Nervous System of Petromyzon: In Petromyzon, the nervous system has a very primitive brain, the main region of the brain, cerebral hemispheres are two in number and they are much separated from each other. The forebrain has two large olfactory lobes, on the posterior region, the cerebral hemispheres are connected to the diencephalon, on the … Read more
Respiratory System of Petromyzon: On the lateral side of the head, seven pairs of gill slits are present, the gills are present inside the gill pouches. Between the respiratory pharynx and the body wall the gill pouches present, on external appearance, each gill pouch looks like a biconvex lens. The gill pouches are separate from … Read more
Digestive System of Petromyzon: Buccal Cavity and Mouth: Petromyzon has a complete digestive system with the alimentary canal starting at the mouth and ending at the anus, the mouth present on the ventral side of the anterior part of the cylindrical head. Petromyzon feed on other fishes, their mouth show adaptation for parasitism. The ventral … Read more
Anatomy of Skin: The skin has muti layered cells coverings, have dermis and epidermis layers, the skin is slimy or smooth due to the presence of mucous gland. The epidermis has different types of cells, the major type of cells present on the epidermis is mucous gland secret mucous, other glandular cells present on the … Read more
Body Shape of Petromyzon: Petromyzon or Lamprey are fish-like animals in external appearance, specially Petromyzon are resemblance less or more with eels. The body is divided into three parts, the anterior cylindrical-shaped head, then the large-sized cylindrical trunk portion, and the posterior post-anal tail. The tail is laterally compressed, the head-tail and trunk are not … Read more
What is Petromyzon (Lamprey): Lamprey is jawless fish like Vertebrate placed under Group Agnatha along with the Ostracoderm. At present-day among all the living Vertebrates, the lamprey is the most primitive Vertebrate and they have only one living class known as Cyclostomata, under Cyclostomata lamprey, Hagfish present. The term Cyclostomata refers to their circular mouth … Read more
Class Ostracodermi: Class Ostracodermi include the primitive Vertebrate fossil found and they help to study the ancestral Vertebrate. They are fish-like jawless Vertebrate known as Ostracoderms. The present-day Cyclostomata also evolved from the Ostracoderm and there are many similarities between them so they are placed under a common group Agnatha. Before Ostracoderms, there are no … Read more
Biological Significance of Class Ostracodermi: Ostracodermi was the most primitive fossil evidence of Vertebrata, before Ostracodermi there was also several Vertebrate on our earth but we have no fossil. Only Ostracoderms fossil give us the idea about the primitive Vertebrate, Ostracoderms help us to understand how invertebrates evolved into Vertebrate. We find the Ostracoderm fossil … Read more
Ostracoderms are today extinct so we can not study all features in a living state but on the basis of available fossils, we can divide class Ostracodermi into 2 subclasses. Subclass 1: Monorhina: The important feature of this subclass is the presence of a large-sized, slit-like median eye present on the head between the two … Read more
Ostracoderms are the primitive members of the subphylum Vertebrata but they were not the first Vertebrate to originate on our earth. Before them, there were the ancestors of Subphylum Vertebrata but their fossil evidence is not available today, there are different opinions about the absence of fossil evidence for the ancestors of Subphylum Vertebrata. Ostracoderms … Read more
