Medusae
swim by jet propulsion
(see below Tissues and muscles). However, most do so weakly and are carried passively by currents over long distances. Polyps are generally sedentary.
What is the free-swimming form of cnidarians?
The medusa
is a free-swimming form; it moves by rhythmic muscular contractions of the bell, providing a slow propulsive action against the water. The other principal body type of the adult cnidarian is the polyp, a stalked, sessile (attached) form.
Are Cnidaria motile?
Animals in this phylum display two distinct morphological body plans: polyp or “stalk” and medusa or “bell”. …
Medusa forms are motile
, with the mouth and tentacles hanging down from an umbrella-shaped bell. Cnidarian morphology: Cnidarians have two distinct body plans, the medusa (a) and the polyp (b).
How do polyps move?
However, most do so weakly and are carried passively by currents over long distances. Polyps are generally sedentary. Pennatulacean colonies move
slowly across soft substrata by action of their inflatable peduncle
(a stalk that attaches to the strata in the lower end and to the polyp body on the higher end).
How does a Cnidaria move?
They contract their
hollow, saucer-shaped bodies (called bells) to force water out
, which propels them forward. Their long. tentacle-like arms, which trail out behind them, are used to sting and capture prey.
What are 2 body forms of cnidarians?
They have a simple body consisting of a central gut cavity surrounded by tentacles. A jelly-like substance called mesoglea lies between the outer and inner layers of the body. There are two basic cnidarian body shapes:
a polyp form, which is attached to a surface
; and an upside-down free-floating form called a medusa.
Can cnidarians reproduce asexually?
All cnidarian species are capable of sexual reproduction, which occurs in only one phase of the life cycle, usually the medusa.
Many cnidarians also reproduce asexually
, which may occur in both phases.
What type of body form is most often seen on free floating cnidarians?
Two distinct body plans are found in Cnidarians: the polyp or tuliplike “stalk” form and
the medusa or “bell” form
. ((Figure)). An example of the polyp form is found in the genus Hydra, whereas the most typical form of medusa is found in the group called the “sea jellies” (jellyfish).
Why are jellyfish called medusa?
The shape of this bell is called a medusa
because it looks like the evil Medusa in Greek mythology
– a woman who had offended the goddess Athena who then changed her hair into snakes and made her face so hideous it turned people into stone.
Is a jellyfish a mollusc?
Ans:
Phylum mollusca
include soft bodied animals with hard shell Eg: snails, octopus, mussels, oysters. Phylum Coelenterata contain special structure called coelenteron where the food digested.It include jelly fish and sea anemones.
Does a polyp turn into a medusa?
An anemone is the polyp shape.
If the polyp shape is turned upside down
, it becomes the medusa shape of the jellyfish.
Is a hydra a polyp or medusa?
Hydra exists in both forms:
Polyp and Medusa
. These forms are dependent upon nutritional content of the living environment. Medusa is the adult and sexual form whereas Polyp is juvenile and asexual form. Under harsh living conditions and starvation, hydra reproduces sexually.
What body parts do polyps have?
A polyp has a
sac-like body and an opening, or mouth, encircled by stinging tentacles
called nematocysts or cnidae. The polyp uses calcium and carbonate ions from seawater to build itself a hard, cup-shaped skeleton made of calcium carbonate (limestone).
Is obelia a plant or an animal?
Obelia is a genus of hydrozoans, a class of mainly marine and some
freshwater animal
species that have both polyp and medusa stages in their life cycle. Hydrozoa belongs to the phylum Cnidaria, which are aquatic (mainly marine) organisms that are relatively simple in structure. Obelia is also called sea fur.
What are 5 characteristics of cnidarians?
- Radially Symmetrical.
- Body multicellular, few tissues, some organelles.
- Body contains an internal cavity and a mouth.
- Two different forms exist, medusa and polyp.
- Reproduction is asexual or sexual.
- Has a simple net like nervous system.
- Has a distinct larval stage which is planktonic.
Are jellyfish polyps or medusa?
A polyp is the form that attaches to a surface, while
a medusa is the form that is free-floating
; a species of cnidarian
