Anatomy

The anatomy of deep sea tube worms (Figure 3) is highly specialised in order to meet the metabolic requirements of the chemoautotrophic bacteria that live inside them as these bacteria provide them with their source of nutrition.  Worms spend their entire post larval life inside their tube, with only the red plume exposed to the surrounding seawater.  This plume can be retracted into the tube for protection (Van Dover, 2000).

Riftia anatomy. Photo by D. Brenner

Figure 3. External anatomy of R.pachyptila. Photo by D. Brenner in Van Dover (2000).

Excluding the tube in which it lives, the body of the adult tubeworm can be defined as having 4 body regions; the obteracular plume, the vestimentum, the trunk and the opisthosome. The tube itself is comprised of chitin and is secreted by the vestimentum as the animal grows (Van Dover, 2000).

The plume is comprised of dense sheets of fine tentacles or lamellae, these sheets are held in place and supported by the central obteraculum.  As a result of this assortment, the plume has a large surface area which it uses to uptake metabolites from its environment.  Tubeworms have a closed system of blood vessels which transport blood from the trophosome along the dorsal blood vessel to the plume and back again via the ventral blood vessel (Van Dover, 2000). 9-20% of tubeworm body mass is made up of blood vessels (Sanders and Childress, 1993). As the symbiotic bacteria require large amounts of oxygen for chemosythesis, the blood of the tube worm contains large amounts of haemoglobin, giving the plume its deep red colour (Childress and Fisher, 1992).

The vestimentum is primarily made up of muscle, its function is to hold the body of the worm in its tube.  The vestimentum can also contract to pull the worm back into the tube for protection against predation if needed. The vestimentum is the portion of the body where the brain, heart and genital pores of the tubeworm are located (Van Dover, 2000).

The trunk of the tubeworm contains the gonads, the paired coelomic cavities and the trophosome.  The trophosome is arranged into lobes of tissue which are well supplied with blood by numerous blood vessels (Van Dover, 2000).  The cells of the trophosomal lobes are filled with trillions of prokaryotic symbionts (Cavanaugh et al., 1981), which provide the worm with energy.  Fifteen percent of the tubeworm’s total biomass is comprised of the trophosome (Van Dover, 2000).

At the base of the worm, the opisthosome secretes the basal disk of the tube, anchoring the tube to the substrate (Van Dover, 2000).

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