Study of tonana larva

Tornaria larva is typical in the life-history of hemichordates. Examine the permanent slide and note the following features:

I. The tornaria larva usually has an ovoid bell-shaped body which is extremely transparent. It swims freely in water.

2. The body of tornaria larva is variously folded into lobes.

3. The margin of lobes is bordered by cilia:

4. There are two circlets of cilia.

(i) an oral circlet of cilia surrounding the mouth or circumoral ciliary band (often not clearly visible in slides).

(ii) a posterior ciliated band or telotroeh that occurs as a ring in front of the anus.

5. The alimentary canal is very simple having a mouth, oesophagus, stomach and intestine.

6. The mouth is ventral and anus is posterior and terminal.

7. Water sac is also found in the body of larva which opens outside through the dorsal pore, the hydropore.

8. An apical sensory plate with two eye spots and a of tuft of sensory hairs occurs at the centre of the narrow anterior end.

(Tornaira larva feeds on minute organisms and when full grown, metamorphoses into adult.)