CLASSIFICATION OF DOLIOLUM
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 :- THALIACEA (Test with circular muscle bands. Free-living, pelagic).
ORDER :- DOLIOLIDA (Complete ring of muscle bands or cyclomyaria present).
FAMILY :- DOLIOLIDAE
Genus : Doliolum
- Doliolum is distributed in tropical and sub-tropical surface water.
HABIT AND HABITAT
Doliolum is a marine, pelagic, free-living and solitary tunicate swimming by forcing water out of atrium after each powerful muscle contraction.
GENERAL CHARACTERSTICS OF DOLIOLUM
- Doliolum is commonly called as chain tunicate. It measures I to 1.5 cm.
- It shows polymorphism and exists in two phases:
- Gonozooid or solitary phase, and
- Oozooid or gregaria phase.
- Fully grown oozooid has a barrel-shaped transparent body, a large mouth, branchial and atrial apertures at opposite ends and 8 complete muscle bands. Body covered by test and below test is mantle :
- Edges of above lobes contain sensory lobes, 10 on branchial and 12 on atrial side,
- Mouth leads into pharynx with a few stigmata. It has ventral endostyle, and peripharyngeal bands. Viscera consists of oesophagus, stomach, intestine, digestive gland, heart and neural complex,
- Oozooids reproduce asexually by stolon budding.
- Life-cycle is peculiar consisting of 1. Sexual form 2. Tailed larva developed sexually 3. First asexual form 4. Second asexual forms (Phorozooid) developed on cadophore and buds developed on stolon.
- The animal moves through water by jet propulsion. The contraction of the muscle bands drives water backwards out of atrial sac and so propels the animal.
- Gonozooid can be differentiated from oozooid in having 12 and 10 sensory lobes in branchial and atrial openings, 8 muscle bands, cadaphore and otocyst absent and with testis and ovary.
- Doliolum is a favourite tunicate. The fertilized egg develops into a free-swimming tailed larva somewhat like that of an ascidian. The larva metamorphoses into a barrel-shaped adult ‘nurse’ stage that by asexual reproduction gives rise to several individuals. Some even produce sperm and ova.
- The animal contains 8 complete circular muscle bands and above features, hence it is Doliolum