Giant tube worm

Giant tube worms, Riftia pachyptila, are marine invertebrates in the phylum Annelida (formerly grouped in phylum Pogonophora and Vestimentifera) related to tube worms commonly found in the intertidal and pelagic zones. Riftia pachyptila live over a mile deep, and up to several miles deep, on the floor of the Pacific Ocean near black smokers, and can tolerate extremely high hydrogen sulfide levels. These worms can reach a length of 2.4 m (7 ft 10 in) and their tubular bodies have a diameter of 4 cm (1.6 in). Ambient temperature in their natural environment ranges from 2 to 30 degrees Celsius.

The common name "giant tube worm" is however also applied to the largest living species of shipworm, Kuphus polythalamia, which despite the name "worm" is a bivalve mollusc, rather than an annelid.

Development

Riftia develop from a free-swimming, pelagic, non-symbiotic trochophore larva, which enters juvenile (metatrochophore) development, becoming sessile and subsequently acquiring symbiotic bacteria. The symbiotic bacteria, on which adult worms depend for sustenance, are not present in the gametes, but are acquired from the environment via the digestive tract. The digestive tract transiently connects from a mouth at the tip of the ventral medial process to a foregut, midgut, hindgut and anus. After symbionts are established in the midgut, it undergoes substantial remodelling and enlargement to become the trophosome, while the remainder of the digestive tract has not been detected in adult specimens.