Raveendhiran Ravinesh

A new species of deep-sea thyasirid (Bivalvia: Thyasiridae), Ascetoaxinus ravichandrani sp. nov., is described and illustrated from material collected in the northern Indian Ocean during the FORV Sagar Sampada deep-sea cruise no. 404. Specimens were collected from a depth between 1007 m and 1038 m off Kanyakumari, Gulf of Mannar, Tamil Nadu, South India. This is the first record of the genus Ascetoaxinus from the Indo-West Pacific. The new species is compared to A. quatsinoensis P.G. Oliver & Frey, 2014 from the Northeast Pacific and A. ovoideus (Dall, 1890) from the Northwest Atlantic. It can be distinguished from these species by its external shell characters. Further comparisons are made between the new species and other larger thyasirids recorded from deep waters around India, notably Channelaxinus investigatoris E.A. Smith, 1895. The distinctions and similarities among these species are discussed, highlighting the key features that set A. ravichandrani apart from related species.

The Conidae are predatory marine gastropods and they produce one of the most potent venoms in nature. They are ecologically vital for regulating trophic positions and act as primary carnivores in oceans. Amateur shell collectors target some species and ecosystems are intensively exploited by collectors of ornamental shells and commercial traders. Moreover, increasing coastal development, habitat modification and fragmentation, and overexploitation of resources threaten cone snail diversity. This study documents 46 species of Conidae from the Kerala coast, India. Fifteen species are newly recorded from the coast, and one species is reported for the first time from the Indian coast. We also revalidate Conus ceylanensis and Conus bizona.

The identity of Nepinnotheres vicajii (Chhapgar, 1957) (described as Pinnotheres vicajii) (Pinnotheridae), a pea crab associated with the bivalve Marcia recens (Holten, 1802), is clarified. On the basis of re-diagnosis of holotype male and freshly collected female specimens from its type locality, P. vicajii is now assigned to Arcotheres Manning, 1993. A second poorly known species from India, Arcotheres casta (Antony & Kuttyamma, 1971), originally collected from Meretrix casta (Gmelin, 1791) is also synonymized with A. vicajii.

The crab fauna (Crustacea: Brachyura) of Lakshadweep (Laccadives), a group of Indian islands in the western Indian Ocean is updated, using material from the intertidal and shallow subtidal areas collected between 2012 and 2015. Fifty-three species were recorded during this study, of which 17 species are newly recorded from the islands, and three are also new records for India. A total of 169 species of brachyuran crabs are now known from Lakshadweep. The taxonomy of Elamena gracilis Borradaile, 1903 (Hymenosomatidae) is clarified and stabilized by the designation of a lectotype.

The rare raninid crab Umalia trirufomaculata (Davie and Short, 1989) is recorded from India for the first time. It is redescribed and compared at length with the related but poorly known U. misakiensis (Sakai, 1937) on the basis of a good series of specimens from the Philippines. Some of the supposed differences which have been documented between the two taxa (e.g., carapace proportions and features of the cheliped) are not valid; while new distinguishing characters associated with the male pleon and gonopods are observed.

A sponge-associated actinomycete (strain MCCB267) was isolated from a marine sponge Mycale sp. collected in the Indian Ocean off the Southeast coast of India. Phylogenetic studies of this strain using 16S rRNA gene sequencing showed high sequence similarity to Streptomyces zhaozhouensis. However, strain MCCB267 showed distinct physiological and biochemical characteristic features and was thus designated as S. zhaozhouensis subsp. mycale. subsp. nov. A cytotoxicity-guided fractionation of the crude ethyl acetate extract of strain MCCB267 culture medium yielded four pure compounds belonging to the polycyclic tetramate macrolactam (PTM) family of natural products: ikarugamycin (IK) (1), clifednamide A (CF) (2), 30-oxo-28-N-methylikarugamycin (OI) (3), and 28-N-methylikarugamycin (MI) (4). The four compounds exhibited promising cytotoxic activity against NCI-H460 lung carcinoma cells in vitro, by inducing cell death via apoptosis. Flow cytometric analysis revealed that 1, 3, and 4 induced cell cycle arrest during G1 phase in the NCI-H460 cell line, whereas 2 induced cell arrest in the S phase. A concentration-dependent accumulation of cells in the sub-G1 phase was also detected upon treatment of the cancer cell line with compounds 1–4. The in vitro cytotoxicity studies were supported by molecular docking and molecular dynamic simulation analyses. An in silico study revealed that the PTMs can bind to the minor groove of DNA and subsequently induce the apoptotic stimuli leading to cell death. The characterization of the isolated actinomycete, the study of the mode of action of the four PTMs, 1–4, and the molecular docking and molecular dynamic simulations analyses are herein described.