Lecture 16-Rotifers.pdf - Classes at U. of L.

Phylum Rotifera—”wheel bearers”
•Microscopic(2000 spp.
•Bilateral symmetrical pseudocoelomates
•Body somewhat cylilndrical with an anterior ciliated disc (corona) and a posterior
forked tail (foot)
•Body covered with a cuticle that is sometimes modified into a hardened shell-like
cover (lorica)
•Digestive tract usually complete with a mouth, pharynx, stomach, intestine and
an anus.
•Pharynx equipped with movable jaws (mastax, trophi) usually for grinding up
algae
•No obvious eyes or other sense organs.
•Parthenogenesis common, males unknown in many species, about 1500 species
•Mostly freshwater species—believed to have originated in FW—common in the
plankton of lakes, and living on plants and attached algae as well in both lakes
and streams.
•Exhibit eutely—body has a constant number (about 1000) of cells, that grow in
size as the animal grows larger.

Anatomy of Euchlanis—a planktonic rotifer
Corona
Nephridia—flame cells
Gastric glands
foot
mastax
Trophi (2)
toe
Urinary bladder
oviduct
intestine
Vitelline gland
stomach

Close-up of the jaws-trophi of a rotifer
Key:
F fulcrum; M
manubrium; R
ramus; U uncus.
Once food is captured by the corona it passes into a mouth and a muscular pharynx called the
mastax, which is equipped with a set of grinding jaws called the trophi. The ground up food is
then passed on to the esophagus and stomach.

Class Bdelloidea—means “leech like”
Body large (> 0.3 mm) elongate, soft bodied forms,
creeping worm-like movement, with no lorica, head
and food flexible and retractile, creeping forms
benthic or epiphytic, foot with two toes, paired
ovaries, corona with two circular lobes
Sex is unknown in bdelloids, only parthenogenetic
females exist, > 300 known species
They are one of the most ancient asexual lineages
(at least 40 million years)
Many are capable of cryptobiosis
Corona, two
circular lobes
paired ovaries
Philodina—mid-section distinct from tail section
Philodina

Closeup of the ramate mastax of
Philodina
trophi of mastax
Ramate mastax—semicircular rami with large grinding teeth
http://bios.sakura.ne.jp/gf/2004/ro
http://www.environmentalleverage.com/bug%20of%20the%20month/rotifer%20for%20web/rotifer2.jpg

Single ovary with one egg
A rotifer carrying a single
egg attached to its body
Lorica—shield-like ‘shell’
sometimes with spines
Class Monogononta—”single ovary”
•Benthic, free swimming, or sessile forms,
•lorica present or absent,
•foot present or absent-toes variable,
•corona usually a single ciliated disk ringing the anterior end,
•mastax not ramate
‣1600 species, mostly dioecious alternating between parthenogenesis and sex
‣Males are usually small, with a vestigial gut, and only for sex

The Monogonont life cycle
Usually while food and survival conditions
are quite good most of the population are
females which produce diploid eggs that
hatch to make identical copies of the
female parent.
During autumn the stimulus to undergo
meiosis, and make haploid (mictic) eggs
occurs, then if those eggs don’t get
fertilized they hatch out as males.
Males will then seek out mictic females
and have sex with them. The eggs
produced are larger and contain more
nutritional reserves than normal
parthenogenetic eggs, and delay
hatching often till the following spring or
when suitable conditions occur.
Some females can do both-Amphoteric
Pseudosexual eggs—parthenogenetic
eggs that look like resting eggs have been
noted in some species.

Critical food populations for population growth of different rotifers.
Kc=Keratella cochlearis, Ke=K. earlinae, Kcr=K.crassa, So=Synchaeta oblongata
Sp=Synchaeta pectinata,Bc=Brachionus calyciflorus, Pr=Polyarthra remata,
Ap=Asplanchna priodonta. (From Stemberger and Gilbert 1985)

Lorica with anterior and posterior projecting spines, foot present--Brachionus

Lorica divided into plaques, 6 anterior spines and 1 or 2 posterior spines, foot
absent--Keratella
The length of rotifer spines increase during the summer months (cyclomorphosis), and
they are generally though of as anti-predator devices and projections that slow sinking

lorica with 3 very long anterior projecting spines and one long
posteriorly projecting spine-- Kellicottia
Female Kellicotia releasing an egg
The length of rotifer spines increase during the summer months (cyclomorphosis), and
they are generally though of as anti-predator devices and projections that reduce
sinking rate.

om Stemberger 1988

What conditions are good for rotifers?

1 mm
Asplanchna—large predatory species
(> 1mm) sac-like body shape,quite
transparent,
Corona a single circumapical ring of
cilia, no lorica, foot present or absent,
but never distinct foot with separated
toes, intestine and anus lacking

The incudate trophi of Asplanchna priodonta—rami shaped as jaw-like pincers
http://users.unimi.it/melone/trophi/start.html

Family Synchaetidae—Synchaeta, most marine/estuarine species in this family
no lorica, foot present, anterior region wide, with 4 stiff anterior styles—