Annelida.

Aschelminthes.

In coelomates the mesoderm is lining the body cavity, while in acoelomates the mesoderm is present in small pouches.

Closed type digestive system.

(a) Forelimbs are modified into wings.
(b) Bones are pneumatic for weight reduction.

Cellular level of organisation

In Urochordata, notochord is present only in larval tail, while in Cephalochordata, it extends from head to tail region and is persistent throughout their life.

Snakes have strong sense of smell because, their forked tongue is frequently linked to pick up smell bearing molecules from the air or ground and are inserted with special sense organs called Jacobson's organs in the roof of the mouth to identify the smell

Fishes have following sense organs to sense their external environment
(i) Ear is formed of only one internal ear having three semicircular canals
(ii) Olfactory sacs (nasal chambers) do not open in buccal cavity as internal nares are absent
(iii) Lateral line sensory system is present to note the changes in surrounding water

The cnidarians complete their life cycle through two phases,i.e., asexually reproducing polyp phase and sexually reproducing medusa phase.Those cnidarians which exist in both forms exhibit alternation of generation(metagenesis).

Birds respire through lungs (pulmonary respiration).The lungs have air sacs which help indouble respiration and act as internal cooling agents.Sound producing organ is syrinx (at the base of trachea) and larynx has no vocal cords

Annelid characters Peripatus have jointed parapodia (legs), haemocoel, trachae for respiration and head with a pair of compound eyes and antennae.

Internal shell-In Sepia(cuttle fish),Loligo(squid)
Shell absent-Octopus(devil fish)

Amphids are pits commonly having olfactory chemoreceptors.
Phasmids are glandulo-secretory porous sensory structures.

Digestive system having only a single opening to the outside of the body that serves as both mouth and anus, called incomplete digestive system while a complete digestive system has two separate openings, i.e mouth and anus.