NEMATODES AND NEMATOMORPHS Flashcards
Many protostomes possess a cuticle
Non-living outer layer secreted by epidermis
Cuticle restricts growth and must be molted via ecdysis
Members of Ecdysozoa molt cuticle as they grow
NEMATODES
- About 25,000 species are described
⚬ As many as half a million may exist - Found in virtually all habitats in all biomes
⚬ Topsoil may contain billions per acre - exist in nearly all animal and plant species
Some are parasites of humans
Most are tropical
Phylum Nematoda: Roundworms
Distinguishing Characteristics Phylum Nematoda
⚬ Cylindrical shape
⚬ Nonliving cuticle
⚬ Cuticle shed during juvenile growth stages
⚬ Lack motile cilia or flagella, except for one species
⚬ Longitudinal muscles in body wall
⚬ Express eutely, a set number of cells
Classification of Phylum Nematoda
Chromadorea
Enoplea
scientific name
(Class Chromadorea)
⚬ Occurs in up to 25% of people in some areas of the southeastern U.S.
⚬ More than 1.27 billion affected worldwide
Ascaris lumbricoides
scientific name
(Class Chromadorea)
is found in intestines of horses
A. megalocephala
scientific name
(Class Chromadorea)
is found in pig intestines
A. suum
A female Ascaris may lay
which pass out in host’s feces
200,000 eggs a day
Ascaris Embryos develop into juveniles in
2 weeks
(Class Chromadorea)
⚬ Anterior end of these small worms has a hook-like curve (9–11 mm)
Sexes are separate
⚬ Large plates in mouth cut into intestinal mucosa and suck host’s blood
Hookworms
most common hookworm.
Necator americanus
(Class Enoplea)
Adult worms burrow into intestinal mucosa and females directly produce juvenile worms
⚬ Juveniles penetrate blood vessels and circulate throughout the body to all tissues and spaces
⚬ Penetrate skeletal muscle cells
Trichina Worm (Class Enoplea)
causes a potentially lethal trichinosis
Trichinella spiralis
(Class Chromadorea)
Most common helminthic parasite in the U.S. but causes little disease
Females, about 12 mm long, migrate to anal region at night and lay eggs, causing itching
Scratching the anal region contaminates hands and bedclothes
Pinworms
Adult Pinworms live in
large intestine and cecum
(Class Chromadorea)
⚬ Eight species of filarial nematodes infect humans
￭ Some cause serious diseases
Filarial Worms
Wucheria bancrofti and Brugia malayi live in
lymphatic system
Wucheria bancrofti and Brugia malayi Cause inflammation and blockage of the lymphatics vessels
caused by repeated exposure
Swelling and growth of connective tissue causes enormous swelling of body parts
Elephantiasis
“Horsehair worms”
resemble coarse hairs
Adult structures resemble those seen in nematodes: cuticle, epidermal cords, only longitudinal muscles, and a nervous system
* Adults are free-living in moist habitats
*Juveniles are parasites of arthropods
Phylum Nematomorpha
About ______ species are known in Phylum Nematomorpha
320
Form and Function
*Up to 1 m long but only 0.5 to 3.0 mm in diameter
* Anterior end is rounded
* Posterior end has two or three caudal lobes
*Body wall resembles nematodes but lateral hypodermal cords are absent
* Ventral nerve cord connected to the ventral hypodermal cord by nervous lamellae
Phylum Nematomorpha
Larvae absorb food from arthropod hosts
vestigial
Digestive system is vestigial
Phylum Nematomorpha
Phylum Nematomorpha
⚬ Juveniles may encyst on vegetation and are eaten by an arthropod such as a grasshopper
⚬ Larval stages have hooks that may be used to bore into a host
⚬ May use hooks to infect the integument or gut
⚬ Marine nematomorphs infect hermit crabs and other crabs
Gordius
Members of clade ecdysozoans do not share a common cleavage pattern
true
- Evolutionary relationships among ecdysozoans are
not well-understood
Cleavage is unique, not spiral or radial
Nematodes and nematomorphs
Cleavage in kinorhynchs, lorificiferans, and tardigrades Has yet to be studied
true
Nearly radial cleavage
Priapulids cleavage
Adaptive Diversifications of nematodes
*Nematodes show the most impressive adaptation
* Found in almost every habitat available to animals
* Body structure is plastic enough to allow adaptation
* Life cycle ranges from simple to complex
*Have been known to survive in suboptimal conditions
