Cnidarians
lack specific response to external stimuli
, such as detecting what direction a stimulus is coming from. However, their stinging cells are regulated in part by their nervous system; these cells play a big part in cnidarian defense and prey capture.
Do cnidarians have a nervous system?
Cnidarians have
simple nervous systems
and it was probably within this group or a closely-related ancestor that nervous systems first evolved.
How do cnidarians respond to stimuli?
To respond to stimuli, cnidarians
use a rudimentary muscular system consisting of muscle cells lying in bands up and down the body wall and in a circle around the mouth cavity
(Fig. 3.27). The body shortens when the vertical bands contract. If muscles on only one side contract, the body bends in that direction.
How can cnidarians sense light?
Abstract: Cnidarians are the most primitive present-day invertebrates to have multicellular light-detecting organs, called ocelli (eyes). These photodetectors include simple eyespots, pigment cups, complex pigment cups with lenses, and camera- type eyes with a cornea, lens, and retina.
What environments do cnidarians live?
Many thousands of cnidarian species live in
the world’s oceans
, from the tropics to the poles, from the surface to the bottom. Some even burrow. A smaller number of species are found in rivers and fresh water lakes. Scyphozoa, the true jellyfish.
What are the similarities and differences between cnidarians and Ctenophores?
Both cnidarians and ctenophores are diploblastic animals. Cnidarians exhibit radial symmetry whereas ctenophores exhibit biradial symmetry. Both contain tentacles, surrounding their mouth. The main difference between cnidarians and ctenophores is
their body symmetry
.
What are 4 functions of nematocysts?
Nematocysts are used by organisms for prey capture and feeding, but also for
defense, transport, digestion and other various functions
[3,4].
What level of nervous Advancement do cnidarians have?
The major evolutionary step that occurred with the phylum cnidaria was
the development of tissue-level organization
. Recall that sponges exhibit cellular-level organization but have no true tissues. A tissue is an aggregation of similar cells that work together to carry out a specific function within the body.
Which organisms do not have a nervous system?
The only multicellular animals that have no nervous system at all are
sponges and microscopic bloblike organisms called placozoans and mesozoans
. The nervous systems of ctenophores (comb jellies) and cnidarians (e.g., anemones, hydras, corals and jellyfishes) consist of a diffuse nerve net
Do nematodes have a nervous system?
In addition, all nematodes have
a major nerve cord running longitudinally along the ventral midline of the body
, from head to tail (Figure 2). This ventral nerve cord contains cell bodies as well as processes, many of which project into the nerve ring where they make and receive synapses with other neurons.
What is the largest class of cnidarians?
The largest class of cnidarians is
class Anthozoa
. Anthozoans exist only as polyps. The most familiar anthozoans are the brightly colored sea anemones and corals. Other members of this class are known by such fanciful names as sea pansies, sea fans, and sea whips.
Does Hydra respond to light?
In the absence of eyes, the fresh water polyp, Hydra
magnipapillata, nevertheless reacts to light
. They are diurnal, hunting during the day, and are known to move, looping end over end, or contract, in response to light.
Are jellyfish sensitive to light?
Jellyfish are 95% water, 3% protein, and 1% mineral. … On the rim of the bell are
eight sets of eye spots sensitive to light
and eight statocysts that help orient jellyfish when swimming.
What’s the difference between Coelenterates and cnidarians?
Both cnidarians and ctenophores
Is Cotenenterata same as Ctenophora?
Ctenophora is
a phylum of Coelenterata
. They are highly distinctive among all the animals due to the presence of the comb plates. Ctenophores have been recorded only from the ocean and never from the freshwater habitats.
What are two differences between the jellyfish and ctenophores?
Ctenophores also differ from jellyfish in
that they don’t necessarily have tentacles
; and when they do, these aren’t located at an extremity of the body, but are rooted to its center.
