Search

The octopus of the genus Tremoctopus from the Arabian Sea has not been investigated in the past. This study reports on the rare pelagic octopus Tremoctopus gracilis from the south-eastern Arabian Sea. Twenty females with dorsal mantle lengths (DML) ranging between 62 and 160 mm and weighing between 31 and 719 g were examined. These specimens were collected from commercial fishing grounds, and amongst them was a single mature female with 12,618 oocytes in the ovary (size varied from 0.61 to 1.67 mm (mean = 1.13 mm). The detailed morphometric and morphological characteristics were recorded, and the specimens were identified up to the genus level. Further molecular species identification was carried out through mitochondrial markers (COI & 16S rRNA). Phylogenetic analysis, based on partial sequences of the above markers, generated a single clade that included sequences from the Indian and Pacific Oceans, including those misidentified as Tremoctopus violaceus from the Pacific. Evolutionary divergence estimation revealed a high inter-specific genetic divergence from T. violaceus sequences in the Mediterranean Sea and Atlantic Ocean, thus confirming the Tremoctopus species in our study as T. gracilis and authenticated that GenBank sequences of T. violaceus from the Pacific Ocean are indeed T. gracilis. [ABSTRACT FROM AUTHOR]

Sthenoteuthis oualaniensis is known for its complex population structure with three major transoceanic forms (viz. middle‐sized, dwarf, and giant forms) whose taxonomic status has been disputed for decades. This integrated taxonomic study examines these prevenient morphotypes gathered on cruises in the Indian Ocean to ascertain their status in the evolutionary history of the species. Molecular analyses employing mitochondrial (COI, ND2) and nuclear (H3) markers revealed four genetically distinct and novel lineages of the species in the Indian Ocean, representing three morphotypes from the Arabian Sea and one from the Southern Indian Ocean. The mitochondrial‐based phylograms revealed two distinct clades in the species: "dwarf forms + giant form" and "middle‐sized forms," which further branch into geographically structured evolutionary units. Species delimitation analyses recovered five distinct clades, namely, the Arabian Sea giant and dwarf forms, Equatorial, Eastern Typical, and Other Middle‐sized forms, representing the consensus molecular operational taxonomic units. H3 being heterozygous could not resolve the phylogeny. Haplotype network and AMOVA analysis of mtDNA genes indicated explicit phylogeographic structuring of haplotypes, whereas these outputs and PCA results were incongruent with the morphological grouping. Phenetic features distinguishing the morphotypes were sometimes plastic and mismatched with the genotypes. The giant form was genetically close to the dwarf forms, contradicting the earlier notion that it descended from the middle‐sized form. It may be assumed that the dwarf form evolved following sympatric speciation and adaptation to warm equatorial waters, while the focal features of the Western Arabian Sea guide toward allopatric speciation of the giant form. [ABSTRACT FROM AUTHOR]