290
25. Bryozoa
D. P. Gordon & P. E. Bock
N WHAT ARE BRYOZOANS?
Anyone seeing bryozoans for the first time might mistake them for turfing seaweeds, hydroids, or tiny corals. Bryozoans are zoologically unrelated to reef corals,
of course, but their hard, calcareous crustose, mounded,
and branching colonies superficially resemble those of
cnidarians. Whereas in the tropics, bryozoans are
mostly dwarfed by stony corals, in cooler temperate
waters they come into their own, and can form bioherms and mini-reefs.
Bushy bryozoans used to be called moss animals
(the literal meaning of Bryozoa) and the flat encrusting
ones sea mats. Lace corals, or lace bryozoans, are the
descriptor for some lacy fenestrate (mesh-like) forms
and even the fragile encrusters can be said to create
lacy sheets over seaweeds, stones and shell, and under
coral rubble. No one common name is adequate for
all, so ‘bryozoan’ is probably the best all-round term.
(Box. 25.1.)
In the 1800s, the Bryozoa were held to comprise two
very distinct groups, respectively named Ectoprocta
(bryozoans in the strict sense) and Entoprocta (also
called Kamptozoa), each of which was raised to phylum rank. Ectoprocta as a phylum name may be found
in some American textbooks, but the International Bryozoology Association has formally adopted only the
name Bryozoa. Entoprocts/kamptozoans (variously
known as goblet worms or nodding animals) appear
BOX 25.1 HOW ARE THEY CONSTRUCTED?
Colonies are made up mostly of feeding zooids (autozooids), but bryozoans are justifiably famous for exhibiting a higher degree of polymorphism (‘many forms’) than almost
any other invertebrate group, having different kinds of non-feeding individuals. The
most famous are avicularia, named by Charles Darwin. They have various roles (cleaning, defence, locomotion). Then there are kenozooids, simple chambers modified to
serve as attachment rootlets (rhizoids, stalks), spines, stolons, space-fillers, or part of the
support structure for large erect colonies. To feed, bryozoans evert a funnel-shaped
plume of tentacles (called a lophophore) through an opening (orifice) in the body wall
that merely puckers inwards upon closure or is variously modified as a pleated collar, as
pair of stiff lip-like folds, or as a lid-like operculum.
25. Bryozoa
D. P. Gordon & P. E. Bock
N WHAT ARE BRYOZOANS?
Anyone seeing bryozoans for the first time might mistake them for turfing seaweeds, hydroids, or tiny corals. Bryozoans are zoologically unrelated to reef corals,
of course, but their hard, calcareous crustose, mounded,
and branching colonies superficially resemble those of
cnidarians. Whereas in the tropics, bryozoans are
mostly dwarfed by stony corals, in cooler temperate
waters they come into their own, and can form bioherms and mini-reefs.
Bushy bryozoans used to be called moss animals
(the literal meaning of Bryozoa) and the flat encrusting
ones sea mats. Lace corals, or lace bryozoans, are the
descriptor for some lacy fenestrate (mesh-like) forms
and even the fragile encrusters can be said to create
lacy sheets over seaweeds, stones and shell, and under
coral rubble. No one common name is adequate for
all, so ‘bryozoan’ is probably the best all-round term.
(Box. 25.1.)
In the 1800s, the Bryozoa were held to comprise two
very distinct groups, respectively named Ectoprocta
(bryozoans in the strict sense) and Entoprocta (also
called Kamptozoa), each of which was raised to phylum rank. Ectoprocta as a phylum name may be found
in some American textbooks, but the International Bryozoology Association has formally adopted only the
name Bryozoa. Entoprocts/kamptozoans (variously
known as goblet worms or nodding animals) appear
BOX 25.1 HOW ARE THEY CONSTRUCTED?
Colonies are made up mostly of feeding zooids (autozooids), but bryozoans are justifiably famous for exhibiting a higher degree of polymorphism (‘many forms’) than almost
any other invertebrate group, having different kinds of non-feeding individuals. The
most famous are avicularia, named by Charles Darwin. They have various roles (cleaning, defence, locomotion). Then there are kenozooids, simple chambers modified to
serve as attachment rootlets (rhizoids, stalks), spines, stolons, space-fillers, or part of the
support structure for large erect colonies. To feed, bryozoans evert a funnel-shaped
plume of tentacles (called a lophophore) through an opening (orifice) in the body wall
that merely puckers inwards upon closure or is variously modified as a pleated collar, as
pair of stiff lip-like folds, or as a lid-like operculum.