Acromegalomma vesiculosum

Appearance

Megalomma vesiculosum is a segmented worm that lives in a cylindrical tube made up of particles of sand and pebbles agglomerated by mucus. The tubes can measure 12 cm in length. They are embedded vertically in the sand or gravel and protrude from the substrate* by one to two centimeters. The diameter of the tubes can reach up to 10 mm. There is no operculum.
The gills constitute a terminal plume surrounding the mouth. They are formed of 2 approximately equal semi-circular gill lobes, each bearing 40 to 60 curved gill filaments. These filaments are lined with 2 rows of ciliated barbules. The gills allow the animal to feed and breathe by capturing nutrient particles and dissolved oxygen in the water. The filaments show areas of spots or bands of various colors (orange to reddish brown) and end in a black eyeball.
Two small relatively thick pointed palps* stand in the center of the plume.
The animal lives concealed inside its tube, only its branchial plume is visible.

Naming

Megalomma: from the Greek [megalo-] = very large, and [-omma] = eye, "large eye".
vesiculosum: from the Latin [vesicula] = small bulb, vesicle.

Distribution

Northeast Atlantic, English Channel, North Sea, Norwegian Sea and Mediterranean.

Behavior

Like most tube worms it is sensitive to vibrations and light: it retracts into its tube as soon as it is approached or receives a flash of light.

Habitat

It lives in a tube made up of sand and small pebbles. This tube is driven vertically into the mud or sand mixed with mud and pebbles, from which it protrudes 1 to 2 cm. Sometimes the tube is fixed under stones or large empty shells. This species is found from the surface down to 25 m depth.

Reproduction

It has separate sexes. Fertilization takes place in the tube. The larvae are planktonic. After metamorphosis, juveniles settle down and lead a life similar to that of adults. It also undergoes asexual multiplication by fission or budding.

Food

It is a filter feeder. The filaments are lined with 2 rows of ciliated barbules. These are covered with an adherent mucus which allows the collection of food particles. Thei regular beating brings the food particles towards the mouth.