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  Phylum Aschelminthes, Biology tutorial

Introduction to Phylum Aschelminthes:

The extremely large and heterogeneous group of animals has usually been categorized together in group variously called as Aschelminthes, Nemathelminthes, and/or Pseudocoelomata. Such organisms are categorized in about 10 separate phyla. However, it is at times helpful to keep name "Aschelminthes" to cover all organisms.

Features of Aschelminthes:

i) They are bilaterally symmetrical, but with the tendency to be radially symmetrical along longitudinal axis.

ii) Contains circular cross sectional area; no segmentation or appendages

iii) They include complex cuticle

iv) Tissues and organs re-present, and body includes more than 2 harcell-layers

v) Circular muscles are absent in body wall

vi) Body cavity is pseudocoel, with body at high pressure

vii) Gut (digestive system) extending from mouth at anterior and to anus

viii) Muscles of body wall are with strange features

ix) They do not have circulatory system, flame cells or nephridia. Do not have no cilia or flagella

x) These growth is direct, with highly determinate kind of cleavage

xi) Development in Aschelminthes engages increase in cell-size rather than cell number

Classification of Aschelminthes:

The phylum Aschelminthes is separated into 5 classes:

These are:

i) Rotifera: They are marine parasites, anterior end of body alters into ciliary organ known as corona. They may or may not share sexual dimorphision. Examples Rotifers, Brachionus

ii) Gastrotricha: are free living, unsegmented, found among algae and debris of stagnant fresh and salt water; mainly hermaphrodite or parthenogenetic female present. For e.g. chaetonotus

iii) Echinodera: they are tiny worm such as marine animals, generally diecious. For e.g. Echimoderes.

iv) Priapulide: they are marine animals, body is separated in probosus and trunk; are diecious. For e.g. is priapulus.

v) Nematode: these are unsegmented roundworms with slender cylindrical body. Sexes are separate; and males smaller than females. For e.g. Oxyuris, Ascaris, Ancylostoma, Trichuris, etc.

External Feature of Ascaris Lumbricoides:

i) Body of Ascaris Lumbricoides is lengthened and Cylindrical; tapering at 2 ends. Its color is generally whitish or yellowish with reddish tinge

ii) External body is surrounded with tough, elastic and semi transparent cutile.

iii) It includes large body size; female is 25-40cm in length and 4-6mm width, while male is 15-30cm in length and 2-4 mm in width.

iv) In female, posterior of body is straight, whereas in male posterior end of body is recurved ventrally.

v) In male and female, body illustrate 4 longitudinal lines running from anterior to posterior end of body

vi) The tri-radiate mouth is present at top of anterior end and it is bounded by 3 lips.

vii) The-excretory pore is present mid-ventrally at the distance of 2mm from anterior end of the body in male and female.

viii) In female, separate genital aperture, known as goriopure or valva, is present mid-ventrally at anterior one - third length 9th of body

ix) Anus is present mid-ventrally at the distance of 2-3mm from porterior end of body.

x) Male has cloacal aperture, instead of anus, at similar position

Structural Adaptation:

i) Outer muster layer of Ascan's Lumbricoides is formed by the thick transparent wrinkled shining cuticle, providing animal false segmented appearance. Cuticle protects it from digestive juices of host. Presence of cuticle can be said to be parasitic adaptation.

ii) It feeds on contents of alimentary canal of its host, much of which is partly or completely digested. Nutritive fluid in psendoloel (space between intestine and muscular layer of wall) propelled by movement of body assist in distribution of food, oxygen and nitrogenous waster matter.

iii) For its respiration, animal goes in inactivity or turns out to be dormant when oxygen is in small supply, and when oxygen is in huge supply, it becomes revived.

iv) The single excretory cell becomes generally large in size and supposes the form of H - shaped structure with excretory canals.

v) These canals gather nitrogenous waste matter in form of urea Zygote formal after fertilization is enclosed by the resistant shell of chitin. Uteri of single worm may has as many as 27 million eggs at one time and every female lays about 15000 to 200,000 egg per day.

vi) Nervous system is well developed and complex, comprising of ganglia, ring and nerves.

Habitat and Habit:

i) Roundworm Ascans Lumbricoides, is the parasite in intestine of man

ii) Worldwide is distribution, parasitizing more than 50% human population in tropical countries generally more in children than adults.

iii) Generally lies in intestinal cavity of man, enclosed by already digested food from which it gets nutrients. It undertakes holozoic mode of nutrition.

iv) Causes weakness, tiredness, dizziness, vomiting, headache, anemia and winding pain in intestine, completes its life cycle in only 1 host, that is man and reproduces sexually.

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