Introduction to Cestodes

General considerations:
-also know as "Tapeworms"
-Intestinal parasites found in aquatic and terrestial vertebrates.
-Flattened, ribbon-like, segmented worms.
-No alimentary canal, respiratory system, circulatory system.
-Ontogenesis of cestoda proceeds in most species.

Medically important:
-Order Pseudophyllidae.
-Order Cyclophyllidae.

Morphology and physiology of adult:
-No body cavity -> organs supported by cellular parenchyma.
-Tegument:
--Surface covered with a complex cuticle which is biochemically active.
--Cuticle with microtriches increasing area.
--Cuticle -> Absorption & Excretion

Osmoregulatory system:
-Flame-cell system:
--Connected to excretory canals which run the length of body.
--Concerned with excretion and osmoregulation.

Muscular system:
-All parts of cestodes are capable of considerable movement.
-Movement completed by muscle cell dispersed within body parenchyma.

Body Structure:
-Scolex:
--Used for attachment and locomotion.
--Pseudophyllidea -> 2 sucking grooves
--Cyclophyllidea -> 4 suckers +(Rostellum) +(hooks)
-Neck:
--Highly active region from which the tapeworm segment grows.
-Strobila:
--Comprising of a chain of Segment(Proglottids).
--Grow from the neck and pushes back.

Mature proglottid is hermaphroditic:
-Containing both male and female reproductive organs.
**Immature proglottids: none to one set of genitalia.
**Mature proglottids: both set of genitalia are fully developoed.
**Gravid proglottids: Uterus contains large numbers of eggs.

Reproductive system (Hermaphroditic)
*Protandry(androgyny): Male organs mature first.
*Gynandry(protogyny): Ovary matures first.

Male reproductive system (Ventral):
-Contain one to a large number of testes.
-Into single vas deferens -> currus sac containing the cirrus (penis-like).

Female reproductive system (Dorsal):
-Single ovary and usually lobed.
-Oviduct leads to ootype (where egg shell formation takes place)
-Ootype leads to vagina, provided with a receptaculum seminis.
-Uterus arise from the ootype.
--Pseudophyllidea:
---Opens to exterior by uterine pore.
--Cyclophyllidea:
---Ends blindly and does not open to the exterior.
---Assumes various shapes as it becomes filled with eggs.
---not discharged until the egg-filled segment break up.
-Genital pore:
--Opens either in the midline(Pseudophylidea) or laterally(Cyclophyllidea)
--Vagina and cirrus sac have common opening to exterior at the genital pore.
-Vitelline gland:
--Pseudophyllidea:
---Dispersed around with shape of small flowers.
--Cyclophyllidea:
---Triangular shape behind the ovary.

Larvae type -> Solid & Vesicular

Eggs:
-Outer->Egg capsule & Inner->Embryophore.
-Hexacanth embryo -> Oncosphaera.
-Pseudophyllidea:
--Operculated, embryo not yet developed.
-Cyclophyllidea:
--Not operculated, with Oncosphaera inside.

Larvae:
-Solid:
--Coracidium, Procercoid, Plerocercoid.
-Visceral:
--Cysticercus, Strobilocercus, Coenurus, Hydatide.
-Pseudophyllidea:
--Coracidium, Procercoid, Plerocercoid.
-Cyclophyllidea:
--Cysticercus, Strobilocercus, Coenurus, Hydatide, Cysticercoid, Tetrathridium.