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Sponges have a motile larval stage and become sessile at maturity. Conversely, many jellyfish develop as sessile polyps early in their life cycle. In the case of the cochineal , it is in the nymph stage (also called the crawler stage) that the cochineal disperses.
Motile marine animals are commonly called free-swimming, [10] [11] [12] and motile non-parasitic organisms are called free-living. [13] Motility includes an organism's ability to move food through its digestive tract. There are two types of intestinal motility – peristalsis and segmentation. [14]
During its motile form, the free-swimming telotroch appears as a long cylinder, moving quickly and erratically. Stalk materials are secreted in order for the cell to become sessile. Stalk precursors are held in dense granules at the aboral or basal end of the telotroch, which are released as a liquid by exocytosis. That liquid solidifies to ...
As with all Cnidarians, these organisms have a complex life cycle including a motile planktonic phase and a later characteristic sessile phase. Hexacorallia also include the significant extinct order of rugose corals.
Non-motile species lack the ability and structures that would allow them to propel themselves, under their own power, through their environment. When non-motile bacteria are cultured in a stab tube, they only grow along the stab line. If the bacteria are mobile, the line will appear diffuse and extend into the medium. [90]
In motile species, spawning females often travel to a suitable location to release their eggs. However, sessile species are less able to move to spawning locations and must release gametes locally. [4] Among vertebrates, external fertilization is most common in amphibians and fish. [5]
One large and sessile, one small and motile (oogamy). The larger sessile megagametes are eggs (ova), and smaller motile microgametes are sperm (spermatozoa, spermatozoids). The degree of motility of the sperm may be very limited (as in the case of flowering plants) but all are able to move towards the sessile eggs.
Some organisms are motile throughout their lives, but others are adapted to move or be moved at precise, limited phases of their life cycles. This is commonly called the dispersive phase of the life cycle. The strategies of organisms' entire life cycles often are predicated on the nature and circumstances of their dispersive phases.