Phylum Cnidaria Flashcards
(10 cards)
includes animals that show radial or biradial symmetry and are diploblastic, that is, they develop from two embryonic layers.
Phylum Cnidaria
Cnidarians contain specialized cells known as _____ / (“stinging cells”) containing organelles called nematocysts (stingers). These cells are present around the mouth and tentacles, and serve to immobilize prey with toxins contained within the cells.
cnidocytes
Nematocysts contain coiled threads that may bear barbs. The outer wall of the cell has hairlike projections called ___ , which are sensitive to touch. When touched, the cells are known to fire coiled threads that can either penetrate the flesh of the prey or predators
cnidocils
Animals in this phylum display two distinct morphological body plans:
a. polyp or “stalk”
b. medusa or “bell
Some cnidarians are ____, that is, they have two body plans during their life cycle.
Polymorphic
This phylum is divided into four classes:
Anthozoa, Scyphozoa, Cubozoa, and Hydrozoa.
This class includes all cnidarians that exhibit a polyp body plan only; in other words, there is no medusa stage within their life cycle. Ex: sea anemones, sea pens, and corals.
Class Anthozoa
The defining characteristic of this class is that the medusa is the prominent stage in the life cycle, although there is a polyp stage present. They display a characteristic bell-like morphology
Class Scyphozoa
This class includes jellies that have a box-shaped medusa, or a bell that is square in cross-section; hence, are colloquially known as “box jellyfish.” They display overall morphological and anatomical characteristics that are similar to those of the scyphozoans. A prominent difference between the two classes is the arrangement of tentacles. This is the most venomous group of all the cnidarians.
Class Cubozoa
Animals in this class are polymorphs, and most exhibit both polypoid and medusoid forms in their lifecycle, although this is variable.
Class Hydrozoa
