Download Chapter 31 Phylum Acanthocephala

Chapter 31
Phylum Acanthocephala
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
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
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
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
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”
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
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
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
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
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
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
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
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
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