9.5.9 General Characteristics of Mammals The name was given by Linnaeus in 1785.
The diagnostic characteristics of mammals are the presence of mammary glands (by which females nurse their young ones).
The body is mostly covered with hairs or fur The CNS is highly developed. Lungs possess numerous alveoli and bronchioles Diaphragm is present (muscular partition between chest and abdomen). External cars (pinnae) are mostly present.
Sweat and sebaceous (oil) glands are also present. Their bodies are of different shapes and mostly divided into head, neck, trunk, and tail. Warm-blooded animals. They have two pairs of pentastyle limbs modified for different habitats. These have two occipital condyles in the skull and a large cranium.
Two sets of teeth during their life span (milk teeth and permanent teeth) dentition is heterodont. Heart with two atria and two ventricles and only left sorta is present Nonnucleated Red blood cells except camels.
Testes mostly have extra abdominal and urinogenital openings and the anus is separated Fertilization is internal and they are mostly viviparous (Birth of living young ones). Classification of mammals: The class Mammalia is divided into three sub-classes: Prototheria, Metatheria, and Eutheria.
Sub Class Prototheria: (Egg Laying Mammals): Order Monotremes
They are connecting link between reptiles and mammals because they exhibit the characteristics of both groups
Mammalian characters are:
The presence of many glands, hair, diaphragm, left aorta. Reptilian characters are the presence of clonal. Its eggs, some reptilian skeleton. found only in Australia Echidna (spiny anteater).
Examples:
Duck-billed platypuses are adaptive for aquatic life, the bill is modified like the book of a duck and webbed feet. Class Metatheria: (Pouched Mammal; Marsupial) wolf. Females possess an abdominal pouch (marsupium) in which they rear their Mammary glands and nipples are present inside the pouch. They are generally burrowing and herbivorous. Found in Australia and America. Examples: Opossum, Kangaroo, Tasmanian.
Sub Class Eutheria: (Placental Mammals):
It is the largest group of mammals in which the development of a young one takes place inside the body of the mother. The young are nourished through the placenta thus true viviparous. Ames and urinogenital openings are completely separated. Possess almost all mammalian Characteristics ie, the diaphragm, external ears, hair, and mammary glands.
In some forms, hair is m, modified into spines like porcupines and hedgehogs while in pangolins into scales. Examples: Goat, dog, horse, elephant, seal, whale, dolphin, man, monkey, etc.
SUMMARY
Radially symmetrical animals are diploblastic, developing two germ layers: an inner layer (endoderm) and an outer layer (ectoderm). Diploblasts have a mesoglea between the endoderm and ectoderm. Bilaterally symmetrical animals are called triploblastic, developing three tissue layers: an inner layer (endoderm), an outer layer (ectoderm), and a middle layer (mesoderm).
True animals can be largely divided into three groups based on the type of symmetry of their body plan: radially symmetrical, bilaterally symmetrical, and asymmetrical.
Triploblasts can be differentiated into three categories: those that do not develop an internal body cavity called a coelom (acoelomates), those with a true coelom (coelomates), and those with "false" coelom (pseudocoelomates).
Bilaterally symmetrical, triploblastic coelomates can be further divided into two groups based on differences in their early embryonic development. These two groups are separated based on which opening of the digestive cavity develops first: mouth (protostomes) or anus (deuterostomes).
Poriferans are characterized by minute pores called ostia on their body.
Cnidarians contain specialized cells known as cnidocytes "stinging cells", which contain organelles called nematocysts (stingers).
Phylum Platyhelminthes is composed of flatworms: acoelomate organisms that include many free-living and parasitic forms.
The name "mollusk" is derived from the Latin molluscus ("soft"), indicating that the mollusks are soft-bodied animals. The group includes snails, bivalves, chitons, squid, and octopus.
The clitellum is the reproductive structure of an annelid. It creates mucus that aids in sperm transfer and gives rise to a cocoon within which fertilization occurs. The name "arthropoda" means "jointed legs" (in Greek, "arthros" means "joint" and "podos" means "leg").
Among the hexapods, the insects are the largest class in terms of species diversity as well as Biomass in Terrestrial habitats.
Echinodermata are so named owing to their spiny skin (from the Greek "echinos" meaning "spiny" and "dermos" meaning "skin").
Echinoderms possess a unique ambulacral or water vascular system, consisting of a central ring canal and radial canals that extend along each arm.
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