Invertebrate Zoology

The pericardium is the protective layer of the heart. It consists of two layers, an outer fibrous layer and the inner serous layer. The serous layer again is made up of two membranes enclosing the pericardial cavity. Molluscs have a true body cavity or coelom. They posses pericardial glands. Antennary glands are also called as green glands. They lie enclosed within the coxal segment of each antenna. Each gland has three parts, namely Sac, labyrinth and bladder. These are seen in crustaceans like arthropods. Protonephridia are of two types, solenocytes and flame bulbs. These are present in animals that lack a true coelom. The protonephridia terminates in the enlarged bulb-like structure and have cilia inside. If there is only one cilium, it is called as solenocyte. If there are more cilia, it is called as flame bulbs.  Lancelets have solenocytes as excretory structure. Rotifers have flame bulbs.

A snail uses its single long, muscular foot to crawl on a layer of mucus-like slime that it secretes. This mucus has unusual physical properties and scientists assumed that these sticky properties were essential for snail movement. 

In earthworms, members of the phylum Annelida, the excretory system consists of structural units called nephridia. The nephridium is an invertebrate organ which occurs in pairs and performs a function similar to the vertebrate kidney. Nephridia remove metabolic wastes from an animal's body. Cockroach belongs to class Arthropoda because it has jointed appendages and the hard exoskeleton. Crocodiles are reptiles, not amphibians because they lay their eggs on the land, not in the water.

•  A cockroach has 10 pairs of spiracles on its body, out of which, two are present on its thorax and the rest are present on its abdomen.
  
• The alimentary canal of Pheretima consists of pharynx among other organs.
  
• The body of the frog is divisible into head and trunk.
  

 Petromyzon, sea lamprey has a simple nasal aperture is present on the top of the head between the eyes. Nasal aperture is single and median. Hence, option A is correct answer.

Petromyzon (lampreys) are all carnivorous and are true predators. The method of attack is very peculiar. It attack fishes, turtles etc and it attach themselves by suctorial mouth which is circular in shape. Mouth acts a sucker, it rasps the flesh of the prey with its tongue. Teeth which are situated around the mouth sink into the flesh of the prey and serve it to hold properly. Hence, option D is correct answer.

Cockroaches belong to phylum Arthropoda which has well developed the digestive system. The digestion of starch in the buccal cavity is followed by complete grinding of food in crop and gizzard which finally enters the stomach. The digestive enzymes secreted by the gastric caeca act upon the food in the stomach. These enzymes include amylase, maltase, invertase, tryptase and lipase. The remaining carbohydrates, proteins and fats are digested here.The digested food is absorbed through the stomach walls into the surrounding space which is called the haemocoel. The haemocoel consists of a large number of fat bodies which are fat cells having fat globules, protein granules and glycogen. They form storage structures which transport to different parts of the body. So, the correct answer is option C.

Malpighian tubules are the excretory organs in all insects. The tubules often occur in two’s or multiples of two. As insects belong to the phylum Arthropoda, the organism must be placed under it. 

The excretory organs of grasshopper are the malpighian tubules which are coiled about in the haemocoel and open into the anterior end of the hindgut. The malpighian tubules have a wall of a single layer of cells with striated inner border. Their free ends are completely closed. In the majority of Arthropods, Malpighian tubules are the excretory organs. So, the correct option is 'Malpighian tubule'.

Nephridia is the earthworm's excretory organ. Earthworms are called septal, integumentary, and pharyngeal nephridia in three kinds of nephridial structures. These three nephridial structures are present in various body positions and differ in structures as well. Septal and pharyngeal nephridia are both enteronephric, i.e. they expel nitrogen products to the gut. Integumentary nephridia is exonephric, i.e. products of nitrogen waste are discharged outside straigh

In most of the invertebrates, the excretory structures are simple tubular forms whereas vertebrates have complex tubular organs called kidneys. Shark is a vertebrate and has kidneys as excretory structures.
Protonephridia or flame cells are the excretory structures in Platyhelminthes (Flatworms, e.g., Planaria), rotifers, some annelids and the cephalochordate Amphioxus. Protonephridia are primarily concerned with ionic and fluid volume regulation, i.e., osmoregulation.
Nephridia are the tubular excretory structures of earthworms and other annelids like Leech. Nephridia help to remove nitrogenous wastes and maintain a fluid and ionic balance.
Malpighian tubules are the excretory structures of most of the insects including cockroaches. Malpighian tubules help in the removal of nitrogenous wastes and osmoregulation.

Nephridial organs, or nephridia, are excretory structures that evolved in many invertebrates, including flatworms, nemerteans, rotifers, annelids, mollusks, and lancelets. Each nephridial organ consists of simple or branching tubes that typically open to the outside of the body through excretory pores, called nephridiopores. Two types of nephridial organs are protonephridia and metanephridia. The excretory system of insects and spiders consists of several hundred Malpighian tubules. Malpighian tubules are slender extensions of the gut wall. Their blind ends lie in the hemocoel (blood cavity) and are bathed in hemolymph. The mammalian urinary system consists of the kidneys, the urinary bladder, and associated ducts. Each kidney has more than 1 million functional units called nephrons. A nephron consists of a cuplike Bowmans capsule connected to a long, partially coiled renal tubule.
In option A typhlosole is an intestinal fold for absorption but contractile vacuole is meant for osmoregulation. In option C antennae of cockroach are sensory but clitellum of earth worm forms cocoon. In option D tube feet of starfish are meant for locomotion and not related to other structures mentioned which have a role in digestion of food.

'Green Gland' is one of the pair of excretory organs in each side of the head region of decapod crustaceans, emptying at the base of the antennae. Prawns have green glands for excretion.

Solenocytes are a type of long, narrow, flagellated cell that functions in excretion of nitrogenous wastes and occurs in a variety of organisms, including certain annelids and molluscs.