The study was carried out in two species (Acromitus maculosus and A. flagellatus) in order to check whether the collected species are only morphologically distinct or indeed congeneric species of Acromitus as reported by earlier authors/previous reports. The samples (72 nos.) are collected during the pre-monsoon seasons (mid-February to end May) of 2019, 2020, 2021 and 2023 from the stake-net fishery operating in the Kumbalam estuary (Lat. 9054' 14" N;Long. 760 18' 17" E) of Vembanad lake, Kerala India. The Scyphozoan jellyfish Acromitus maculosus and A. flagellatus are considered to be valid species under the genus Acromitus. In laboratory, following morphometric measurements of each specimen were taken for analysis such as Oral Arm Length, Oral Arm Stalk, Oral Arm Wing, Radius of Oral Disk, Ring Canal Radius, Inner Muscle, Outer Anastomosing Canal System and weight of the specimens. On analysis, specimens of A. maculosus and A. flagellatus from Kochi backwaters, India indicate that the two putative species differ only in their morphologic features and that there are no significant variations in their morphometric and genetic traits except for the medusa diameter- stabilized wet weight relation. On DNA analysis, the genetic distance in the CO1 gene sequence of the putative species A. maculosus and A. flagellatus (0.4%) were below the threshold value suggesting that the two species are similar in their genetic traits. As the observed variations in two species were limited to morphologic features with transitional morphologic forms in between and the lack of significant morphometric and/ or genetic variations among the two putative species necessitate a through recheck on the species status of A. maculosus and A. flagellatus.

This study was supported by the Centre of Excellence for Aquatic Resource Management and Conservation and the Kerala governmental research fund at the Kerala University of Fisheries and Ocean Studies.