CIONA

Contents hide

1) Introduction

2) Classification of Ciona

3) Geographical distribution

4) Habit and habitat

5) General Characteristics of Ciona

6) Ecological Importance

7) Conservation Status

8) Special features

9) Identification

Introduction

Ciona is a genus of sea squirts, marine invertebrates belonging to the subphylum Tunicata (Urochordata) within the phylum Chordata. Often called “sea vase” due to their vase-like appearance, species in this genus are sessile filter feeders, thriving in marine environments around the world. They are characterized by their translucent, soft-bodied tunics, which are made of a cellulose-like substance called tunicin.

Ciona is of significant biological importance because it exhibits key features of chordates, such as a notochord and dorsal nerve cord during its larval stage, making it an important model organism in evolutionary and developmental biology. The genome of Ciona intestinalis, one of the most studied species, has been fully sequenced, offering invaluable insights into chordate evolution and genetics.

Classification of Ciona

Phylum :- Chordata (Dorsal tubular nerve cord, notochord 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 :- Phlebobranchia (Neural gland ventral to nerve ganglion. Gonad one.)
Family :- Cionidae
Genus :- Ciona

Geographical distribution

Found in temperate and tropical marine environments worldwide.
Commonly inhabit coastal waters, harbors, and estuaries.
Often found attached to hard substrates like rocks, docks, and ship hulls.
Ciona is a common mono-ascidian found in shallow waters.

Habit and habitat

Habit:
- Sessile as adults, permanently attached to substrates.
- Free-swimming larvae that settle and metamorphose into sessile adults
Habitat:
- Found in shallow marine environments, especially where there is abundant plankton.
- Thrive in polluted or nutrient-rich waters, sometimes regarded as biofouling organisms
- Solitary and sedentary animal found in shallow waters attached with rocks

General Characteristics of 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 rectangular. 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

Ecological Importance

Filter Feeding: Contribute to water clarity and quality by filtering plankton and organic particles.
Nutrient Cycling: Play a role in nutrient recycling by consuming and breaking down organic matter.
Habitat for Microorganisms: Provide surfaces for colonization by algae, bacteria, and other microorganisms.
Prey Species: Serve as a food source for predators like fish, starfish, and crustaceans.

Conservation Status

Not globally threatened but can face localized impacts from:
- Habitat degradation and pollution.
- Competition with invasive species in some regions.
- Biofouling control measures that may remove them unintentionally

Special features

Chordate Characteristics in Larvae: Larvae possess a notochord and dorsal nerve cord, making them key to understanding chordate evolution.
Model Organism: Ciona intestinalis is extensively used in genetic, developmental, and evolutionary studies.
Tunic Composition: Their outer tunic contains tunicin, a cellulose-like material unique to tunicates.
Efficient Filter Feeding: Can filter large amounts of water, aiding in plankton population control.
Rapid Metamorphosis: Transition from free-swimming larvae to sessile adults within a few hours.
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.