Question

2) The annelids are one of the numerous vermiform (worm like) species that we’ve examined this semester.

i) What are three features distinguish the annelids from other worms?

ii) How does their movement compare with the Platyhelminthes which prominently use adhesive/releaser glands to facilitate movement? Describe their movement using two examples from specific groups of annelids (in terms of structures and how they use them) in one or two paragraphs

iii) Describe the nervous and circulatory systems of the annelids and how it relates to their metermerism.

iv) Compare your answer from part iii with the myriopods

Answer 1

2.1. Three features distinguish the annelids from other worms are

I) True coelomates (eucoelomate)

• The true coelom is a body cavity which arises as a cavity in embryonic mesoderm.
• Annelids are Schizocoelom which develops by splitting up of mesoderm.

II) Closed type of circulatory system.

• The blood is red colored due to the presence of respiratory pigment like haemoglobin dissolved in the plasma. Blood flows in blood vessels( except leech)

III)True mesmeric organisms.

• The external segmentation of the body corresponds to the internal segmentations. They are the first animals to possess true body segmentations.

2.2 The annelids have the capability of locomote with two types muscles groups, circular and longitudinal muscle fibers which are present in the body wall.

• Some aquatic annelids also possess locomotory appendages. They bear fleshy, flattened, laterally projected structure in Nereis called parapodia.
• In Pheretima (earthworm) each body segment, except the first and last and clitellar segments, bears a ring of tiny, curved, chitinous structure known as setae embedded in epidermal pits. These pits have special muscle to move the seta in OR out and to bend back and forward hence help in locomotion.

2.3 Circulatory system.

A closed circulatory system is present, the blood circulation occurs by vessels. In earthworm four pairs of tubular heart are present 7th - 9th segment. Heart pumps the blood in earthworm to maintain it's flow in the blood vessels.

Nervous system.

Body control is provided by the nervous system consisting of paired ganglia which are connected to the double ventral nerve cord by lateral nerve. These paired ganglia act like brain a annelids.

2.4 Myriapoda are subphylum of arthropods and they accomplish locomotion by paired legs. These organisms are diplosegmented and have two pairs of legs attached to each segments.

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