Practical No.

03

Aim: Museum study of phylum Coelenterata: Hydra,

Physalia, Aurelia, Metridium

Coelenterata (Greek, koilos-hollow; enteron -intestine) includes

primitive multicellular animals containing gastrovascular cavity.

General characters:
1. Coelenterates are metazoan (multicellular) animals with tissue grade
of organization. They are aquatic, mostly marine and very few are
fresh water forms.

2. They are sedentary or free swimming and solitary or colonial

organisms.

3. Animals are radially or biradially symmetrical with a central

gastrovascular cavity communicating with exterior by the mouth.

4. Exoskeleton is either chitinous or calcareous.

5. They are diploblastic with two cellular layer i.e. outer epidermis and
inner gastrodermis and both are separated by gelatinous mass called
mesoglea.

6. Individuals are either attached polyps or free swimming medusa

and shows polymorphism.
7. Mouth of polyps and bell margin of medusae often encircled by
short and slender tentacles.

8. Tentacles bear the stinging cells or cnidoblast cells called as

nematocyst which serves for adhesion, food capturing, injecting
poison, offense and defense.

9. Body cavity, respiratory, circulatory and excretory systems are

absent.

10. Single internal cavity lined with gastrodermis called gastrovascular

cavity or coelenteron.

11. Digestion is intracellular as well as extracellular (Contact digestion).

12.Nervous system primitive, consists of nerve net. Ocelli and

statocysts are sensory organ.

1. Hydra
Systematic Position:
Phylum: Coelenterata: Acoelomate, diploblastic multicellular
organisms with tissue grade organization.
Class: Hydrozoa Aquatic solitary or colonial. Medusae
with true velum
Order: Hydroida Polyploid stage is predominant.
Medusae short lived.
Suborder: Anthomedusae Hydrotheca and gonotheca absent.
Statocysts absent
Family: Hydridae Exclusively fresh water group
represented by solitary hydroid.
Genus: Hydra
Salient Features:

1. It is fresh water sedentary organism attached to substratum.

2. Hydra is elongated, elastic cylindrical plant like organism
measuring about 1-3 cm in length.
3. Basal or proximal end is attached to substratum with basal disc
while free distal end or oral end bears the mouth situated on
conical elevation called as hypostome.
4. Hypostome is encircled by 6 to 10 tentacles which are hallow,
slender finger like projection provided with nematocysts.
5. Body wall encloses gastrovascular cavity which extends into the
tentacles.
6. Hydra is hermaphrodite animal gonads appear as buds; Testis lie
near oral end, while ovaries near the base.
7. Asexual reproduction by budding and sexual by gametes
formation.
2. PHysalia (Portuguese man of war):

Phylum: Coelenterata Acoelomate, diploblastic multicellular

organisms with tissue grade body
Organization.

Class: Hydrozoa Aquatic solitary or colonial animals.

Medusae with velum.

Order: Siphonophora Pelagic colonial free swimming or

floating forms and highly polymorphic.
Polyps without oral tentacles. Medusae
incomplete and rarely freed.

Suborder: Physophorida Upper end of colony bears a gas filled

float or pneumatophore.
Family: Physaliidae Large oceanic siphonophores include
Portuguese man-of-war.
Genus: Physalia

Salient Features:
1. Physalia forms huge free floating pelagic colony known as Portuguese
man of war.

2. It has a characteristic huge bladder like brightly coloured float or

pneumatophore. The upper surface of float is produced into crest or
sail.

3. From underside of pneumatophore hangs dactylozoids with

tentacles, gastrozooids without tentacles and branching blastostyles.
4. Tentacles have a great capacity for contraction and expansions.

5. Tentacles are large and bear stinging batteries or nematocysts to kill

fishes and preys.

6. Colony exhibit polymorphism and the division of labor.

fig PHysalia
3. aurelia (Jelly fisH/umbrella):

Systematic Position:
Phylum: Coelenterata Multicellular organisms with tissue
grade body organization

Class: Scyphozoa Exclusively marine, solitary forms.

Medusa large umbrella shaped without
true velum. Polyp stage reduced or
absent. Gastrovascular cavity with
gastric pouches and gastric filaments.

Order : Discomedusae/ Semaeostomeae

Flat saucer or disc like umbrella. Eight
tentaculocysts present. Square shaped
mouth extending into 4 long oral arms.
Gastric pouches and filaments are
absent.

Family: Ulmaridae Simple or branched radial canal. With /

without subgenital pits.

Genus: Aurelia
Salient Features:

1. They are easily recognized by their soft bell or umbrella shaped

body with four red or purple horseshoe shaped gonads on its
upper surface and four long narrow oral lobes hanging
downwards from lower surface.
2. The medusa is bowl or saucer shaped having tetramerous radial
symmetry.

3. Medusa or umbrella has a slightly convex upper surface known as

exumbrellar surface and a lower concave the subumbrellar surface.

4. Manubrium is short and inconspicuous which hangs down from

center of subumbrellar surface. At its free distal end a square
mouth is present. From corner of the mouth, hang 4 oral arms.

5. Margin of the umbrella is divided into eight lobes by notches which

contains tentaculocyst enclosed by a pair of marginal lappets.
 Fig. Aurellia
6. Many short hallow tentacles are present on whole margin of
umbrella and are called as marginal tentacles.

7. It is unisexual. The four gonads testes or ovaries lie on the floor of

gastric pouch.
4. metridium (sea anemone):

Systematic Position:
Phylum: Coelenterata Acoelomate, diploblastic multicellular organisms
with tissue grade body organization

Class: Anthozoa Well known as flower animals. Exclusively marine

solitary or colonial. All polypoid forms, medusae are
absent. Gastrovascular cavity subdivided by 8 or
more septa or mesenteries. Hexamerous symmetry.

Subclass: Hexacorallia Tentacles usually unbranched, numerous but never

eight. monomorphic. Gullet with two siphonoglyphs.
Polyps usually monomorphic

Order: Actiniaria Solitary sea anemone with large sized muscular

body often with an aboral pedal disc. Skeleton is
absent. Numerous tentacles.

Family: Metridiidae Known as sea anemones. Mesogleal sphincter

muscles present. Mesenteries not divided into
macronemes and micronemes.

Genus: Metridium

Salient Features:
1. Metridium is solitary marine sea anemone found in shallow water, mostly
attached to rocky substratum with pedal disc.
2. Body is short, cylindrical and radially symmetrical, divisible into three
regions viz. pedal disc, column and oral disc.

3. Column is differentiated into two portion, distal thin walled short capitulum
and proximal thick walled scapus by the groove and collar.
4. Oral disc is slightly convex and bears a slit like central mouth. Mouth is
encircled by large number of hallow tentacle forming a sort of crown.

5. Mouth leads into short gullet which opens into gastrovascular cavity.

6. Sexes are separate. Gonads are borne on the mesentries.

7. Asexual reproduction by fragmentation and budding.

Fig. Metridium dianthus