• Historical account
• A.  Acanthocephala not noticed until beginning of the 18th century, not distinguished until Koelreuther (1771) proposes the name Acanthocephala .
• B.  Muller (1776) unaware,of Koelreuther's work calls them Echinorhynchus.
• C.  Rudolphi (1809) formally gives them the name Acanthocephala.
• D.  Many species were described in the 19th century and all were placed under one generic name- Echinorhynchus.
• E.  Position of Acanthocephala was very uncertain; placed among flatworms, roundworms, chaetognatha, and finally lumped into the Aschelminthes.
• F.  Hyman removes Acanthocephala from the Aschelminthes making them into a separate phylum.

• Definition of the phylum- Endoparasitic, pseudocoelomate, and wormlike Bilateria, lacking a digestive tract, with the anterior end formed into an invaginated proboscis armed with hooks.

• External features:
• Body is elongated, becoming tapered at both ends, with size ranging from 1.5mm-.5m in length.
• Body wall is covered with a thin epicuticle of muccopolysacchorides and a noncelbular cuticle (1 micron or less).
• Body is divided into two major regions- the presoma and the trunk.
• Presoma is composed of the proboscis- a retractile organ armed with hooks and spines, and the neck- an unarmed region  posterior to the proboscis.
• Trunk is the major bulk of the animal, surface may be smooth, wrinkled, or irregularly ringed; some genera arm the trunk with spines.
• Proboscis serves as an attachment organ within the hosts intestine or for locomotion.
• Contains alternating rows of hooks and spines in a definite pattern.
• Hooks are larger structures with roots sunken deep in proboscis walls; spines are smaller structures lacking roots.
• Proboscis is invaginable and can be withdrawn into a muscular sac - the proboscis receptacle.
• Proboscis musculature-
• retractors: attach to base of proboscis sheath and run posteriorly dividing into ventral and dorsal retractors; function to withdraw proboscis into receptacle.
• protractor: originate in a circle at the base of neck and attach to posterior end of sheath; function to extend proboscis out of receptacle.
• Sense Organs are generally deficient and are of a tactile nature.
• Proboscis contains a terminal, small pit with a nerve ending.
• Male bursa and penis have genital ganglion which terminate into bulbous or spherical sense organs.
• Usually lack coloration but may appear red, orange, yellow or brown due to absorption of food.

• IV. Internal Features:   cuticle, epidermis, dermis
• A. Body wall made up of epicuticle, and muscle layer.
• B. Syncytial epidermis is composed of three layers.
• 1. Thin outer layer of parallel radial fibers and pores extending into the middle layer.
• 2. Middle layer of randomly arranged fibers.
• 3. -Very thick inner layer of radial fibers and a series of channels known as lacunae;s without definite walls but having
• C.  Lacunae- fluid filled channe3 a definite pattern; thought to be a food distributing system. Fluid moves only with body movements and system does not connect onto any body structures. circular
• D.  Musculature is a syncytial fibrous network of thin outer muscles and inner longitudinal muscles.
• E.  Pseudocoel is found in trunk region and slightly into presoma.
• F.  Inner layer epidermis extending into the trunk pseudocoel forms a pair of projections called leignisci that act as rese~iriors for the fluid of the lacunar system.
• G.  Nervous system-
• 1. "Brain" is a cerebral ganglionic mass located along the ventral border of the proboscis sheath.
• 2. System has two main lateral nerve bundles wrapped in a muscular sheath called a retinacula.
• 3. Male has two genital ganglia connected by a nerve ring.
• H.  Digestive system- mouth, anus, and digestive tube are completely lacking, nutrients taken in via pores and diffusion.
• I.  Circulatory system is absent.
• J.  Excretory system consists of a mass of flame bulb protonephridia which empty into a common sac (bladder). The bladder leads to the sperm duct in the male and the terminal portion of the uterus in the female.
• K.  Reproductive system is unique in Acanthocephala because the organs are suspended within a ligament sac.
• 1. Ligament sacs are hollow tubes of connective tissue w/wo muscle fibers that run the length of the body.
• a. Females have two sacs, a dorsal and a ventral.
• b. Males have one sac, a dorsal enclosing the testes.
• 2. All are dioecious with females generally longer that males.
• 3. Male system:
• a. Two testes, two sperm ducts that unite in the genital sheath to form the vas deferens which ends in a muscular cup, the bursa.
• b. Penis projects into the bursa which is eversible to grasp female.
• c. Cement glands are present and-drain into the sperm duct.
• 4. Female system:
• a. Fragmented ovaries are unattached in liagament sac forming free floating ovarian balls.
• b. Ligament sac ruptures when ova are ripe sending them into the pseudocoel.
• c. Uterine bell uses peristaltic contractions to collect developing eggs and pass them to the uterus.
• d. Vagina is also present.

• V. Reproduction:
• A. Sexual:
• 1. Internal fertilization; male bursa is wrapped around posterior of the females, cirrus is introduced into the gonopore, sperm migrate up the vagina, uterus, uterine tube. Male cement glands secrete a cement plug sealing up the gonopore preventing sperm escape.
• 2. Eggs develop in the pseudocoel until a larval stage provided with rostellum and hooks is reached; hard shell forms.
• 3. Uterine bell contractions pass larvae to exterior.
• 4. Expelled eggs are highly resisitant and remain viable for months.

• VI. Embryology:
• A.  Elliptical egg enclosed in four membranes.
• B.  Spiral determinate cleavage.
• C.  Four blastomeres are displaced due to elliptical shape.
• D.  Cleavage is not synchronous, stereoblastula is formed at 34 cell stage, syncytium forms.
• E.  Gastrulation by in wandering of nucleii, not definite.
• F.  Acanthor larvae forms, development stops until ingested by proper invertebrate host.

• VII. Life cycle:
• A. Vertebrate host- eggs containing partially developed acanthors are passed out in feces and are ingested by intermediate host.
• B. Intermediate host- usually an arthropod
• 1. Acanthor ruptures from egg, penetrates gut wall and lodges in the hemocoel.
• 2. Acanthor rounds up develops proboscis and loses hooks, rostellum larvae now called acanthella.
• 3. Once all the features of the adult are developed the animal is termed a cystacanth; gonads are nonfunctional.
• C. Second vertebrate ingests the intermediate host, cystacanth develops to sexual maturity in the intestine.

• VIII. Ecology and Physiology:
• A. Primarily anaerobic though they can survive in the presence of 02.
• B. Eggs can withstand temp. of -10 to 45 degrees C. and are viable up to three years.
• C. Number of worms per host is large: 1000 in a duck intestine.
• D. Reproductive capacity is high, up to 10,000,000 eggs per female.
• E. Very injurious to host as proboscis hooks cause damage to intestinal tissues.
• F. Glycogen stored in body wall and lacunar fluid,fatty substances deposited in epidermis and female reproductive system (ovaries).

• IX. Classification:
• 1. Order Archiacanthocephala- intestinal parasites of terrestial hosts primarily birds and mammals. Invertebrate hosts are roaches and grubs. Proboscial spines concentrically arranged, possess protonephridia
• 2. Order Palaeacanthocephala- parasites of fish, aquatic birds and mammals. Invertebrate host are crustaceans. Proboscis spines in alternating radial rows, no protonephridia.
• 3. Order Eoacanthocephala- parasites of fishes and reptiles. Invertebrate host are crustaceans. Proboscis hooks are radially arranged, no protonephridia, cement glands in male are syncytial.

• X. Phylogeny:
• A.  Acanthocephala closegy associated to Platyhelminthes:
• 1. Armed proboscis found in Cestodes.
• 2. Body wall musculature is distinctly flatworm-like.
• 3. Presence of flamebulb protonephridia.
• 4. Embryology is strongly Cestode- like.
• B.  Acanthocephala closely associated to Aschelminthes.
• 1. Body structure, presoma + trunk, seen in many groups.
• 2. Superficial segmentation found in several Aschelminthe groups rotifers,priapulids.
• 3. Pseudocoel is present although formation is not typical.
• 4. Flamebulb protonephridia.

Barnes, R. 1980. Invertebrate Zoolpgy. Philadelphia:Saunders Company. pp. 309-311.
Cheng, T. 1973· General Parasitology. New York: Academic Press. PP· 54~5-563-
Cleave, H. 1952. Speciation and Formation of Genera in Acanthocephala. Systematic Zoology. Vol. 1, No. 2.
Hyman, L. 1951. The Invertebrates: Acanthocephala, Aschelminthes, and Entoprocta. Vol. 3. New York: McGraw Hill. pp.459-531.