Discuss the affinities, ancestry and evolution of hemichordates and protochordates.
Answers
- hemichordates affinities with chordates:
both have same three structures that are a notochord, central nervous system, and pharyngeal gills.
- hemichordates affinities with annelida
both have same body form and burrowing habits.
- hemichordates affinities with echinodermata
both have same gastrula stage in embryological development. also have coelom.
similarly there are many ancestrial relationship among these phylas that can be clearly seen in their phylogenetic tress.
hemichordates affinities:hemichordates and chordates are supported by the presence of the three fundamental chordate characters in each group, viz., a notochord, central nervous system, and pharyngeal gill-clefts.
The interconnection between the hemichordates and chordates present in the pharynx and its gill- clefts. ancestry and evolution of hemichordates from chordates: But the endostyle and epibranchial groove are absent from the pharynx of hemichordates. common ancestry is responsible for such similarity, and phylogenetic relationship of hemichordates and chordates cannot be denied.hemichordates affinities with Annelida:
The general body and burrowing habit of tuberculous forms such as Balanoglossus are similar :
• The clitellum of an earthworm is alike to the collar of Balanoglossus.
• There is a similarity between the proboscis of Balanoglossus and prostomium of an earthworm.
• most hemichordates and annelids have a similar vascular system with blood flowing anteriorly in the dorsal vessel and posteriorly in the ventral vessels.hemichordates affinities with Echinodermata: there is a strong affinity among two phyla on embryological evidence, the method of formation of the gastrula and the coelom is alike in the two phyla.
The auricularia larva and especially with bipinnaria of Asteroidea have similar torn aria larva.