Herdimania is a sedendentory animal body is divisible into Body proper Foot adn Test

1. Dr.S.J.M.Prathap Kumar
Lecturer in Zoology
Govt.College for Women (A)
Guntur

2. Herdimania Structure

3. Shape
The body of Herdmania pallida is roughly oblong in outline, narrower
at its attached than at its free end.
At its free end, it is provided with two external openings the branchial
and atrial apertures.
Size
The average size of the adult is about 9.5 cm long, 7 cm broad and
4 cm thick.
Older animals may even attain to a size of 12 x 8 x 4 cm.
while an exceptionally large measures 13 x 8 x 4.5 cm.

4. Colour
The general colour of the body in a fresh specimen is pink.
The presence of bright red patches, formed of terminal knobs
(ampullae) in the blood vessels of the test, is a characteristic feature of
Herdmania. Body Divisions
The body is divided into two parts, body proper and foot, and the entire
animal is covered by the test.
Body Proper
 It is the distal free portion of the body.

5.  The branchial aperture marks the anterior end of the animal
consequently the opposite end attached to the substratum is the posterior
end.
 The side on which the atrial aperture is placed marks the dorsal side of
the body, which is very limited.
 The side opposite to that on which the atrial opening is placed and
which is partly attached to the substratum is ventral side which is
extensive.
 The branchial and atrial apertures are situated on short protuberances
of the body called branchial and atrial siphons respectively.

6.  When fully extended, the atrial siphon is longer than the branchial. In
a large-sized animal the atrial siphon measures about 1.5 cm, while the
branchial siphon is only about 1 cm in length.
 The atrial siphon is almost always directed upwards, the atrial aperture
being more or less upright, while the branchial siphon is always bent a
little outwards and the branchial aperture opens more or less laterally,
always directed away from the atrial aperture.
 The average diameter of the branchial aperture, when fully expanded,
is about 2 cm and that of the atrial aperture about 1.2 cm.

7.  At the base of branchial siphon, there is a ring of long branchial
tentacles, while at the base of the atrial siphon there is a ring of slightly
serrated folds which constitute the atrial tentacles.
The test of the siphons is very elastic and can contract to close the
apertures at the slightest disturbance of sea water.
Foot
The foot, when present varies in character according to the nature of
the substratum which the animal inhabits. If the substratum is of fine
sand, the foot has an oval shape and a smooth surface and the test is quite
hard in consistency. But if the substratum consists of coarse and the
broken shell-pieces, the foot is irregular in outline and more or less soft
in consistency.

8. Test or Tunic
The test is soft and leathery. It is more or less transparent in a young
animal, but in an adult becomes usually opaque.
The general surface of the test is much corrugated all over with lines,
some shallow and others fairly deep, running in a criss-cross manner.
The external covering surrounding the animal is a leathery, translucent
test or tunic composed of tunicin, a substance akin to cellulose of plants.
The foot is made entirely of test. It acts as a receptor as well as a
respiratory organ. It is about 4-8 mm thick. It is ectodermal in origin.

9. The test has
 A clear matrix in which is embedded, Cells of various shapes,
Interlacing fibrils, Calcareous spicules and Branching vascular vessels.
 Matrix: It is gelatinous and made of a polysaccharide called
tunicine.
 Cells: These are mesodermal in origin and have migrated into the
test. Large eosinophilous cells, Small eosinophilous cells, Small
amoeboid cells, Granular cells, Round vacuolated cells, Nerve cells with
several processes and Squamous epithelial cells.
 Interlacing fibrils: These form a fine network in the test and
resemble with smooth muscle fibres.

10.  Calcareous spicules: Herdmania has large number of calcareous
spicules of two types. All the spicules bear several equidistant rings of
minute spines all pointing in the same direction all along their length
 Blood vessels: These blood vessels form a network in the test and end
in bulb-like dilations called vascular ampullae. The vascular ampullae
form vascular areas of bright red patches on the test. Vascular vessels and
ampullae transport blood and, thus bring food to the test; they also act as
accessory respiratory organs. The ampullae are also receptor organs.