2. Morphology
Rotatoria (=Rotifera) belong to the smallest metazoa of
which over 1000 species
have been described, 90% of which inhabit freshwater habitats. They
seldom reach 2 mm in body length. Males have reduced sizes and are less
developed than females; some measure only 60 µm.
The body of all species consists of a constant number of cells, the
different Brachionus species contain approximately 1000 cells which
should not be considered as single identities but as a plasma area. The growth
of the animal is assured by plasma increase and not by cell division.
Figure 3.1. Brachionus plicatilis, female and male (modified from Koste, 1980).
The epidermis contains a densely packed layer of keratin-like proteins
and is called the lorica. The shape of the lorica and the profile of the spines
and ornaments allow the determination of the different species and
morphotypes. The
rotifer's body is differentiated in three distinct parts consisting of the
head, trunk and foot (Fig. 3.1.). The head carries the rotatory organ or
corona(this is
a Quick Time movie)..
corona(this is a Real Player movie).. which is
easily recognized by its annular ciliation and which is at the origin of the
name of the Rotatoria (bearing wheels). The retractable corona assures
locomotion and a
whirling water movement(this is a Quick Time movie)..
whirling water movement (this is a Real
Player movie)..which facilitates the uptake of small food particles (mainly
algae and detritus).
The trunk contains the digestive tract, the excretory system and the
genital organs. A characteristic organ for the rotifers is the
mastax(this is
a Quick Time movie)..mastax (this is a Real Player movie)..,
i.e. a calcified apparatus in the mouth region, that is very effective in
grinding ingested particles.
The
foot(this is a Quick Time movie).. foot (this is a Real Player movie)..is a
ring-type retractable structure without segmentation ending in one or four
toes.
1. Introduction
2. Morphology
3. Biology and Life History
4. Strain Differences
5. General Culture Procedures
