(Paleoiiithe Bryozoa)
(The Brachiopoda)
THE BRYOZOA
The
Bryozoa (moss animals) are a geologically important group of small animals, Some
superficially resemble corals, 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, 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 BRYOZOA
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:
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, 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.
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.
EDITORS
Gery
Purnomo Aji Sutrisno
Fisheries
Aquaculture Brawijaya University
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