Phylogenetics of Trachylina (Cnidaria: Hydrozoa) with new insights on the evolution of some problematical taxa

Abstract

Some of the most interesting and enigmatic cnidarians are classified within the hydrozoan subclass Trachylina. Despite being relatively depauperate in species richness, the clade contains four taxa typically accorded ordinal status: Actinulida, Limnomedusae, Narcomedusae and Trachymedusae. We bring molecular data (mitochondrial 16S and nuclear small and large subunit ribosomal genes) to bear on the question of phylogenetic relationships within Trachylina. Surprisingly, we find that a diminutive polyp form, Microhydrula limopsicola (classified within Limnomedusae) is actually a previously unknown life stage of a species of Stauromedusae. Our data confirm that the interstitial form Halammohydra sp. (Actinulida) is derived from holopelagic direct developing ancestors, likely within the trachymedusan family Rhopalonematidae. Trachymedusae is shown to be diphyletic, suggesting that the polyp stage has been lost independently at least two times within trachyline evolution. Narcomedusae is supported as a monophyletic group likely also arising from trachymedusan ancestors. Finally, some data, albeit limited, suggest that some trachyline species names refer to cryptic species that have yet to be sorted taxonomically.

Spatio-temporal structure of the jellyfish community in the transition zone of cold and warm currents in the northwest Pacific

“…Cnidarians and Ctenophores, referred hereafter as Jellyfish, were later sorted from the samples, transferred into 5% formalin-seawater buffered with borax and identified to the lowest taxonomic level possible under a dissecting microscope. Taxonomy followed Naumov (1960), Kramp (1968), Arai & BrinckmannVoss (1980), Pagès & Gili (1992), Bouillon (1999), Bouillon et al (2006), Collins et al (2008) and Lindsay et al (2008Lindsay et al ( , 2017 for Hydromedusae; Totton (1965aTotton ( , 1965b, Kirkpatrick & Pugh (1984), Pagès & Gili (1992), Pugh (1999Pugh ( , 2006, Bouillon et al (2006) and Mapstone (2009) for Siphonophorae; Mianzan & Cornelius (1999) and for Scyphomedusae; Mianzan (1999) and Mills & Haddock (2007) for Ctenophora.…”

Scolionema sanshin sp. n., a new species (Hydrozoa, Limnomedusae, Olindiidae) from the Ryukyu Archipelago, southern Japan

“…Genomic DNA was extracted from the 99.5 % ethanolpreserved tissue of cultured specimens using the DNeasy Blood and Tissue Kit (Qiagen, Germany) following the manufacturer's protocol. 18S rDNA was PCR amplified and sequenced using primers and protocols outlined in Collins et al (2008). The new sequences were aligned using MEGA 6.06 with built in ClustalW.…”

DNA barcodes unite two problematic taxa: the meiobenthic Boreohydra simplex is a life-cycle stage of Plotocnide borealis (Hydrozoa: Aplanulata)

“…DNA extractions were carried out on single individuals using the AutoGenPrep 965 high-throughput DNA extraction robotic system (AutoGen) following the manufacturer's instructions for Whole Blood extraction. PCR amplification of mitochondrial 16S and nuclear 18S was carried out according to the protocols established in Collins et al (2008), whereas COI was amplified and sequenced using the primers and protocol of Geller et al (2013). Barcoding at multiple loci was done in light of the concerns raised by Lindsay et al (2015) and because a lack of close relatives precluded identification of a "barcoding gap".…”