IDENTIFICATION (with reason) OF Obelia sp. (B.Sc. ZOOLOGY_CCF-CC5_SEM4)

  Identifying features are:

1. Multicellular heterotroph.
2. embryonic development, preceded by heterogametic fertilization.

            Hence, the specimen belongs to the Kingdom Animalia.

1. Soft-bodied, polymorphic mesozoa with radial and biradial symmetry.
2. Ectoderm & endoderm separated by a noncellular mesoglea.
3. Single gastrovascular cavity.
4. Polypoid zooids which possess single body cavity,the coelenteron, with a solitary mouth.
5. Mouth is guarded by a circlet of tentacles.
6. Outer body wall possesses numerous cnidoblasts (or cnidocytes).

                  Hence, the specimen belongs to the Phylum Cnidaria .

1. Presence of polypoid or medusoid or both forms of zooids.
2. Polypoid forms are surrounded by a chitinous or calcareous skeleton.
3. Polyp without ridges or gastric filaments.
4. Undivided gastrovascular cavity.
5. gonads ectodermal.
6. Presence of non-cellular mesoglea.

                 Hence. the specimen belongs to the Class Hydrozoa.

1. Presence of hollow, thread-like, horizontal hydrorhiza and vertical hydrocaulus.
2. Hydrocaulus bears polypoid zooids on either side of it.
3. Tree like branched,trimorphic colony.
4. Gastrozooid barrel-shaped bearing hypostome with mouth & tentacles at the distal end.
5. Blastostyle bears medusae.
6. The entire colony is covered by an inner living coenosarc and an outer chitinous perisarc.
7. Presence of manubrium encircled by 24 solid, long, tapering, filliform tentacles.

              Hence, the specimen seems to be Obelia sp. (Polyp stage).

1. Umbrella-like,free swimming zooid form.
2. A concave subumbrella and a convex exumbrella surface is present.
3. Manubrium, bears mouth, hangs from the centre of the subumnbrella.
4. Margin thickened to form a velum.
5. Tentacles of the velum bear sense organs at the base.
6. A gastric cavity, four radial canals and a circular canal constitute the gastrovascular system.
7. Gonads are four rounded, hang from the subumbreller surface at about the middle of radial canals.

               Hence, the specimen seems to be Obelia sp. (Medusa stage).

Systematic Position (Ruppert & Barnes 1994)

Kingdom: Animalia

  Phylum: Cnidaria

     Class: Hydrozoa

         Genus: Obelia