BIS 2C Lecture Notes - Lecture 33: Agnatha, Filter Feeder, Chordate
16 Mar 2018
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Lancelets, sea squirts (tunicates), jawless fishes, jawed fishes, and tetrapods (amphibians, reptiles, mammals) Diverse (and often dominant) group of animals on land and in water. Dorsal supporting rod, semi- rigid yet flexible. Develops in embryo (replaced by vertebrae in most vertebrates in adults: dorsal hollow nerve cord, postanal tail. Develops from infolding of ectoderm above the notochord. Combined with notochord and musculature propulsion: pharyngeal slits (cid:523)not a synapomorphy lost in echinodermata(cid:524) Associated with filter feeding or respiration vertebrae, jaws, two pairs of walking limbs arose within chordates. Non-vertebrate clades: lancelets (cephalochordates) lancelets (or (cid:498)amphioxus(cid:499)(cid:524); small filter-feeding marine animals (sandy, muddy places) Vertebrates did not come from lancelets, but from a common ancestor of vertebrae and lancelets; lancelets show the ancestral condition. Bag-like with enlarge perforated pharynx for filter-feeding incurrent and excurrent siphon. Sea squirt larvae have chordate features (also adults of larvaceans) Larvaceans: adults are larva-like and retain chordate features. Vertebral column (jointed, supporting dorsal structure) of bone or.
