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Rotifers biology and diversity
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1
Question
What is the etymological origin of the name 'Rotifera'?
Page 1
Answer
From Latin: \$rota\$ (wheel) + \$fera\$ (those that bear) — literally 'wheel-bearers'.
2
Question
Why are rotifers often described as having an impression of rotating wheels?
Page 1
Answer
Because they possess a characteristic ciliated crown (corona) whose beating often gives the appearance of rotating wheels.
3
Question
Give the typical size range reported for rotifers and the size range most species fall into.
Page 1
Answer
Size range: \$40\ \mu m\$ to \$3\ mm\$ in length. Most species are between \$100\ \mu m\$ and \$500\ \mu m\$ long.
4
Question
How does transparency and coloration generally vary among rotifer species?
Page 1
Answer
Although some rotifers display beautiful colors, most rotifer species are transparent.
5
Question
What correlations exist between rotifer body shapes and their modes of life?
Page 1
Answer
Body shape often correlates with lifestyle: floaters tend to be globular and saclike; creepers and swimmers are elongated and wormlike; sessile types are commonly vaselike and protected by a thickened outer epidermis (lorica).
6
Question
Describe the lorica in sessile rotifer types.
Page 1
Answer
The lorica is a thickened outer epidermis that commonly encloses sessile rotifers, giving a vase-like protective covering.
7
Question
Approximately how many rotifer species are known and what is their general geographic distribution?
Page 1
Answer
Rotifers are a cosmopolitan group of about 1,800 species, occurring worldwide.
8
Question
What are the primary habitats occupied by most rotifer species?
Page 1
Answer
Most species are freshwater inhabitants. A few are marine, some are terrestrial, and some are epizoic (living on the body of another animal) or parasitic.
9
Question
How many toes does the rotifer foot typically bear and how is the foot described?
Page 3
Answer
The foot is narrower and usually bears one to four toes; it functions as an attachment organ.
10
Question
What are pedal glands in rotifers and where are they located?
Page 3
Answer
Pedal glands are glands located in the foot that secrete an adhesive material used by sessile and creeping rotifer forms for attachment.
11
Question
How does the foot differ in pelagic swimming rotifers compared to sessile forms?
Page 3
Answer
In swimming pelagic forms the foot is usually reduced, whereas sessile forms retain a more developed foot with pedal glands for attachment.
12
Question
Describe the two main modes of locomotion used by rotifers.
Page 3
Answer
Rotifers move either by creeping with leech-like movements aided by the foot or by swimming using the coronal (ciliated) crown — some species use both methods.
13
Question
What are the distinctive features of the class Seisonidea among rotifers?
Page 3
Answer
Seisonidea are a class of marine rotifers that are commensals of crustaceans; they have a large elongated body with a reduced corona and include only two known species.
14
Question
List key morphological and reproductive features of the class Bdelloidea.
Page 3
Answer
Bdelloidea characteristics: anterior end retractile bearing two trochal disks; mastax adapted for grinding; paired ovaries; cylindrical body form; males are absent. About 590 species are described in this class.
15
Question
What is notable about sexual males in the Bdelloidea, and what implication does this have for reproduction?
Page 3
Answer
Males in Bdelloidea are entirely unknown; Bdelloidea reproduce asexually (parthenogenetically) with no observed male stage.
16
Question
Give the defining reproductive and anatomical features of the class Monogononta.
Page 3
Answer
Monogononta have a single ovary, a mastax not designed for grinding, they produce mictic and amictic eggs, males appear only sporadically (often seasonally), and the class contains about 1,400 species.
17
Question
What are mictic and amictic eggs in Monogonont rotifers and why are they important?
Page 3
Answer
Amictic eggs develop parthenogenetically into females without fertilization, whereas mictic eggs, when unfertilized, develop into haploid males or, if fertilized by males, form resting diploid eggs capable of surviving adverse conditions—this alternation allows both clonal growth and periodic sexual reproduction.
18
Question
Are rotifers generally dioecious, and what important exceptions exist?
Page 3
Answer
While rotifers are often dioecious with males usually smaller than females, there are important exceptions: Bdelloidea have no known males (entirely asexual), and Monogononta males occur only sporadically/seasonally.
19
Question
Describe the female reproductive system in Bdelloidea and Monogononta rotifers.
Page 3
Answer
The female reproductive system consists of combined ovaries and yolk glands (germovitellaria) and oviducts that open into the cloaca.
20
Question
What is the mastax in rotifers and how does its form differ between groups?
Page 3
Answer
The mastax is a muscular pharynx containing sclerotized jaws used for processing food; in Bdelloidea it is adapted for grinding, whereas in Monogononta it is generally not specialized for grinding.
21
Question
Why are pedal glands important to sessile and creeping rotifers?
Page 3
Answer
Pedal glands secrete adhesive substances that enable sessile and creeping rotifers to attach to substrates or anchor themselves while feeding or moving.
22
Question
How does being epizoic or parasitic affect where certain rotifers are found?
Page 1
Answer
Epizoic or parasitic rotifers live on or in other animals, respectively, so these species are found associated with host organisms rather than free in the environment.
23
Question
Explain the adaptive significance of rotifers having a reduced foot in pelagic forms.
Page 3
Answer
A reduced foot in pelagic rotifers reduces drag and unnecessary attachment structures, optimizing body plan for free-swimming life where coronal cilia are the primary locomotory organ.
24
Question
What is the functional role of the corona in rotifers beyond producing the wheel-like appearance?
Page 1
Answer
The corona, composed of cilia, generates feeding currents to direct food particles toward the mouth and also functions in locomotion (swimming).
25
Question
Which rotifer class contains the largest number of described species and approximately how many?
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Answer
The class Monogononta contains the largest number with about 1,400 described species.
26
Question
Name three representative genera of Bdelloidea and three of Monogononta cited in the slides.
Page 3
Answer
Bdelloidea: Adineta, Philodina, Rotaria. Monogononta: Conochilus, Collotheca, Notommata.