PHYLUM-
HEMICHORDATA
Hemichordata (Hemi — half; chordata — notochord)
earlier placed as a subphylum under Phylum—Chordata
But, now it is considered as a separate phylum under
Non-chordata. These are also called half chordates. This
phylum consists of a small group of worm-like animi’
General Features
Some important general features of
phylum—Hemichordata are discussed below
(i) Habit and Habitat They are exclusively
marine and mostly live in burrows.
(ii) Symmetry and Body Organisation They
are bilaterally symmetrical and
triploblastic. They have organ system level
of organisation.
(iii) Body Form They are soft bodied,
cylindrical and unsegmented body is
divisible into proboscis, collar and trunk.
The body cavity is true coelom. A true
notochord is absent.
(iv) Digestive System Digestive system is
complete.
(v) Respiraton Respiration occurs through
several pairs of gill slits or through the
general body surface.
(vi) Circulatory System is open type. It
contains a dorsal heart.
(vii) Excretory System It consists of proboscis
gland.
(viii) Nervous System It is primitive, consists
mainly of an intraepidermal nerve plexus.
(ix) Sensation Sensory cells of the epidermis act
as sense organs.
(x) Reproduction It is mostly sexual. Sexes are
separate. Development is indirect with
tornaria larva.
Note
Subphylum—Hemichordata is the connecting link
between echinoderms and chordates.
e.g., Balanoglossus (acorn or tongue worm),
Saccoglossus, Cephalodiscus, etc.