The physiology of respiration is known in Nereis virens.
The size varies from species to species; it may range from 30 to 40 and 2 to 6 mm in width.The peripheral nervous system mainly includes the nerves coming directly from the brain and nerve cord to supply the different regions of the body. The larva grows from the anal end as an elongated cylinder which forms segments of the body by metameric segmentation.The anterior end of the body possesses a distinct, prominent and well developed head which consists of two main parts, prostomium and peristomium.In the middle of each bundle of setae and deeply embedded in the parapodium is found stout, straight, thick and dark coloured chitinous rod the aciculum which projects only a short distance but does not project beyond the outer edge or the parapodium. Nereis ist eine Gattung der Vielborster aus der Familie der Nereidae.Sie besteht aus vielen meist marinen Arten, darunter die Seeringelwürmer Nereis diversicolor und Nereis virens.. Ihre der Fortbewegung dienenden Parapodien sind durch zungenförmige dorsale und ventrale Lappen gekennzeichnet. 65.22) is rounded and transparent, it has a thin external ectodermal epithelium which is thickened at the two ends and along an equatorial ring.The vessels have muscular walls and the constant circulation of blood is maintained by peristaltic waves passing over the walls of the large blood vessels. D is larger than the others and forms the dorsal side of the embryo, B is ventral, and A and C are lateral.Before sharing your knowledge on this site, please read the following pages:The epidermis is thick and glandular ventrally particularly near the bases of the Para podia because the glands are larger and more numerous in this region in comparison to the dorsal epidermis. Nereis worms are commonly known as rag worms or calm worms. The combined effective and recovery strokes of numerous Para podia propel the worm forward.
N. virens (Sandworm), N. pelagica (Type-species) and N. succinea (Clam worm) are common species of Nereis. The epidermis is richly vascularized and helps in respiration.Gills or any other special organs of respiration are lacking in Neanthes. It feeds on micro-organisms. Prey is captured by the eversion of pharynx, which brings the jaws in front to grasp the prey. Thus, the sexually mature Neanthes having these two regions in the body is called Heteroneanthes (= Heteronereis).4. This retraction brings the jaws close and cross one another to hold the prey and to carry into the pharynx.The nervous system controls and co-ordinates the working of muscles by reflexes, there is a correlation of circular and longitudinal muscles in each segment so that contraction of one layer automatically brings about relaxation of the other. The undigested part of the food passes on to the rectum from where it is egested through the terminal anus situated on the posterior end of the anal segment.6. The stomach-intestine opens into a rectum which lies in the last segment.
The dorsal margin of notopodium is produced into a short, cylindrical, tactile appendage, the dorsal cirrus and a similar structure is produced at the ventral margin of the neuropodium, the ventral cirrus. The lower end, thus, becomes to be known as vegetal pole and the upper end as animal pole; the egg is, thus, telolecithal. All muscle layers are syncytial tissue.The gonads are formed by the proliferation of the cells of coelomic epithelium and can be seen as groups of masses of germ cells.
An ovum contains yolk granules and is rounded in shape surrounded by a vitelline membrane.The coelom is an extensive perivisceral cavity having an outer parietal peritoneum and an inner visceral peritoneum which encloses the alimentary canal.
When small animals come close to Neanthes it suddenly everts its proboscis to catch the prey which is dragged inside the buccal cavity during the course of inversion or retraction.