Morphological and molecular identification of marine copepod Dioithona rigida Giesbrecht, 1896 (Crustacea:Cyclopoida) based on mitochondrial COI gene sequences, from Lakshadweep sea, India

Abstract

Morphological identification of the marine cyclopoid copepod Dioithona rigida in combination with sequencing a 645 bp fragment of mitochondrial cytochrome oxidase c subunit I (mtCOI) gene, collected from offshore waters of Kavarathi Island, Lakshadweep Sea, is presented in this study. Kiefer in 1935 classified Dioithona as a separate genus from Oithona. The main distinguishing characters observed in the collected samples, such as the presence of well-developed P5 with 2 setae, 5 segmented urosome, 12 segmented antennule, compact dagger-like setae on the inner margin of proximal segment of exopod ramus in P1-P4 and engorged portion of P1-bearing a spine, confirmed their morphology to D. rigida. A comparison of setal formulae of the exopod and endopod of D. rigida with those recorded previously by various authors are also presented here. Maximum likelihood Tree analysis exhibited the clustering of D. rigida sequences into a single clade (accession numbers KP972540.1-KR528588.1), which in contrast was 37-42% divergent from other Oithona species. Further intra-specific divergence values of 0-2% also confirmed the genetic identity of D. rigida species. Paracyclopina nana was selected as an out group displayed a diverged array. The present results distinctly differentiated D. rigida from other Oithona species.

Molecular characterization and culture optimization of marine copepod Oithona dissimilis (Landberg, 1940) from Nagore coastal waters, Southern India

“…Identifying copepods of this specific genus on a regular basis is still difficult because of their petite size and inconspicuous morphological features that are used for diagnosis. (Radhika et. al., 2017).…”

“…The copepod, identified in our study was very well characterized by the presence of the prominent features of O. dissimilis based on antenna (A1) which is shorter and both are geniculate in males and descriptive features confirmed that the males are usually smaller than females, urosome was 6 segmented in male and 5 segmented in female (Inshida 1985). To differentiate species within the genus, the prominent characters being conventionally followed are based on the arrangement of setae and spines on the exopod of swimming legs 1-4 (Radhika et al, 2017). Presently, the setae and spines of P1-P4 arranged in our specimen were consistent with the keys provided by Wellershaus (1969) and hence our copepod was identified as O. dissimilis .…”

“…There is a lack of information regarding cyclopoid copepods, particularly in relation to Oithona species. So far, studies have been concentrated on O. similis, O. atlantica, O. nana (Georgina et al, 2012) and Dioithona rigida (Radhika et al, al 2017). It's important to note that there is currently no available data for the species Oithona dissimilis, which creates some uncertainty in the taxonomic classification of the Oithona group at the species level.…”