Pleurobrachia pileus (O. F. Müller, 1776)

Purushothaman, Jasmine, Siddique, Alfisa, Bhowal, Aishee & Chandra, Kailash, 2020, Diversity of Ctenophores in the Sundarban Mangroves, Northern Indian Ocean, Records of the Zoological Survey of India 120 (2), pp. 133-140 : 136-137

2. Pleurobrachia pileus (O. F. Müller, 1776)

1776. Beroe pileus Müller, O. F. Hafniae, Typiis Hallageriis , 1-274. 1860. Pleurobrachia rhododactyla Agassiz, L. Contrib. Nat. His. U.S.A.

Vol. 3, Boston. 301 pp.

Material examined: WN-CTEN-002; 5 specimens, 4-7 mm in diameter, length 10-16 mm from oral to aboral end. Matla Channel: Surface water, 10 m (21°46' 10.7" N, 88° 37' 44.8" E and 21°48' 28.1" N, 88° 34' 04.8" E); Thakuran Channel: depth 0 m, 20 m (21°42' 18.1" N, 88° 30' 51.0" E), Surface water, 10 m (21°39' 18" N, 88° 28'

13.9" E); Jagaddal Creek: Surface water and 10 m (21°37'

35.9" N, 88° 26' 15.4" E), Sundarbans , West Bengal, India ,

19.1.2018, 20.1.2018, 21.1.2018. Coll. Jasmine P.and Party.

Description: Body oval or spherical in shape. Oral surface is wider than the aboral surface. Presence of eight ciliary comb plates equal in length, beginning from aboral pole ending at three-quarters of its length towards the oral pole. The comb plates are opalescent with transparent ectomesoderm; tentacles, sheaths, and stomodeum make be milky or pale orange. Length fluctuates between 10- 25 mm. Tentacle sheath is distant from stomodeum. Contractile tentacles which may be fifteen to twenty times longer than the body length, they can retract into the tentacle sheaths ( Moser, 1903). The unique features of Pleurobrachia pileus are: it is spherical i.e. its length and width are almost equal. The comb plates run three-quarters the distance between the oral and aboral pole, the tentacular sheath has an orangish hue.

Diagnosis: Specimens range from 4-7 mm in diameter, 10-16 mm in length from oral to aboral end. Eight ciliary comb plates begin from aboral pole and end at three quarters of its length towards the oral pole. Tentacular sheath varies from the stomodeum ( Figure 2a ).

Distribution: North-western Bay of Bengal, off Rushikulya estuary ( Srichandan et al., 2015), southeastern Arabian Sea, Kanyakumari to off Kollam ( Peter et al., 2018). Elsewhere: East Adriatic Sea ( Gamulin, 1979) , North Atlantic and the coastal waters of NW Europe ( Greve, 1975; Liley, 1958), Black Sea ( Mutlu & Bingel, 1999) , Kiel Bight ( Schneider, 1987).

Remark: Most of these specimens were obtained from swarm stations (Thakuran Channel). More than 600 specimens per 500 ml of sea water were obtained, but only 5 specimens have been preserved in the museum collections for further study. Abundance of P. pileus was reported as a swarm and according to the local fishermen this causes a huge menace to the fishery community by clogging the fishing nets as well as causing skin irritation.

Figures

Figure 2. Collected ctenophore species of Sundarbans, Bay of Bengal, Northern Indian Ocean. (a) Pleurobrachia pileus; (b) Pleurobrachia globosa; (c) Beroe gracilis; (d) Beroe ovata.