Category: Essays

Important parts in the water vascular system or ambulacral system of asterias are listed below: (1) Madreporite: ADVERTISEMENTS: It is a thick sieve like calcareous plate situated on the aboral surface of the central disc. It bears as many as 250 minute pores on the surface and they lead into pore canals. All pore canals unite to form collecting canals within the substance of madreporite. Below the madreporite, collecting canal communicates with stone canal through ampulla. Image Source: 1.bp.blogspot.com (2) Stone canal: It is S-shaped tube, which opens on the oral side into a ring canal around the mouth. It is also known as madreporite canal. Its walls are supported by a series of calcareous rings, hence the name stone canal. Inner lining of the wall bears cilia or flagella,…

External features of palaemon or prawn of phylum arthropoda Phylum Arthropoda is the largest phylum of the animal kingdom and crustacea is a large and important class of the phylum Arthropoda. It includes prawns, crabs, lobesters, shrimps, barnacles, water fleas and related forms. Image Source: 185.26.182.219 ADVERTISEMENTS: Habits and habitat : Palaemon or prawn, found in fresh water ponds, rivers and lakes. It is a nocturnal animal. It comes out at the water surface in the night in search of food. It is an omnivorous. It is an active swimmer and swims with the help of pleopods. It breeds from May to July. Shape and Size: ADVERTISEMENTS: Palaemon has elongated, spindle shaped, bilaterally symmetrical body. Different species have different sizes. P. malcomsonii (Macrobrachium malcomsonii) the giant prawn found in Tamilnadu,…

Shape size and colouration: The body is laterally compressed and somewhat oblong or rectangular in shape with the attached end slightly narrower than the free end. It measures about 9.5 cm long, 7.0 cm broad and 4.0 cm thick. The foot, when present, measures, 3.0 to 4.0 cm long. Fresh specimens are pinkish in colour. Image Source: cdn.shopify.com ADVERTISEMENTS: Division of Body: The body is covered by the test and is divisible into two parts, body proper and foot. (1) Body Proper: ADVERTISEMENTS: The distal free part of the animal is body proper. Two short cylindrical projections called the branchial and atrial siphons or funnels arise from the anterior and the dorsal end respectively. Both the siphons are situated at the same level. The branchial or oral siphon is smaller,…

Important parts of digestive system in herdmania are mentioned below: In Herdmania it is coiled and complete and contains the following parts. ADVERTISEMENTS: (1) Mouth: It forms the opening of branchial siphon marking the anterior end of the body. It is guarded by four lobes derived from the test. Image Source: wp4.cdn.brainsins.com (2) Buccal Cavity: Mouth leads into a laterally compressed cavity of branchial siphon, called buccal cavity or stomodaeum. ADVERTISEMENTS: A strong branchial sphincter present at the base of siphon which regulates the opening of mouth. A circlet of highly branched delicate branchial tentacles, richly supplied by nerves is also found at the base of siphon. These are 64 in number and of four different sizes like 8 large (5 mm) 8 medium (2.5 mm) 16 small (1.5 mm)…

Important types of circulatory system in herdmania are given below: The circulatory system is well developed and closed type. It includes (1) heart and pericardium (2) blood vessels and (3) Blood (1) Heart and Pericardium: ADVERTISEMENTS: It is a non contractile, elongated and transparent tube about 7.0 cm long and 3.0 mm wide running obliquely below the right gonad. It is closed at both the ends and is filled with a colourless pericardial fluid with corpuscles similar to those of blood. Its wall is thick, made of connective tissue and contains blood sinuses and is internally lined by squamous epithelium. Image Source: s3.amazonaws.com ADVERTISEMENTS: The heart is enclosed within the pericardium and is attached to its wall along its entire length by a thin mesentery like connective tissue flap. It…

The origin and ancestory of modern chordates is not very clear and remains obscure. Because their early ancestors most liably were soft bodied and left no definite fossils. The earliest known fossils of truly vertebrate animals were, freshwater forms abundant during the late Silurian and middle devonian periods. Their fossils are collectively known as ostracoderms. They are placed in the group of jawless animals called Agnatha. Image Source: 3.bp.blogspot.com ADVERTISEMENTS: The oldest fragmentary fossils belonging to ostracoderms occur in the late cambrian and middle ordovician. About the place of origin of chordates an American geologist Chamberlain gave the idea of fresh-water origin of chordates in 1900. This idea was supported by Romer and Homer Smith also. Theories of Invertebrate ancestory of chordates: ADVERTISEMENTS: The invertebrate ancestory of chordates is now…

Important body features of scoliodon are given below: 1. Mouth: It is situated a little behind the apex on the ventral side of the anterior region of the body. Mouth is bounded by upper and lower jaws each bearing 1 or 2 rows of sharply, pointed and backwardly directed teeth. Teeth are adapted for holding and tearing of the prey. Image Source: d.fastcompany.net ADVERTISEMENTS: 2. Nares: Two crescentic apertures, the nares or nostrils are present ventro-laterally and anterior to mouth. They are exclusively olfactory, have no role in respiration, as they are not connected to mouth cavity by internal nostrils. ADVERTISEMENTS: 3. External gill slits: Anterior to each pectoral fin, on either side of the body vertically elongated external gill slits or branchial clefts are present in a series of…

320 words short essay on A Rainy Day for kids. This year the summer season was unduly long and extremely hot. It was July and the schools had reopened. The scorching sun and the extreme heat made life miserable. Going to the school, studying in the class or playing on the grounds all seemed to be a punishment.One morning, clouds gathered in the sky. Thunder rolled. Suddenly it started raining. There was a downpour for a short while but soon it turned into a steady rain. It was time for school. So, we took our umbrellas and set off.It was refreshing to go out in the cool air. Everyone and everything looked fresh. The trees were a vivid green. The sound of falling rain was pleasing to the ears. No…

Free sample essay on Scene at a Bus Stop for kids. A bus stop hums with life and activity. At peak hours there is a mad rush. The school and college students as well as the office-goers vie with each other to get into the already crowded buses.All sorts of people can be seen at a bus stop. Some are impatient and look at their watches every few seconds, others are worried and fret. But there are some who wait patiently. They even smile at others. Students stand in groups and talk. It presents a good opportunity to study human nature.At most of the stops people try to stand in queues but as soon as a bus is visible, the queue is broken. Everyone just pushes and jostles. There is…

Short essay on The Man Who Inspired Me for kids. Can I ever forget the octogenarian who stayed with us for two days? He was a tall, frail-looking man who commanded respect. He had immense patience and strove for perfection in everything.He was sent to stay in our house to avoid the hustle and bustle—the crowd and noise due to a wedding in our neighbor’s house. My mother had agreed to have him as she was confident of giving him a calm and peaceful atmosphere in our house. But lo and behold, my sister arrived with her boisterous, naughty kids for a week.My mother got up early in the morning to give milk to the kids before they started screaming. Mr. Joseph was up too, so mother offered him tea.…