(^) Settlement, observed on plates set on near-vent substrate, begins a sequence of
metamorphosis from a somewhat modified trochophore with mouth, gut containing
some particles and anus, to a juvenile living in a tube and nourished by a trophosome.
The symbionts are either ingested or “infect” through the body wall; there are bacteria
in the wall and coelom of these early juveniles that stain with genetic probes from the
symbionts. Genetically identical bacteria do live on surfaces and in the water around
vents. There have been no observations of Riftia releasing symbionts to supply these
larvae with an inoculum. The trophosome develops from the vicinity of the foregut,
which then disappears (Nussbaumer et al. 2006).
(^) Different vestimentiferans harbor different symbionts, but the closely studied
species each have only one “phylotype” of internal gammaproteobacteria. The
symbionts of all three East Pacific Rise species share “phylotype 2”. It has not been
cultured, but its genome has been sequenced and a name proposed: Endoriftia
persephone (“Candidatus” status). The genome of this bacterium, unlike
endosymbionts passed from mother to egg and obligately symbiotic, retains a full
repertoire of enzymes for independent life. That includes chemoreceptor functions
and motility, possibly enabling them to find and “infect” advertising larvae by
chemotaxis (Robidart et al. 2008). Metabolic studies of Riftia in pressurized aquaria
showed only sulfide oxidation (via ATP sulfurylase) as the energy source for
chemosynthesis. RuBisCO is present, and recent work suggests there are also proteins
present for an alternative carbon-fixation pathway (Markert et al. 2007).
(^) Riftia are found primarily in crevices conducting warm vent fluids, only 3° to 12°C
with occasional higher pulses, with maximum sulfide and typical oxygen in the
vicinity of 150 μM and 50 μM, respectively. As flow slows, cools, and becomes more
dilute, Riftia is often replaced by Bathymodiolus or Calyptogena.
Alvinella pompejana Desbruyères and Laubier, 1980
(^) Pompeii worms, the polychaete Alvinella pompejana and relatives (Fig. 15.4), live in
parchment-like (glycoprotein) tubes, secreted from an anterior-ventral gland plate, on
the sides of vent chimneys on the East Pacific Rise (9° and 13°N) and Galapagos
Ridge. The tubes may direct some of the subsequent deposition of metallic sulfides so
that the outer ends of the tubes project from the accreting mineral mass. The largest
adults are very large worms for the deep sea: 12 mm diameter by 95 mm length, living
in tubes up to 2 cm diameter. Observations of A. pompejana behavior vary.
Desbruyères et al. (1998) reported an activity cycle of 5–10 min down in the tube,
followed by short intervals, less than 30 s, with the gill plumes extended into the
surrounding flow, whereas Cary et al. (1998) reported that they mostly sit with the
plumes outside. Most temperature measures in the vicinity of the tube colonies are
20–45°C, but it is much hotter a few centimeters deeper in the chimney wall. Cary et