Chapter 34 Group Assignment: Chordates
Lancelets and tunicates Lancelets and tunicates are two groups of chordates. Classify each statement as applying to lancelets, tunicates, both lancelets and tunicates, or neither. Drag each item to the appropriate bin.
Lancelets: •all chordate characters present in adults •adults swim by the contraction of a series of muscles along the notochord •adults bury themselves into the sediment of the sea floor Tunicates: •in adults, water enters through one siphon and leaves through another •most chordate characters not present in adults •larvae swim using the notochord, but adults may be sessile Both: •adults feed with the aid of pharyngeal slits Neither: •adults swim using the vertebral column *Tunicates and lancelets are two groups of chordates. Both possess the four derived characters of chordates during their development. However, whereas adult lancelets retain all four of these characters, adult tunicates retain only one (pharyngeal slits). Lancelets swim by contracting a series of muscles located along the side of the notochord, which results in a motion similar to the swimming motion of fishes. Larval tunicates are mobile, using their tail muscles and notochord to propel themselves through the water; adult tunicates are sessile or float with the current. Adult lancelets and tunicates use their pharyngeal slits to filter suspended food particles from the water.*
Phylogeny of chordates The phylogenetic tree shown here displays the major clades of chordates. Which statements about the phylogenetic tree are true?
Mammals and turtles are more closely related than are lungfishes and sharks. Rays and frogs have vertebrae. Descendants of organism (d) have limbs with digits. Organism (a) is a common ancestor of all chordates. Birds and ray-finned fishes have a notochord and jaws. *The phylogenetic tree shown above represents the evolutionary relationships between the major clades of chordates. The hatch marks on the tree indicate derived characters shared by all the groups to the right of each mark. For example, all chordates have a notochord, and all mammals produce milk. The phylogenetic tree also shows the degree of relatedness of particular groups of chordates. For example, mammals are more closely related to hagfishes than to lancelets.*
Derived characters of chordates: All chordates share a set of derived characters during at least some part of their life. Drag the labels to their correct locations on the diagram of chordate characters below. Use blue labels for blue targets and pink labels for pink targets.
notochord-- a flexible rod that runs along the anterior posterior axis-- may be associated with a jointed skeleton pharyngeal clefts-- grooves that separate pouches along the side of the pharynx-- may develop into parts of the ear Pharyngeal slits-- openings to the outside of the body along the side of the pharynx-- may develop into gill slits Dorsal, hollow nerve cord-- a bundle of nervous tissue running the length of the body-- may develop into the brain and spinal cord Muscular post anal tail-- a structure that contains muscles and extends past the anus-- may be used to propel some species in water *All chordate embryos exhibit four derived characters: a notochord; a dorsal, hollow nerve cord; a muscular, post-anal tail; and pharyngeal slits or clefts. A structure of a chordate. Chordates share four derived characters: a notochord; pharyngeal clefts or slits; a dorsal, hollow nerve cord; and a muscular, post-anal tail. The mouth and anus are part of pharyngeal clefts or slits. Muscle segments are part of the muscular, post-anal tail. The nerve cord is the most dorsal structure going along the whole length of the chordate. The notochord lies just ventral to it. Pharyngeal slits are located at the cranial end of the animal, opposite to the tail. The mouth is located at the very cranial end of the chordate. In many chordates, these characters develop into different structures or are reduced in form as the animal continues its development. For example, the pharyngeal slits develop into gill slits in aquatic vertebrates, and a jointed skeleton forms around a reduced notochord in most vertebrates.*
