ZOO202 Midterm Subjective and Objective Notes by Sulman Ali

ZOO202 MID TERM SUBJECTIV+OBJECTIV · BEST OVER ALL FILES BY · SULMAN ALI · BS-ZOOLOGY 4TH SEMESTER · SPRING 2022

Why are protochordates not classified as true Chordata?

Protochordates are an informal group made up of cephalochordates and urochordates. They do not have a vertebral column like vertebrates. Thus, the main difference between chordates and protochordates is the presence of a vertebral column. So the protochordates are not classified as true Chordata.

Characteristics of Protochordata (Tunicates & Amphioxus)

•  They are generally found in marine water.
•  Their body is bilaterally symmetrical, triploblastic, and coelomated.
•  At a certain stage of their lives, their body develops a long, rod-like structure for support called the notochord.
•  They exhibit organ system level of organization.
•  E.g., Herdmania, Amphioxus.

What are Protochordates?

Protochordate is an informal category of organisms to describe the invertebrates that are closely related to vertebrates.

Classification of Protochordates:

This group is composed of the Phylum Hemichordata and the Subphyla Urochordata and Cephalochordata.

What are the Hemichordata (Tunicates & Amphioxus) or characteristics of Hemichordata:

Hemichordates are the sister group to echinoderms, not chordates. Phylogenomics suggest that the tunicates are the sister group to vertebrates, while lancelets are more distantly related to

The main characteristics of Hemichordata are the presence of a stomochord. They are bilaterally symmetrical, triploblastic and have a true coelom. They have gills for respiration and proboscis glands for excretion.

clasification of Hemichordata:

The Hemichordata consist of four classes: Enteropneusta, Pterobranchia, Planctosphaeroidea and Graptolita. Enteropneusts, or acorn worms (about 70 species), are solitary, wormlike, bilaterally symmetrical animals, often brilliantly coloured. They are known as acorn worms because of the appearance of the proboscis and collar.

What is the mode of feeding in Enteropneusta:

An important method of feeding in all enteropneusts is by a sheet of mucus, which is secreted by the proboscis epithelium, to which particles will adhere.

what is the mode of digestion in Enteropneusta:

The digestive tract of enteropneusts is a simple tube. Food is digested as diverticula of the gut, called hepatic sacs, release enzymes.

The Nervous system of Enteropneusta:

The nervous system of enteropneustsis ectodermal in origin Lies at the base of the ciliated epidermis. Consists of dorsal and ventral nerve tracts and a network of epidermal nerve cells, called a nerve plexus.

what is the mode of Respiration in Enteropneusta:

Because acorn worms are small, respiratory gases and metabolic waste products (principally ammonia) probably are exchanged by diffusion across the body wall. In addition, respiratory gases are exchanged at the pharyngeal slits.

what is the mode of Circulation in Enteropneusta:

The circulatory system of acorn worms consists of one dorsal and one ventral contractile vessel. Blood moves anteriorly in the dorsal vessel and posteriorly in the ventral vessel.

what is the mode of Excretion in Enteropneusta:

Excretory wastes may be filtered through the glomerulus, into the coelom of the proboscis, Later on release to the outside through one or two pores in the wall of the proboscis.

Reproduction and Development in Enteropneusta:

Enteropneusts are dioecious, they are normally reproduce sexually via external fertilization, and develop either directly or via tornaria larvae.

what are the phylum Chordata or Chordates and their characteristics:

a large phylum of animals that includes the vertebrates together with the sea squirts and lancelets. They are distinguished by the possession of a notochord at some stage during their development.

Bilaterally symmetrical • deuterostomate animals • Four unique characteristics present at some stage in development: notochord, pharyngeal slits or pouches, dorsal tubular nerve cord, and postanal tail Presence of an endostyle or thyroid gland • Complete digestive tract. • Ventral, contractileblood vessel (heart)

what are the subphylum Urochordata and their characteristics:

The subphylum Urochordata constitutes a unique group of animals under the, Phylum Chordata. The members of this subphylum exhibit a high degree of diversity in form, habit and habitat.

• Tail chordate • Most primitive of the chordates • They are found in the marine environment. • They are sessile and filter-feeders. • They are also known as tunicates because their body is surrounded by a leathery sheath composed of tunicin (cellulose).

classification of Urochordata:

The members of Urochordata are classified under three classes: Ascidiacea, Thaliacea and Larvacea or Appendicularia.

what are the Ascidians ( tunicates ):

Ascidiacea, commonly known as the ascidians, tunicates (in part), and sea squirts (in part), is a polyphyletic class in the subphylum Tunicata of sac-like marine invertebrate filter feeders. Ascidians are characterized by a tough outer "tunic" made of a polysaccharide.

Body organization of Ascidians ( tunicates ):

Tunicates derive their name from a thick extracellular body covering, called a tunic that is made up of cellulose-like, complex sugars. The adult tunicate body is shaped like a small barrel with two large openings called siphons.

mode of digestion in Ascidians ( tunicates ):

The digestive tract of adult tunicates continues from the pharynx and ends at the anus near the atrial siphon. Tunicates mainly eat phytoplankton, zooplankton, detritus and other small organisms in the water, these organisms are filtered through the tunicate. They have cilia in the pharynx and they also produce mucus.

mode of Respiration in Ascidians

the pharynx also functions in gas exchange. Gases are exchanged as water circulates through the tunicate.

Blood circulatory system of tunicates:

Tunicates have a well-developed heart and circulatory system. The heart is a double U-shaped tube situated just below the gut. One vessel from the heart runs anteriorly under the endostyle, and another runs posteriorly to the digestive organs and gonads. Blood flow through the heart is not unidirectional.

Excretory system of tunicates:

Ammonia diffuses into water that passes through the pharynx and is excreted.

Reproduction in tunicates:

Urochordates are monoecious. Gametes may be shed through the atrial siphon for external fertilization or eggs may be retained in the atrium for fertilization and early development. Although self-fertilization occurs in some species, crossfertilization is the rule.

Development results in the formation of a tadpole like larva with all four chordate characteristics.

What are the Cephalochordata and their Characteristics:

Members of the subphylum Cephalochordata are called lancelets. • The cephalochordates consist of two genera, Branchiostoma(amphioxus) and Asymmetron, and about 45 species. • They are distributed throughout the world’s oceans in shallow waters that have clean sand substrates. • Cephalochordates are small (up to 5 cm long), tadpole like animals.

Feeding in Cephalochordates:

Cephalochordates are filter feeders. During feeding, they are partially or mostly buried in sandy substrates with their mouths pointed upward.

Digestion in Cephalochordates:

Digestion is both extracellular and intracellular. The cephalochordate commonly is buried in the substrate and positions its mouth above the surface of the sand. During feeding, the cirri form a kind of grid that keeps out large particles. Water is drawn into the mouth by the beating action of cilia on the gills.

Blood circulatory system in Cephalochordates:

Cephalochordates do not possess a true heart.

Excretory system in Cephalochordates:

Excretory tubules are modified coelomic cells closely associated with blood vessels. This arrangement suggests active transport of materials between the blood and excretory tubules.

Reproduction and Development in Cephalochordates:

Cephalochordates are dioecious. Gametes are shed into the atrium and leave the body through the atriopore. External fertilization leads to a bilaterally symmetrical larva.