Abstract
Sclerolinum annulatus n. sp. (Annelida: Siboglinidae) is described based on specimens collected from soft sediment of the Haima cold seep in the South China Sea. Morphologically, S. annulatus n. sp. is distinct in having a tube with transverse rings and a forepart (i.e., anterior region) containing one arched row of elongated plaques on both sides of the dorsal furrow. Genome skimming, assembly, and annotation produced a nearly complete mitogenome of S. annulatus n. sp. with 15,553 bp nucleotides that encodes 13 protein-coding genes, two rRNA, and 22 tRNA. Phylogenetic analyses based on the mitochondrial cytochrome c oxidase I (cox1) gene and a concatenated dataset comprising the mitochondrial cox1 and 16S rRNA genes along with the nuclear 18S rRNA gene both strongly support the placement of S. annulatus n. sp. in the genus SclerolinumSouthward, 1961. Based on cox1, S. annulatus n. sp. is most closely related to an undescribed siboglinid from off Kushiro in Japan (“Pogonophora” sp. Kushiro-SK-2003). Transmission electron microscopy, microbial 16S rRNA amplicon sequencing, phylogenetic reconstruction, and stable isotope analyses together indicate that S. annulatus n. sp. hosts a single phylotype of sulfur-oxidizing endosymbionts.
Highlights
Siboglinids are annelid tubeworms inhabiting deep-sea chemosynthesis-based ecosystems, including hydrothermal vents, hydrocarbon seeps, decaying organic materials, and reduced sediment (Hilário et al, 2011)
During a remotely operated vehicle (ROV) cruise in 2019, we discovered dense aggregations of Sclerolinum tubeworms in the Haima cold seep (Figure 2)
Type Material Type specimens are incomplete, with the anterior and/or trunk regions but lacking the opisthosomal region. They were collected in May 2019 and are currently deposited in Tropical Marine Biodiversity Collections of the South China Sea, Chinese Academy of Sciences (Guangzhou, China)
Summary
Siboglinids are annelid tubeworms inhabiting deep-sea chemosynthesis-based ecosystems, including hydrothermal vents, hydrocarbon seeps, decaying organic materials (e.g., sunken wood and whale falls), and reduced sediment (Hilário et al, 2011). Sclerolinum, and vestimentiferans harbor chemosynthetic sulfur-oxidizing symbionts within the host cells termed bacteriocytes, located in an organ of their trunk region known as the trophosome (Bright and Giere, 2005; Li et al, 2018). Osedax is the only group of siboglinids that lacks a discrete trophosome, with females harboring heterotrophic symbionts in their branching roots to penetrate into whale bones for nutrition (Rouse et al, 2004)
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