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19. Mesozoa:-Cestode (Tapeworm):-Part 1 - Coggle Diagram
19. Mesozoa:-Cestode (Tapeworm):-Part 1
Scolex
Consist of holdfast structures like
1.Bothria - muscular grooves that provide attachment by pinching host tissue between them
2.Bothridia - semicircular, muscular structures that act by pinching host tissue
3.Acetabula – suckers
4.Rostellum - cone-like muscular structure that is located on the apical end of the scolex, and in most species is armed with hooks
Strobila – consist of proglottids
Acraspedote - indicating the proglottids are not overlapping
Craspedote - any given proglottid is overlapped by the previous proglottid
Can be broken down into three parts:
Immature – no well developed organs
Mature – with well developed organs
Gravid - proglottid segment contains fully developed eggs or shelled embryos
Cestode consisting of only one proglottid is known as monozoic, while cestode consisting of multiple proglottid is known as polyzoic
Older segments are pushed toward the tip of the tail as new segments are produced by the neckpiece
By the time a segment has reached the end of the worm's tail, only the reproductive tract is left.
The segment then separates, carrying the tapeworm eggs out of the definitive host as what is basically a sack of eggs - gravid
Strobilation: asexual process of forming segments
New proglottids are continuously formed in the neck just below the scolex
2.Along the length of the worm the proglottids increase in size and maturity, developing from premature to mature, carrying fully functional and active sexual organs), to the “gravid” stage in which essentially the entire proglottid is filled with the uterus and eggs
Detechment of proglottids
:
Apolysis –
detachment when reaching end of its strobilia
Pseudapolysis/ anapolysis
– eggs are released from a gravid segment through uterine pore
Hyperapolysis –
segment shed while immature and lead an independent existence in the gut while developing maturity
Tegument – covering layer
Cestodes do not have a mouth or any form of intestine
The entire uptake of nutrients occurs through multinucleate syncytial tegument ie absorb all their nutrients through their skin (lack of digestive tract)
projects out toward the host as numerous finger shaped tubes called microtriches similar to microvilli on gut mucosal cell
Microtriches serve to increase absorptive area of the tegument
Organ system
No digestive, circulatory, respiratory or skeletal system
Nervous system
Main nerve center = scolex
Osmoregulation (excretory)
cestodes use flame cells (protonephridia), located in the proglottids, for excretion
The main excretory canals run the length of the strobili from the scolex to the posterior end.
Posteriorly the two pairs of canals merge into an excretory bladder with a single pore to the outside
Embedded throughout the parenchyma are flame cell protonephridia
have a cluster of flagella that looks like a flickering flame when viewed under the microscope
function like a kidney, removing waste materials through filtration
Reproductive System of Cestod
e
Mostly monoecious (hermaphrodite)
Usually, male organs mature first and produce sperm that are stored until the maturation of ovary = protandry / androgyny
In a few species, ovary mature first = protogyny / gynandry
Male reproductive organ
Consist of many testes each with very thin vas efferens that channels sperm to genetal pore
Vas deferens may be simple duct or may have sperm storage capacity in convolution (coil/twist) or spherical external seminal vesicle
Female reproductive organ
Consist of ovary and associated structures = oogenotop
Vitelline cells contribute yolk and shell material
Oocytes mature and leave ovary through oviduct while Meiosis I takes place
Sperm than penetrate completion of meiotic divisions
Vitelline cells from vitelline glands pass through vitelline duct join with zygote
Mehli’s gland then secrete thin membrane around zygote and its associated vitelline cells
Shell formation is then completed from within
Developmental stages
The zygote develops into an oncosphere
In some species with aquatic hosts the inner envelope develops into a ciliated epithelium.
These motile coracidia have to be taken up by an intermediate host within a short time
Once inside the gut of the host the oncosphere sheds the ciliated layer and invades and differentiates into a procercoid