Marine biologists have described a third species of branching syllid worm — and the second within the genus Ramisyllis — living inside an undescribed species of the sponge genus Petrosia found in shallow waters at Sado Island, Japan.
Both have unusual ramified bodies with one head and multiple branches and live inside the canals of host sponges.
“In 1879, Scottish physician and marine zoologist William Carmichael M’Intosh 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,” explained lead author University of Göttingen’s Professor M. Teresa Aguado and colleagues.
“The worms were found inside the hexactinellid sponge Crateromorpha meyeri at 175 m deep near Cebu, in the Philippines.”
“In relation to their lateral branches, McIntosh said: ‘the body of the annelid appears to have a furor for budding laterally, terminally, and wherever a broken surface occurs,’ which represented the first instance of an annelid species described with a randomly branching asymmetrical body.”
“The second known branching species, Ramisyllis multicaudata, was described from the coastal shallows of Darwin, Northern Australia, in 2012.”
“That study demonstrated notable differences in biology and morphology between this species and Syllis ramosa and analyzed its phylogenetic relationships inside the family Syllidae.”
“Ramisyllis multicaudata shares with Syllis ramosa a randomly branching asymmetrical body and its way of living inside the labyrinthic internal canals of sponges, but differs (except for the Red Sea and Imajima’s 2005 Sagami Bay reports of Syllis ramosa) in the host sponge (Petrosia vs. Crateromorpha), depth (0-20 m vs. 100-1,000 m deep), and key morphological and anatomical details.”
The home of the branching worm Ramisyllis kingghidorahi: the host sponge Petrosia sp. in its natural habitat; the posterior end of the branching worm can be seen on the surface of the sponge. Image credit: Toru Miura.
The newly-described species belongs to the genus Ramisyllis and inhabits the coastal waters of Sado Island, Japan.
Its name, Ramisyllis kingghidorahi, refers to King Ghidorah, the three-headed and two-tailed monster enemy of Godzilla.
“King Ghidorah is a branching fictitious animal that can regenerate its lost ends, so we thought this was an appropriate name for the new species of branching worm,” Professor Aguado said.
“We were astonished to find another of these bizarre creatures with only one head and a body formed from multiple branching,” she added.
“This discovery reveals a higher diversity of these tree-like animals than anyone expected.”
Professor Aguado and co-authors also provided a hypothesis for the evolution of branching body patterns as an adaptation to live inside the labyrinthic canals system of their host sponges.
“The capacity to produce new posterior segments throughout their whole lives (typical of many worms), together with their regenerative capacities and the worms’ ability to produce several simultaneous newly formed segments during reproduction, may be the basis of the evolution of a branching body,” they said.
“Scientists don’t yet understand the nature of the relationship between the branching worm and its host sponge,” Professor Aguado said.
“Is it a symbiotic relationship where both creatures somehow benefit? And how do the worms manage to feed to maintain their huge bodies having just one tiny mouth in their single head?”
The results were published in the journal Organisms Diversity & Evolution.
M.T. Aguado et al. Ramisyllis kingghidorahi n. sp., a new branching annelid from Japan. Org Divers Evol, published online January 22, 2022; doi: 10.1007/s13127-021-00538-4