B.

the pattern of cleavage

The mode of cleavage is determined by the amount of yolk and its distribution.
(I) Holoblastic - The cleavage, in which the segmentation lines pass through the entire egg, dividing it completely, eg, frog, human egg, etc.
(II) Meroblastic -The lines of segmentation do not completely pass through the egg and remain confined to a part of the egg, eg , insects, birds, reptiles.

D.

Petromyzon

Petromyzon(the lamprey) belongs to the section Agnatha of the sub-phylum-Vertebrata. They have long, greenish brown, cylindrical body with smooth scaleless, slimy skin, jawless mouth, etc. They lay eggs in freshwater but their ammocoete larvae(lower) after metamorphosis return to the ocean. 

B.

Torpedo

Torpedo is a marine cartilaginous fish which produces 8-220 volt electric charge (current) depending on species. Their electric organs are modified lateral muscle plates innervatted by carnrial nerves.
Trygon (sting ray) resembles electric ray in many aspects but is devoid of electricity discharging (or producing) organs. 
Scoliodon (dog fish) is known for its great sense of smell. Pristis or common saw fish (also known as carpenters shark) is charactesised by a long, narrow, flattened rostrum lined with sharp transverse teeth to resembles a saw.

C.

commensalism

This type of mutualisn to called protocooperation. In this type, the sea anemone grows on the back of the hermit crab.  It protects the crab with the help of its nematocysts. Ectoparasites live on the outside of host., e.g., Human body louse. In this interaction, the parasite gets the benefits at the expense of the host.
Commensalism is an association between organisms in which one or both the species are benefitted and neither species is harmed. In amensalism, one species is harmed whereas the other is unaffected. Predation parasitism and commensalism share a common characteristic, the interacting species live closely together.

C.

Pharynx with gill slits

Pharyngeal gill slits are present in hemichordates as well as in chordates. Notochord is present in chordates only. Ventral tubular nerve cord is characteristic feature of non-chordates