The document discusses the classification and evolution of various worm-like phyla. It describes two main hypotheses for their phylogeny, whether they are monophyletic or polyphyletic. The document then summarizes several aschelminth phyla, including their defining characteristics, representative genera, habitat and lifestyle. It notes that some phyla are now grouped under Lophotrochozoa or Ecdysozoa based on whether they molt. In conclusion, it discusses the concept of worms and their possible evolution from a common worm-like ancestor.

1. (Lophotrochozoan and
Ecdysozoan Phyla)

2. EVOLUTIONARY PERSPECTIVE
The seven different phyla grouped for convenience as the
aschelminthes are very diverse animals. They have obscure
phylogenetic affinities, and their fossil record is meager. Two
hypothesis have been proposed for their phylogeny. First (a
pseudocoelom, a cuticle, a muscular pharynx, and adhesive
glands.) and second, (various aschelminth phyla are not
related to each other; thus’ they are probably polyphyletic.
The absence of any single unique feature found in all groups
strongly suggests independent evolution of each phylum.
The similarities among the living aschelminths may simply
be the result of convergent evolution as those various
animals adapted to similar environments.

3. ASCHELMINTHES THAT DO NOT MOLT
(LOPHOTROCHOZOAN PHYLA)
Those aschelminthes (rotifer and acanthocephalans)
that do not molt are currently placed in the
superphylum Lophotrochozoa.
Since the rotifers and acanthocephalans are so
closely related, some zoologists have recently
proposed that they be included as a single phylum
called Syndermata.

5. CLASSIFICATION OF THE ROTIFERA
Phylum Rotifera
A ciliated corona surrounding a mouth; muscular pjharynx present
with jawlike features; nonchitinous cuticle; both freshwater and
marine species. About 2,000 species.
Class Seisonidea
A single genus of marine rotifers that are commensals of
crustaceans; large and elongate body with reduced corona. Seison .
Only 2 species.
Class Monogononta
Rotifers with one ovary; mastax not designed for grinding; produce
mictic and amictic eggs. Males appear only sporadically.
Conochilus, Collotheca, Notommata. About 1,400 species.

6. PHYLUM ACANTHOCEPHALA
Adults acanthocephalan are endoparasites in the intestinal
tract of vertebrates. Two hosts are required to complete the
life cycle. Acanthocephalans are generally small, although
one important species, Macracanthorhynchus hirudinaceus,
which occurs in pigs can be up to 80 cm long.
Once in the invertebrate, the larva emerges from the egg and
is now called an acanthor. It burrows through the gut wall
and develops into acanthella and, eventually, into a
cystacanth.

7. ASCHELMINTHES THAT MOLT
(ECDYSOZOAN PHYLA)
Zoologists have now placed in the superphylum Ecdysozoa
the following Aschelminth phyla: Nematoda,
Nematomorpha, Kinorhyncha, Loricera, and Priapulida. All
animals that molt their cuticle are more closely related to the
arthropods than to other aschelminths.

9. PHYLUM NEMATODA
Nematodes, or roundworms. About 16,000 species
have been described to date.
Class Secernentae (Phasmidea)
Both free living and parasitic species; excretory
system present. Ascaris, Enterobius, Rhabditis,
Necator, Tubatrix, Wuchereria. About 5,000
described species.
Class Adenophorea (Aphasmidia)
Some parasitic species occur. Dioctophyme,
Trichinella,Trichuris. About 3,000 species.

10. Ascaris lumbricoides: The Giant Intestinal Roundworm of Humans
As many as 800 million people are infected with this roundworm.
Adults live in the small intestine of humans. They produce large
numbers of eggs that exit with the feces. They molt twice in the lungs,
migrate up the trachea, and are swallowed.
Enterobius vermicularis: The Human Pinworm
Pinworms are the most common roundworm parasites in the United
States. Adults become established in the lower region of the large
intestine. At night, gravid females migrate out of the rectum to the
perianal area, where they deposit eggs contanining a first-stage larva
and then die.
Necator americanus: The New World Hookworm
The adults live in the small intestine, where they hold onto the
intestinal wall with teeth and feed on blood and tissue fluids.

11. Trichenella spiralis: The Porkworm
Adult Trichinella spiralis live in the mucosa of the small intestine of
humans and other carnovores and omnivores. In the intestine, adult
females give birth to young larvae that then enter the circulatory
system and are carried to skeletal muscles of the same host. Diseases is
called trichinosis.
Wuchereria spp: The Filarial Worms
These elongate and, threadlike nematodes live in the lymphatic system,
where they block the vessels. The fluid and connective tissue
accumulation causes the anlargment of various appendages, a condition
called elephantiasis.

12. PHYLUM NEMATOMORPHA
Commonly called either horsehair worms or Gordian worms.
The adults are free-living , but the juveniles are all parasitic
in arthropods. They have a worldwide distribution and can
be found in both running and standing water. Once mature,
the worm leaves its host only when the arthropod is near
water. Sexual maturity is attained during the free-living adult
phase of the life cycle.

13. PHYLUM KINORHYNCHA
Kinorhynchs are small, elongate, bilaterally symmetrical worms
found exclusively in marine environments, where they live in
mud and sand. Because they have no external cilia or locomotor
appendages, they simply burrow through the mud.
PHYLUM PRIAPULIDA
The priapulids are a small group (only 16 species) of marine
worms found in cold waters. They live buried in the mud and
sand of the seafloor, where they feed on small annelids and other
invertebrates.

14. EVOLUTIONARY INSIGHTS
What Are Worms?
The generic use of the word “worm” also occurs in roundworms,
hookworm, porkworm, filarial worm, horsehair or Gordian
worms. Worms can be defined as animals that do not possess
legs, are not covered by a protective shell, are not deuterostomes,
do not bear a lophophore, are soft-bodied, and are either
flattened or rounded in section.
If ancestral animal was wormlike, as many phylogenetic
schemes postulate, it would follow that a wide variety of worms
might evovlve from vermiform ancestor, and that ultimately
some of these worms might give rise to non-worms.