Ramisyllis kingghidorahi n. sp., a new branching annelid from Japan

M Teresa Aguado,Toru Miura,Christian Fischer,Mayuko Nakamura,Naoto Jimi,Guillermo Ponz-Segrelles,Akihito Omori,Kohei Oguchi,Yuji Ise,Christopher J Glasby,Hisanori Kohtsuka,Rannyele P Ribeiro

doi:10.1007/s13127-021-00538-4

Abstract

Among over 20,000 species of Annelida, only two branching species with a highly modified body-pattern are known until now: the Syllidae Syllis ramosa McIntosh, 1879, and Ramisyllis multicaudata Glasby et al. (Zoological Journal of the Linnean Society, 164, 481–497, 2012). Both have unusual ramified bodies with one head and multiple branches and live inside the canals of host sponges. Using an integrative approach (combining morphology, internal anatomy, ecology, phylogeny, genetic divergence, and the complete mitochondrial genome), we describe a new branching species from Japan, Ramisyllis kingghidorahi n. sp., inhabiting an undescribed species of Petrosia (Porifera: Demospongiae) from shallow waters. We compare the new species with its closest relative, R. multicaudata; emend the diagnosis of Ramisyllis; and discuss previous reports of S. ramosa. This study suggests a much higher diversity of branching syllids than currently known. Finally, we discuss possible explanations for the feeding behaviour in the new species in relation to its highly ciliated wall of the digestive tubes (especially at the distal branches and anus), and provide a hypothesis for the evolution of branching body patterns as the result of an adaptation to the host sponge labyrinthic canal system.

Highlights

In 1879, McIntosh published the description of a “remarkable branched Syllid,” Syllis ramosa, collected during the Challenger Expedition, one of the most significant natural history expeditions from the nineteenth century
This study demonstrated notable differences in biology and morphology between this species and S. ramosa and analysed its phylogenetic relationships inside Syllidae
The remaining complete sponges were brought to Misaki Marine Biological Station (MMBS) of The University of Tokyo and placed in tanks with running sea water, where they survived for 3 months; three more sponges were dissected during this period

Summary

Introduction

In 1879, McIntosh published the description of a “remarkable branched Syllid,” Syllis ramosa, collected during the Challenger Expedition, one of the most significant natural history expeditions from the nineteenth century. Another finding of a branching annelid from a distant geographic area (the northern Red Sea) was attributed to S. ramosa by Crossland (1933) It was found inside a small, fragile 10-mm diameter unidentified siliceous sponge attached to a dead coral [Lobophyllia corymbosa (Forsskål, 1775)] at 1.8 m deep and, no drawings or detailed descriptions were provided. It was not until Read (2001) that another report of S. ramosa surfaced, this time from a specimen of Crateromorpha about 600 mm long found at 1000 m deep in the Tasman Sea of New Zealand. Imajima identified as S. ramosa one specimen from Sagami Bay, found in 2005 at 36–50 m and deposited in the National Museum of Nature and Science of Tokyo (collection code: NSMT-Pol S; Catalogue number: 1568)

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Conclusion