With specific examples, compare and contrast organisms from the classes Polychaeta and Diplopoda
The clade, Protostomia can be split into two superphyla, namely Lophotrochozoa and Ecdysozoa. Polychaeta is a class of annelids that falls under Lophotrochozoa, while Diplopoda is a class of arthropods that falls under Ecdysozoa. Class Polychaeta refers to a group of generally marine segmented worms, which can be either sessile or free-moving. Each segment possesses a pair of parapodia, which are fleshy appendages that may be modified to aid various functions such as locomotion, filter feeding and gaseous exchange. The parapodia possess many chaetae, which may also be modified to serve a particular function. Class Diplopoda refers to a group of terrestrial arthropods, commonly known as millipedes. They are all free-moving. Diplopods are also segmented, with each segment possessing two pairs of legs (except for the first four and the last segment, which have none). This essay aims identify the major differences and similarities between these two classesTABLE 1.
Both polychaetes and diplopods are triploblastic coelomates. So, both have a true coelom. However, in the polychaete, the coelom is filled with fluid and behaves as a hydrostatic skeleton. On the other hand, in diplopods, the coelom is reduced into a haemocoel, which is integrated into their circulatory system. In terms of skeletal support, diplopods utilise a hard exoskeleton composed of α-chitin, to support and protect their body. The presence of this exoskeleton dictates that diplopods will have to periodically shed it in order to allow for growth, in a process known as ecdysis. Ecdysis, of course is unnecessary in polychaete worms.
Both classes exhibit two different types of segmentation. Polychaetes exhibit metamerism. Their body begins with a prostomium exhibiting cephalization in the anterior region, repeated segments known as metameres, ending in an anal segment in the posterior region. The metameres...