Chapter 31 Phylum Acanthocephala

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. 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 • 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. 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