Animal diversity of chordates��Zoology Practicals
B.Sujatha,
Lecturer in Zoology,
Govt. Degree College, Rajampet.
Herdmania
Herdmania
The body of Herdmania pallida is roughly oblong in outline, narrower at its attached than at its free end.
It is the distal free portion of the body. The bronchial aperture marks the anterior end of the animal; consequently the opposite end attached to the substratum is the posterior end.
The foot, when present varies in character according to the nature of the substratum which the animal inhabits.
Matrix is gelatinous and made of a polysaccharide called tunicine.
These are mesodermal in origin and have migrated into the test.
Herdmania has large number of calcareous spicules.
Herdmania
There are two types of spicules found in the body- small microscleres and large megascleres.
Inside the test is the body wall or mantle.
It is formed of single layer of flat polygonal cells and forms the lining of the atrium.
These blood vessels form a network in the test and end in bulb-like dilations called vascular ampullae.
Amphioxus
Amphioxus
Branchiostoma is about 3.5 to 6.0 cm in length. The body is slender, somewhat translucent, superficially fish-like, laterally compressed and pointed at both ends, hence, the name lancelet.
The body is distinguished in two regions- the trunk and tail. The true head is lacking.
Branchiostoma has three unpaired fins- dorsal, caudal and ventral. Paired fins are absent.
The oral hood is continuous posteriorly with two lateral membranous hollow metapleural folds running ventrally up to the atriopore.
Beneath the myotomes on both sides are present a series of gonads between mouth and atriopore.�
Amphioxus
Below the pointed anterior extremity is a large median aperture, the mouth surrounded by a frill-like membrane, the oral hood.
The muscles present beneath the body wall exhibit metameric segmentation.
On the dorsal side the myotomes are very thick enclosing the nerve cord and notochord, this is characteristic of vertebrates also, but in many invertebrates the muscles are of uniform thickness all around.
Ventrally between the metapleural folds in the floor of atrial cavity are present a special set of transverse muscles in the anterior two-thirds of the body. No such muscles are seen in vertebrates.
Amphioxus T.S through pharynx
Amphioxus T.S through pharynx
The atrial cavity or atrium is an extensive space lined with ectoderm.
It is formed by a pair of metapleural folds one on either side above gill-slits of embryo, growing down and getting united ventrally by a transverse shelf so that a portion of the outside space becomes enclosed within the body.
Thus, the gill-slits open into the atrium and not directly outside as in other chordates. The atrium opens outside through a small rounded, mid-ventral atriopore placed just in front of the ventral fin.
Amphioxus T.S through pharynx
Posteriorly it also extends back on the right side of the intestine as a blind pouch which runs almost up to the anus.
From near the hind end of the pharynx the atrium gives out two conical pouches, each projecting in front into the coelom on either side of the pharynx, these pouches are brown funnels or atrio-coelomic canals of unknown function. The atrium lined with ectoderm, protects the pharyngeal region of the animal.
Cyclostomata :Petromyzon
Cyclostomata :Petromyzon
The body of adult Petromyzon is elongated, cylindrical and eel-like.
Petromyzon marinus (sea-lamprey) attains a length of a metre, Lampetra fluviatilis (Lampern or common freshwater lamprey) reaches a length of about 90 cm, and Lampetra planeri (Sandpride or lesser freshwater lamprey) does not exceed 45 cm in length.
The upper surface of the body is usually dark mottled greenish-brown. The surface of the body is smooth and slimy due to secretory epidermal glands. The scales are absent.
The body of Petromyzon is divisible in three regions, viz., head, trunk, and tail, which are not clearly demarcated. The head and trunk are nearly cylindrical and the tail is more or less laterally flattened.
Paired fins are absent. There is a median dorsal fin which is divided into two unequal parts by a notch are placed near the posterior end.
On either lateral side of head is present a well developed eye having no eyelids, but are covered by a transparent area of skin.
Cyclostomata :Petromyzon
Mouth lies at the apex of the buccal funnel bordered by a ring of cartilage.
Nostril or nasohypophyseal aperture is single located mid-dorsally over the head in between the two eyes.
Just behind each eye are present a row of seven rounded external gill-slits.
At the junction of trunk and tail, on the ventral side is present a slit-like depression, the cloaca. Protruding through the cloaca is a urinogenital papilla bearing at its tip a minute urinogenital aperture. Anus lies just in front of papilla within the cloacal depression.
Along each lateral side of the body and below the head are present numerous small sensory pores of the lateral line septum. In male Petromyzon is present an eversible penis.
Cyclostomata :Myxin
Cyclostomata :Myxin
Mouth terminal and surrounded by 8 small tentades. Teeth few. No buccal funnel.
Nostril terminal. Nasohypophyseal sac opens posteriorly in the pharynx.
Gill-pouches and gill-slits 6 to 14 pairs.
Dorsal fin feeble or absent.
Branchial basket poorly developed.
Dorsal and ventral roots of spinal nerves united.
Ear with only 1 semi circular canal.
Eggs few, large. Development dark.
Hagfishes are all marine species.
Cyclostomata :Myxin
Members belonging to the order Myxiniformes are commonly known as hagfishes.
They are exclusively marine. Myxine is found buried in the sea bottom.
Myxine has a wide distribution along sea coasts of both Atlantic and pacific Oceans, occurring in the waters of Northern Europe, North Atlantic, America, Chili, Africa and Japan, etc.
Body is eel-like, measuring about 2 feet (50-60 cm) in length and differentiated into head, trunk and tail.
Hagfishes do not migrate to freshwater to spawn. Development is direct.�
Slender Suckerfish, Echeneis�
Identification