Phylum- Mollusca.... Animal- Nautilus

NAUTILUS

DESCRIPTION

It is a marine cephalopod found in sea-water in Indo-Pacific region, in shallow waters and between the coral walls. It belongs to sub-class Nautiloidea.

NAUTILUS.

The shell of Nautilus is external and spirally coiled. Its outer surface has yellow-brown stripes like ZEBRA. Internal layer of shell is shiny like bead. The cavity of shell is divided into many chambers by a septa. The outermost chamber is the largest and called body chamber which encloses the entire body of Nautilus.

Nautilus: (A) Animal with shell, (B) Shell in section.

Centre pore is present in each septa. From these pores emerge a mantle cord called siphuncle. It helps the animal to excrete gas into the empty chambers. It is differentiated into trunk, head is long and conical bearing a mouth, a pair of eyes and about 90 filiform tentacles without suckers.

Nautilus

Trunk is round and bag-like. Ink-gland is absent. Ospharidium is present. It is nocturnal and rests on the sea surface during day.

Phylum- Protozoa.... Animal- Nycotherus

NYCTOTHERUS

CLASSIFICATION

Phylum- Protozoa

Sub-phylum- Ciliophora

Class- Holotricha

Order- Trichostomatida

Genus- Nycotherus

DESCRIPTION

Nyctotherus is found as symbiont in the intestine of vertebrate and invertrbrate animals. Its body is dorsoventrally flattened and bean-shaped. Longitudinal rows of equal sized cilia are found all over the body.

Vestibule leading to cytostome is on lateral side and extended up to the middle of the body. Cytostome has dermal membrane and the cytopharynx is like spring of watch. There is one macronucleus. One micronucleus, one contractile vacuole, food vacuoles and glycogen granules in cytoplasm (endoplasm) cytopyge (anal aperture) in the form of a permanent pore. Asexual reproduction in nyctotherus takes place by binary fission.

It forms preconjuganṭs in the rectum of tadpole which conjugate during the metamorphosis of tadpole into adult frog. They assume normal size and shape in young frogs and pass out in the form of cyst with faeces. Infection takes place by consuming water and food contaminated with cysts.

Phylum- Porifera.... Animal- Chalina

CHALINA

CLASSIFICATION

Phylum- Porifera

     Class- Demospongiae

Sub-class- Ceractinomorpha

   Order- Haplosclerida

  Genus- Clalina

Chalina       

DESCRIPTION

This is found in deep water sea of Europe and America. Body is red, brown (burnt amber) or yellow brown in colour. It looks like a small plant. Several flat and finger-shaped branches arise from the body. Because if its resemblance with hand it is popularly known as Deadmans finger or Mermaids gloves.

Its skeleton is made up of monaxon spicules and spongin fibres. Asxeual reproduction takes place by budding and regeneration. Freely swimming larva is formed on sexual reproduction.

Phylum- Coelenterata.... Animal- Metridium

PHYLUM- COELENTERATA

ANIMAL- Metridium.

CLASSIFICATION

Phylum- Cnidaria or Coelenterata

     Class- Anthozoa

Sub-class- Hexacorallia

       Order- Actiniaria

Genus- Metridium

DESCRIPTION

Metridium is a common Sea anemone also referred as Sea flower. They are large, solitary, sessile, marine animals found along the coastal regions of Pacific and Atlantic oceans. The body is divided into an oral and basal disc. A large mouth is present in the centre of the oral disc and surrounded by a whorl of tentacles. The main body can be differentiated into a dorsal capitulum below the oral disc and a ventral or lower, thick-walled scapus or column. Both these portions are separated by a narrow collar. Basal disc is highly muscular and flattened, which remains attached to the substratum. They are unisexual, example,  the sexes are separate and gonads develop on the mesenteries.

Digestive system of sea star(Asterias)

Digestive system

The digestive system of Asterias can be divided into the following parts-

[1] Alimentary canal,

[2] Digestive glands.

[1] ALIMENTARY CANAL

In star fish, the alimentary canal is small, wider and complete and is situated in the center disc. This can be divide into the following parts-

[1] Mouth- This is situated as a pentagonal aperture in the center of central disc on its oral surfaces and is surrounded by a delicate perioral membrane called peristome. It is guarded by five groups of tubercles called mouth papillae or oral spines situated at interradial position. The mouth is surrounded by sphincter muscles which are capable of opening and closing the mouth aperture.

[2] Oesophagus- Mouth opens in a small and wide vertical tube situated in the central disc. This is called oesophagus. The basal parts of oesophagus expands to form a wide stomach.

[3] Stomach- This is in the form of aboard chamber acquiring most of the inner area of central disc. It is differentiated into the following two parts-

[1] Cardiac stomach- This part of stomach is large, oval and differentiated into five lobes. All the five lobes are situated straight forwards the five arms. Its wall are thin, muscular and highly folded. During feeding the cardiac stomach can be everted out through the mouth. This action occurs as a result of contradiction of muscles of body wall and pressure created by the coelomic fluid. Whereas the stomach is withdrawn inside the body as a result of contraction of five pairs of retractor muscles. These five muscles connect the cardiac stomach with the ambulacral ridges of all the five arms. These retractor muscles are largely composed of connective tissues and few muscles fibers which are commonly called as mesenteries or gastic filaments.

[2] Pyloric stomach- This is a small, flat and pentagonal part of stomach which opens in the intestine inside the aboral surface of the body. Each arm of this stomach is situated straight towards each arm of the star fish. In each arm of the pyloric stomach, pyloric duet of the concerned pyloric caeca or digestive gland opens.  

[4] Intestine- It is in the form of a small, narrow pentagonal tube which extend vertically towards the aboral surface and open out through the anus. Two or three branched brown-coloured processes called intestine or rectal caeca arise from the intestine in the inter-radial position. These caeca secrete a type of brown-coloured fluid which is probably excretory in nature. The portion of the intestine behind the caeca is called as rectum.

[5] Anus- This is in the form of a small, circular aperture situated on the aboral surface towards one side of central disc.

[2] DIGESTIVE GLANDS

In Asterias, the digestive gland is found in the form of five pairs of pyloric caeca whose every pair is situated inside each arm and remains extended upto its end. Inside the arm it is connected to the aboral body surface by a pair of longitudinal mesenteries. Each pyloric caecum consists of a hollow longitudinal axis or duct from which many green or almond-coloured sacs are connected. The longitudinal pyloric ducts of both the pyloric caeca of an arm open in a common pyloric duct whose terminal and opens into pyloric stomach.

                                     Asterias : Showing alimentary canal in aboral view.

       All the sacs of pyloric caeca are internally lined with epithelial layer containing four types of flagellated columnar cells-

[1] Secretory or granular cells- These cells secrete proteolytic, amylolytic and lipolytic enzymes that is why the pyloric caeca of these animals is considered to be equivalent to the pancreas of vertebrates.

                                  Asterias : V.S. of disc and an arm (digrammatic) 

[2] Mucous cells- These cells secrete mucus.

[3] Storage cells- These cells store reserve food like lipids, glycogen and protein polysaccharide complex etc.

                                  Asterias : Pyloric stomach and intestine.

[4] Current producing cells- The cells have long flagellae which drive secreted enzymes towards stomach.

FOOD AND FEEDING MECHANISM

Food- Sea star is carnivorous animal. It feeds upon marine sedentary animals such as clams, oysters, mussels, snails, crabs, barnacles, worms, etc. It also feeds upon small fishes.

Feeding Machanism- Star fish catches and feeds upon its prey by a peculiar method. It catches crawling shelled molluscs like oysters, clams etc. with the help of its arms and the tube feet and brings the free ends of shell near its mouth. Simultaneously it curves its body like an arch or umbrella and manages to pull apart both the valves of shell by holding the shell valves tightly with the help of tube feet. Meanwhile the tube feet present at the tips of its arm tightly attach with the substratum. The tube feet holding the valves of the prey maintain a continuous pressure over the valves so that the adductor muscles of the prey which close the valve and cannot remain in contraction phase for a longer period ultimately become relaxed resulting into opening of the valves. Now, the star fish everts out its cardiac stomach to engulf the prey.

                                                 

                                                  

DIGESTION, ABSORPTION AND EGESTION

The star fish while everting its cardiac stomach over its prey simultaneously ejaculates digestive enzymes secreted by the stomach and pyloric caeca over the prey. These enzymes are chiefly proteolytic, amylase and lipase which digest proteins into amino acids, carbohydrates into glucose and fats into fatty acids and glycerol respectively. Thus in the star fish, most of the digestion occurs outside the body. With the retraction of cardiac stomach the semi-digested food reaches into the alimentary canal. The retraction of cardiac stomach occurs as a result of contraction of gastric ligaments. Semi-digested food is completely digested in stomach and pyloric caeca.

Digested food is absorbed in pyloric caeca and is distributed throughout the body by the coelomic fluid. Additional food is stored in the storage cells of pyloric caeca.

As it has been described above that the star fish engulfs semi-digested food, the undigested residue is very less which is egested out through mouth itself but small amount of undigested food is egested out through the amus also.