|
Bryozoans
Moss Animals "Polyzoa" in Europe
Always colonial
Zooecium - individual, smaller than coral zooids
All fossils marine; freshwater forms exist today, but do not preserve
Reproduction sexual; free swimming larvae
Individual zooecium contains both male and female sex cells
Colony called a zoarium
Waste excreted out of a separate opening away from mouth
Numerous tentacles gather food - eat forams and diatoms
Ectoprocta (subphylum) have anus outside the tentacle area (all fossils)
Entoprocta (subphylum) have anus within tentacle area (Recent bryozoans only)
Simple nervous system
Hard parts - CaC03
Classification - based on size and shape of zooid and zoarium -
must be thin sectioned for species identification
Class Gymnolaemata (Ord. - Holocene) Fossils common in U Jr,
dominant bryozoan fossils in the L K to Holocene
Dominate class of bryozoans in the modern marine environment
circular lophophore about mouth
anus outside lophophore
epistome (lip overhanging mouth) absent
generally marine, but found in brackish and fresh water
Order Ctenostomata (Ord. - Rec.)
ctenon = comb + mouth
terminal aperture with terminal projections
commensural; living on or with other animals, sharing food
individuals bud from internodes on a tubular stem
chitinous or gelatinous skeleton - do NOT calcify
best seen when they encrust or bore into other shells.
Commonly found as external molds mainly Paleozoic, but
rare as fossils
some fresh water species
represented by Vinella, Ropalonaria, Ascondictyon, Spathipora
branching determines classification
no diaphragm in tube and no operculum (lid over aperture)
(some species have a few diaphragms)
represented by Fistulipora, Ceramopora, Meekopora, Petalopora
Order Cheilostomata (Jr - Holocene)
often resemble "coffins" lined up in geometric patterns
apertures covered with opercula
free-standing or encrustuting. Common in Tertiary and later marine sediments
Class Stenolaemata:
Order Trepostomata (Ord. - Triassic) trepo = changed mouth
twiglike colonies - tube divided into an exozone and endozone
thin-walled inner portion of colony made up of early formed, rapidly growing
portions of autopore (immature zone
thick-walled outer portion represents slow growing or static position of tubes
(mature zone)
compose reef-like structures during Paleozoic lived in environments similar to
corals
coral and bryozoa very rarely found together
mesopore has many diaphragms
autopore has few diaphragms
acanthopores have no diaphragms
no mesopores or acanthopores in the immature region
Order Cystoporata (Ord. - Triassic)
resemble trepostomes in size,
diaphrams usually not present in this order. For species with diaphragms, only a
few are present.
surface often displays "star" pattern (Constellaria)
"star-shaped" maculae in thin section
Order Cryptostomata (Ord. - Permian)
crypto = hidden mouth
short calcareous tubes
fronds delicate, reticulate (netlike)
walls near periphery of colony much thickened
distinct break between mature and immature zone
smaller and more delicate than Trepostomata
Order Fenestrata (Ord. - Triassic) fenestrate bryozoa (lacy bryozoa)
zooids on upper surface only
grow in fan-shaped or funnel-shaped extensions
cemented to foreign object by calcareous tissue
branching stalk has open spaces between zooids
genus Archemides - corkscrew stalk common in Mississippian
zooecia on upper side of fan structure only
fenestrates served as substrate binders - similar to marine grasses today
Order Tubuliporata (Cyclostomata) Ord. - Holocene
small, insignificant colonies, few genera recognized
each zooid closed off from others in the colony - lived essentially as a solitary animal
only stenolaemates found after the Triassic
little studied due to relative insignificance of the order
Class Phylactolaemata (ectoprocts)
fresh water bryozoans
no hard parts
Controlling factors for Bryozoa
Substrate - seldom seen in shale or Ss, found mainly in Ls
Depth - 0-200' (must be in one of light (food source)
Temperature - Arctic to Tropical
Turbidity - can tolerate some suspended matter
Fenestrates definitely lived in muddy water
Agitation - cannot tolerate a great deal, but must have
circulation
Salinity - 15 to 50 ppt and fresh water
|
|
