Recomendados
Mais conteúdo relacionado
Mais procurados
Mais procurados (20)
Semelhante a Phylum annelides.pptx
Semelhante a Phylum annelides.pptx (20)
Último
Último (20)
Phylum annelides.pptx
- 1. PHYLUM ANNELIDA CLASS POLYCHAETA(marine worms) CLASS OLIGOCHAETA(earthworms) CLASS HIRUDINEA(leeches) 1
- 2. Introduction •Includes elongate, vermiform creatures characterized by segmented bodies •Usually called segmented worms which distinguishes them from Platyhelminthes and Nematoda •Includes familiar leeches, earthworms and nereis, besides a large multitude of marine and freshwater species •Show metamerism: linear repetition of similar body parts along the main axis called metameres. •Annelids are the first to indicate cephalization(modification of the anterior end of the body to form a head) •Annelids are the first to have a true coelom 2
- 4. I. Polychaeta general reproductive features •Gonads are unspecialized and serially repeated •Sexes usually separate •Type: Neanthles or Nereis •Testes and ovaries are very simple consisting of masses of cells formed only during breeding season •By rapid proliferation and modification of coelomic epithelial cells surrounding the principle blood vessels •Reproductive cells are formed in each segment except near anterior end •Sexual cells detach from the coelomic epithelium and remain in the coelom till they are ripe 4
- 5. Reproductive system •In males, the sperm mother cells undergo active cell division forming smaller cells which eventually will develop into a mature sperm with a rod- shaped head and a long vibratile flagellum or tail •In females, the ovaries develop similarly and the relatively large rounded ova become fille with yolk globules •No gonoducts in Neanthes, the ripe ova and sperms escape into the sea through nephridia or temporary ruptures of body-wall •Larval typically a free swimming trochophore 5
- 6. Swarming (occurs at night during certain phase of the moon) •Reproduction occurs at definite periods(late July and August) •Sexually mature worms, well-filled wit eggs or sperms leave their burrows and swim to the surface of the sea in great numbers •Both sexes swim actively liberating eggs and sperms in the form of white clouds in the surrounding water •Eggs of gravid females give off a substances which triggers the males to shed sperms •Both sexes die soon after shedding their reproductive cells 6
- 7. Fertilization •As ripe ova and sperms are discharged into the sea, fertilization occurs externally into the surface layers •Concentration of breeding activities within a short time insures fertilization of huge numbers of eggs Heteronereis Phase- sexual phase •During a particular phase of the moon, the individuals leave their burrows and come out in large swarms for spawning •They swim actively in surface waters by undulating movements of the body with active paddling of the parapodia •The females attract the male and they shed ova and sperms like white cloud into the seawater fllowed by the death of the sexual individuals. 7
- 8. Embryogeny 1)Eggs •Surrounded by a thick, transparent gelatinous coat •Zona radiate disappears in fertilized egg(zygote) •Yolk granules accumulate at the vegetal pole making the egg telolecithal •Two polar bodies are extruded out at the pole and cleavage sets in 8
- 9. 2)Cleavage •Unequal and spiral type, but first two cleavage of the zygote are equal and vertical, resulting in four blastomeres lying in the same plane(picture) •After the 4 -celled stage, each blastomere shall give rise to only one quadrant of the embryo •Cells D and F will form the lateral quadrants •E the ventral quadrant •G (larger than the others) will form the dorsal quadrant •All succeeding cleavages are unequal and of the spiral type, so that the cells of one quarter are not placed directly over or below the cells of the adjacent quarters but somewhat displaced to the left or right. 9
- 10. •The micromeres give rise to the ectoderm and the macromeres to the mesoderm •One of the macromeres called somatoblast produces the mesoderm of the larva and the adult •Gastrulation occurs by epiboly •The blastopore forms the mouth and the stomodaeum Anus forms at a new site below the closed blastopore 10
- 11. 3) Trochophore •Usually minute, unsegmented, ciliated and almost pear-shaped pelagic creature with a protruded equator and the head end broader than the anal end •The front end shows the apical plate bearing apical cilia, sometimes a pair of pigmentes larval eyes and the cerebral ganglion •The ventral mouth, lying in the middle of the body, opens into a short ectodermal stomadaeum (oesophagus) leading into a wide endodermal mid-gut(stomach), followed by the ectodermal proctodaeum which opens to the exterior anus, lying at the narrow posterior end of the body 11
- 12. •Coelom absent at this stage, but a large space present between the alimentary canal (endoderm) and the ectoderm called the blastocoels, with a pair of larval excretory organs(protonephridia) •The body is surrounded by two circlets of cilia: prototroch and metatroch, sometimes telotroch, mesotroch and polytroch and rarely atroch 12
- 13. 13
- 14. Metamorphosis of trochophore •While drifting in the sea, the trochophore undergoes metamorphosis to change into the adult •Pre-oral part becomes the prostomium •Post-oral region elongates and becomes constricted into segments which develop the parapodia with long setae that can either be provisional or larval •First segment becomes the peristomium and last the pygidium 14
- 15. •Mesodermal band divides into three pairs of somites, each developing a cavity •Coelom later obliterates the blastocoels •Ciliary band disappear •Larva grow in size and length with the addition of new segments •After metamorphosis the young worm sinks to the bottom to become the burrowing adult worm 15
- 16. 16 Life cycle of the marine polychaete worm P . dumerilii
- 17. Asexual reproduction in polychaetes • Show various regenerative capabilities such as regenerating lost appendages like palps, tentacles, cirri and parapodia • Most can also regenerate posterior body segments however most cannot regenerate lost head • Regeneration is controlled by neuroendocrine secretions released by the central nervous system at sites of regrowth • Normal growth and addition of segments in young worms takes place immediately anterior to the pygidium in the growth zone • When the trunk is severed, the cut region heals over and then a patch of generative tissue, blastema forms 17
- 18. • The process occur simultaneously with the growth of the gut, which contributes part of the ecodermal origin • Undifferentiated cells from mesenchyme-like layers of the body also migrate to injured areas and contribute to the regenerative process • Neoblast cells which are ectomesodermal in origin contribute to tissues and structures associated with true mesoderm and other germ layers • Macroseptum is also produced by the ingrowth of the epidermis • Asexual reproduction results in a variety of regeneration patterns, including chain of individual, budlike outgrowth, or direct growth to new individuals from isolated fragments 18 Reproductive individuals budding from parents parapodia in syllis
- 20. 20
- 21. oligochaeta general reproductive features(Type: Pheretima) • Monoecious or hermaphroditic • Possess gonads which are limited within a few body segments only Male reproductive organs includes testes, testis sacs, seminal vesicles, vasa diferentia, prostate glands and accessory glands • Testes -minute, white and lobed, made up of a compact narrow base, from which arise 4 to 8 small digitate processes containing rounded cells called the spermatogonia • Testis sacs- encloses a pair of testes and behind each testis a ciliated spermiducal funnel and also communicates behind with a pair of seminal vesicles of the succeeding segment 21
- 22. • Seminal vesicles- also referred to as septal pouches are large and white, lies in the 11 and 12 segments • Spermiducal funnels- there are two pairs of ciliated spermiducal funnels(sperm- rosettes), one of them lying behind each testis in the same segment and enclosed within the same testis sac • Vasa deferentia- each spermiducal funnel leads behind into a slender, ciliated and thread-like sperm duct also known as the vas duct • Prostate glands-upon emergence, enclosed immediately in a common muscular sheath, along with the two vasa deferentia of the side, forming the common spermatic and prostatic duct which curve to open to the exterior by a pair of male genital pores • Accessory glands- -open to the exterior by a number of ducts on two pairs of genital papillae, situated externally 22
- 23. From the testes the spermatogonia are shed into the testis sacs, wherefrom they enter the seminal vesicles to undergo maturation and develop into spermatozoa. The mature sperms move back to the testis sacs, enter the spermiducal funnels, travel along the vasa deferentia and finally pass out through the male genital pores Female reproductive organs include ovaries, oviduct and spermathecae •Ovaries-Each ovary is a white compact mass made up of finger-like processes in which the ova are arranged in a linear series •Oviducal funnels- usually large saucer-shaped with much folded and ciliated margins lying behind each ovary in the 13th segment leading into the oviduct 23
- 24. • Oviducts-- two oviducts form short common oviduct, which opens to the exterior through the female genital aperture situated mid-ventrally on the 14th segment • Spermathecae-the spernathecae receive sperms from another worm during copulation which are stored in their diverticula in Pheretima and in the ampullae in other worms The mature ova shed from the ovaries are entangled by the oviduct funnels, travel along the oviducts, and pass out to the exterior through the female genital aperture to be laid inside the cocoon 24
- 25. Fertilization Earthworms are bisexual however self-fertilization does not occur. This is because they are protandrous, that is their testes ripen earlier than their ovaries. As a rule, cross fertilization takes place accompanied by copulation, after which eggs are laid in the cocoon. In earthworms, due to hermaphroditism, all individuals can lay eggs. However, have no specific role except increasing the rate of their reproduction 25
- 26. Copulation • The spermatozoa of one worm are transferred to another during a process termed copulation • Generally takes place at night or in the morning before sunrise, during rainy season, from July to October, and lasts for about one hour • During copulation, two worms apply on each other by their ventral surfaces with the head ends pointing in opposite directions, so that the male genital pores of each lie against the spermathecal pores of the other. • The areas surrounding the male genital apertures are raised into papillae, which are inserted successively from behind forwards, into the spermathecal pores of the other worm and discharge the spermatic and prosthetic fluid containing spermatozoa which are stored in the spermathecae, thus there is a reciprocal cross-fertilization 26
- 27. • After this interchange of sperms, the two worms separate and later lay their eggs in cocoons; fertilization is external, taking place in the cocoons Cocoon Formation (Type : Eisenia and Rhynchelmis) • The cocoon is Secreted as a vicid and gelatinous substance, forming a broad membranous band or girdle around the clittellum • It hardens gradually on exposure to the air into a tough but elastic tube which becomes the cocoon(egg capsule) • Slime tube is produced by the epidermal mucous cells around the clitellum over the cocoon • As the worm wriggles behind the slime tube, the cocoon is slipped forward towards the head 27
- 28. • On its way, the cocoon receives several ova from the female genital aperture and spermatozoa and an albuminous fluid is also deposited inside • Finally, when the cocoon is thrown off the head, its elastic ends close up and a yellowish and rounded cocoon is formed • Fertilization occurs after the cocoon has been deposited in moist earth For example: cocoon formation in Pheretima takes place in summer, during and after monsoon 28
- 29. • A cocoon may contain many fertilized eggs, but only one embyo develops further, growing at the expense of the others, serving as the nurse cells • Cleavage is holoblastic and unequal and the development is direct without any free larval stage • A hollow blastula is formed and later a gastrula by invagination • The mesoderm develops from two cells of blastula, called mesoblasts. They divide to form two mesoblastic bands, which later give rise to the coelomic epithelial lining • Swimming larval stage does not occur unlike the polychetes • The young worm, when fully grown crawls out of the cocoon in about 2 or 3 weeks • The baby worm resembles the adult at hatching, except for size and the absence of clitellum 29 Development
- 30. Regeneration • Earthworms do not reproduce asexually but have high power of regenerating segments removed at the ends of the body • When a worm is cut into 2, the front half will regenerate the tail but the posterior will not regenerate the head if 14 or more segments are cut off. The head will only regenerate if only 4 or 6 segments are cut off at the anterior end • Regeneration of a tail instead of a head sometimes occur, the posterior half may regenerate a tail instead of a head. Such a double tailed worm cannot feed and slowly starve to death 30
- 31. Grafting • Occurs in planaria normally • Experimentally, worms with two tails were produced by grafting the terminal parts of two short worms and long worms, by joining parts of 3 or more worms • Earthworms probably do not survive due to regeneration in the same way as planarians or sea-stars 31
- 32. Thank You
- 33. References