A new cryptic species of Asteronyx Müller and Troschel, 1842 (Echinodermata: Ophiuroidea), based on molecular phylogeny and morphology, from off Pacific Coast of Japan

Abstract

The first phylogenetic and phylogeographic studies of the cosmopolitan deep-sea species, Asteronyx loveni Müller and Troschel, 1842, were conducted, based on specimens collected from off the Pacific coast of Japan. Partial sequences of mitochondrial 16S (68 specimens) and COI ( 24specimens) genes were analyzed. Phylogenetic trees and network analyses revealed three lineages and five sub-lineages of A. loveni. Genetic distance and AMOVA (analysis of molecular variance)analyses suggested that the lineages should be considered three cryptic species. Skin on the aboral disc is partly thickened and forms a mesh-like pattern, which has never been reported in previous descriptions of Asteronyx; this is provided as a new taxonomic character. Based on absence/presence of mesh-like skin, one of the three lineages was assigned to A. loveni and another was described as Asteronyx reticulata new species. This new species can be distinguished from congeners by having reticulated external ossicles and small genital slits at the innermost position on the interradial oral disc.

Order Euryalida (Echinodermata, Ophiuroidea), new species and new records from the South China Sea and the Northwest Pacific seamounts

“…The molecular phylogenetic trees of these species of Gorgonocephalidae and Euryalidae were in agreement with previous studies ( Okanishi and Fujita 2013 ; Christodoulou et al 2019 ; O’Hara et al 2019 ). Previous molecular studies indicated that intraspecific genetic distance ranges approximately from 0.5% to 6.4%, with a mean of 2.2%, but species from the family Euryalidae usually showed less than 2% mean genetic distance ( Okanishi et al 2011 , 2018 ; Okanishi and Fujita 2013 ; Boissin et al 2017 ). In this study, we focused on the genera Asteroschema , Asterostegus , and Astrodendrum .…”

“…Two new species are described and seven species are redescribed, including seven new records from the South China Sea and one new record from the Northwest Pacific, all richly illustrated. DNA barcoding was used to identify ophiuroid species in the past two decades ( Ward et al 2008 ; Hoareau and Boissin 2010 ; Okanishi et al 2011 , 2018 ; Okanishi and Fujita 2013 ). Hence, we use barcoding to test our morphological identifications and to understand the interrelationships within genera.…”

Multilevel fine-scale diversity challenges the ‘cryptic species’ concept

“…Finally, there are the cases when the term ‘cryptic’ species was applied to externally diagnosable species (e.g. in the echinoderm ophiuroids 13 ). Thus, a considerable amount of non-cryptic diversity is still currently included under the ‘cryptic species’ concept.…”

“…However, to define an exact degree of morphological disparity is very difficult, if it is possible at all, so Heethoff 10 further concluded that the current ‘cryptic species’ concept represents either conceptual or terminological chaos. Additional complications arise from the most recent practice in different animal groups such as crustaceans 11 , insects 12 or echinoderms 13 when the term ‘cryptic’ species is used for morphologically diagnosable species.…”

Size variation and geographical distribution of the luminous earthworm Pontodrilus litoralis (Grube, 1855) (Clitellata, Megascolecidae) in Southeast Asia and Japan

“…Phylogenetic reconstruction was performed using the maximum likelihood (ML) analysis in RAxML v. 8.1.20 (Stamatakis 2014), and 1,000 bootstraps were used to estimate the node reliability as bootstrap support values. Bootstrap values lower than 75% for each node were considered as insignificant (Okanishi et al 2018). Pontodriluslongissimus was used as the outgroup (Accession number MK642683 and MK642684).…”