marginal papillae absent. Peristomium fused to prostomium.

Parapodia poorly developed, ovoid, truncate and papillose. Cirri present on all parapodia. Two pairs of tentacular cirri, conical, papillose and inserted laterally. Dorsal cirri present from 1 st chaetiger, ovoid, papillose, papillae minute and quadrate, slightly longer than subsequent ones. Neuropodia truncate and straight, dorsal cirri smaller than ventral ones in segments which bears both of them (i.e. from 2 nd segment onwards). Notochaetae present from chaetiger 7; a large hook above dorsal cirrus resembling barbless fish hook ( Fig. 4a, b ). Neurochaetae sabre shaped, with bent falcate bidentate tips ( Fig. 3d ), smaller neurochaetae with minute serrated blades ( Fig. 4c, d ).

Pygidium bilobed with two lateral digitate anal cirri, covered with minute quadrate papillae ( Fig. 2d ).

Variations in Paratypes: except for minor variation in size they are entirely identical to the holotype ( Fig. 3b, c ).

Distribution. Ancistrosyllis matlaensis n. sp. is only known from the type locality river Matla. It represents the first record of the genus from Sundarban Estuarine System, India.

Comparison. Comprehensive comparisons with all other species assigned under genus Ancistrosyllis are provided in Table 2. Ancistrosyllis matlaensis n. sp. differs from A. groenlandica , A. hartmanae , A. commensalis , A. breviceps , A. fironii , A. jonesi and A. cingulata in lacking a median antenna. A. matlaensis n. sp. is different from A. quellina , A. papillosa and A. carolinensis in showing the first appearance of notopodial hooks from 7 th chaetiger. Among all the species currently classified under Ancistrosyllis , A. matlaensis n. sp. is most similar to A. falcata in having the first notopodial hooked setae from chaetiger 7. However, A. matlaensis n. sp. differs from A. falcata in lacking eyes (vs. presence of eyes in A. falcata ). These two species also differ in the shape of their tentacular cirri, conical and fusiform in A. matlaensis n. sp. and A. falcata respectively. Furthermore, ventral cirri are larger than the dorsal ones in the new species and start from the second segment whereas in A. falcata the character state is exactly opposite—ventral cirri are smaller than dorsal ones and starts from first segment. Neuropodia truncate and straight in new species but truncate, bent and downwards in A. falcata ( Table 2).

The neurochaetae of A. matlaensis n. sp. are similar, but vary in length and shape (curved serrated cutting edges and bidentate tips); whereas in other species of Ancistrosyllis neurochaetae are of varying length, where the shorter ones are limbate, poorly spiny or indented and the longer capillaries are narrow and smooth.

Ecological notes. Ancistrosyllis matlaensis n. sp. lives in silty-sand at depth of 2 m, in a salinity of 16.68 PSU. One important abiotic variable, salinity, is quite different between the A. matlaensis n. sp. and A. falcata —which the former closely resembles. The new species has been recorded from 16.68 PSU (the average annual salinity of the two collecting stations are 21.68 PSU [M3] and 20.91 PSU [M4]) and A. falcata has usually been recorded in waters with salinity 28-38.6 PSU ( Bogdanos & Satsmadjis 1983, Bogdanos & Satsmadjis 1987 and Nicolaidou & Papadopoulou 1989); ( Day [1957] did not provide ecological data for the type locality but at Inhaca Island which is the type locality of A. falcata the salinity is usually much higher than the new species collection locality [ Macnae & Kalk 1962]).

Etymology. This species is being named after the river Matla, one of the largest river of Sundarban Estuarine System.

Conclusion. Ancistrosyllis matlaensis n. sp. is described from the Indian waters and contributes to the knowledge about the morphological features and its relation to various ecological factors of this species. This report will contribute to the polychaete checklist of Indian waters. As has also been said above there are important morphological and ecological differences between the new species and A. falcata which proves that the present species is a different evolutionary lineage. Hence, it is a different species according to General Lineage Concept ( Queiroz 1998).

Figures

FIGURE 2. Ancistrosyllis matlaensis n. sp. holotype PUZ- 323 a) Anterior end, dorsal view; b) anterior end with palps and antennae, ventral view; c) pharynx with denticles; d) Posterior end, dorsal view showing anal cirri (enlarged, papillated). (scales: a, 60 µm; b, d, 30 µm; c, 10 µm) (dc—dorsal cirri, vc—ventral cirri, la—lateral antennae, tc—tentacular cirri, dndenticles, ac—anal cirri).

FIGURE 3. Ancistrosyllis matlaensis n. sp. holotype PUZ- 323 a) Anterior end, ventral view; b) paratype PUZ-357 anterior end, ventral view showing the dorsal hook from chaetiger 7; c) paratype PUZ-357 neuropodia with non limbate neurochaetae d) holotype PUZ- 323 sabre-like neurosetae with curved serrated cutting edges and bidented tips (scales: a, 60 µm; b, 100 µm; c, 50 µm; d, 5 µm) (la—lateral antennae, tc—tentacular cirri, nh—notopodial hook, dc—dorsal cirri, vc—ventral cirri, ncneurochaete).

FIGURE 4. Ancistrosyllis matlaensis n. sp. holotype PUZ- 323. a) dorsal hooks and non limbate capillary chaetae; b) neurosetae with dorsal hook; c) neuropodia with non limbate neurochaetae; d) sabre-like neurochaetae with small hooked tip (scales: a, 25 µm; b, c, 15 µm; d, 5 µm) (nh—notopodial hook, nc—neurochaeta).