Beroe mitrata

BEROE MITRATA (MOSER, 1907)

Synonym: Pandora mitrata Moser, 1907.

Adult individuals of Beroe mitrata are not large compared to other Beroe species. Their average length is about 60 mm (Wrobel & Mills, 1998). The body is mitre-shaped, flattened in cross-section. Its length to width ratio (l/w) is 1.33–1.78. Inside the large mouth, a macrocilia carpet is located, covering about 50% of the total area of the stomodaeum cavity. Macrocilia of B. mitrata are similar to that of B. forskaIii and have blunt, serrated tips, as viewed at the end of the effective stroke. The aboral end is oval or slightly tapered (Fig. 11A, B). The aboral pole is fringed with a row of short branched papillae (Fig. 11B). Like all Beroida, B. mitrata has eight meridional canals with eight comb rows, which are located beginning from the aboral organ and elongated maximally to the middle of the body. Comb rows might be of various lengths, extending from about half or two-thirds to threequarters of the body length. Meridional canals have many diverticulae that all bend toward the mouth. The numbers of branches of meridional canals increase with the growth of the individual (Moser, 1907; Komai, 1915). They are simple, showing only a few bifurcations and no anastomoses appear among them. Meridional canals are extremely flexible and can even turn inside-out as it was noted by Moser (1907) and Wrobel & Mills (1998). The overall colour is white or pale pink, with diffuse orange or red spots or pair of stripes on either side of the body (Fig. 11A, B).

Geographical distribution: Beroe mitrata was first described from Japanese waters (Moser, 1907; Komai, 1915). Other findings in this area and elsewhere in the Indo-Pacific are somewhat doubtful (Moss, 2009; Minemizu et al., 2015; Lungren, 2020). In addition, Beroe mitrata was found in the southern Pacific, northwestern Pacific, off South Africa (Wrobel & Mills 1998; Mills & Haddock, 2007) and in the Gulf of Mexico (Moss, 2009).

In the Atlantic Ocean, B. mitrata has been recorded from the western Atlantic (Report of RV Ronald H. Brown Cruise 06-03 to the western subtropical and tropical north Atlantic 10 April to 30 April, 2006). It was also recorded from the Mediterranean, in the Ligurian Sea (Madin, 1991; Tamm & Tamm, 1993). Mills (2005) has mentioned B. mitrata as an infrequent visitor to the Mediterranean.

Observations of Beroe mitrata were performed in the southern Aegean Sea in Turkish Bays: Gökova, Marmaris, Bodrum and Fethiye Bays (Killi et al., 2019). In Gökova Bay, the invader M. leidyi and the native B. mitrata first arrived from the northern Aegean Sea with currents from the north (Killi & Tarkan, 2013). Now both ctenophores are observed regularly in Gökova Bay and in its several smaller bays and coves, where B. mitrata controls the M. leidyi population by preying on it (Killi & Tarkan, 2013).

Habitat: Occurs in the warm surface waters, on the outer continental shelf and on the slopes (Wrobel & Mills, 1998; Moss, 2009).