The Bryozoa & The Brachiopoda
Paleontology Laboratory III
The Bryozoa
• The Bryozoa (moss animals) are a
geologically important group of small
animals.
• Some superficially resemble corals.
• All bryozoans are colonial and most are
marine.
• Bryozoans are most abundant in temperatetropical waters that are not too turbid.
• They require a hard or firm substrate to
attach or encrust, and clear agitated water
from which they obtain their suspended food.
Bryozoa
• There are about 5000 living species, with
several times that number of fossil
species.
• Bryozoan colonies range from millimeters
to meters in size, but the individuals that
make up the colonies are rarely larger
than a millimeter.
• Colonies may be mistaken for hydroids,
corals, or even seaweeds.
Bryozoa
• Bryozoans are considered nuisances species by
some
• Over 125 species are known to grow on the bottoms
of ships, causing drag and reducing the efficiency
and maneuverability of the fouled ships.
• Bryozoans may also foul pilings, piers, and docks.
• Certain freshwater species occasionally form great
jellylike colonies so huge they clog public or
industrial water intakes.
• Bryozoans produce a remarkable variety of chemical
compounds, some of which may find uses in
medicine.
– One compound produced by a common marine bryozoan, the drug
bryostatin 1, is currently under serious testing as an anti-cancer
drug.
MORPHOLOGY
Classification & Range
• Phylum Bryozoa
– Class Stenolaemata (Ordovician-Recent)
• Order Trepostomata (Ordovician-Triassic)
• Order Fenestrata (Ordovician-Permian)
• Order Cyclostomata (Ordovician-Recent)
– Class Gymnolaemata (Ordovician-Recent)
• Order Cheilostomata (Jurassic-Recent)
General Morphology and Ecology
• As bryozoan individuals are quite small, they are
commonly observed under the microscope from
longitudinal or transverse thin-sections.
• Bryozoans come in a variety of colonial growth
habits that can easily be observed without thinsections.
• Like corals, the growth habit of bryozoans can
be classified as encrusting, massive or domal, or
erect.
• Generally speaking, byozoan growth-habits are
a function of water energy similar to corals which
lived in level-bottom communities;
– encrusting and massive forms are found in highenergy environments
– delicate branching and erect forms lived in quite
environments.
Encrusting
Massive or Domal
Erect
CLASSIFICATION
• Division of bryozoan groups is based on surficial
morphology, extra-zooidal structures, colonial
growth habits, zooid morphology, presence of
specialized zooids (e.g., maternal zooids), and
internal structures of the zooecium.
• Colonial bryozoans come in two basic types:
– 1. Those with tightly packed zooecia which share
zooecium walls, they have multiple pores and a well
defined mature and immature region such as in the
trepostomes, cyclostomes, and the fenestrates.
– 2. Those with moderately to loosely packed zooecia
usually encrusting one-zooecium-thick, and
commonly with frontal walls as typified by the
Cheilostomes
Class Stenolaemata
• Ordovician-Recent
• The stenolaemate bryozoans quickly radiated in the early
Paleozoic and are very characteristic fossils of Paleozoic
rocks, sometimes making substantial contributions to the
formation of reefs, calcareous shales, and limestones.
• They included forms with robust skeletons
• There were also forms with delicate, branching fanlike
skeletons such as the fenestrates.
• With the exception of one order of stenolaemates, the
Tubuliporata or Cyclostomata, all of these Paleozoic
bryozoan lineages were severely impacted in the Permian
extinction: cryptostomates disappeared at the end of the
Permian (245 million years ago), while a few other lineages
lingered until the end of the Triassic, about 210 million
years ago.
• Tubuliporate bryozoans have survived to this day, and in
fact underwent a remarkable radiation in the Cretaceous,
but are no longer dominant today.
Order TREPOSTOMATA
• Trepostomes are characterized by long-curved
zooecia separated by thin walls.
• Each zooecium has mature and immature
regions.
• Apertures of autopores are typically polygonal.
• Trepostomes can be differentiated from similarlooking cryptostomes by the thinner walls
between their zooecia.
• The specimens are erect forms, whereas these
specimens are massive.
TREPOSTOMATA
Order CYCLOSTOMATA
• Cyclostomes are characterized by zooecia
that are simple tubes which lack partitions
(diaphragms) and have rounded apertures
and well defined mature and immature
regions.
• Most cyclostomes are encrusting forms
and some, can be quite small and very
loosely arranged creeping zooecia.
CYCLOSTOMATA
Order FENESTRATA
• Fenestrates are characterized by their zooaria
morphology which form a mesh or net-like shape
with zooecia-bearing rods and open window-like
regions called fenstrules.
• Most fenestrates have considerable extra-zooid
skeleton material which is necessary for support.
• This order is typified by erect, delicate
morphology.
• Some fenestrates have considerable extrazooidal material such Archimedes which is an
axial rod that supports the net-like zooecia.
FENESTRATA
Class Gymnolaemata
• Ordovician-Recent
• Uncalcified gymnolaemates are known as fossils
almost exclusively as distinctive borings in
carbonate substrates such as shells.
• Non-boring, non-calcified gymnolaemate bryozoans
are extremely rare as fossils and known from the
Jurassic and Cretaceous only.
• Calcareous gymnolaemates did not appear in the
oceans until the Cretaceous, during which time they
diversified rapidly from a very few species in the
early Cretaceous.
• By the end of the Cretaceous, there were over 100
genera of gymnolaemates.
• They continued to diversify in the Cenozoic: today
there are over 1000 genera, comprising the bulk of
bryozoan diversity in today's seas.
Order CHEILOSTOMATA
• Cheilostomes are characterized by their
loosely packed colonies of box or coffinshaped zooecium.
• Many have round apertures and large
frontal areas on which brood pouches
which house the maternal zooids can often
be observed.
CHEILOSTOMATA
The Brachiopoda
Brachiopods
• The brachiopods are a large group of solitary and
exclusively marine organisms with a very good geologic
history throughout most of the Phanerozoic and are
among the most successful benthic macroinvertebrates
of the Paleozoic.
• They are typified by two mineralized valves which
enclose most of the animal.
• Brachiopods are filter feeders, which collect food
particles on a ciliated organ called the lophophore.
• Brachiopods differ in many ways from bryozoans (in both
soft and hard-part morphology), and are thus considered
by most workers as a separate but closely related
phylum.
• However, one of the most distinguishing features of
brachiopods is the presence of a pedicle, a fleshy stalklike structure that aids the animal in burrowing and
maintaining stability.
Pedicle
Lophophore
Morphology
BRACHIOPODA- Classification
Phylum Brachiopoda (Cambrian-Recent)
Class Inarticulata (Cambrian-Recent)
Class Articulata (Cambrian-Recent)
Order Orthida (Cambrian-Permian)
Order Strophomenida (Ordovician-Jurassic)
Order Pentamerida (Cambrian-Devonian)
Order Rhynchonellida (Ordovician-Recent)
Order Spiriferida (Ordovician-Jurassic)
Order Terebratulida (Devonian-Recent
Class Inarticulata
• Inarticulate brachiopods do not posses teeth and
sockets, nor do they have clearly defined diductor
muscles.
• Instead, the valves are held together by a complex of
adductor muscles.
• Although some inarticulates construct their valves of
calcite, most have shells of a mineral composition of
chitin and calcium phosphate which can be recognized
by its shiny, enamel-like luster.
• Inarticulate brachiopods usually lack surficial
ornamentation except growth lines.
• The classic example of the inarticulates belong to the
order Lingulida.
• The linguloids are small, biconvex, with usually oval or
circular outlines.
• This order has quite a long geologic history with some
genera (and possible species) remaining relatively
unchanged since the Cambrian
Class Inarticulata
• The only brachiopods to support a minor
commercial fishery, lingulate brachiopods are
also among the oldest of all brachiopods, and
the most morphologically conservative, having
lasted since the Cambrian with very little change
in shape.
• The preserved specimen of a living lingulate,
Lingula, shows the typical tongue-shaped shell
(hence the name Lingulata, from the Latin word
for "tongue") with a long stalk, or pedicle, with
which the animal burrows into sandy or muddy
sediments.
Unlike the shells of almost all other marine organisms, which
are typically made of calcium carbonate, the shells of lingulids
are composed of calcium phosphate. The rest of the body is
fairly typical of brachiopods in general, but the pedicle is quite
long. This facilitates burrowing; extant Lingula is typically found
burrowed in soft muddy sediments with only the valve edges
protruding.
Class Articulata
• Articulate brachiopods differ from inarticulates in
that the articulates posses teeth and sockets
and mineralized lophophore supports.
• The classification of articulate orders and
suborders depends primarily upon characters of
the hinge and beak areas (including hinge
length, teeth and sockets, pedicle opening,
etc....) and perhaps more importantly, although
more difficult to asses, the nature of the
lophophore support.
• Other features (such as the shell microstructure,
surface ornamentation) sometimes are quite
diagnostic of several orders and suborders of
brachiopods.
Order Orthida
• Shells of orthids are typically strophic
(having an elongated hinge line)
• The shape is generally semi- or subcircular in outline.
• Valve convexity is usually unequally
biconvex with a slightly inflated pedicle
valve.
• Orthids are typically covered with fine
diverging radial costae.
Orthida
Platystrophia
Late Ordovician
Strophomenida
• The Strophomenida were the largest order of
brachiopods, with about 400 genera.
• They were also by far the most
morphologically diverse group, and included
some very unusual forms, as well as more
"normal" forms.
• Strophomenids first appeared in the
Ordovician and persisted until the middle
Jurassic.
Strophomenida
• Strophomenids may be identified by their supra-apically
located pedicle foramen, at least in young shells.
• Adult strophomenids lacked an open pedicle foramen, and
usually lived attached to the bottom or to other objects by the
pedicle valve.
• One group of strophomenids, theproductids, were
characterized by very long spines extending from the shell.
• These are thought to have functioned as a sort of "snowshoe,"
supporting and stabilizing the organism on soft muds.
• Other strophomenids were attached to the bottom by a coneshaped pedicle valve, with the upper valve covering the cone
like a pot lid.
• The unusual brachiopod Prorichthofenia from the Permian of
Texas is one of these unusual conical forms.
• This shape is convergent on that of other attached organisms,
such as Paleozoic rugose corals and living scleractinian corals,
and it is though that, like corals, some strophomenids bore
photosynthetic algae inside their tissues that helped to supply
them with food.
Prorichthofenia
Rugose Coral
Order Pentamerida
• Shells of pentamerids are generally biconvex.
• Pentamerids are typically ovoid, circular,
triangular, or more commonly pentameral in
outline.
• The interior of the shell is typified by a prominent
medial ridge or septa in the brachial and/or
pedicle valve.
• Also diagnostic of pentamerids is a spoon
shaped structure modified from plates in the
pedicle valve called the spondylium which
supported muscle tissues
Pentamerida
Pentamerids grew to sizes of over 10 cm, and they
represent one of the largest types of dwellers within
Silurian reefs. A thickened beak area served as a
weight to stabilize the shell in the sediment, and
there was no fixed attachment. Pentamerid
brachiopods often lived as clumps of individuals.
Rhynchonellida
• Rhynchonellids look a bit like little nuts.
• Their hinges come to a point, a condition
paleontologists call non-strophic.
• They are often ridged.
• The commisure, the line between the two valves or
shells, is zig-zagged, as can be seen in the
somewhat unusual asymmetric rhynchonellid
Rhactorhynchia.
• The earliest fossil rhynchonellids are from the
Ordovician period.
• During the Mesozoic Era, rhynchonellids were the
most abundant brachiopods.
• A few species still exist today.
Rhynchonellida
Rhactorhynchia
Spiriferida
• Spiriferids are easy to identify.
• They often have an extended hinge
line so wide they look winged.
• Other prominent characters are the
fold and the sulcus that you can
see.
• The feature that gives the spiriferids
their name ("spiral-bearers") is the
internal support for the lophophore;
this support, which is often
preserved in fossils, is a thin strip
of calcareous material that is
typically coiled tightly within the
shell.
• Fossil spiriferids first appear in the
Ordovician period.
• They were extremely diverse during the
Devonian period and later went extinct
during the Jurassic period.
• Some fossil brachiopods make
spectacular finds, replaced by pyrite
Terebratulida
• Most living brachiopod, are
representative of the group;
terebratulids.
• Terebratulids first appear as fossils in
the Devonian.
• Terebratulids are responsible for the
name of "lamp shells" for brachiopods;
their shells resemble ancient oil lamps,
with the pedicle foramen resembling a
wick.
Terebratulida
Paleoecology
• All brachiopods are filter feeding, sessile (nonmobile) bottom dwellers.
• They are exclusively marine, but inhabit a variety
of bottom environments at various depths and
latitudes.
• Brachiopods are either free-living or rooted by
their pedicle to the substrate.
• During life, they can be oriented either vertically,
inclined, or horizontally to the substrate.
• Typically brachiopods oriented vertically during
life will have equally biconvex shells, whereas
inclined and horizontally oriented ones will be
unequal inflation being plano-convex, concavoconvex
Infaunal
• Living totally buried within the sediment.
Brachiopods living this way are oriented
posterior downward, and are usually
stabilized by their downward projecting
pedicle.
• Lingulid inarticulates are among the only
brachiopods to exploit this infaunal
environment
The pedicle is quite long. This facilitates burrowing; extant
Lingula is typically found burrowed in soft muddy sediments
with only the valve edges protruding.
Semi-Infaunal
• In this position, the animal is oriented
vertically (posterior downward) and is only
partially buried in the sediment; they may
or may not be attached by their pedicle.
Reclining
• In this position, the animal is in effect floating
horizontally on (or partially within) the sediment
with the pedicle valve as the lower valve.
• Generally, reclining brachiopods have a
concavo-convex or plano-convex shape.
• Other modifications include large surface area
and spines to help the critter float.
• The pedicle opening is usually not present.
• Note that one of the specimens also bears
attachment points for spines, which served as an
additional adaptation for reclining in soft
sediments.
Epifaunal
• In this position, the brachiopod is attached
either to the sediment or other object (e.g.,
marine plants) by their pedicle.