''Syllis ramosa'' is a

species In biology, a species is the basic unit of 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 the appropriate s ...

polychaete Polychaeta () is a paraphyletic class (biology), class of generally marine invertebrate, marine annelid worms, common name, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that ...

worm in the

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

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 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 head and multiple anuses.

History

During the period 1872 to 1876, the

Royal Navy The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against F ...

's HMS ''Challenger'' was used in the ''Challenger'' expedition to survey and explore the world's oceans. One of the unknown animals dredged from the ocean depths near the Philippines was a species of

sponge Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through t ...

which was found to contain numerous branching worms inside its cavities. In 1879, one of these worms was formally described by the Scottish marine biologist William Carmichael McIntosh, who named it ''Syllis ramosa''. Branching polychaete worms were previously unknown.

Distribution

This bristle worm was first discovered living commensally with a sponge at a depth of about near the Philippines and at a depth of in the

Arafura Sea The Arafura Sea (or Arafuru Sea) lies west of the Pacific Ocean, overlying the continental shelf between Australia and Western New Guinea (also called Papua), which is the Indonesian part of the Island of New Guinea. Geography The Arafura Sea is ...

. Further branching worms have occasionally been found in different locations and have been ascribed to ''S. ramosa'' despite subtle differences in morphology; they are hard to examine because of the difficulty of extracting them from the sponge tissue. However a new species of branching worm (''

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 ...

'') was described in 2012.

Ecology

The heads of the two individual ''S. ramosa'' brought to the surface by the ''Challenger'' were located in the bases of glass sponges of the class

Hexactinellid Hexactinellid sponges are sponges with a skeleton made of four- and/or six-pointed siliceous spicules, often referred to as glass sponges. They are usually classified along with other sponges in the phylum Porifera, but some researchers consi ...

a. The rest of the worms' bodies were in the passages of the sponges. The bodies branched repeatedly so that each worm had a single head and many

anus The anus (Latin, 'ring' or 'circle') is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, the residual semi-solid waste that remains after food digestion, which, d ...

es. ''S. ramosa'' is a "stolonate" worm and has a bizarre

life cycle Life cycle, life-cycle, or lifecycle may refer to: Science and academia *Biological life cycle, the sequence of life stages that an organism undergoes from birth to reproduction ending with the production of the offspring *Life-cycle hypothesis, ...

. The terminal portion of a branch is known as a "

stolon In biology, stolons (from Latin '' stolō'', genitive ''stolōnis'' – "branch"), also known as runners, are horizontal connections between organisms. They may be part of the organism, or of its skeleton; typically, animal stolons are external s ...

", and develops an extra head with large eyes and no mouth. The gut in this part of the animal is absorbed, the muscles are rearranged to facilitate swimming and the stolon becomes a storage receptacle for the eggs or sperm. When the breeding period arrives, the stolon becomes detached and swims to the surface of the sea, in a process termed "

epitoky Epitoky is a process that occurs in many species of polychaete marine worms wherein a sexually immature worm (the atoke) is modified or transformed into a sexually mature worm (the epitoke). Epitokes are pelagic morphs capable of sexual reproduc ...

". Here the gametes are released and the stolon dies. Meanwhile, the parent worm remains safely in its sponge home and produces more stolons.

References

{{Taxonbar, from=Q1932407 Syllidae Animals described in 1879