BIOL 1604 Lecture Notes - Lecture 18: External Fertilization, Asexual Reproduction, Pterobranchia

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27 Feb 2017
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Phylum Hemichordata
Characteristics
Three part coelom similar to echinoderms
Bilaterally symmetric
Pharyngeal gill slits or pouches similar to chordates
Complete digestive system
Circulatory system of dorsal and ventral vessels and dorsal heart
Nerve plexus and some have hollow nerve cord
Marine
Wormlike bottom dwellers
Mostly sedentary or sessile
Class Enteropneusta: acorn or tongue worms
Mucus covered body is divided into
o Proboscis
o Collar
o Long trunk
Ventral nerve cord and a larger dorsal nerve cord
Intertidal, solitary
Small
U-shaped gill slits in the sides of the pharynx to remove excess water
Feeding
o Deposit feeders (extract organic components of sediments)
o Suspension feeders (plankton and detritus)
Reproduction and development
o Dioecious
o External fertilization
o In some species, a ciliated tornaria larva develops similar to echinoderms
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