OIKOPLEURA

Contents hide

1) Introduction

2) Classification of Oikopleura

3) Geographical distribution

4) Habit and habitat

5) Comments on Oikopleura

6) Ecological Importance

7) Conservation Status

8) Special features

9) Identification

Introduction

Oikopleura is a genus of small, free-floating, pelagic tunicates belonging to the class Appendicularia. These fascinating marine organisms are noted for their unique ability to produce intricate mucus houses, which they use to filter microscopic food particles from the water. Despite their small size, Oikopleura species play a vital role in marine ecosystems as a significant component of zooplankton.

The mucus houses of Oikopleura are marvels of biological engineering, acting as a highly efficient filtration system. When clogged, the house is discarded, contributing to marine snow, which helps in carbon sequestration by transporting organic material to the deep ocean. Their rapid reproduction and short life cycle allow them to respond dynamically to changes in plankton populations, making them an important indicator of oceanic health.

Classification of Oikopleura

Phylum :- Chordata (Dorsal tubular nerve cord, notochord and gill-slits present.)
Group :- Acraniata (No head, cranium or brain)
Sub phylum :- Urochordata (Tunicata) (Marine. Body covered by a thick test. Notochord present only in larval tail.)
Class :- Appendicularia (Test with circular muscle bands. Free-living, pelagic.)
Order :- Copelata (Incomplete muscle bands. No larva.)
Family :- Oikopleuridae
Genus :- Oikopleura

Geographical distribution

Found in all oceans, with a preference for temperate and tropical waters.
Often observed in nutrient-rich areas such as upwelling zones.
Distributed widely in the epipelagic and mesopelagic zones.

Habit and habitat

Oikopleura lives in upper levels of the sea and swims by contractions of the bent tail. Some are brilliantly pigmented (coloured) with orange or violet and when abundant, may colour the water. It is a neotenous and planktonic tunicate.

Habit:
- Free-floating and planktonic.
- Exhibits both solitary and colonial forms during its life cycle.
Habitat:
- Lives in open ocean waters, thriving in regions with abundant plankton.
- Can be found at various depths, primarily in the upper water column.

Comments on Oikopleura

Oikopleura is minute and microscopic measuring about 2 mm.
Animal lives in a ‘house or test’ made by secretion from a special part of the skin, c~ed as oikoplastic epithelium. Body wall contains test and ectoderm.
It has larva-like appearance comprising body, tail and persistent notochord.
Body narrows towards mouth and expands posteriorly dorsoventrally. The caudal appendages have undergone torsion of 90°.
Tail is a broad structure, which rests at an angle to the rest of the body. It has notochord, nerve cord, broad tail fin and 7 to 12 striped muscle cells.
Movement of the tail produces water current. Food particles are filtered by an elaborate arrangement in the house. Water enters into house by a pair of posterior filtering windows and is passed through filter pipes in front of mouth. Minute flagellates are sucked by mouth.
Dorsal lamina and tentacles are absent. Otocyst present.
Mouth leads into alimentation comprising of pharynx, oesophagus, stomach and intestine. Pharynx has gill-slits opening to outside. The food consists of microorganisms. Sense organs, oral gland, otocyst, tail ganglous, atrial opening muscle bonds epipharyngeal ridge, otocyst, epipharyngeal ridge.
Protandrously hermaphroditic, kidney-shaped two testis. Left testis encloses, ovary.
Internal space filled by haemocoelomic lacunae having blood circulation by a transport heart.

Ecological Importance

Efficient Filter Feeder: Removes microscopic plankton and organic particles from the water, helping maintain ecosystem balance.
Carbon Cycling: Discarded mucus houses sink to the ocean floor, contributing to carbon sequestration and nutrient transport.
Food Web Role: Serves as prey for larger zooplankton, fish, and other marine organisms.
Indicator Species: Their populations respond quickly to changes in environmental conditions, providing insights into oceanic health.

Conservation Status

Oikopleura species are not currently listed as endangered or threatened.
Their populations are influenced by oceanic conditions, including temperature, nutrient availability, and pollution.

Special features

The general structural organization resembles with a typical ascidian tadpole and it can be very safely concluded that these forms have arisen from tunicates by the acceleration of the fate of development of alimentation and reproductive systems, so that the metamorphosis and the adult stage are omitted and it shows phenomenon of neoteny or paedomorphosis.
The anatomy of the animal suggests that larvaceans are not like the ancestral chordates but are neotenic descendants of the sessile ancestors resembling Urochordata.
Mucus House Production:
- Continuously builds and discards intricate mucus houses for feeding.
- Each house filters large volumes of water, extracting food efficiently.
Rapid Reproduction: Short life cycles and high reproductive rates enable quick population growth in favorable conditions.
Transparency: Almost completely transparent, providing camouflage in the open ocean.
Adaptability: Can thrive in varying environmental conditions, making them resilient and widespread.