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216 PROCEEDINGS OF THE CALIFORNIA ACADEMY OF SCIENCES
Series 4, Volume 60, No. 10
and nemerteans or ribbon worms (Nemertea). Some annelids or segmented worms (Annelida) have
defensive metabolites. Poisonous annelids are eaten by one very obscure group of opisthobranchs,
cephalaspideans related to Acteon and Hydatina, but data on their secondary metabolites are known
for only one of these, Micromelo undata, and its polypropionates (Atlas 152, 153) are probably
biosynthesized de novo, not derived from food.
Part 9. Animals: Ectoprocta and Mollusca
The Ectoprocta, or Bryozoa in the strict sense, are popularly known as “moss animals” because
the branching colonies may resemble moss. They are sessile, colonial animals that feed on particles
in the water by means of a crown of tentacles. The small zooids that bear the tentacles are generally
protected by some kind of external covering. This is in addition to chemical defense
(reviews: Christophersen, 1985; Sharp, Winston & Porter, 2007). Ectoprocts are rich in alkaloids
and macrocyclic polyethers, and for both of these compounds a bacterial origin has been claimed
(Anthoni, Nielsen, Pereira & Christophersen, 1990). Ectoprocts brood the developing embryos,
and this evidently facilitates the transfer of symbionts from one generation to the next. Woollacott
(1981) found, in the larvae of some ectoprocts, bacteria that are suspected of producing macrocyclic
polyethers called bryostatins (review in Newman, 2005). Formerly it was thought that the
ectoproct Bugula neritina contains a variety of bryostatins. It turns out, however, that Bugula neritina
is not a single species, but rather a complex of several cryptic ones, which have different bacterial
symbionts (Davidson & Haygood, 1999).
Mollusks for the most part are slow-moving animals that are defended from predators by a
strong shell. Bivalves of the genus Pinna live attached to the bottom in the tropics and their shell
is not very strong. They have been found to contain the polyether alkaloid pinnatoxin (Atlas 62)
(Chou, Haino, Kuramoto & Uemura, 1996). Some other bivalves contain secondary metabolites
derived from food that render them poisonous to human beings and other animals. A shell has been
dispensed with in the fast-moving cephalopods such as squid, which are adept at evading predators.
The powerful beaks that cephalopods use in subduing prey and dealing with predators are supplemented
by venomous secretions.
CHAPTER IV
INTRODUCTION TO GASTROPOD DIVERSITY AND SYSTEMATICS
The gastropod common ancestor probably was herbivorous, or perhaps omnivorous with a
substantial amount of plant material in its diet. The radula allowed it to scrape up algal materials,
which were then swallowed and digested. Numerous lineages subsequently switched to other kinds
of food, although many remained herbivorous. In other words, the broad picture of gastropod evolution
has been an adaptive radiation based on taking advantage of a diverse food supply. It is perhaps
better to view the gastropods as “entrepreneurs” rather than as avoiders of competition.
Reiterating what has been said about their higher taxonomy, gastropods have been subdivided
into three subclasses: Prosobranchia, Opisthobranchia, and Pulmonata. Pulmonates and opisthobranchs
are modified prosobranchs, and Prosobranchia is a paraphyletic grade that represents what
is left over after Opisthobranchia and Pulmonata have been removed. The pulmonates and opisthobranchs
form a group called Euthyneura, and share a common ancestry with some of the more
advanced prosobranchs called mesogastropods. This group forms a grade in an old fashioned clas-