CIONA

Contents hide

CLASSIFICATION OF CIONA

PHYLUM :- CHORDATA (Notochord, dorsal tubular nerve cord present and gill slits present)

GROUP :- ACRANIATA (No head, cranium or brain)

SUB-PHYLUM :- UROCHORDATA (Marine. Body covered by a thick test. Notochord present only in larval tail)

CLASS :- ASCIDIACEA (Test with scattered muscles. Many pharyngeal gill-slits. Bottom-dwelling).

ORDER :- ENTEROGONA (Neural gland ventral to nerve ganglion. Gonad one).

FAMILY :- CIONIDAE

Genus : Ciona

Ciona resembles with Herdmania and measures 9 to 12 cm in length.
Body of the animal cylindrical, tubular, transparent and longer than broad.
It contains 8-lobed branchial siphon and 6-lobed atrial siphon anteriorly.
Branchial and atrial siphons contain mouth and atriopore respectively. Tentacles present at the base of branchial siphon. One left side nerve ganglia present.
Body covered by a transparent test and through the test, prominent thick longitudinal muscle bands can be seen. Below test is mantle.
Alimentary canal is complete, V-shaped and consists of pharynx, oesophagus, stomach and intestine and it lies in the epicardial cavity. Heart is surrounded by pericardium.
Different parts of gut occupy the same topographical parts as that in Herdmania. The gill-slits are rectaagular. The dorsal lamina present. Intestine contains typhlosole. Running parallel with the endostyle are right and left ciliated bands which continue posteriorly as retropharyngeal bands.
Gonads lie in the loop of intestine. Gonads open by genital pore through the genital duct.
Longitudinal muscle bands are clearly seen.
Fertilization external and the floating egg develops into an Oikopleura-like larva which settles and undergoes metamorphosis to change into adult.

Ciona is hermaphroditic and protogynous. The blood of Ciona is rich in a green pigment, called as haemovanadin, containing vanadium produced by vanadocytes. The pigment probably does not take part in oxygen transport. Ciona intestinalis is the common species.