The super class Gnathostomata includes craniates, in which one pair of the visceral arches is modified into this jaws. They how internal ear with three semi-circular canals and provided with…
Fishes are first evolved in silurian period of palaeozoic era. They increased their number in Devonian period. Devonian Period is Called Age of Fishes.   Fishes are first jawed vertebrates.…
Ammocoetes Larvae: Matamorphosis   In the life history of Petromyzon a larval form is seen. It is called Ammocoetes larva.   Ammocoetes larva is transparent and 1 cm., in length.…
Branchial Basket   In Petromyzon the visceral skeleton contains branchial basket. It lies external to the gill pouches. It shows 9 irregular vertical bars and 4 longitudinal bars on either…
Myxine (Hagfish) Petromyzon (Lamprey) 1. Hag fishes are scavengers. They penetrate into the dead fishes bodies and eat the tissues. 1. They are semi parasitic. But the Larvae(Ammocoetes) leads an…
The class Cyclostomata is divided into two orders:1) Petromyzonia and 2) Myxinoidea   Order 1: Pefromyzonia   Lampreys are included in this order. The buccal funnel is suctorial and shows…
Cyclostomes’ are jawless vertebrates. They are primitive vertebrates. The cyclostomes are marine or fresh-water vertebrates.   It includes the lampreys and hag fishes.   The body is long, eel like.…
SUB-PHYLUM VERTEBRATA is further divided into two super-classes.   AGNATHA, AND GNATHOSTOMATA.   SUPER-CLASS 1. AGNATHA: (A = Without; Gnathos = Jaw).   Earlier vertebrates are included in it They…
Vertebrates show the following characters, besides the chordate characters.   1. PRESENCE OF ENDO AND EXO-SKELETON: Vertebrates include internal skeleton which is a notochord or vertebral column. Vertebrates contain exoskeleton,…
LARVAE OF PORIFERA   1. Parenchymula (Stereo- gastrula) - Leucosolenia 2. Rhagon - Higher sponges 3. Amphiblastula - Sycon   LARVAE OF COELENTERATA   1. Planula - Obelia, Sea Anemone…

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