''Polydora glycymerica'' is a species of annelid worm in the family

Spionidae Spionidae is a family of marine worms within the Polychaeta. Spionids are selective deposit feeders that use their two grooved palps Pedipalps (commonly shortened to palps or palpi) are the second pair of appendages of chelicerates – a grou ...

, native to the northwestern Pacific Ocean, where it lives commensally in association with a bivalve mollusc, usually ''

Glycymeris yessoensis ''Glycymeris yessoensis'' is a species of bivalve mollusc in the family Glycymerididae. It can be found burrowing in soft sediment in shallow water in the Pacific Ocean around the coasts of China and Japan. It is often associated with a polycha ...

'' but occasionally with another species of

clam Clam is a common name for several kinds of bivalve molluscs. The word is often applied only to those that are edible and live as infauna, spending most of their lives halfway buried in the sand of the seafloor or riverbeds. Clams have two shel ...

. The worm intercepts food particles being drawn into the mollusc by its feeding current.

Taxonomy

This species was first described in 1993 by the Russian marine biologist Vasily I. Radashevsky, who placed it in the genus ''

Polydora Polydora (; grc, Πολυδώρᾱ in Attic and in Ionic, means 'many-gifts' or 'the shapely') was the name of several characters in Greek mythology: *Polydora, the 'handsome' Oceanid, one of the 3,000 water-nymph daughters of the Titans ...

'' and gave it the specific epithet "''glycymerica''" because of its commensal relationship with the bivalve ''Glycymeris yessoensis''. The new species resembled '' Polydora vulgaris'', a worm from the

South China Sea The South China Sea is a marginal sea of the Western Pacific Ocean. It is bounded in the north by the shores of South China (hence the name), in the west by the Indochinese Peninsula, in the east by the islands of Taiwan and northwestern Phi ...

that is also associated with bivalve molluscs, although in this instance, ''

Pinctada margaritifera ''Pinctada margaritifera'', commonly known as the black-lip pearl oyster, is a species of pearl oyster, a saltwater mollusk, a marine bivalve mollusk in the family Pteriidae. This species is common in the Indo-Pacific within tropical coral ree ...

'' and '' Hyotissa hyotis'' are the hosts. Researchers used starch gel electrophoresis to compare the number of

isozyme In biochemistry, isozymes (also known as isoenzymes or more generally as multiple forms of enzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction. Isozymes usually have different kinetic parameters (e.g. dif ...

loci and the allozymic variation present in both species, and the results suggest that the two are valid, separate species.

Description

This worm grows to a length of about for a 250 segment worm, and is a greenish-brown colour. The

prostomium The prostomium (From Ancient Greek, meaning "before the mouth"; plural: prostomia; sometimes also called the "acron") is the cephalized first body segment in an annelid worm's body at the anterior end. It is in front of (but does not include) t ...

has an incision that is bent down at the front, but no eyes are present in adult worms. The fifth body segment is larger than its neighbours and the seventh has a pair of white, glandular spots ventrally. There are palps on the first eight segments.

Distribution and habitat

''Polydora glycymerica'' is found in the

Sea of Japan The Sea of Japan is the marginal sea between the Japanese archipelago, Sakhalin, the Korean Peninsula, and the mainland of the Russian Far East. The Japanese archipelago separates the sea from the Pacific Ocean. Like the Mediterranean Sea, i ...

where it lives commensally on the seabed, boring into the shells of

bivalve molluscs Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

such as ''Glycymeris yessoensis''.

Ecology

''Polydora glycymerica'' is an obligate commensal of a bivalve mollusc, boring into its shell. It is nearly always associated with ''Glycymeris yessoensis'', but has also been found living in association with the

ark clam Ark clam is the common name for a family of small to large-sized saltwater clams or marine bivalve molluscs in the family Arcidae. Ark clams vary both in shape and size. They number about 200 species worldwide. The shells of ark clams are of ...

Anadara broughtonii Anadara broughtonii is a species of Ark clam. The species was described by Shrenck in 1867. Originally belonging to the genus '' Scapharca'', the genus has merged with '' Anadara'' now. Adult blood clams can reach a shell length of 100 mm and a ...

''. Sometimes several worms occupy one host, with up to six per valve, and a maximum of eight per mollusc. The burrows made by the worms are U-shaped and are located near the posterior end of the mollusc shell, close to the siphons. The worm extends its anterior end from the burrow, intercepting food particles in the feeding current created by the mollusc. The boring activities of the worm may weaken the mollusc shell, perhaps making it more vulnerable to damage or

predation Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...

. However the worm may also be of benefit to the mollusc as it may be able to handle particles that are too large for the mollusc to deal with, thus preventing the inflow siphon of the mollusc from getting clogged.

References

{{taxonbar, from=Q2750506 Polychaetes Animals described in 1993