Hint: Any aquatic annelids have feathery organs with thin walls in which gasses are transferred between both the atmosphere and the blood. Most annelids, however, have no special organs for the exchange of gases.
In general, gas exchange takes place through the skin, but it can occur in certain polychaetes through gill filaments or through the aquatic oligochaete’s rectum. While oxygen may be transferred directly into the blood, a respiratory pigment, like haemoglobin or chlorocruorin, typically carries it. In most free-moving and most sedentary polychaetes, but in most oligochaetes and leeches, hemoglobin, the most abundant pigment, is present. In many polychaete communities, Chlorocruorin is found (Flabelligeridae, Terebellomorpha, and Serpulimorpha). There is colourless blood in a few free-moving polychaetes, some oligochaetes, and rhynchobdellida leeches. The blood of the polychaete Serpula vermicularis contains both pigments, the young having more haemoglobin and the old more chlorocruorin.
Hence, the correct answer is an option (C) 'Respiration occurs in annelids by both Skin & Gills'.
There is segmentation in all annelids. Segments are structures that appear repeatedly along the animal's body, often referred to as metameres. Each portion of the annelid comprises circulatory, nervous, and excretory systems units.
Segmentation extends to the interior of the body of the earthworms and bristle worms, but not the leeches, which covers the coelom, which is partly broken into units by structures called septa.
The body of the annelid is covered by a damp outer cuticle that the epidermis secretes. Hairlike setae, consisting of chitin, the hard substance that also shapes the exoskeletons of insects, are also available for both earthworms and bristle worms. These leeches are missing.
Annelids have a true coelom, such that, one which is packed with cells from the mesoderm of the embryo. The coelom, which induces hydrostatic (water) pressure and functions as a hydrostatic skeleton, is fluid-filled. Annelids have a segmentally organized, well-developed, closed circulatory system (one in which blood is confined to vessels). With a mouth and anus, they also have a full, single-way digestive tract. It does not section the digestive tract.
Annelids have muscle fibres both circular and longitudinal. This allows for great versatility in movement, combined with their segmentation and hydrostatic skeleton.
One part of the body, without impacting the rest of the body, is able to contract or change its diameter and volume. The need for intricate mechanisms to control motion is thought to have contributed to the development of the relatively complex nervous system of annelids.
The characteristics of respiratory pigments of the annelid are correlated with the worm's way of existence. The lugworm haemoglobin Arenicola, a polychaete, releases oxygen to the tissues only under extreme oxygen deprivation conditions. Some earthworms' haemoglobin absorbs oxygen from the normal atmosphere and releases it only when tissue oxygen is poor and can thus shield the worm from oxygen.