Porifera/Cnidaria Flashcards
Types of cells in porifera
Multicellular, but not organized into organs or tissues.
What is considered to be the sister group to all metazoans?
Porifera
Porifera
*Mostly marine, a few freshwater *Virtually all are sessile, epifaunal, filter feeders *Porifera = “pore bearers” - bodies punctured by numerous pores
Pores in Porifera
*Water flows into the body through the pores-incurrent *Associated with pores are cells with flagella - whip like process - aid in moving water through body of sponge
Choanoflagellates
*small single celled protists *Found in freshwaters and the ocean *take their name (“collar-flagellates”) fromthe circle of closely packed microvilli, or slender fingerlike projections, that surrounds the single flagellum by which choanoflagellates both move and take in food. *Closest protist relative to metazoa
microvilli
Slender fingerlike projections that surrounds that single flagellum by which chanoflagellates move and take in food.
spongocoel
In sponges, a central chaimber that water moves into.
osculum
In sponges water leaves via a large opening.
Ascon grade sponges
generally small (small ratio area/volume)
leuconoid sponges
Most sponges, and all large ones, (large ratio area/volume)
Sycon sponges
The middle sponges in terms of ratio area/volume. Shows folding along the edges
Sponge skeletons
*calcareous plates *Organic collagen like fibers (bath sponges) *siliceous and calcareous spicules
spicules
Needle like elements in sponge skeletons
Sponge skeleton fossilization
Plates and spicules fossilize well, but most skeletons dissagregate at death
Class Calcarea
*Cambrain-Recent ❁skeleton composed of separate calcareous spicules ❁all three grades ❁marine, usually shallow ❁Generally small
Class Demospongiae
❁90-95% sponge species ❁siliceous spicules, of spongin fibres, or both. ❁Leuconoid only ❁Most marine, some freshwater
Class Hexactinellida
Late Precambrian-Recent ❁”glass sponges”, ❁construct a skeleton composed of 6-rayed siliceous spicules ❁syconoid pattern ❁Exclusively marine, usually deep ocean
Stromotoporoid
❁extinct group of massive calcareous colonial marine organisms ❁ important Paleozoic and Mesozoic reef builders. ❁For a long time affinities were unclear ❁Massive calcareous skeletons - up to 5 m in diameter, variety growth forms ❁Horizontal and vertical structures
When do stromotoporoid reef builders disappear?
Paleozoic forms dissapear end Devonian - collapse reef ecosytems, unclear if Mesozoic forms are same group
laminae
Horizontal layers parallel to substrate in stromotoporoids
mammelons
Raised surfaces, bumps, in stromotoporoids
astrorhizae
“Star roots” look like stars in stromotoporoids
Coralline Sponges
❁Originally discoverd in 1970’s in cryptic habitats in reefs ❁leuconoid sponges with siliceous spicules (”sclerosponges”), calcareous spicules, or no spicules; with a massive calcareous basal skeleton ❁May be polyphyletic (most demosponges; some Calcarea) ❁Almost certainly living relatives of stromatoporoids ❁Experimental work on model “stroms” show they could function as sponges. ❁Grow slowly; can be used as climate proxies
Archeocyathids
Another enigmatic group ❁Calcareous sessile marine organisms ❁Range restricted to Lower-Middle Cambrian ❁Very diverse in lower Cambrian ❁Shallow water, usually carbonates ❁Reef builders ❁Tropical
Receptaculitids
“Sunflower coral” ❁Radially symmetrical carbonate skeleton made of rods ❁Shallow water tropical environments - reefs ❁Ordovician - Pemian; most Ord.-Dev. -common in Ordovician of Illinois (and Missouri) ❁Resemble sponges - probably superficial ❁Current view is that they may be calcareous green algae
What type of animals are Cnidarians?
Sea anemones, corals, jellyfish, sea pens, hydra
cnidarians
the “nettle keepers” *Wide variety body forms and complex life cycles *All possess nematocysts *Bodies made of two layers of tissue (epidermis and gastrodermis) *In between epidermis and gastrodermis is the mesoglea, a layer of jellylike substance which contains scattered cells and collagen fibers.
Forms of cnidarians
❁Solitary or colonial (colonies can be massive) ❁Free-living or sessile ❁Soft bodied or calcareous
nematocysts
Stinging threads used to protect animal and/or capture prey.
Epidermis in cnidarians
contains the cnidocysts, the stinging cells that are characteristic of the phylum
Two general body forms of cnidarians
Medusa-Generally free living (tentacles on bottom)
Polyp-Generally sessile; may secrete calcareous skeleton
Hydrozoa
alternate between a polyp and a medusa stage - siphonophores, hydroids, fire corals, and many medusae
Anthozoa
live only as polyps - true corals, anemones, and sea pens
Cubozoa
Box Jellies-toxic
Scyphozoa
medusa stage dominates; true jellyfish
What type of living form is this?
medusa-free living form
What type of body form is this?
Polyp-generally sessile. May secrete a calcareous skeleton.
Coral like fossil forms first appear…
In the Cambrian
Earliest Cnidarians are known from the
Ediacarian (late Pre Cambrian)
Scleractinian Corals
❁Body internally divided by partitions: mesenteries ❁Secrete skeleton of aragonite = corallite ❁Radial sheets of aragonite = septa, secreted between pairs of mesentaries ❁Septa show six -fold radial symmetry (cyclic insertion) ❁Can be solitary or colonial ❁Many have symbiotic alga which allow them to become quite large - especially in tropics ❁Middle Triassic -Recent
Body internally divided by partitions
mesentaries
Rugose Corals
Horn corals
❁Skeletons of calcite ❁Important in ancient reefs ❁Both solitary and colonial (compound) ❁Bilateral pattern of septa (serial insertion) ❁Ordovician - Permian
Tabulate Corals
❁Exclusively colonial
❁Calcite skeleton
❁Important reef builders
❁Corallite made of slender tubes crossed by horizontal internal partition - tabulae
❁Septa reduced or absent
Secreted skeleton of aragonite
corrallite
How are coral groups related?
❁Mineralogy- calcite vs. Aragonite
❁Morphology - insertion
❁Time gaps - no Lower Triassic corals
Original meaning of a reef
a ridge or shoal a ship could ground on - still used in this sense - we have “reefs” in Lake Michigan
Reefs are composed of…
carbonates (limestone dolomite)
Carbonate buildup
a body of locally formed and laterally restricted carbonate sediment possessing topographic relief
moundlike organic buildup
bioherm
Reef
buildup formed in part by a wave-resistant framework constructed by organisms - a waveresistant bioherm
If a reef is not wave resistant it is called a….
bank
Where are reefs located?
In less that 1% of the oceans. They are restricted to 30N and 30S. TEmp must be between 18 and 36C. Clear, shallow waters, with low nutrients and low sedimentation.
modern reefs are built by
scleractinian corals
zooxanthellae in reefs
symbiotic algae. This means the reefs need light.
Is it easier to precipitate calcium carbonate in colder or warmer waters?
warmer waters.
Fringing Reef.
builds directly out from coast
Barrier Reef
separated from coast by a shallow lagoon
Atoll
ringlike, surrounds lagoon - most modern IndoPacific island reefs
3 basic classes of modern reef builders
❁Frame builders: make structure of reef; generally scleractinian corals
❁Binders: cement reef materials together - algae
❁Debris producers: all organisms living on or around reef
Why are reefs of particular interest to geologists?
Important source rock for petroleum due to high productivity of the reef environment and porous structure
proterozoic reefs
Algal stomatalites produce small scale buildups
Decline markedly end Proterozoic - evolution grazers?
when was the beginning of true reefs?
Ordovician. bioherms.
❁These reefs become large and widespread in the Silurian and Devonian
What were reefs like in the carboniferous?
There were none, only mounds.
Permian reefs
❁Widespread reefs reappear, e.g., west Texas ❁Framebuilders are bryozoans and calcareous sponges ❁Disappear end Permian
Triassic reefs
first scleractinian corals; few reefs similar to those in Permian
Jurassic reefs
explosion diversity scleractinian corals - become major reef element
Cretaceous reefs
dominated by rudistid bivalves! - become extinct Late Cretaceous
