Detailed Summary of Phylum Chordata
Phylum Chordata includes organisms that are fundamentally characterized by the presence of a notochord, a rod-like structure formed during embryonic development. This phylum encompasses a wide range of animals, including both simple and complex forms, all of which are bilaterally symmetrical, triploblastic, and coelomate, displaying an organized structure at the organ-system level.
Key Characteristics of Chordates:
- Notochord: A flexible rod that provides support and is present at some stage in the animal's life cycle.
- Dorsal Hollow Nerve Cord: A nerve cord located on the dorsal side of the body, distinguishing chordates from non-chordates.
- Pharyngeal Gill Slits: These are perforations in the pharynx that can function in respiration.
- Post-anal Tail: A tail that extends beyond the anus, which is present during various life stages in some chordates.
- Closed Circulatory System: Blood is contained within vessels, allowing for efficient transport of nutrients and oxygen.
Subphyla of Chordata:
- Urochordata (Tunicata): Primarily marine organisms with a notochord only in the larval stage. Examples include Ascidia and Salpa.
- Cephalochordata: These are small, fish-like organisms such as Branchiostoma (Lancelet) that retain the notochord throughout their lives.
- Vertebrata: Organisms where the notochord is replaced by a vertebral column during development. This group is further divided into classes like Agnatha and Gnathostomata, encompassing a vast range of animals, from jawless fish to mammals.
In summary, Phylum Chordata is vital in the animal kingdom due to its diverse forms and complexity, leading to the evolution of vertebrates that dominate many ecosystems.