Gemmules are internal
buds
In botany, a bud is an undeveloped or Plant embryogenesis, embryonic Shoot (botany), shoot and normally occurs in the axil of a leaf or at the tip of a Plant stem, stem. Once formed, a bud may remain for some time in a dormancy, dormant conditi ...
found in
sponge
Sponges or sea sponges are primarily marine invertebrates of the animal phylum Porifera (; meaning 'pore bearer'), a basal clade and a sister taxon of the diploblasts. They are sessile filter feeders that are bound to the seabed, and a ...
s and are involved in
asexual reproduction
Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the f ...
. It is an asexually reproduced mass of cells, that is capable of developing into a new organism i.e., an adult sponge.
Role in asexual reproduction
Asexual reproduction in sponges occurs via
budding
Budding or blastogenesis is a type of asexual reproduction in which a new organism develops from an outgrowth or bud due to cell division at one particular site. For example, the small bulb-like projection coming out from the yeast cell is kno ...
, either by external or internal buds. The internal buds are called gemmules. Only endogenous types of buds develop into new sponges.
Characteristics
Gemmules are resistant to
desiccation
Desiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic (attracts and holds water) substance that induces or sustains such a state in its local vicinity in a moderately sealed container. The ...
(drying out), freezing, and
anoxia (lack of
oxygen
Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
) and can lie around for long periods of time. Gemmules are analogous to a bacterium's
endospore
An endospore is a dormant, tough, and non-reproductive structure produced by some bacteria in the phylum Bacillota. The name "endospore" is suggestive of a spore or seed-like form (''endo'' means 'within'), but it is not a true spore (i.e., not ...
and are made up of
amoebocytes surrounded by a layer of
spicules and can survive conditions that would kill adult sponges. When the environment becomes less hostile, the gemmule resumes growing.
References
*Feldkamp, Susan (2002). ''Modern Biology.'' United States: Holt, Rinehart, and Winston. p. 695. Accessed on May 23, 2006.
Sponge anatomy
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