Sponges, Corals and Pre-Bilaterian Life Flashcards
A species can be defined as
a group of organisms which can interbreed to produce viable offspring
Phylum rank can be defined as
- organisational clade that has a unique body plan
- exhibit similarly-placed, similar structures
- found together on the phylogenetic tree
Give examples of animal Phyla
- Porifera (sponges)
- Cnidaria
- Arthropoda
- Mollusca
- Nematoda
- Annelida (roundworms)
- Chordata
Describe the phylogeny the ‘early branches’ of the Animalia
- originating roughly 550-570Mya on the time sequence tree
- Porifera, Placozoa, Ctenophora and Cnidaria
Describe Porifera morphology
- globe-like
- two germ layers
- pore cells which punctuate these two layers
- actin-conjoined choanocytes infiltrating the inner germ layer and pressing against the pinacocytes
- active and sticky supporting tentacles
Describe Porifera germ layers
- pinacocytic outer germ layer
- convoluted inner germ layer
Choanocytes
- sometimes exist in chambers
- aka collar cells
Describe Porifera feeding
- filter feeding mechanism
- water is wafted away from the cell by choanocytic flagella, setting up a water current that allows the tentacles to contract bacterial food
- water expelled from the Porifera through their anterior osculum, expunging planktonic competition
- efficiency mediated by germ convolution and choanocytic abundance
Describe Poriferan symmetry
none
Describe Poriferan nerve cells
none
Describe carnivorous Porifera
- harp-shaped deep-sea Porifera in the Family Cladorhizidae
- ping-pong tree sponge
- harp sponge
- spicule-and-envelope mediated carnivory of shrimp
- adaptation to a lack of environmental planktonic food source
Describe Placozoa
- marine
- approximately 20 species
- e.g. Trichoplax adhaerens
Describe Placozoa morphology
- double germ layer structure
- semi-ciliated upper germ layer
- lower germ layer exhibiting some secretory gland cells, separated by contractile fibre cells
- no symmetry
- no nerve cells
- very disorganised, amorphous shape
- small size of 3-4mm
Describe Placozoan feeding
- grazers
- secrete enzymes over the reef rock in tropical seas
- crawling over algae and absorbing digestants
Describe Placozoan taxonomy
four Classes:
- Anthozoa (the sea anemones and corals)
- Cubozoa (the box jellies)
- Hydrozoa (the hydroids)
- Scyphozoa (the jellyfish).
Describe Cnidarian morphology
- body plan is extremely diverse
- 2 germ layers
- mesoglea
- blind-ending gut cavity
- approximately radial symmetry
- nerve net
Describe mesoglea in Cnidaria
- intermediate
- jelly-like
- allows a few cells to crawl through
Describe the Cnidarian germ layers
- epidermis and gastrodermis
- unspecialised actin and myosin contractile and extensile cells in both layers.
Describe Cnidarian dual morphology
- sedentary Polyps and mobile Medusas
- alternation of generations as two different morphs in the same Cnidarian’s life cycle
Describe Polyps
- anterior double mouth and anus surrounded by tentacles and leading to the gastrovascular cavity
- rest of the body is stalked
Describe the Medusa
- more active
- posterior double mouth and anus, still surrounded by tentacles and leading into the gastrovascular cavity
- outer layer fibres more contractile
- mesoglea more stiff to generate more power for its motile swimming lifestyle
Describe Medusa mesoglea
almost skeletal
Describe slow-moving Cnidarian feeding adaptations
- predatory feeding behaviours
- nematocysts contained within the cnidocyte, and store the nematocyte cells
Describe nematocysts
stinging organelles that allow predation upon fast-moving fish and crustaceans
Describe nematocyst cells
- contain a hollow, tightly wound venom-delivering thread coil and barb
- fired on mechanical activation of their touch-sensitive hairlike projection
Describe the hydrozoan Portuguese man o’war
polyps bud to form genetically identical but individually specialised colonial entities
Describe the photosynthetic dinoflagellates
- polyps bud to form genetically identical but individually specialised colonial entities
- provides symbiotic corals with photosynthates harvested from the energy of the sun
Describe the myxozoans
- parasitic
- anomalous vermiform morphology of just a few mms
- nematocyst-like cell
Describe the Ctenophores
- dual germ layering
- approximate radial symmetry
- nerve net
- shimmering appearance
- predatory
- slow motility achieved by synchronous beating of their cilia
- colloblasts
Describe colloblasrs
