Crowned jellyfish ( Cnidaria : Scyphozoa : Rhizostomeae : Cepheidae ) from waters off the coast of Pakistan , northern Arabian Sea

This report presents the occurrence of two species of crowned jellyfish, Cephea coerulea and Netrostoma setouchianum, recorded for the first time from waters off the coast of Pakistan in the northern Arabian Sea. Diagnosis of the genera Cephea and Netrostoma are provided. We also provide simple keys for the identification of cepheid genera. We found that long filaments on mouth arms in Cephea easily distinguish it from Netrostoma, which has no such filaments.

In recent years there have been an increasing interest in jellyfish (Gibbons and Richardson 2013) due to their apparent more frequent population explosion events or blooms (Condon et al. 2012).Among the gelatinous zooplankton (Braconnot and Carré 1989) or gelata (Haddock 2004), jellyfish-meaning the free-swimming stage of some cnidarians (medusozoans)-seem to be the most conspicuous members that exhibit blooms.Many taxa are known by their beautiful morphology including members of the rhizostome family Cepheidae Agassiz (1862).Some genera of this family (e.g., Cephea Péron & Lesueur, 1810 and Netrostoma Schultze, 1898) have a marked depression and several protuberances on the exumbrella and are commonly known as crowned jellyfish.These jellyfish are known to be distributed in the tropical waters of the Indo-West Pacific (Mayer 1910;Kramp 1970).
While scuba diving on 19 December 2010 two specimens of crowned jellyfish (later referred to the genus Netrostoma) were photographed at Charna Island (24°53′56.422ʺN, 066°36′15.297ʺE), off the Pakistani coast (Figure 1).However, the specimens could not be collected and identification was based on examination of photographs.On 8 February 2014, during fishing activities off Pakistani coast (24°59.03′N, 065°43.62′E) (Figure 1), three specimens of another crowned jellyfish (later identified as belonging to the genus Cephea) were separated from the gill net and photographed in life.But as there were no technical facilities or preservatives, the specimens were kept in ice and brought to laboratory in As we had no opportunity to study the canal system, thus the identification of the genera was made on the basis of exumbrellar morphology and subumbrellar appendages, in particular presence or absence of long filaments on the oral arms.We revise the diagnosis of the genus Netrostoma to include this feature (long filaments).We include keys that allow easy identification of cepheid genera and valid species of the genera Cephea and Netrostoma.Identification of the species was based upon their original descriptions (Kishinouye 1902;Vanhöffen 1902), Mayer (1910), and Kramp (1961).developed, greatly fused velar lappets per octant; sometimes markedly differ in width and, flat to oblique at the margins.Rhopalia and rhopalar lappets could not be identified.Oral arms short 1.5 × bell radius, stout, branched; each arm with 2-3 long, slender filaments of different sizes but lacking in some arms.Colour in life: umbrella and oral arms blue with brown ventral surfaces of arms, in good agreement with Vanhöffen's (1902) description.
Genus Netrostoma Schultze, 1898 Cepheidae with a protuberances-bearing exumbrellar central dome or a large, smooth central knob on the exumbrella; with 3 inter-rhopalar canals per octant; mouth arms with or without short, stiff appendages, but no long filaments.
Exumbrella with low central dome bearing about 10-15 conical, pointed protuberances.Deep annular furrow on the exumbrella, ca.¾ away from bell margin.Umbrella margin with 7 oblong-shaped, round velar lappets per octant.Rhopalia and rhopalar lappets could not be seen.Oral arms short 1.2 × bell radius, stout and branched.The oral arms bear frilled mouth openings with numerous tiny, pointed dark blue short appendages among them and are devoid of any form of long filaments.Colour in life: bright blue as also mentioned by Kishinouye (1902: 13).
Remarks: N. setouchianum can be easily distinguished from its congeners due its pointed protuberances on the exumbrellar central dome.
There is no consensus in the literature regarding the validity of the genus Netrostoma and its species.The majority of authors consider Netrostoma a distinct and valid genus, but Mayer (1910: 651-652) regarded it as a junior synonym of Cephea (see also Tokioka 1964: 155).Kramp (1961), however, recognized these two genera distinct from each other based on the number of inter-rhopalar canals per octant and the characteristic subumbrellar appendages.The number of species of Cephea and Netrostoma is also a matter of dispute.For Stiasny (1937b: 114), Netrostoma typhlodendrium is identical to N. coerulescens.Based on the literature, we found that the different species of Cephea resemble each other more than the ones in the genus Netrostoma.The synonyms among Cephea species seem to be more established, being valid only two species: Cephea cephea and C. coerulea (see Stiasny, 1938: 23).
As cepheid medusae are not easy to distinguish, we provide keys to identify the genera of the family Cepheidae and species of Cephea and Netrostoma using easily recognizable characters.