Phylum Echinodermata
- Pentaradial, coelomate deuterostomes. Despite their obvious unique characters, they are one of the most closely related phyla to chordates.
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All echinoderms have calcareous plates or spines embedded in the skin, forming an endoskeleton, and part of the coelom is modified into a unique water vascular system, used for feeding, gas exchange and movement via tube feet. -
Major classes: sea urchins and sand dollars (herbivores and detritivores; Echinoidea), sea stars (predators; Asteroidea), and sea cucumbers (suspension feeders; Holothuroidea) -
They are a moderately diverse group (7,000 sp, all marine). However, they often comprise a large portion of marine ecosystem biomass, especially in deep-sea habitats. Urchin fisheries are becoming a greater part of north American economies
Phylum Chordata
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Chordata are the phylum to which we belong, and are bilateral coelomate deuterostomes. They are a moderately diverse phylum, with about 60,000 spp. -
All chordates posses at one point of their life cycle: -
Primitive chordates are typically suspension feeders and feed using their gill slits and a mucous net. -
Sea squirts, salps and larvaceans (Subphylum Urochordata) are the tunicates, marine animals with a variety of lifestyles. Other chordate plans may have evolved from this group via paedomorphosis. -
Lancelets (Subphylum Cephalochordata) are a small group that look like a cross between fish and segmented worms.
Chordata: Subphylum Vertebrata
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Subphylum Vertebrata are the most diverse group of chordates, and all have a segmented backbone and a skull that encloses the brain. -
The vertebrate endoskeleton is made of living cells and non-living cartilage or bone. -
Primitive vertebrates (Agnatha) lack jaws, and are detritivores or parasites. Hagfishes are not true vertebrates but possess a skull, lampreys have both skull and backbone. -
Two modifications of the vertebrate plan allowed the development of great diversity: - the formation of jaws from fused gill arches
- limbs via the external formation of bone.
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