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Chapter 31 Phylum Acanthocephala

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1 Chapter 31 Phylum Acanthocephala

2 Form and Function Throughout their evolution there has been a reduction in muscular, nervous, circulatory and excretory systems; a complete loss of a digestive system They are pseudocoelomates; pseudocoelom is essentially filled with reproductive organs

3 General Morphology The body consists of an anterior proboscis, a neck, and a trunk The proboscis is highly variable in shape and is covered by numerous sclerotized hooks The proboscis is hollow and fluid filled; it can be everted (extended) or retracted into a proboscis receptacle

4 General Morphology cont.
Lemnisci are paired organs that extend into the body cavity from the neck region; central canal of each lemniscus is continuous with the lacunar system The lemniscus serves as a fluid reservoir when the proboscis is invaginated; may also have a function in fat metabolism

5 The rest of the body, posterior to the neck is called the trunk
General Morphology cont. Located within the receptacle is a nerve ganglion that comprises the cerebral ganglion (brain) The rest of the body, posterior to the neck is called the trunk Many species have spines embedded in the trunk to aid in the attachment to the host’s mucosa of the intestine The trunk houses the reproductive structures; also functions in absorbing and distributing nutrients

6 Tegument The tegument is a syncytium with many functions, including protection, inactivation of the host’s digestive enzymes by charge effects, osmoregulation, concentration of nutrients, ion transport, etc The outer surface coat is a carbohydrate rich glycocalyx Closely packed pores at the tegument surface lead to pore canals that branch and anastomose This fluid filled system of channels is called the lacunar system It’s function is obscure; it may be important to the body wall musculature or serve as some kind of “circulatory system”

7 Reproductive System Male System
2 testes, each with vas efferens leading to a common vas deferens and/or a small penis Males typically have cement glands; secrete a copulatory cement, allowing the vagina to be plugged following sperm transfer Males also have a copulatory bursa, a bell shaped structure that is typically invaginated into the posterior end of the body cavity A muscular sac is attached to the bursa and when it contracts fluid is forced from the lacuna system of the bursa causing it to evert

8 Reproductive System cont.
Female System Ovary is actually fragments of ovarian balls, that lie in the ligament sac or pseudocoel Posterior end of the ligament sac is attached to a muscular uterine bell; allows mature eggs to pass through into the uterus, vagina, and out the genital pore into the feces; immature eggs are returned to the ligament sac

9 Excretory System Nervous System
Protonephidria serve as excretory organs Nervous System Consists mainly of a ganglion in the proboscis sheath and of nerves that connect the ganglion to other organs and tissues A pair of genital ganglia, with nerves is present in the male Sense organs are found in the proboscis and in the penis and male bursa

10 Early Development Fertilized eggs go through early embryological development in the ligament sac or pseudocoel When eggs emerge from the gonopore they contain hooked larvae called the acanthor A host must eat the eggs before the embryos can hatch There is typically one intermediate host; no free-living stages occur

11 Generalized Life Cycle
An egg eaten by an arthropod hatches into an acanthor, develops into an acathella, becomes a juvenile (which may progress to a cystacanth), and is eaten by the final, vertebrate host, in which it becomes an adult Within the invertebrate host, the acanthor is liberated from the egg, bores through the gut wall, and develops into an acanthella The acanthella then becomes a juvenile The vertebrate host becomes infected by eating the arthropod intermediate host

12 Life Cycle of Moniliformes moniliformes/dubius
Lives in the small intestine of rats, mice, dogs, and cats Eggs are eaten by beetles (flour beetles) or cockroaches Acanthors are deposited in the gut and leave with the feces If acanthors are ingested by a cockroach, they hatche from the shell and penetrate the wall of the digestive tract

13 The acanthellae develop into the infective stage - cystacanth
Life Cycle of M. moniliformes/dubius cont. They pass through the gut wall, enter the homocoel and undergo growth and differentiation into an acanthellae The acanthellae develop into the infective stage - cystacanth If a cockroach is eaten by a rodent, it everts its proboscis and embeds in the small intestine Male and females grow to maturity and copulate; shelled acanthors then develop in the pseudocoel of the female

14 Development in the Cockroach
The shelled acanthor is stimulated by pH and carbon dioxoxide tonicity of the external medium to secrete a chitinase which acts upon the chiton layer of the shell Acanthor then penetrates the gut and goes to the hemocoel Development in the Rat Dormant cystacanth in the cockroach are eaten by the rat It is then activated by bile salts and bicarbonate of the small intestine Results in the eversion of the proboscis and its attachment to the host mucosa

15 Effects on Behavior Cockroaches infected with Moniliformes moniliformes move more slowly, travel less and spend more time on exposed surfaces These behavioral changes apparently increase the probability of transmission

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