Development involves an indirect or larval form in which of the following? (1) Pleurobrachia (2) Euspongia (3) both (1) and (2) (4) none of the above

Solution: (3) both (1) and (2)

Phylum – Ctenophora
Ctenophores, commonly known as sea walnuts or comb jellies
are exclusively marine, radially symmetrical, diploblastic
organisms with tissue level of organisation. The body bears
eight external rows of ciliated comb plates, which help in
locomotion (Figure 4.8). Digestion is both extracellular and
intracellular. Bioluminescence (the property of a living
organism to emit light) is well-marked in ctenophores. Sexes
are not separate. Reproduction takes place only by sexual
means. Fertilisation is external with indirect development.
Examples: Pleurobrachia and Ctenoplana.

Phylum – Porifera

Members of this phylum are commonly known

as sponges. They are generally marine and mostly

asymmetrical animals (Figure 4.5). These are

primitive multicellular animals and have cellular

level of organisation. Sponges have a water

transport or canal system. Water enters through

minute pores (ostia) in the body wall into a central

cavity, spongocoel, from where it goes out

through the osculum. This pathway of water

transport is helpful in food gathering, respiratory

exchange and removal of waste. Choanocytes

or collar cells line the spongocoel and the canals.

Digestion is intracellular. The body is supported

by a skeleton made up of spicules or spongin

fibres. Sexes are not separate (hermaphrodite),

i.e., eggs and sperms are produced by the same

individual. Sponges reproduce asexually by

fragmentation and sexually by formation of

gametes. Fertilisation is internal and development

is indirect having a larval stage which is

morphologically distinct from the adult.

Examples: Sycon (Scypha), Spongilla (Fresh water sponge) and Euspongia

(Bath sponge).