with the gonopore just behind the tuft of gills. Males have a modified pair of tentacles
near the gonopore that are somehow involved in copulation, which has to occur
outside adjacent tubes of males and females. Development to maturity is rapid, a few
months according to settling plate studies. Both sperm and eggs are of unusual form
(reviewed by Padillon & Gaill 2007). Fully grown females can be developing up to
80,000 oocytes in the body cavity with ∼3000 eggs ready for spawning in the
oviducts. Spawning apparently is not synchronous across a colony. Studies of zygote
development (see Padillon & Gaill 2007) comparable to those for Riftia give
somewhat different results. Deep-sea pressure is required for development, but, unlike
Riftia zygotes, greater warmth is tolerated and necessary, with optimal development at
∼10°C but none at 2°C or >20°C.
(^) The pompeii worm is an example of something else. It is the type species of a new
family, Alvinellidae (Desbruyères & Laubier 1986), although initially they seemed
satisfactorily placed in the Ampharetidae (Desbruyères & Laubier 1980). There is a
tendency to enhance the importance of vent research by elevating the systematic level
of the animals. Thus, at one point the vestimentiferan pogonophora were raised to
phylum status. Oddly, all the pogonophora were later demoted, based on molecular
genetic evidence, to family level among the annelids as Siboglinidae, some of which
have been known from sedimentary habitats since 1900. That seems extreme, given
the dramatic divergence of pogonophora from other annelids. However, devotion to
the principle that higher-level nomenclature must reflect phylogeny does dictate the
demotion. In the case of Alvinellidae, the separation of a new family is based on
careful evaluation of morphological and molecular data. Examination of very large
collections from vent sites has shown that there are a number of distinct species,
divided at present into two genera: Alvinella and Paralvinella (Desbruyères &
Laubier 1986).
Rimicaris exoculata Williams and Rona, 1986
(^) These are a 6 cm shrimp (Fig. 15.7) discovered swarming in masses on the order of
3000 m−2 over the sides of black-smoker chimneys along the Mid-Atlantic Ridge
(MAR). Originally Rimicaris, now a genus with several species, including R. kairei
from vents on the Central Indian Ridge, were placed in a subgroup of Caridean
shrimps, the Bresiliidae, that mostly live in bore holes on shallow sponges. Later, in
line with the tradition of vent taxonomy, they came to represent a distinctive family,
the Alvinocarididae, sometimes listed as a group of Bresilioidea. There are, for now,
seven genera, including Rimicaris, Alvinocaris, and Chorocaris, that live with similar
life patterns on mid-Atlantic and Indian Ocean smokers. The maxillary exopodites
(limbs near the mouth) of R. exoculata carry fields of short setae, all of which are
covered with a fur of filamentous, sulfide-oxidizing, chemosynthetic bacteria. Similar