Abstract
During a survey of the siphonophore community in the Kuroshio Extension, Northwest Pacific Ocean, a new Halistemma Huxley, 1859 was described using integrated molecular and morphological approaches. The Halistemma isabu sp. nov. nectophore is most closely related morphologically to H. striata Totton, 1965 and H. maculatum Pugh and Baxter, 2014. These species can be differentiated by their nectosac shape, thrust block size, ectodermal cell patches and ridge patterns. The new species’ bracts are divided into two distinct types according to the number of teeth. Type A bracts are more closely related to ventral bracts in H. foliacea (Quoy and Gaimard, 1833) while Type B bracts are more similar to H. rubrum (Vogt, 1852). Each type differs, however, from the proximal end shape, distal process and bracteal canal. Both of the new species’ morphological type and phylogenetic position within the genus Halistemma are supported by phylogenetic analysis of concatenated DNA dataset (mtCOI, 16S rRNA and 18S rRNA). Integrated morphological and molecular approaches to the taxonomy of siphonophores showed a clear delimitation of the new species from the congeners. Halistemma isabu sp. nov. is distributed with the congeners H. rubrum, H. cupulifera, H. foliacea and H. striata in the northwestern Pacific Ocean.
Highlights
Siphonophores, belonging to the class Hydrozoa Owen, 1843, live in oceans and are mostly holoplanktonic organisms [1]
Integrated morphological and molecular approaches to the taxonomy of siphonophores showed a clear delimitation of the new species from the congeners
We conducted a morphological and molecular analysis of H. isabu sp. nov. found in the Kuroshio Extension of Northwest Pacific Ocean
Summary
Siphonophores, belonging to the class Hydrozoa Owen, 1843, live in oceans and are mostly holoplanktonic organisms [1]. 190 species have been described as siphonophores, though there are likely more in the marine environment [2]. Siphonophores have gelatinous bodies and form unique colonies throughout their life [3]. 65 species with pneumatophores and nectophores are recognized as Physonectae [7]. Physonects’s descriptions are often incomplete because Siphonophores have fragile gelatinous bodies and many research records are based on dissociated specimens, where only a few nectophores or bracts were collected [1,8]. Morphological changes throughout their life cycle, phenotypic plasticity and cryptic species are responsible for erroneous species diversity estimations
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