GENERAL CHARACTER AND AFFINITY OF ERIPATUS

Dr.Sujit KumarDepartment of Zoology

Allma Iqbal CollegeBiharSharif,Nalanda

Mob.no.--7004774289 B.Sc-Part-1Group-A

INTRODUCTION:Peripatus belongs to class- onychophora of phylum- Arthopoda. It

is smallest division of Arthropoda. Peripatus are small worm or catterpiler like animal withsoft delicate and flexible body.

Peripatus has restricted distribution. It is generally found in neotropicalregion of the world including West indies and America.

The animal lives under stone, rock bark, lives etc in moist and dark place. It isnocturnal in habit and becomes active during night but lazy in day time.

Peripatus prefers insects, worms, termites, larvae pupae etc as food.

EXTERNAL FEATURE:The body of the animal is dark gray to brown on the dorsal

surface and pole on the ventral surface. Sometimes it is also red, blue or green colour.The body is elongated cylindrical and divided into head and trunk.

Head of the animal is small and round structure with an anterior acorn or prostomium. Thelater bears a pair of small eyes and antennae. Both antennae are made up of numerous ringlike structure and arranged in linear fashion. A pair of oral papillae present behind theantennae. It is small elevated structure with the opening of slime gland.

Mouth and anus lies at two ends of body. The former is ventral while thelater is internal in position. Mouth has a circular lip bearing small papellae. Only a pair ofmandible is present in the mouth. It has cuticular lining on the inner margin. While the outermargin bears suckle shaped chitinous teeth. Dorsal surface of buccal cavity has a musculartongue, which also bears chitinous teeth.

Trunk of the animal is divided into small segment. Each segment bears apair of legs. Segments are not distinctly marked externally. It can be counted by the no. oflegs. Peripatus has generally 14 – 93 pair of legs. Each leg has a large proximal triangularpart and pointed distal part. Proximal part has ring of papilla while the distal part iscomposed of paired claw.

Numerous small papilla presents over the body. They are more on the dorsal andless on the ventral surface. Each papilla has fine spines on the free end.

BODY - WALLIt is composed of an outer layer of epidermis. Inner layerof body wall is composed of muscle which hasouter coatof longitudinal and inner coat of circular muscles.Muscular layer is followed by a thin layer of coelomicepithelium. It not only forms the inner lining of body wallbut also forms outer covering of viscera.

COELOM:Body cavity of peripatus is the haemocoel.The actual

coelom is restricted in the gonad and nephridia. Thehaemocoel is divided into four longitudinal compartmentby the formation of incomplete septa. They are central,two lateral and a pericardial sinus or coelom. Alimentarycanal and nervous system are located in the centralhaemocoelomic, sinus while excretory organs are presentin lateral sinus and the heart lies in pericardial sinus.

DIGESTIVE SYSTEMIt comprises of alimentary canal and digestive gland. The alimentary canal leads to frommouth into pharynx. The latter is small structure and confined in the head region. It has‘X’ – shaped lumen lined by cuticular lining. Pharynx opens into reduced esophagus. It is

also thin walled structure composed of outer muscular, middle epithelial and innercuticular layer.The oesophagus open into a long tubular intestine running from anterior to posterior end

of trunk. It is composed of peritropic membrane which is absorptive in nature. The rectumis follows by the intestine. It is small tubular structure.Digestive gland is a pair of salivary gland. It is small tubular structure present between3rd- 10th trunk. It opens into pharynx through a narrow duct.

CIRCULATORY SYSTEM:It is of open type. The heart lies on the dorsal surface of gut in the pericardial sinus from1st to last segment of trunk. It is composed of small chambers which depends on the no.of body segment.Each chamber of heart communicates the flow chamber by small sphincter. Heart also

communicate with the pericardial sinus through ostia.

RESPIRATORY SYSTEM:Peripatus respires through trachea. It is branching system

present in the entire tissue of animal. Trachea open outside bodythrough minute segments. Nearly 75 stigmata are present in eachsegment. It has similar dorsal and ventral lip but the mouth of it is apermanent open structure. Flow of air is controlled by muscular.

EXCRETORY SYSTEMExcretion is performed by nephridia of annelidian pattern. A pair of

nephridia lie in each segment of the trunk, on in each lateralcompartment of haemocel. Each nephridium has a long tubularexcretory duct. It has different histology at different level. The duct iscoiled in its cores and open into long excretory vesicle, which is saclike structure. The vesicle opens outside body through excretory pore,located at the base of each leg. It has been calculated that peripatusexcretes a few drop of urine after 3 or 4 days.

NERVOUS SYSTEMIt is of primitive type. A pair of supra oesophagial ganglia present in the head

region. They are placed close to each other and fused to form brain of the animal.Anternualar end oesophageal nerve arise from it which supply respectively antennaand oesophagaus.A pair of ventro lateral nerve cord arise from its posterior aspects. They are placed

a part each other. Each nerve cord swells to form segmental ganglia at the level ofeach leg. Both nerve cord is connected by large no. of transverse branches. It showsbalder like structure.SENSORY ORGAN

Only a pair of small eyes are the sensory organ of this animal. It is generally 0.2-o.3mm in diameter. Each eye has an outer cuticular lens and inner rod cells. They lietogether. Therefore, paripatus is unable to perform image. It can only differentiatebetween light and dark.REPRODUCTIVE SYSTEMSexes are separate. Male reproductive organs are composed of a pair of tubulartestis followed by vasa-efferentia and vasdefene. Both vasdeferens unite to formejaculatory duct. Spermatophore are formed in this part. It opens outside bodythrough genital aperture lying a little anterior to the anus.

Female reproductive system has a pairs of small ovary. They areirregular and tubular. Each of it opens into a common sac likerespaticulum overum. A small oviduct arises from the anterior margin ofoverum. It also carries a lateral receptecula semines. The laterreceives sperm during copulation. A pair of uterus arise from theoviduct. It moves anteriorly from its origin and bent shapely towardsthe posterior end. Both of it unite again to form a small vagina. Thelater opens outside body through female genital aperture.

Actual fertilization takes place in the oviduct and embryonicdevelopment occur in the uterus. The peripatus is oviparous. Hencegives birth a minute youngs.

AFFINITYThis peculiar animal has combinations of both

Annelida and Arthropod characters. Before making any conclusionregarding its systemic position. Let us study its Annelida andArthropods characters.:

ANNELIDIAN CHARACTER:1. Thin flexi able cuticle over epidermis.2. Paired nephredia in each segment.3. True head absents.4. Muscular sheeth of body wall similar.5. Simple eye like Polychaeta.6. Slime gland present.7. Appendages hollow.8. Cilia present in reproductive track.

ARTHROPODIAN CHARACTER:1. Respiration by trachea.2. Excretory organ close type.3. Jaws with striped muscles.4. Salivary gland insects like.5. Haemocoel present.6. Heart with ostia.7. Head appendages modified to form mouth part.8. Nature and position of gonad similar to insects.9. Leg as locomotary organ.10.Leg are clawed.11.Brain large.

CONCLUSION:After the description of its characters it can be

concluded that the annelids characters prove it convergence towardsAnnelida. But arthropods character keeps it more close toarthropoda.

Previously it was regarded that peripatus was a connectingbridge between Annelida and Arthropoda. But present day studyproved that the trashed arthropods and peripatus have evolved fromthe same ancestor. The peripatus form a blind offshoot from the mainline of Arthropodian evolution. Due to certain differences withtracheal arthropods they have been kept in independent classOnycophora of Arthropoda.

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