For educational purposes only:
Information on the basics of Invertebrate Zoology
Kingdom: Animalia, Phylum: Arthropoda
Subphylum: Hexapoda, Class: Entognatha
CLICK on underlined file names and included illustrations to enlarge:
The Entognatha is a class of arthropods that along with the Insecta comprises the Hexapoda. Their mouthparts are entognathous or retracted within the head. They are apterous. Three orders are the Diplura, Protura and Collembola. These orders were previously included with the Insecta.
All members are tiny arthropods that no longer possess wings, although their ancestors are thought to have been winged. They are found in moist environments. Their mouthparts are contained within a pocket in the head capsule so that only the tips of the mandibles and maxillae are visible. They possess styli, which are vestigial abdominal legs. There is no tentorium, no external genitalia and only a one-condyle articulation of the mouthparts. A tracheal system is also lacking.
The individual segments of the antennae bear muscles, unlike the Insecta where only the two lower segments are musculated.
Sperm transfer is always indirect and there is an ovipositor in the female.
Orders of Entognatha
Protura. -- The cone heads lack antennae and eyes. Their mouthparts consist of a labrum, labium, mandibles and seven maxillae that have been modified to rods, all recessed into the head. They have abdominal styli that are believed to be vestigial legs. [Illustrations: PROTURA ].
Diplura. -- The forked tails have antennae present. Their maxilla is differentiated into a galea and a lacinia. All their mouthparts are also recessed into the head. They also have a pair of caudal cerci that has given them their name [Illustrations: DIPLURA ].
Collembola. -- The springtails and snow fleas have antennae present. The mouthparts are recessed, and only the Collembola have eyes even thought they have lost their function in most species. When compound eyes are present they have no more than 8 ommatidia. Springtails are found under rocks and on the ground, etc., in the springtime when they are most active. [Illustrations: COLLEMBO].
Springtails emerge before snow melts, often blanketing the surface. Their mouthparts are largely chewing. The abdomen is developed into six segments, which is a decided reduction in the normal number found in insects.
They possess a collophore or ventral tube on the first abdominal segment, which is able to absorb moisture. This is essentially a glue peg, which is modified from abdominal legs. It allows the animal to stick to surfaces. They also have a tenaculum on the third abdominal segment, which is a hook modified from abdominal legs. A furcula is present on the fourth abdominal segment. This allows for the "spring" of the springtail. It bends forward and hooks with the tenaculum.
Springtails are of some economic importance in alfalfa fields (Lucerne flea), in home gardens and for the mushroom industry. Along the Mississippi River at Minneapolis they are very destructive to mushroom culture that is located in caves along the banks of the river.