Chapter 15 - Nematodes and Rotifers

Notes for Chapter 15:
Nematodes and Rotifers ("Pseudocoelomates")

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or back to Chapter 14
or ahead to Chapter 16

Under Construction!

Note, Ch. 15 is not listed on the schedule. We will cover nematodes to some extent when we discuss flatworm parasites (Ch. 14). Rotifers were already covered a bit in relationship to parthenogenesis (Ch. 7). Both nematodes and rotifers will be covered in lab as representative pseudocoelomates. Even though both groups, and other pseudocoelomates, can be extremely important, they have been deemphasized this semester in order to devote more lectures to general topics in the first part of the course and particular molluscan/arthropod/vertebrate groups in the latter part of the course. I provide notes to them below for those who would like to explore these important or simply fascinating groups. See these links for generally neglected taxa in this course: Nematoda, Priapulida, Chaetognath, Acanthocephala, Nematomorpha

Four Phyla with a lophophore: Entoprocts, Bryozoans (or Ectoprocts), Brachiopods, Phoronids

interstitial animals: Gnathostomulida, Gastrotricha, Kinorhyncha, Rotifera, Loricifera, Tardigrada

Introduction:

Concepts

pseudocoelom (from embryonic blastocoel)
tube-within-a-tube
cuticle (often made of chitin)
molting
eutely (nuclear constancy)
two views of bilaterian ancestor
pseudocoelomates are polyphyletic
common traits of tiny animals
alternate asexual/sexual reproduction in rotifers

Phyla whose members are "pseudocoelomate"

Priapulida (large free-living worm)
Kinorhyncha (tiny free-living)
Loricifera (tiny free-living)
Gastrotricha (tiny free-living)
Nematoda (tiny free-living to huge parasites)
Nematomorpha (medium-sized parasite)
Rotifera (tiny free-living)
Acanthocephala (medium-sized parasite)
Tardigrada (tiny free-living)

Features common to "micrometazoans" (not a taxon)
1. Minute animals
2. Copulate
3. Eutely (cell or nuclear constancy)
4. Body does not divide asexually
5. Little or no regeneration
6. Presence of anus (some reduced)
7. body cavity modified
(pseudocoelom with more or less
fluid depending on whether or not
there is eversible organ present)

I. Nematodes
More Links

Key Terms:

Featured organisms:

Enormous number of species
– Ranks 3rd after arthropods and molluscs (number of described species)
– Probably should be 1st (Not enough nematode taxonomists)
Every conceivable habitat on Earth
– Enormous numbers
– Many are free-living
– Also important animal/plant parasites
– Parasites resemble flatworms in adaptations
Extremely important as model system
– C. elegans ("the worm") is nematode lab rat

II. Rotifers
Rotifers and How to Find Them

Key Terms:

Featured organisms:

feed with ciliated crown, the corona
- "chew" with mastax
hang on with pedal glands
about 1,800 species, mostly in freshwater
show nuclear constancy (eutely)
can often endure prolonged desiccation
- "just add water" for resumed activity
usually large females and small males
- the bdelloids have only females
- these females are parthenogens (asexual)
- the monogononts alternate between asexual and sexual reproduction (Fig. 15-4)
- haploid egg + sperm = dormant zygote

Click link to return to Lecture Schedule
or back to Chapter 14
or ahead to Chapter 16