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#biology notes

2 public questions tagged with this topic.

Animal Classification

Most annelids possess which type of circulatory system?

Most annelid taxa possess well-developed closed circulatory system representing advancement over open hemocoel of arthropods and molluscs except cephalopods. Basic plan includes two major trunks: dorsal vessel collecting blood from sinus and capillaries pumping anteriorly via peristaltic wave, and ventral vessel distributing oxygenated blood posteriorly interconnected by segmental commissural vessels aortic arches in parapodia and gills. Blood typically contains respiratory pigments hemoglobin dissolved or in corpuscles occasionally chlorocruorin. Auxiliary hearts from enlarged muscular commis

Ref: NCERT Class 11 Biology, Chapter 4: Annelida closed circulation; Campbell Biology Chapter 33

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Animal Classification

Excretory structures of nemerteans include

Nemertean excretion and osmoregulation rely on protonephridial system superficially similar to flatworm protonephridia but uniquely associated with circulatory vessels enabling filtration of blood. System comprises terminal flame bulbs with ultrafiltration weir leading to ciliated tubules converging to paired ducts opening via nephridiopores laterally in anterior region typically one to three pairs. Tubules intimately associated with lateral blood vessels facilitating ultrafiltration from blood into lumen driven by pressure. Number variable some highly branched others reduced. Unlike metanephr

Ref: Brusca & Brusca, Chapter 20: Nemertea protonephridia excretory system; NCBI

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