last common ancestor of all animals - multicellular, heterotrophic - asymmetry (= no symmetry)
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Sponges. Last common ancestor of all animals - multicellular, heterotrophic - asymmetry (= no symmetry) - cellular level of organization (no tissues) - intracellular digestion (ate bacteria) - similar to choanoflagellate protists. Sponges. Cnidarians. - PowerPoint PPT PresentationTRANSCRIPT
Last common ancestor of all animals
- multicellular, heterotrophic
- asymmetry (= no symmetry)
- cellular level of organization (no tissues)
- intracellular digestion (ate bacteria)
- similar to choanoflagellate protists
Sponges
Sponges
Cnidarians
Last common ancestor of the Metazoa
- radial symmetry
- 2 embryonic tissue layers (ectoderm + endoderm)
- extracellular digestion, but with an incomplete gut
Sponges
Cnidarians
Acoelflatworms
Last common ancestor of the Bilateria
- bilateral symmetry
- cephalized (had a head)
- embryos had mesoderm
- still had an incomplete gut
coelomates
Organization of Body Plans: Symmetry
Asymmetrical - sponges- without tissues
Radial symmetry - Cnidarians- 2 embryonic tissues layers (diploblastic)
Bilateral symmetry- 3 embryonic tissue layers (triploblastic)
- with organs
Features of Bilateral SymmetryAnterior (= head end)
Posterior (= tail end)
Ventral (belly, or bottom side)
Dorsal (top side, or back)
rightleft
- only internal cavity is the gut
- space between gut and body wall is tissue-filled
- no fluid-filled space (coelom) to provide rigidity, hence no hydroskeleton for muscles to attach to
Acoelomates
Acoels – the first hunters?
tiny, common marine worms
- no permanent gut, gonads or excretory organs; stomach form temporarily after eating, then cells disband!
- space between temporary gut and body wall is solid (tissue-filled), no coelom
- often live between grains of sand
A true coelom is a fluid-filled cavity enclosed in tissue that develops from mesoderm layer in embryo
- acts as hydrostatic skeleton: point of muscle attachment; gives solidity and strength (so you aren’t just a wet noodle)
Coelomates
Sponges
Cnidarians
Deuterostomes
Protostomes
coelomate animals are divided into 2 major lineages that are distinguishable by features of their embryos:acoel
flatworms
Sponges
Cnidarians
acoelflatworms
Deuterostomes (starfish, us)
Platyhelminthes(flatworms)
Annelidworms
Molluscs
Nematodes
Arthropods
- coelom- complete gut- nephridia (kidneys)
Last common ancestor of coelomates
DeuterostomesEchinoderms
Chordates
ProtostomesPlatyhelminthes(flatworms)
Annelidworms
Molluscs
Nematodes
Arthropods
coelomateancestor
Echinoderms
Chordates
Platyhelminthes(flatworms)
Annelidworms
Molluscs
Nematodes
Arthropods
coelomateancestor
Echinoderms
Chordates
Platyhelminthes(flatworms)
Annelidworms
Molluscs
Nematodes
Arthropods
coelomateancestor
Sponges
Cnidarians
acoelflatworms
Deuterostomes (starfish, us)
Platyhelminthes(flatworms)
Annelidworms
Molluscs
Nematodes
Arthropods
We now recognize two distinct kinds of flatworms:
- primitive acoels (never had a coelom)
- advanced (but simple-looking) Platyhelminthes (lost the ancestral coelom + complete gut)
PlatyhelminthesNemerteans
(ribbon worms)
“false” acoelomates
Although lacking any functional coelom, molecular phylogenetic studies indicate both groups evolved from an ancestor that did have a coelom (because all their relatives have one)
- indicates secondary loss of an ancestral trait, likely an adaptation to their environment and mode of hunting
Phylum Platyhelminthes- Bilateral symmetry (forward movement) but no coelom;
glide on sheet of mucus
- Cephalized: nerves concentrated in cerebral ganglion at front of head, near sense organs
- Triploblastic: mesoderm
gives rise to a muscular
tissue layer in adult body
- Incomplete digestive system
with complex, branched gut
- NO coelom (but ancestor had one)
~20,000species
3 Classes of Platyhelminthes(1) Turbellaria – free-living flatworms
- rely on diffusion of gas across their
thin body wall for respiration
(2) Trematoda – parasites with
2 or more hosts
(3) Cestoda – tapeworms
Fasciola, liver fluke
Taenia
many larval stages in life cycle
Class Turbellaria
Freshwater planaria have a simple,
3-branched gut
Many colorful marine species have
multi-branched guts
Dugesia
Branched digestive systems also used as a circulatory system
Class Turbelaria: Anatomy of a Planarian
Pharynx (muscular eating tube) emerges from middle of posterior side of body
Cerebral ganglion (cluster of nerves) is fed by sensory neurons from eyespots, nerve chords running along either side of body
branched GVC
Class Trematoda: Complex life cycles
Redia, packed full of developing cercaria
2nd, infects fish or crab
1. miracidum2. redia3. cercaria4. metacercaria5. adult
1st infects a snail
Head, w/ hooksfor attachingto intestine wall
Class Cestoda: Tapeworms
chain of sex organs
Intestinal parasites of vertebrates; up to 20 m long
Innovations of Bilaterians, seen in Platyhelmithes
- bilateral symmetry (dorsal - ventral, anterior – posterior axes)
- triploblastic: mesoderm complex organs, muscle tissue
- cephalization: sensory structures concentrated on head, the 1st region to encounter new environments
Limitations of flatworm body plan:
- rely on diffusion for respiration: must stay wet and thin for O2 to randomly wander in through tissues, and CO2 out
- no coelom = can only move by gliding over surfaces
despite having muscle, there’s nothing for muscles to attach to and work off of (no skeleton)
Movement – 3 kinds of wormsCompare movement in worm phyla with different body plans:
1. flatworms – Planaria
- watch them glide on cilia and a sheet of secreted mucus
2. nematodes (roundworms) – “vinegar worms”
- longitudinal muscles run along the body, but no circular muscles around the middle
- look for distinctive, twitchy movements in lab
3. annelids: earthworms and marine polychaetes
- coelom acts as an internal skeleton: solid bodies
- circular muscles: make one end fat or skinny
- parapodia used as paddle-feet in marine worms