Lugworm
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 Lugworm, Arenicola marina, casts on the beach at Ballyholme, Northern Ireland
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| Arenicola marina |
The lugworm or sandworm is a large marine worm of the phylum Annelida. Its coiled castings are a familiar sight on a beach at low tide but the animal itself is not seen except by those who, from curiosity or to use as fishing bait, dig the worm out of the sand.
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[edit] Overview
Fully grown, the lugworm of the coasts of Europe is up to 9 in. long and 3/8ths in. diameter. Other species on the North American coast range from 3 to 12 in. The body is, like that of an earthworm, ringed or segmented. Its head end, which is blackish red and bears no tentacles or bristles, passes into a fatter middle part which is red. This in turn passes into a thinner yellowish red tail end. The middle part has bristles along its sides and also pairs of feathery gills. There is a well developed system of blood vessels with red blood rich in the oxygen-carrying pigment, haemoglobin.
[edit] Life in a burrow
A lugworm lives in a U-shaped burrow in sand. The U is made of an L-shaped gallery lined with mucus, from the toe of which a vertical unlined shaft runs up to the surface. This is a head shaft. At the surface the head shaft is marked by a small saucer-shaped depression. The tail shaft, 2-3 in. from it, is marked by a much coiled casting of sand. The lugworm lies in this burrow with its head at the base of the head shaft, swallowing sand from time to time. This makes the column of sand drop slightly, so there is a periodic sinking of the sand in the saucer-shaped depression. When it first digs its burrow the lugworm softens the sand in its head up into the head shaft by pushing its head up into it with a piston action. After that it is kept loose by a current of water driven through the burrow from the hind end by the waves of contraction passing along its body.It weighs 2-5 oz.
[edit] Eating Sand
The lugworm can move backwards and forwards in its burrow by waves of contraction and expansion of the body, using the bristles on the middle part of the body to grip the sides. It moves towards the head shaft to swallow sand and later moves backwards so its rear end goes up the top of the tail shaft, in order to pass the indigestible sand out at the surface as a long thin cylinder. As the sand passes through the stomach and intestine small particles of dead plant and animal matter in it are digested. The sand is taken in by evertible proboscis, that is, the front end of the throat can be pushed out through the mouth as a swollen obal proboscis which gives out a sticky secretion to which sand and particles of food adhere. The proboscis is then pulled on again and the material sticking to it is swallowed. In one species the action of swallowing takes place every 5 seconds and after 8-15 swallows the lugworm rests for a few minutes. It takes about an hour for the sand to pass through the body. Then the lugworm moves backwards through the burrow and ejects this as the cylindrical castings familiar on the beach.
[edit] Burrowing Babies
Once it burrows into the sand a lugworm seldom leaves it. It can stay there for weeks on end, sometimes changing its position slightly in the sand. But it may leave the burrow completely and re-enter the sand, making a fresh burrow for breeding but for 2 days in early October there is a genital crisis. This is when all the lugworms liberate their ova and sperms into the water above, and there the ova are fertilized. The ova are enclosed in tongue-shaped masses of jelly about 8 in. long, 3 in. wide and 1 in thick. Each mass is anchored at one end. The larvae hatching from the eggs feed on the jelly and eventually break out when they have grown to a dozen segments and are beginning to look like their parents. They burrow into the sand, usually higher up the beach than the adults, and gradually move down the beach as they get older.
