DOLIOLUM

Contents hide

1) Introduction

2) Classification of Doliolum

3) Geographical distribution

4) Habit and habitat

5) Comments on Doliolum

6) Ecological Importance

7) Conservation Status

8) Special features

9) Identification

Introduction

Doliolum is a genus of small, free-swimming, barrel-shaped tunicates belonging to the class Thaliacea within the subphylum Tunicata (Urochordata) of the phylum Chordata. These pelagic organisms are found in oceans worldwide, typically in warm and temperate regions. Doliolum is known for its streamlined body, which is well-adapted for efficient swimming, and its fascinating alternation of generations in its life cycle.

As a filter feeder, Doliolum plays an essential role in marine ecosystems by consuming phytoplankton and small particles from the water. Its life cycle involves both sexual and asexual stages, contributing to rapid population growth in nutrient-rich environments. These tunicates are part of the planktonic community and serve as an important link in the marine food web.

Classification of Doliolum

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 :- Thaliacea (Test with circular muscle bands. Free-living, pelagic.)
Order :- Doliolida (Compact tubular colony. No larva. Muscle bands at end of body.)
Family :- Doliolidae
Genus :- Pyrosoma

Geographical distribution

Doliolum is distributed in tropical and sub-tropical surface water.
Primarily inhabits open ocean waters in the epipelagic zone but may occur at greater depths in the mesopelagic zone.
Distribution often influenced by ocean currents and plankton availability.

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.

Habit:
- Free-swimming and planktonic.
- Exists as part of the holoplankton community.
Habitat:
- Inhabit open oceans, particularly nutrient-rich regions.
- Thrive in water columns with abundant phytoplankton and zooplankton.

Comments on 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
- 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.

Ecological Importance

Filter Feeding: Plays a vital role in controlling phytoplankton populations by consuming microscopic algae and particles.
Carbon Sequestration:
- Contributes to the biological pump by transporting organic carbon to deeper ocean layers through fecal pellets.
Nutrient Cycling:
- Helps recycle nutrients in the ocean, supporting the productivity of other marine organisms.
Food Web Contribution: Serves as prey for larger marine organisms such as fish and jellyfish.

Conservation Status

Doliolum species are not considered endangered or threatened.
Their populations can fluctuate due to environmental factors, including changes in water temperature, salinity, and nutrient availability.

Special features

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 adn1t ‘nurse’ stage that by asexual reproduction gives rise to several individuals. Some even produce sperm and ova
Alternation of Generations: Exhibits a complex life cycle with sexual and asexual phases, allowing for rapid population expansion.
Efficient Locomotion: Uses muscular contractions to propel itself through the water, a unique feature among planktonic organisms.
Filter Feeding Efficiency: Capable of processing large volumes of water, helping to maintain water clarity.
Adaptability: Rapidly adjusts to changes in environmental conditions, enabling survival in diverse oceanic regions.
Transparent Body: Almost entirely transparent, aiding in camouflage and reducing predation.