''Ramisyllis multicaudata'' is a

species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...

polychaete Polychaeta () is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are ...

worm in the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Syllidae Syllidae is a family of small to medium-sized polychaete worms. Syllids are distinguished from other polychaetes by the presence of a muscular region of the anterior digestive tract known as the ''proventricle''. Syllid worms range in size from ...

. It was found in

Darwin Harbour Darwin Harbour is the body of water close to Darwin in the Northern Territory of Australia. It opens to the north at a line from Charles Point in the west to Lee Point in the east into the Beagle Gulf and connects via the Clarence Strait wi ...

, Australia, where it was living within the tissues of a sponge of the genus ''

Petrosia ''Petrosia'' is a genus of sponges belonging to the family Petrosiidae. The genus has almost cosmopolitan distribution. Species Species: *''Petrosia alfiani'' *''Petrosia armata'' *''Petrosia australis ''Petrosia'' is a genus of sponges ...

''. It was the second branching species of polychaete worm to have been discovered, the first having been ''

Syllis ramosa ''Syllis ramosa'' is a species of polychaete worm in the family Syllidae. It is found in the deep sea where it lives within the tissues of a sponge. It was the first branching polychaete worm to be discovered, with each worm having a single hea ...

'', a deep water species, more than a century earlier. In 2022, a second species in ''R. multicaudata'''s genus, '' Ramisyllis kingghidorahi'', was described from specimens taken off the coast of

Sado Island is a city located on in Niigata Prefecture, Japan. Since 2004, the city has comprised the entire island, although not all of its total area is urbanized. Sado is the sixth largest island of Japan in area following the four main islands and O ...

, Japan.

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 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 Giovanni Battista Cirri (1 October 1724 – 11 June 1808) was an Italian cellist and composer in the 18th century. Biography Cirri was born in Forlì in the Emilia-Romagna Region of Italy. He had his first musical training with his brother ...

(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

chaeta A chaeta or cheta (from Greek χαίτη “crest, mane, flowing hair"; plural: chaetae) is a chitinous bristle or seta found in annelid worms, (although the term is also frequently used to describe similar structures in other invertebrates such ...

e (bristles) are simple and shaped somewhat like

tomahawk A tomahawk is a type of single-handed axe used by the many Indigenous peoples and nations of North America. It traditionally resembles a hatchet with a straight shaft. In pre-colonial times the head was made of stone, bone, or antler, and Eur ...

s. 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. 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 In invertebrates, the term parapodium ( Gr. ''para'', beyond or beside + ''podia'', feet; plural: parapodia) refers to lateral outgrowths or protrusions from the body. Parapodia are predominantly found in annelids, where they are paired, unjointed ...

whereas in the former, an area between the parapodia is involved.

Distribution

''Ramisyllis multicaudata'' was found living symbiotically inside both white and purple sponges of the genus ''

'' in Darwin Harbour, Australia, by Christopher Glasby, who works at the

Museum and Art Gallery of the Northern Territory The Museum and Art Gallery of the Northern Territory (MAGNT) is the main museum in the Northern Territory. The museum is located in the inner Darwin suburb of Fannie Bay. The MAGNT is governed by the Board of the Museum and Art Gallery of the N ...

. The depth ranges from low tide level down to about . The worm was discovered in 2006 and first described in 2012, being given the name ''multicaudata'' from the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power ...

''multus'' for "many", and ''caudata'' for "tailed".

Ecology

''Ramisyllis 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. Researchers are puzzled as to how this worm obtains enough nourishment; the head may be eating the sponge tissues, but the worm is not thought to be able to move around inside the sponge and it is difficult to envisage how it could obtain enough nourishment through its mouth to sustain its much-branched body. The gut is continuous throughout the branches, but has been found to contain very few of the sponge's spicules. One possible solution to this puzzle is that the worm may be surviving on

dissolved organic carbon Dissolved organic carbon (DOC) is the fraction of organic carbon operationally defined as that which can pass through a filter with a pore size typically between 0.22 and 0.7 micrometers. The fraction remaining on the filter is called partic ...

absorbed through its integument, as some other invertebrates, including polychaete worms, do.

References

External links

Taxonomy Australia: The World's Weirdest Worm
(for drawings of ''Ramisyllis multicaudata'' and of stolon morphologies in syllid worms) {{Taxonbar, from=Q39086826 Syllidae Animals described in 2012