stages of development. Clutches of eggs are produced and she attaches them to her
legs for brooding. Very few brooding females have been collected from vent swarms,
and Ramirez Llorda et al. speculate that they leave the massive swarms during egg
development to avoid having the eggs brushed off in traffic. The few broods that have
been counted were just fewer than 1000 eggs. Larval Rimicaris, identified by
molecular genetics (Dixon & Dixon 1996), have ordinary compound eyes and
phytoplankton in their guts. They are believed to ascend high in the water column and
have a long planktotrophic phase providing extended potential transport. The rate of
successful return to vents must be small.
The Scaly-foot Gastropod
(^) An extraordinary, coiled snail (Plate 15.2), up to 5 cm in diameter, was found
clustered around the bases of a vent field on the Central Indian Ridge in 1999 (Van
Dover et al. 2001). A Linnean binomen has been suggested for it and can be found on
the web, but it is not properly published to date. However, Warén et al. (2003) give a
good description in their on-line supplementary materials, with molecular sequence
evidence of its relationship to snails classified in a group termed Neomphalina:
Hirtopelta and Peltospira, snails abundant near western Pacific vents.
(^) The scaly-foot snail is unusual in two respects. First, its foot, that appears not fully
retractable, is covered by overlapping plates formed of iron–sulfur minerals: pyrite
(FeS 2 , which has S–S bonds, as well as Fe–S) and greigite (Fe 3 S 4 , a mixed-valence
compound). These plates can be drawn together, making a closed armor round the
foot, and they seem to derive from an extensively modified operculum. The outer
layer of the entire shell coil is also covered with a pyrite–greigite layer. Mechanical
properties of the armor have been studied in detail (Suzuki et al. 2006; Yao et al.
2010). The mineral outer coating of the coiled shell is underlain by a thick sheet of
resilient protein termed “conchiolin”, and the layer next to soft tissue is rather
ordinary molluscan periostracum. Apparently, this provides a combination of puncture
and compression resistances. There are crabs on the Indian Ridge vents that likely
could crush less well-protected snails or nip their feet. Yao et al. speculate about
designing military armor based on this pattern. It seems warfare is never far from our
minds or research budgets. Finding hard parts constituted of iron compounds does
occur elsewhere among mollusks, particularly the hematite coatings on chiton radulas.
Nevertheless, the scaly-foot minerals are substantially different, a suite strongly
favored by the high iron and sulfide content of vent emissions.
(^) Second, the esophagus has large side expansions of soft tissue, the cells of which
harbor dense masses of gammaproteobacteria related to thiotrophic (sulfide oxidizing)
chemosynthetic forms from other vent endosymbioses (Goffredi et al. 2004). The
details of the physiology that supplies oxygen and sulfide to these internal structures