|A colony of Rhamphostomella
costata on the surface of a Chlamys
hastata scallop. Notice that the colony is a
thick yellow crust,
about 1/2 cm thick. The orange patch is a Boltenia
Dave Cowles, August 2017)
This Cheilostome bryozoan
forms a thick, encrusting colony. The zooecia are more complex than
calcified tubes. The aperture
of each zooecium
has an operculum.
At least 3/4 of the frontal
portion is calcified, so that there are no obvious pores on the frontal
portion. Moderate-sized avicularia
can be found mounted on a mound (umbo) on the frontal
of each zooid
edge of the aperture,
but they are not on the midline of the zooid
frontal. The rostrum and mandible of the avicularium, though it is
quite close to the aperture,
do not hang over the aperture.
The mandible of the avicularium is spatulate. The zooids have no
but do have a lyrula. The frontal has prominent ribs running from the
to the umbo.
How to Distinguish
from Similar Species:Rhamphostomella
cellata has a small avicularium that fits into the rim of
Several other Rhamphostomella
species have an avicularium that overhangs the aperture.
and Arctic Oceans including Kodiak, Alaska, the coastline of Russia,
Svalbard Island north of Norway.
(It is uncommon to find
this bryozoan encrusting a scallop, as this one was)
History: This species
incubates a few large eggs at a time within a brood chamber (Ostrovsky
et al., 2009).
Kozloff, 1987, 1996
Ostrovsky, Andrew N., Dennis P. Gordon, and Scott Lidgard, 2009.
evolution of matrotrophy in the major classes of Bryozoa: transitions
reproductive patterns and their ecological background. Marine Ecology
Series 378: pp 113-124
General Notes and
Observations: Locations, abundances,
This view of the border of the colony shows that the living surface
seems to be built up over the remains of many dead zooids
underneath, and that the crust builds up thickly enough to enclose the
tubes of small tubeworms (bottom right)
The surface of the colony is crowded with actively feeding zooids,
as shown here. For a movie of their action, click here.
The apertures with their associated avicularia
are most easily seen in a part of the colony where either calcification
or some mortality has provided some space. Most of the zooids
in this view are still alive. Note that the apertures are closed with
operculum when the lophophore
is withdrawn, and also that each aperture
has a mound next to it with a smaller aperture for the avicularium
to protrude. The avicularium
is close to the aperture
but does not overhang it.
This view shows more of the apertures
with associated avicularia.
Authors and Editors
Dave Cowles (2017): Created original page
CSS coding for page developed by Jonathan Cowles
Salish Sea Invertebrates web site provided courtesy of Walla