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What is a Worm?

The word worm is derived from the Latin word Vermes which used to describe any kind of worm-like animal. Worms are different things to different people. To a gardener a worm is an earthworm, to a nurse a worm is a tapeworm or roundworm, and to a diver a worm is a tube-dwelling polychaete. Generalizations, then, just do not work with regard to worms. So, what is a worm?  

Worms fall into four non-related distinct groups or phyla. The simplest are the flatworms, best known for their parasitic members the tapeworm and liver fluke. Also pararasitic are the round worms or Nematodes, well known to dog owners as parasites of the intestine.

The third group is of minor interest and comprises the ribbon worms or Nemertines. These unsegmented ribbon-like worms vary from a fraction of an inch up to 20 feet in length. They have a unique method of feeding; they can shoot out a proboscis armed with a sharp spike or stylet from a muscular sheath at the front end of the body to trap their prey. They can vary in colour from black to white through almost every colour. Unfortunately, these fascinating marine worms tend to be nocturnal and fairly uncommon. I have only seen two in many years of diving in Nassau.

Of interest to every diver, especially those specialising in phototography, are the true worms or Annelids. The three groups or classes of true worm are the earthworms and their kin, the leeches, and lastly the Polychaetes or Bristle worms, the true marine worms.

For convenience, Polychaetes are divided into two loose groups — those that live freely and three that live in some sort of tube. We have comparatively few free-living worms in the seas of the Bahamas. We do not see the large Nereis -  the common textbook example of a Polychaete, known in the States as a Clamworm and in Britain  as a rag worm. Nor do we see Aphrodite -  a short fat furry worm resembling, in size and shape, a mouse — hence its name, the Sea Mouse. We do have, however, two or three other species of bristle worm that may be seen roaming freely across the reef or sand. They owe their relative freedom to the multitude of delicate bristles that cover them. If they are picked up the bristles break off in the skin and cause extreme irritation.

The tubeworms are among the most beautiful of marine animals. Resembling flowers, they have been thought in the past by many to be plants. The petal-like tentacles are, in fact, a combination of respiratory and feeding mechanism, for they take both oxygen and food particles out of the surrounding water. The tiny food particles are passed in a never-ending mucus band back to the mouth where the whole thing, mucus and food, is taken in together. Along the tentacles are light sensors that can detect shadows and signal the worm to pull its gills into the tube with remarkable speed when danger threatens. 

The beautiful spiral Christmas tree worms that grow out of coral heads have another means of defence, for hidden under the ex­tended gills and arching out over the entrance to the tube is an extremely sharp limestone spike, so that if a worm swim to the surface predator were to lunge at the ex­tended worm it might find an un­pleasant surprise In wait.

The tube itself is usually made out of a cement secreted by glands behind the mouth. It may be reinforced by sand grains and mud particles or pieces of broken shell. The tubes of most polychaete worms are con­cealed, but those of the honeycomb worm (Sabellaria) grow in such masses that the reefs formed may be a danger to shipping.

Annelid worms all have interesting mating habits. Even the humble earthworm is hermaphrodite (male and female) and goes through an amazing process to ensure that both worms o a ir are fertilized. The Palolo worm loses its rear end once a year on one particular night during the last quarter of the moon in June and July. Millions of these pieces of worm swim to the surface to release their eggs and sperms while the front halves of the worms go about their normal business on the seabed. The larva remain planktonic and can be carried great distances by the tides before a fraction of one per cent eventually settle and metamorphose into worms, to renew the cycle once again. 

The tubeworms show some remarkable adaptations to their habitats. One, the Medusa worm (Loimia Medusa), has a crown of whitish tentacles which display the most amazing muscular powers, The two-inch worm, like most polychaetes, remains in its tube under a rock or ledge, but extends its ten­tacles out for maybe as much as four feet to seek for food particles and draw them back to its mouth. The feat is amazing when one considers that the tentacles are more than a thousand times longer than they are thick! This lowly worm has achieved a mechanical skill that man may never match, despite the complexity of his machines.  

Worms, along with the individuals belonging to other invertebrate groups, are countless by human standards; they are all around us in the ground, in the sea, in our domestic animals, and sometimes in our pets and even us. Most worms are ignored and unseen, and in most cases never threatened by man.

If only this were true for higher forms of life. For them – as for so many species of amphibian, reptile, bird, and mammal, life is a struggle that can only end in oblivion.

Those of us that are concerned with man’s impact upon his environment may never be able to avert the day when extinction comes to another species, but we can certainly slow it down.

Meanwhile, worms will still be with us!

 

© R. Attrill 2000