Ramisyllis multicaudata

Ramisyllis multicaudata is a species of polychaete worm in the family Syllidae. It was found in Darwin Harbour, Australia, where it was living within the tissues of a sponge of the genus Petrosia. It was the second branching species of polychaete worm to have been discovered, the first having been Syllis ramosa, a deep water species, more than a century earlier.^[2]

Description

This worm inhabits the interior of a sponge and except for the tips of its branches, is not visible to the naked eye. It is cylindrical, about 1mm in diameter and up to 4 cm (1.6 in) in length. The head is buried deep in the sponge and is difficult to locate during a dissection of the sponge. It has three antennae, two pairs of eyes, a pair of palps and two pairs of tentacular cirri. The body is fragile and easily broken in pieces. The dorsal cirri (thread-like growths) on the body segments are elongated and sometimes of unequal length; they are articulated while the ventral cirri are short and conical and not articulated. The chaetae (bristles) are simple and shaped somewhat like tomahawks. Some branches of the worm develop into stolons, reproductive elements that contain the eggs or sperm and which later become detached from the parent worm.^[3] Molecular evidence from rDNA indicates that R. multicaudata and S. ramosa have evolved a branching habit independently of each other; in the latter case, the worm initiates branching from a parapodium whereas in the former, an area between the parapodia is involved.^[3]

Distribution

R. multicaudata was found living symbiotically inside both white and purple sponges of the Petrosia genus in Darwin Harbour, Australia, by Christopher Glasby, who works at the Museum and Art Gallery of the Northern Territory. The depth ranges from low tide level down to about 20 m (66 ft). The worm was discovered in 2006 and first described in 2012, being given the name multicaudata from the Latin multus for "many", and caudata for "tailed".^[2]

Ecology

R. multicaudata is a branching worm with its head hidden deep inside the sponge. The worm branches repeatedly, forming a tree-like structure. The side branches occupy the channels in the sponge, and their tips sometimes emerge into the open water, making the sponge appear to have white, hairy tentacles.^[2]

Researchers state that it is not clear on what the worm feeds; it may be eating the sponge tissues, but they might not provide enough nourishment, alternatively it may be absorbing dissolved organic material direct through its cuticle.^[2]

References