Beroe gracilis Künne, 1939

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 : 137

3. Beroe gracilis Künne, 1939

1939. Beroe gracilis Künne, C. Zoologischer Anzeiger , 127: 172-174.

Material examined: WN-CTEN-004; 5 specimens. The samples were collected from the Thakuran Channel (Stations 3 and 4): Surface water, 10 m (21°42' 18.1" N, 88° 30' 51.0" E; 21°39' 18" N, 88° 28' 13.9" E), Sundarbans , West Bengal, India, 20.1.2018. Coll. Jasmine P. and Party.

Description: Body is barrel-shaped, oral-aboral ends are rounded, and very subtle lateral compression is evident in the tentacular plane. The comb plates, substomodeal and subtentacular which are equal in length run to threefourths the body length, starting from the aboral pole to the oral pole. A wide semicircular mouth opening into a large pharynx, which covers almost all space of the inner part of the body. A row of macrocilia formed as a wideband on the oral part of the pharynx. The meridional canals lack branches. The four meridional canals meet the pharyngeal canal via the oral fork. The body has whitish to pink colouration with maximum height of 30 mm ( Greve, 1975; Liley, 1958). Apical organ consists of a statolith at the middle and surrounded by unsplit aboral papillae with a smaller length than statolith dome.

Diagnosis: Specimens are 3-6 mm in diameter or width. Total length 9 mm from oral to aboral end, the width of the mouth is about 4.2 mm. The ctene plates in the subtentacular rows is 29 – 31 and the ctene plates in substomodeal are 36 – 39, the size of the statocyst dome is about 230 µm ( Figure 2c ).

Remarks: The specimens collected from this area are almost similar to those collected from Chilean waters ( Oliveira et al., 2014). The specimens of Künne (1939) and Wrobel & Mills (2003) are slender than the present specimens. The present specimens are characterized with broadband of macrocilia inside the oral part of the pharynx, which is same as described by Tamm & Tamm (1993). This species has not been reported by earlier workers from this region, so it may be an alien species. This is the first record of this species from the coast of Sundarbans, Bay of Bengal.

Other observation notes: The specimens observed were alive and active swimmers. The samples were collected from the same station having swarms of Pleurobrachia pileus.

Distribution: This is the first instance of sighting of this species from the Northern Indian Ocean, Bay of Bengal. Elsewhere: North Sea ( Kunne, 1939) , North Atlantic Ocean ( Greve, 1975), Pacific Ocean ( Wrobel & Mills, 2003) and Chilean waters ( Oliveira et al., 2014).

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.