BSc 1st Year Lower Non-chordates Phylum Platyhelminthes Sample Model Practice Question Answer Papers
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Q.1. Mention the distinguishing characters of Phylum Platyhelminthes. Classify giving characters and examples of different orders.
Ans.1. Distinguishing Characters
1. Possess tissue-organ level of organisation.
2. Bilaterally symmetrical and dorso-ventrally flattened, soft bodied unsegmented worms.
3 There is beginning of cephalisation. The anterior end forms an incepient head with sensory cells and sense organs or with hooks or suckers or both.
4. With three embryonic layers-the ectoderm, mesoderm and endoderm.
5. The exo and endoskeletons are absent and hard parts if any (hooks, spines, etc.) are formed of scleroproteins.
6. The epidermis is soft, syncytial and ciliated (Turbellaria) or is covered over by cuticle (Trematoda and Cestoda).
7. Mesoderm layer gives rise to :
(a) Muscles : Circular, longitudinal, diagonal muscle fibres develop from mesoderm and form bundles. These help in wriggling movement of worms.
(b) Protonephridia : These are called flame cells. These help in excretion and osmoregulation.
(c) Reproductive organs : The genital ducts, penis, seminal vesicles, yolk glands or vitelline glands, etc. all accessory organs develop from mesoderm. These help in internal fertilisation.
Classification
Phylum Platyhelminthes is divided into three classes :
Class 1. Turbellaria (Eddy worms)
1. Mostly free-living or non-parasitic forms.
2. These may be marine, freshwater or terrestrial.
3. Body unsegmented, dorsoventrally flattened and leaf-like or rounded or oval.
4. Epidermis cellular, syncytial and partly or wholly ciliated with unicellular cyanophilous glands and specialized rod-shaped hyaline bodies, the rhabdites. Rhabdites produce mucus.
5. Suckers are absent. The adhesive organs are in the form of glandulo-epidermal and glandulo-muscular adhesive organs.
6. Skin variously coloured and pigmented.
7. Intestine either absent (Acoela), simple and sac-like (Rhabdocoela) or branched. Mouth is ventral.
8. Tango-chemo-and photo-receptors are present.
9. These move by cilia or by cilia and muscular undulations of the body. Mucus produced by rhabdites and other epidermal glands help the animal to slip on the substratum.
10. Nearly all are predators, some are scavangers and a few may be parasitic.
11. Have great power of regeneration and asexual reproduction.
12. Mostly hermaphroditic; development is direct.
Class Turbellaria includes both primitive and specialised flatworms. These are separated into two groups :
Group A. Archophorans
1. Primitive turbellarians.
2. Yolk glands absent.
3. Eggs endolecithal (i.e. eggs with internal yolk).
4. Cleavage spiral.
ORDER 1. Acoela
1. Small, marine, less than 2 mm in length.
2. Mouth ventral; pharynx non-muscular and intestine absent.
3. Protonephridia (i.e. flame cells), gonads, gonoducts, vitelline glands absent.
4. Gametes are produced by scattered gametogonia (the specialised mesenchyme cells).
5. Mostly free living, found under stones, algae or on bottom mud. Some are commensal living in the intestine of sea urchins and sea-cucumbers.
Examples: Convoluta, Afronta, Amphiscolops
ORDER 2. Macrostomida
1. Marine or freshwater forms, small in size (0.8-11 mm)
2. Pharynx is simple and non-muscular, intestine sac-like.
3. One pair of ventro-lateral nerve cords.
4. Protonephridia and gonads present.
Examples: Microstomum, Macrostomum.
Microstomum feeds on Hydra and stores its undischarged nematocysts in its skin.
ORDER 3. Polycladida
1. Marine, moderate in size (3-20 mm in length)
2 Pharynx plicate; intestine highly branched.
3. Gonads many, scattered, yolk glands absent.
4. Male and female gonopores separate.
5. Greatly flattened and oval body with one pair of dorsal or marginal tentacles. Have a well-developed brain and numerous eyes.
6. They feed on coelenterates and store their undischarged nematocysts in their skin.
Examples: Leptoplana, Notoplana, Cestoplana, Thysanozoon.
ORDER 4. Catenulida
1. Freshwater turbellarians; small in size (0-9-9 mm).
2. Pharynx simple and ciliated; intestine sac-like.
3. Gonads unpaired, male gonopore dorsal and above pharynx.
4. Female genital ducts absent.
Examples: Catenula, Stenostomum.
ORDER 5. Nemertodermatida
1. Small, marine flatworms, similar to Acoela.
2. Contain a digestive tract.
3. Sperms are uniflagellate.
Example: Nemertoderma
ORDER 6. Haplopharyngida
1. Small, marine flatworms, similar to Macrostomatids.
2. A proboscis and a permanent anus present.
Example: Haplopharynx.
Group B. Neoophorans
1. Advanced turbellarians.
2. Yolk glands present.
3. Eggs ectolecithal (ovum or egg nucleus is surrounded by a mass of yolk cells).
4. Cleavage is modified spiral.
ORDER 1. Rhabdocoela
1. Small, marine and freshwater turbellarians (less than 3 mm).
2. Pharynx bulbous and forms a proboscis that can protrude out of mouth.
3. Intestine simple and unbranched.
4. Nerve cords one pair and ventro-lateral.
5. Gonads one or two pairs. Yolk glands present.
Examples: Mesostoma, Gyratrix.
ORDER 2. Tricladida
1. Marine, freshwater or terrestrial; large in size (3 to 60 cm in length).
2. Mouth midventral; pharynx plicate and protrusible; intestine has highly branched branches.
3. Protonephridia form paired lateral network with many nephridiopores.
4. Testes numerous, ovaries two: penis with penis papilla and oviduct with copulatory bursa.
Examples: Planaria, Dugesia. Gunda, Geoplana, Bipalium.
ORDER 3. Prolecithophora or Allocoela
1. Small, marine or freshwater forms.
2. Pharynx bulbous or plicate; intestine simple and straight or branched but no diverticula.
3. Protonephridia paired with two or three branches.
4. Testes numerous, ovaries one pair; follicle-like yolk cells present.
Example: Plagiostomum.
Class 2. Trematoda (Flukes)
1. All parasitic; may be ectoparasites or endoparasites.
2. Commonly known as ‘flukes’ (=flat).
3. Body unsegmented, flattened and leaf-like or cylindrical.
4. Epidermis, cilia, hooks and spines absent.
5. The outermost covering of the body is thick cuticle, called tegument.
6. Usually with two sets of suckers, anterior oral sucker and posterior ventral sucker.
7. Digestive tract bifurcated and highly diverticulated. Mouth is present but anus is absent.
8. These have three pairs of longitudinal nerves.
9. Mostly hermaphrodite. Development is direct in ectoparasites and indirect in endoparasites. Endoparasites may have one or more larval stages. Class Trematoda is divided into following 3 orders:
ORDER 1. Monogenea or Heterocotylea
1. Monogenetic trematodes, found as ectoparasites in cold blooded vertebrates.
2. Only one host in the life-cycle.
3. Oral suckers absent or poorly developed.
4. Posterior adhesive organ (opisthaptor) bears suckers and hooks.
5. Excretory pores are paired.
Examples : Gyrodactylus, Dactylogyrus, Polystomum, Diplozoon.
ORDER 2. Digenea
1. Endoparaiste in vertebrates and invertebrates.
2. Two to four hosts in the life-cycle.
3 Suckers two : oral sucker around mouth and ventral sucker acetabulum on the ventral surface.
4. Hooks and posterior adhesive organ (opisthaptor) absent.
5. Excretory pore single and median.
6. Life-cycle complicated with the numerous larval stages and 2 to intermediate hosts.
Examples: Fasciola, Schistosoma (blood fluke). Aspidogaster Cotylogaster, paragonimus, Chlonorchis.
ORDER 3. Aspidobothrea or Aspidogastrea
1. Endoparasites in the gut of fishes and reptiles.
2. Life cycle includes only one host.
3. Oral sucker absent; ventral sucker large covering the entire ventral surface and is subdivided by septa.
4. Hooks absent. Intestine simple and unbranched.
5. Excretory pore single.
Examples : Aspidogaster, Cotylogaster.
Class 3. Cestoda or Cestoidea (Tapeworms)
1. Highly specialised endoparasites.
2. Body flattened and ribbon-like differentiated into scolex, neck and strobila.
3. Body covered with thick and non-ciliated cuticle called tegument. It is without spines.
4. Scolex with hooks and suckers for attachment.
5. Neck is very short and keeps on adding new proglottids. It is region of proliferation.
6. Strobila is differentiated into proglottids.
7. Mouth, digestive tract and sense organs absent.
8. Hermaphrodites, embryo bears hooks.
Subclass (1) Cestodaria
1. Body unsegmented and without scolex.
2. Only one set of reproductive organs.
3. Larva lycophore or decacanth with 10 hooks.
4. Endoparasite in the intestine and coelomiec cavities of most fishes and rarely in reptiles. (BSc 1st Year Lower Non-chordates Phylum Platyhelminthes Sample Model Practice Question Answer Papers)
ORDER 1. Amphilinidea
1. Endoparasite in the coelom of primitive fishes.
2. Anterior end with protrusible proboscis and frontal glands.
3. Sucker and bothria absent.
4. Male genital pore and vagina posterior and uterus coiled and opens at the anterior end.
Example: Amphilina, Gigantolina.
ORDER 2. Gyrocotylidea
1. Endoparasite in chimaeroid fishes.
2. Anterior end with eversible proboscis.
3. Anterior sucker cup-like and there is a posterior rosette-shaped adhesive organ.
4. Uterus straight
5. All genital pores open at the anterior end.
Example: Gyrocotyle.
Subclass (2) Eucestoda
1. Body differentiated into scolex, neck and strobila.
2. Scolex with hooks and suckers.
3. Each proglottid contains one set of reproductive organs.
4. Larvae with 6-hooks (Hexacanth).
5. Endoparasites in gut of vertebrate hosts.
6. Very large, size ranges from 1mm to 25 metres.
ORDER 1. Proteocephalidea
1. Scolex mobile with four cup-shaped suckers and a terminal sucker or glandular organ. (BSc 1st Year Lower Non-chordates Phylum Platyhelminthes Sample Model Practice Question Answer Papers)
2. Common genital atrium marginal.
3. Ovary bilobed; uterus with many lateral diverticula.
4. Parasite in freshwater fishes, amphibians and reptiles.
Examples: Proteocephalus, Ophiotaenia.
ORDER 2. Tetraphyllidea
1. Scolex with four suckers present on ear-like outgrowth (bothridia); hooks are also present. (BSc 1st Year Lower Non-chordates Phylum Platyhelminthes Sample Model Practice Question Answer Papers)
2. Common genital atrium marginal.
3. Parasitic in intestine of elasmobranch fishes.
Examples: Phyllobothrium, Antobothrium.
ORDER 3. Diphyllidea
1. Scolex with two stalked suckers (bothridia) and a spiny head stalk. (BSc 1st Year Lower Non-chordates Phylum Platyhelminthes Sample Model Practice Question Answer Papers)
2. Intestinal parasites of elasmobranchs.
Example: Echinobothrium.
ORDER 4. Cyclophyllidea or Taenioidea
1. Scolex with four suckers and two rows of hooks.
2. Rostellum retractile.
3. Genital pores lateral.
4. Parasites in amphibians, reptiles, birds and mammals.
Examples : Taenia, Moniezia, Echinococcus. Contugnia.
ORDER 5. Pseudophyllidea
1. Scolex with 2 shallow bothridia; one dorsal and one ventral.
2. Genital aperture midventral.
3. Parasites in fishes and terrestrial vertebrates.
Examples: Dibothriocephalus, Amphicotyle, Diphyllobothrium.
ORDER 6. Aporidea
1. Scolex without suckers; in some cases glandular rostellum and large suckers are present. (BSc 1st Year Lower Non-chordates Phylum Platyhelminthes Sample Model Practice Question Answer Papers)
2. External segmentation absent.
3. Male and female genital apertures not external.
4. Parasite in birds.
Examples: Nematoparataenia, Gastrotaenia.
ORDER 7. Caryophyllidea
1. Body unsegmented.
2. Genital and uterine apertures on same flat surface.
3. Eggs non-embryonated at the time of laying.
Examples: Glaridacris, Caryophyllaeus.
ORDER 8. Trypanorhyncha
1. Scolex with 2 or 4 sucking grooves or bothria and four tentacles armed with hooks and spines. (BSc 1st Year Lower Non-chordates Phylum Platyhelminthes Sample Model Practice Question Answer Papers)
2. Vitellaria in a continuous layer in cortical parenchyma.
3. Parasite in elasmobranch fishes.
Examples: Hepatoxylon, Tetrarhynchus.
ORDER 9. Spathebothridea
1. Scolex without suckers.
2. Strobila with internal segmentation.
3. Parasite in primitive fishes.
Examples: Bothrimonus, Diplocotyle.
BSc 1st Year Lower Non-chordates Phylum Platyhelminthes Sample Model Practice Question Answer Papers
BSc 1st Year Lower Non-chordates Phylum Platyhelminthes Sample Model Practice Question Answer Papers
BSc 1st Year Sample Model Practice Mock Test Question Answer Papers
BSc 1st Year Lower Non-chordates Phylum Platyhelminthes Sample Model Practice Question Answer Papers