BRANCHIOSTOMA LANCEOLATUM

Contents hide

1) Introduction

2) Classification of Branchiostoma lanceolatum (Amphioxus lanceolatus)

3) Geographical distribution

4) Habit and habitat

5) Comments on Branchiostoma lanceolatum (Amphioxus lanceolatus)

6) Ecological Importance

7) Conservation Status

8) Special features

9) Identification

Introduction

Branchiostoma lanceolatum (Amphioxus lanceolatus)), commonly known as the European lancelet, is a small, fish-like marine organism belonging to the subphylum Cephalochordata in the phylum Chordata. Often regarded as a “living fossil,” this species holds significant importance in evolutionary biology as it provides insight into the transition from invertebrates to vertebrates.

Found in shallow coastal waters, Branchiostoma lanceolatum spends most of its life buried in sandy substrates with only its anterior end exposed. It feeds by filter-feeding, drawing in water and capturing planktonic particles through its gill slits. Its simple body plan, with a notochord extending the length of the body, makes it an excellent model for studying chordate characteristics

Classification of Branchiostoma lanceolatum (Amphioxus lanceolatus)

Phylum :- Chordata (Dorsal tubular nerve cord, notochord and gill-slits present.)
Group :- Acraniata (No head, cranium or brain)
Sub phylum :- Cephalochordata (Marine. Body covered by a thick test. Notochord present only in larval tail.)
Class :- Leptocardii (Test with circular muscle bands. Free-living, pelagic.)
Family :- Branchiostomatidae
Genus :- Branchiostoma ((Amphioxus)
Genus :- lanceolatum

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

Amphioxus (Branchiostoma lanceolatum) burrows in clean shifting and shallow shore waters leaving only its anterior end protruded. For most of the times, it remains buried in the sand but in darkness it swims very rapidly by lashing movements of the tail. It is a ciliary feeder.

Habit:
- Semi-sedentary, burrowing into sandy substrates.
- Filter-feeding organism that remains stationary for extended periods.
Habitat:
- Shallow coastal waters with sandy or muddy bottoms.
- Often found in regions with strong currents that provide a steady supply of plankton.

Comments on Branchiostoma lanceolatum (Amphioxus lanceolatus)

Commonly called as lancelet.
It was first discovered by Pallas (1778).
Adult is less than 5 cm long and has superficially fish-like structural make up.
Body is elongated, flattened, non-pigmented and pointed at both ends as the name implies. Anterior end projects forwards as the rostrum.
Dorsal, ventral and caudal fins are low and continuous. There are 2 lateral fins or metapleural folds. Dorsal fin has fin rays.
Ventral mouth is guarded by oral hood containing oral cirri.
Atriopore is median and ventral. Anus on left side.
Myotomes are arranged on both sides of die body as metamerical blocks of striated muscle fibres separated by V-shaped partitions called as myosepta or myocommata.
Notochord is an axial skeletal rod extending from anterior to posterior end. Nerve cord lies just above the notochord.
Gonads 26 pairs, metamerically arranged on pharynx. The two sexes are separate but without sexual dimorphism.

Ecological Importance

Nutrient Cycling: Contributes to nutrient dynamics in benthic ecosystems by filtering organic particles.
Food Web Role: Acts as a prey species for fish and other marine predators, linking primary producers to higher trophic levels.
Indicator Species: Sensitive to environmental changes, making it a valuable indicator of ecosystem health and sediment quality.

Conservation Status

Not currently listed as endangered or threatened by the IUCN.
Populations are stable but may be affected by coastal pollution, habitat destruction, and sediment disruption.

Special features

Although eyes, nose, ears, jaws and appendages are completely absent, yet Amphioxus is of special zoological interest, because it shows three distinctive characters of the phylum Chordata in simple form i.e., presence of notochord, nerve cord and gill-slits. It is considered to resemble some ancient ancestor of the phylum Chordata. Further Amphioxus shows combination of primitive, specialized and degenerate features.
Primitive features include notochord extending into snout, segmented myotomes, straight intestine, absence of jaws and paired fins, ciliary feeding and no specialized heart. The specialized features comprise of elaborate velum and oral hood and several gill-slits. The reduced brain and sense organs are degenerate features.
Evolutionary Importance: Possesses primitive chordate features such as a notochord, pharyngeal slits, and dorsal nerve cord, offering insights into vertebrate evolution.
Simple Body Plan: Lack of a true brain, paired fins, or jaws, highlighting its position as a basal chordate.
Efficient Filter Feeding: Uses its pharyngeal slits and cilia to filter plankton and organic particles from water.
Transparent Body: Its translucent body aids in camouflage within sandy substrates.
Regenerative Ability: Demonstrates the ability to regenerate body parts, a feature shared with other chordates.