BIS 2C Lecture Notes - Lecture 30: Circulatory System, Ecdysone, Ommatidium
16 Mar 2018
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Within ecdysozoans (subgroup of protostomes); undergo periodic molting of exoskeleton, regulated by ecdysone found in all habitats (marine, freshwater, terrestrial) Hyperdiverse group: extraordinary diversity; of all described animal species. Segmented body, with structures repeated in each segment. Paired jointed appendages with internal muscle attachments. Strong tendency toward tagmosis: regional specialization of body. Many undescribed and undescribed; perhaps 50+ million species altogether. Clusters of segments organized into functional subunits. V arying degree of tagmosis in different kinds of arthropod s. Exo skeleton: composed of chitin and cuticle proteins; organized into articulating plates. Growth by periodic molting of exoskeleton (ecdysis) Reduced coelom and open circulatory system (hemocoel) Paired compound eyes composed of many photoreceptive units (ommatidia) Complex but variable excretory and respiratory system. Development often involved larval stages (but some taxa have direct development) Complex metamorphosis in some insects and crustaceans. New view based on dna sequence appendage structures not seen in crustaceans.
