How are starfish different to humans?


starfish (asteroidea) echinodermes, invertebrate deuterostomes, unlike other invertebrates protostomes. echinoderms , chordates deuterostomes embryonic blastopore forming anus first, mouth second in development.

1-echinoderms evolved bilateral ancestors , bilateral in free-swimming juvenile life stage. adults assume pentamerous or radial symmetry metamorphosis of juvenile adult form.
2- have no head, brain, nor eyes, brittle stars seem have light sensitive parts on arms. nervous system includes circum-oesophageal ring.
3- mouth situated on underside , anus on top (except feather stars, sea cucumbers , urchins).
4- no heart , poorly defined open circulatory system.
5- echinoderms have water moving vascular system (the ambulacral system) set of muscle driven hydraulic canals, derived part of coelom, hydraulics power tube foot suction , release.
6 external fertilization

humans mammalian terrestrial chordates.

1 -bilateral symmetry (two halves) , cephalization (a head end)
2. outer covering of protective cellular skin, hair
3. metamerism (segmenting) found in skeletal, muscular , nervous system. includes ribs, vertebrae, muscles, , ganglia/peripheral nerves;
http://en.wikipedia.org/wiki/metamerism_...
4. well-developed coelom or body cavity lined epithelium (cellular tissue of mesodermal origin) divided 2 compartments diaphragm
5. well-developed internal skeleton of cartilage and/or bone, separated axial skeleton (skull, vertebrae, ribs, sternum) , appendicular skeleton (pelvic , pectoral girdles , limbs), post anal tail (vestigial coccyx)
6. highly developed brain enclosed skull , dorsal nerve cord enclosed vertebrae - these provide advanced neural structures highly protected damage
7. well-developed sense organs (eyes, ears, nostrils) located on head (cephalization)
8. respiratory system, including either gills or lungs, located closely pharynx or throat
9. closed circulatory system ventral heart , median dorsal artery
10 placental birth parental care lactation



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