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Cephalopod fisheries are increasing, but little is known about the cryptic diversity of some key commercial species. Recent studies have shown that cryptic speciation is common in cephalopods, including several oceanic squids formerly considered 'cosmopolitan species.' Further efforts are needed to investigate the cryptic diversity of commercial species, to inform management and support sustainable fisheries practices. Thysanoteuthis rhombus is an oceanic squid, currently recognized as the single species of the family Thysanoteuthidae. Thysanoteuthis. rhombus has a global distribution in tropical and subtropical waters and is an economically important species, with the highest catches occurring off Okinawa in Japan and of potential fishery resource for other countries due to its high abundance and large size. Here, we used sequences from 12S rRNA, 16S rRNA, and cytochrome c oxidase I to characterize its cryptic diversity using samples collected throughout most of its known geographic range. We identified three different putative species whose distributions are concordant with main ocean basins: Thysanoteuthis major, the most abundant species, is widely distributed in the North Pacific Ocean, North Indian Ocean, and limits of the South Atlantic Ocean; Thysanoteuthis rhombus is distributed in the North and South Atlantic Ocean and Mediterranean Sea; and Thysanoteuthis cf. filiferum, likely the least sampled to date, is found in the southwestern Pacific Ocean. A sister relationship was observed between T. rhombus and T. major, and T. cf. filiferum was found to be the most divergent species. Based on our divergence estimation, we hypothesize that the closure of the Isthmus of Panama during the early Pliocene played a significant role in the split of T. rhombus and T. major, while the split of their ancestor from T. cf. filiferum coincided with an increase in the Pacific Walker Circulation and the longitudinal gradient of surface temperatures in the Pacific Ocean during the Late Oligocene and Early Miocene. Our work identifies three different putative species within Thysanoteuthis and has potential use for improving fishery management and conserving the diversity in these species. [ABSTRACT FROM AUTHOR]

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]

The bathypelagic squid Bathyteuthis bacidifera was collected in an open net towed at 200 m over a bottom depth range from 1200 to 2340 m in the southern Arabian Sea, near Laccadive Archipelago (09°54′32″N; 73°39′12″E, 11°16′18″N; 72°51′09″E, and 10°48′08″N; 72°41′11″ E). Morphometric and molecular analyses are presented here. This is the first record of Bathyteuthis bacidifera from the southeastern Arabian Sea and the first description of the species at the molecular level. Specimens were collected from April 2015 to January 2016 in warmer (15.2 to 15.6 °C) and shallower (∼200 m) water than previously reported. The first observations of countable increments in the statolith of the genus Bathyteuthis are reported. The statolith microstructure of the specimens (15.6 to 39.0 mm dorsal mantle length) revealed that Bathyteuthis bacidifera is a slow growing squid, with a growth rate of 0.12 to 0.20 mm/day. The record of this rare squid from the Arabian Sea is an addition to the cephalopod fauna of India and contributes to biogeographic knowledge of this unusual deep sea family. [ABSTRACT FROM AUTHOR]