Furcula (Collembola)
Encyclopedia
The furcula, or furca, is a tail-like appendage shaped like a fork, found ventrally on the fourth abdominal
segment of springtail
s. Present in most species dwelling the upper soil layers, it is used for jumping when the animal is threatened. While at rest, it is retracted under the abdomen and held there by a structure variously called the retinaculum
or hamula, located on the third abdominal segment. When the retinaculum releases the furcula, it springs open and hits the substrate, propelling the springtail into the air. This mechanism is not used for locomotion, but only for escaping from predators or severe stress.
One reason not to use it for locomotion is that its action is extremely unpredictable; when the furcula is released, the organism is sent tumbling through the air on an unpredictable trajectory, and lands practically randomly.
Not surprisingly, some species, such as the intertidal marine inhabitant Anurida maritima
do without an organ that might get them into more trouble than it rescues them from. Some other species, such as in the genus
Hypogastrura have only a verry short furcula. At the same time the device is hard to predict and is versatile. Even a springtail drifting on the surface tension layer of water often can jump successfully. Also, most predators of springtails are small and often have little power of sight, so if the prey leaps in time, the chances are that from the hunter's point of view, it simply vanishes.
Abdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...
segment of springtail
Springtail
Springtails form the largest of the three lineages of modern hexapods that are no longer considered insects...
s. Present in most species dwelling the upper soil layers, it is used for jumping when the animal is threatened. While at rest, it is retracted under the abdomen and held there by a structure variously called the retinaculum
Retinaculum
Occurs where in some places, groups of tendons from separate muscle pass under a band of connective tissueRetinaculum, from the Latin verb retinere , plural: retinacula may be:* In the wrist:** Flexor retinaculum of the hand...
or hamula, located on the third abdominal segment. When the retinaculum releases the furcula, it springs open and hits the substrate, propelling the springtail into the air. This mechanism is not used for locomotion, but only for escaping from predators or severe stress.
One reason not to use it for locomotion is that its action is extremely unpredictable; when the furcula is released, the organism is sent tumbling through the air on an unpredictable trajectory, and lands practically randomly.
Not surprisingly, some species, such as the intertidal marine inhabitant Anurida maritima
Anurida maritima
Anurida maritima is a cosmopolitan collembolan of the intertidal zone. It is often found in aggregations of up to several hundred on the surface of rock-pools.-Description:...
do without an organ that might get them into more trouble than it rescues them from. Some other species, such as in the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Hypogastrura have only a verry short furcula. At the same time the device is hard to predict and is versatile. Even a springtail drifting on the surface tension layer of water often can jump successfully. Also, most predators of springtails are small and often have little power of sight, so if the prey leaps in time, the chances are that from the hunter's point of view, it simply vanishes.