Question

5) Every vertebrate is a chordate but not every chordate is a vertebrate. Compare the three groups we discussed in the non-vertebrate chordate lecture (Hemichordata, cephalochordate, urochordata) and explain the differences between the following in one or two paragraphs:

i) between the groups

ii) between those phyla and the vertebrates.

iii) describe the relationship of the hemichordates to other deuterostomes.

iv) What physical feature found in all of these groups is an advantage that has led to “pre-adaptedness” in the chordates? What does that physical feature allow that creates this opportunity?

Answer 1

Yes, Every vertebrate is a chordate but not every chordate is a vertebrate.

i) In urochordates, the dorsal tubular nerve cord is present in the larval form and degenerates in the adults in the form of small ganglion. In cephalochordates, notochord and nerve cord extend the entire length of body and is present throughout life unlike urochordates. Hemichordates, on the other hand, completely lack notochord and true dorsal nerve cord.This is what makes them different from theothertwo groups.Hemichordates and urochordates are non-metameric whereas cephalochordates are metameric, i.e. their body is divided into many body segments called somites.Hemichordates are worm-like animals whereas urochordates are bag-like in shape. Cephalochordates are fish-like in shape.Urochordates are hermaphrodites(bisexual), whereas cephalochordates are unisexual , that is,males an females are separate sexes.In urochordates, the adult body is covered by a tunic, whereas in hemichordates and cephalochordates the adult body is not covered by an exoskeleton.

Hemichordata- Acorn Worms: Balanoglossus; Urochordata- Tunicates (Sea Squirts); Cephalochordata- Amphioxus

ii) Chordates and vertebrates are two groups of higher animals. Both chordates and vertebrates are deuterostomes. Vertebrates are a type of advanced chordates. Chordates are characterized by the presence of a notochord. Both chordates and vertebrates contain a nerve cord, pharyngeal gill slits, and post-anal tail at some points of their life. The main difference between chordates and vertebrates is that some chordates do not have a vertebral column whereas all vertebrates have a vertebral column. In vertebrates, the vertebral column surrounds and protects the nerve cord. Both chordates and vertebrates consist of a central nervous system. The brain of the vertebrates is protected by the skull.

iii) Hemichordata and Chordata are two deuterostome phyla. Along with the phylum Echinodermata, Hemichrodata and Chordate belong to a common ancestor. Both hemichordates and chordates are coelomates. Hemichordates are worm-like, marine animals while chordates live in water, land, and air. The main difference between Hemichordata and Chordata is that Hemichordata contains an epidermal nervous system whereas Chordata contains a central nervous system. Chordates contain a dorsal, tubular nerve cord. Both Hemichordata and Chordata contain pharyngeal gill slits. Chordates also contain a post-anal tail. The three classes of hemichordates are Enteropneusta, Pterobranchia, and Planctosphaeroidea. The three subphyla of chordates are Urochordata, Cephalochordata, and Vertebrata.