Question

Haemocoel is present in
(a) Hydra
(b) Earthworm
(c) Nereis
(d) Scolopendra

Answer 1

Hint: The organism in which haemocoel is present is known for its long trail of legs which are capable of injecting venom in its prey. The presence of jointed appendages is a key feature of the phylum to which it belongs.

Complete answer:
Haemocoel is the main body cavity in insects. Scolopendra belongs to the phylum Arthropoda. It possesses the open circulatory system, wherein the blood flows freely in the body cavity i.e. haemocoel. It bathes the cells directly.
- The blood-filled spaces in arthropods are of three types– dorsal or pericardial sinus, middle or perivisceral sinus and ventral or perineural sinus. Dorsal sinus encloses heart, middle sinus encloses digestive, respiratory, excretory, and reproductive systems, ventral sinus encloses sterna and nerve cord.
- Haemocoel is filled by haemolymph whose function is comparable to our blood. Just like blood fulfils nutrients and oxygen requirements of all the cells in our body, haemolymph does the same.
- The only difference is that haemolymph uses copper as the binding agent of oxygen rather than iron in the blood.
- Phylum Arthropoda is divisible into seven classes on the basis of body division and presence or absence of certain appendages Scolopendra belongs to class Chilopoda.
- The body is divisible into the head and trunk. A pair of legs are present on each trunk segment. Modification of the first pair of legs into poison claws can be observed. A single pair of antennae is also present. It is also commonly known as a centipede.
- In hydra, the Circulatory system is absent. Its oxygen and nutrient demands are met directly by diffusion from the water surrounding it. Earthworm and Nereis are members of phylum Annelida. They exhibit a closed circulatory system.
- Blood is red due to the presence of respiratory pigment haemoglobin which is found dissolved in the blood plasma. No red blood corpuscles are present in the blood.
So, the correct answer is ‘Scolopendra.’


Note:
Centipede is usually confused with millipedes. Centipedes are nocturnal and carnivorous wherein millipedes are herbivorous or saprozoic. The abdominal segments of millipedes contain stink glands and thus produce a foul smell. The main difference lies in their number of legs. Centipedes have a lesser number of legs than millipedes who can have 70-100 pairs of legs.