Cephalochordata: Definition, Meaning, Classification, characteristics, Structure, Function

Cephalochordata is a small subgroup of primitive, fish-like chordates belonging to the phylum Chordata. They are also known as lancelets due to their blade-like, long body shape. Cephalochordates are marine animals that inhabit shallow waters on beaches, usually buried in sand. They are approximately 5 to 8 centimetres in length and exhibit all the fundamental chordate features, including notochord, dorsal nerve cord, pharyngeal slits, and post-anal tail during their entire life.

This Story also Contains

1. What Are Cephalochordata?
2. Taxonomy and Classification Of Cephalochordata
3. Morphological Characteristics Of Cephalochordata
4. Habitat And Distribution Of Cephalochordata
5. Life Cycle And Reproduction of Cephalochordata
6. Feeding And Nutrition of Cephalochordata
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These animals breathe primarily through their skin, since they lack true gills like fish. Cephalochordates eat by filter feeding water passes through the mouth and out of pharyngeal slits in which food particles are captured. The most well-known member of this group is Branchiostoma (also referred to as Amphioxus). Cephalochordates are significant in the study of evolution since they aid scientists in understanding the connection between invertebrates and vertebrates.

What Are Cephalochordata?

Cephalochordata is a subphylum that belongs to the phylum Chordata and refers to small, marine invertebrates collectively called lancet or amphioxus. These animals are long and thin, somewhat similar to fish, and are transparent, also they have notochords, nerve cords, and pharyngeal slits in the entire life cycle. Cephalochordate occupies an important place in animal classification because it has sensed the evolution of vertebrates.

They are basal to the majority of chordates; therefore, they prove useful in giving details into the early adaptations that were probably present in chordates before the vertebrates evolved.

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• Animal Kingdom
• Coelom
• Notochord

Taxonomy and Classification Of Cephalochordata

Cephalochordata is a subphylum of the phylum Chordata, consisting of small marine animals that exhibit the key chordate characteristics but lack a backbone. Such animals are important since they contribute to the understanding of early vertebrate evolution. Cephalochordates represent a primitive and basic group that has evolved little over the years, and their body form holds the key to the connection between invertebrates and vertebrates.

• Cephalochordata is a subphylum of the phylum Chordata.
• It consists of animals having a notochord along the length of their life.
• They do not possess a vertebral column or backbone.
• The group belongs to the class Leptocardii.
• The sole surviving genus of the group is Branchiostoma (Amphioxus).
• Cephalochordates are marine invertebrates that inhabit shallow coastal areas.
• Their body pattern is simple, with no paired fins or limbs.
• They are used as a model for studying the evolution of early vertebrates.

Classification of Cephalochordata

Some families of Cephalochordata are Branchiostomatidae, which include the majority of lancelets are included in, and Asymmetronidae, for example, Asymmetron. Some of the major genera comprise Branchiostoma and Epigonichthys. It also helps in analysing the levels of diversity, evolution and roles of lancelets in different marine habitats. They are discussed below in the table:

Morphological Characteristics Of Cephalochordata

Cephalochordata, or lancelets, possess fish-like, slender bodies that are semi-transparent and laterally compressed. The body has evident bilateral symmetry and a notochord running from head to tail that serves to support it. They have a dorsal nerve cord positioned above the notochord and various pharyngeal slits on the pharynx sides utilized for filter feeding. The mouth is rimmed by small structures known as oral cirri that help in the collection of food. Their post-anal tail helps in swimming, while the body surface is protected by a thin, soft outer covering with no scales.

The morphological characteristics are listed below-

Habitat And Distribution Of Cephalochordata

Cephalochordata, or lancelets, are small sea animals that inhabit shallow coastal environments. They live on sandy or muddy bottoms of the sea, from which they bury themselves, leaving only their heads exposed to filter food from the water. Lancelets inhabit warm and temperate seas globally. They favour pristine, well-oxygenated waters and generally shun dirty or disturbed environments. Lancelets have an important role to play in the marine ecosystem through their contribution to nutrient cycling through filter feeding. The distribution is discussed below:

• Cephalochordata are mostly present in shallow water along coasts and estuaries.
• They like burrowing and hiding in sandy or muddy bottoms.
• They are mostly buried with their anterior end exposed for filter feeding.
• They are found in temperate and tropical marine habitats around the world.
• Lancelets occur more frequently in unpolluted, oxygenated waters.
• They are found along continental shelves and surrounding coral reefs.
• Some are located at depths as much as 50 metres below sea level.
• Distribution spans regions such as the Atlantic Ocean, Pacific Ocean, Indian Ocean, and Mediterranean Sea.

Life Cycle And Reproduction of Cephalochordata

The Cephalochordata, or lancelets, undergo external fertilisation, with the eggs and sperm released into the water. The fertilised egg then becomes a free-swimming larva displaying major chordate characteristics such as a notochord and dorsal nerve cord. The larva develops and then experiences metamorphosis, settles on the sea bed, and develops into the adult. Lancelets are primarily gonochoristic, i.e., they have distinct sexes and sexually reproduce. They have a basic reproductive system and external fertilisation, allowing them to produce numerous offspring in marine environments.

The life cycle and reproduction are listed below-

Feeding And Nutrition of Cephalochordata

Cephalochordata, or lancelets, are filter feeders and primarily consume planktonic micron-sized particles and suspended organic matter in the water. They utilise their oral cirri to prevent large particles from entering the mouth. Water is taken in through the mouth and then through pharyngeal slits, where food particles are caught up in mucus secreted by the endostyle. Cilia help in moving the captured food into the gut for digestion. This mechanism helps them to gather food well while buried beneath the sand.

• Cephalochordata are filter feeders on plankton and small organic particles.
• They employ oral cirri to reject large, unwanted particles.
• Water containing food enters the mouth.
• Pharyngeal slits serve to filter food particles.
• Mucus from the endostyle traps food for digestion.
• Cilia transport the food towards the digestive tract.
• Digestion occurs in the intestine, where nutrients are absorbed.
• Their filter-feeding process maintains the harmony of marine ecosystems.

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