Hediste diversicolor
Hediste diversicolor, commonly known as a ragworm, is a polychaete worm in the family Nereidae. It lives in a burrow in the sand or mud of beaches and estuaries in intertidal zones in the north Atlantic. This species is used in research but its classification is in dispute and in the literature it is often classified as Nereis diversicolor (O.F. Müller, 1776). Its specific name "diversicolor" refers to the fact that its colour changes from brown to green as the breeding season approaches. Description Hediste diversicolor can grow up to in length and may have from ninety to one hundred and twenty segments when mature. The head has a pair of palps, two pairs of antennae, four pairs of tentacles and four eyes. Each body segment has a pair of bristly appendages known as parapodia which are used for swimming. There is a prominent blood vessel running along the dorsal surface of the animal. This ragworm is pale brown but changes to green as the gonads mature and the breeding season approaches. Distribution and habitat Hediste diversicolor is native to the north-east Atlantic. Its range extends from the Baltic Sea and North Sea southwards to the Azores and Mediterranean Sea. It has been introduced to the north-west Atlantic in the areas of Cobscook Bay, the Gulf of Maine and the Gulf of St Lawrence. It is plentiful on beaches of sand, muddy sand and mud, including areas of low salinity, where it lives in a semi-permanent "J"-shaped or "U"-shaped burrow and under adjoining stones in the intertidal zone. Biology Examination of the contents of the gut shows that Hediste diversicolor is a predator and generalist scavenger, able to adapt its diet to whatever is currently available. It spins a mucus net at the entrance of its burrow in which it traps phytoplankton, zooplankton, diatoms, bacteria and other small particles. It creates a water current through its tube by writhing about inside to draw particles through the net. Periodically it rolls the net up and swallows it before spinning another. When the availability of suitably-sized food particles is low it emerges from its burrow and hunts for small invertebrates, seizing them with its strong jaws. It also eats detritus and even animal faeces. They also draw, otherwise not edible, cordgrass seeds into their burrows and let them sprout to produce high-quality food, one of the rare examples of “gardening” by animals. The sexes are separate in Hediste diversicolor, and females heavily outnumber the males. As the breeding season approaches, the males, which were previously indistinguishable from the females, turn bright green. At the same time, the females turn a duller dark green on the dorsal surface with their earlier orange-brown pigmentation still showing through. Eggs develop within the female's body cavity. Histolysis then occurs and the body wall becomes brittle and eventually bursts, liberating the eggs into the burrow. Synchronized spawning takes place in early spring, usually at the time of the new or full moon when the water has warmed