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Phylum Hemichordata● Three body regions
-Proboscis-Collar-Trunk
● Deuterostomes
● Ciliated, pharyngeal gill slits
● Complete digestive system
● Dorsal and ventral nerve cord
Phylum Hemichordata
● Acorn worms feed as they burrow
● Detritus and other material adheres to the proboscis and is moved to the mouth
● The posterior end is extended out of the burrow during defecation
● Coils of fecal material are called castings
Characteristics of Phylum Chordata● Bilaterally symmetrical
● Dorsal, hollow nerve cord
● Notochord – flexible, supportive rod parallel to dorsal nerve cord
● Gill slits or pharyngeal pouches
● Postanal tail
● Segmented muscles
● All deuterostomes
Evolutionary Adaptations of Chordates
● From filter feeding ancestors to active predators. Major improvements occurred in the following areas:
● Mobility● Oxygen capture● Digestion● Circulation● Nervous system
Skeletal Changes
● Skeleton becomes stronger to work with bigger muscles
● Allows for more rapid movement
● Vertebrae develop around nerve cord and notochord for protection
Oxygen Capture
● Gill slits and muscular pharynx work to move more water over gills than occurred in lower animals
● Leads to more oxygen uptake for fueling a higher metabolism
Circulation
● Stronger heart to circulate blood faster
● Works to bring those higher oxygen loads to body tissues more quickly & efficiently
Digestion● Digest more kinds of food
more efficiently
● Muscularized gut grinds down food physically
● Liver and pancreas secrete substances that break down food chemically
● Leads to better overall efficiency
Nervous System
● More complex
● Better motor control allows for improved hunting and defense
● More finely tuned sensory receptors allows for clearer picture of environment
● Compartmentalization of brain allows for improved cognition and sensory input processing
Chordate Subphyla● Phylum Chordata
○ Subphylum Urochordata○ Subphylum Cephalochordata○ Subphylum Vertebrata
Subphylum Urochordata
● Sea squirts (Tunicates)
● Larvae are free-swimming, but adults are usually sessile
● Notochord found only in larvae. Dorsal nerve cord highly reduced in adult
● Adult body has a tough, though sometimes clear covering called a tunic
Subphylum Urochordata● Feeding and gas exchange
occurs via the same mechanism
● Water laden with oxygen and food enters via the incurrent siphon
● Oxygen & food is extracted by the pharyngeal gill slits
● Water and waste exits via the excurrent siphon
Subphylum Cephalochordata
● Small, tadpole-like animals collectively called lancelets
● Usually nearly translucent
● Notochord extends from the head to the tail in adults
● Live in shallow waters with clean, sandy substrates
Subphylum Cephalochordata
● Spend most of life with the body buried in the substrate & the mouth exposed to the water
● Cilia around the mouth called cirri pull water into the mouth and through the gill slits
● Food & oxygen are extracted in a similar manner to that seen in Urochordates
Subphylum Vertebrata
● Characterized by vertebrae that form around the dorsal nerve cord & serve as the organism’s primary axial support
● All other characteristics of lesser chordates are conserved in vertebrates at some stage of their life cycles (embryonic)
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