Question

Genes found in amphioxus which control the location and development of the nerve chord and related structures have been conserved in humans. In people, these genes control:

Select one:

a. the forebrain, midbrain, and hindbrain

b. the brain, spinal chord, and peripheral nervous system

c. the central and peripheral nervous systems

d. the five senses

Sacabambapsis, an early fish, had armor composed of:

Select one:

a. dentine, aspidin and enameloid

b. chitin and calcium carbonate

c. hard cartilage and thick scales

d. bone

One of the innovations of Osteostracan fish (those with bony head-shields) was:

Select one:

a. Jaws

b. large, plated scales covering the rest of their bodies

c. image forming eyes

d. Bony fins and skull

Aside from protection, what is another potential reason that armor may have evolved in many fishes?

Select one:

a. Because having armor made fish better competitors for resources and territories

b. Because armor seemed cool

c. Because the armor is an honest signal for sexual selection

d. Because it helped store essential minerals like calcium and phosphorus

Answer 1

Amphioxus or Branchiostoma is cephalochordate animal.A well developed brain is absent in amphioxus. It's central nervous system include a hollow dorsal neural tube or nerve cord which present mid dorsally just above the notochord.It has no ganglia.It's slightly enlarged part is called brain or cerebral vesicle and posterior part is called spinal cord.

In human being, central nervous system include brain and spinal cord.Peripheral nervous system include cranial nerve and their branches,spinal nerve and their branches.