CHAPTER 2 



Aquatic Collembola 



By D. B. Scott, Jr. 

 Salinas, California 



Collembola, more commonly referred to as springtails, 

 are generally placed with the primitive insects of the 

 subclass Apterygota. However, they are not closely 

 related to other apterygotans, such as silverfish, 

 campodoids, and proturids. With a few exceptions, 

 Collembola are very small, generally less than three 

 mm. in length. A few species, however, may reach 

 ten mm. The body may be elongate (distinctly seg- 

 mented) or globular (indefinite segmentation) and 

 clothed with either scales or hairs. Coloration con- 

 sists of brilliant pigmentation in hair-clothed species, 

 bright irridescence in the scaled types, or no color 

 at all in subterranean species. The mouth parts are 

 adapted for sucking in some species and for chewing 

 in others, and the head may be either prognathous or 

 hypognathous. 



The antennae, often a key characteristic, vary 

 greatly in structure and length. The joints may be 

 simple, or the terminal one may be annulated as in 

 the family Smynthuridae. Eyes are present in most 

 Collembolans; they occur as simple ocelli in patches 

 behind the antennae. The eyes are never compound, 

 and the ocelli never exceed eight to a patch. In many 

 species pseudocelli occur on various parts of the 

 dorsal surface (figs. 2:2a; 2:4e). 



A specialized sensory organ, the postantennal organ 

 is a distinct and unique structure in many groups. 

 It exhibits a variety of designs and arrangements from 

 simple, elliptical depressions to elaborate rosettes 

 or fernlike protuberances (fig. 2:Sa-e). Sensory organs 

 are found behind the base of each antenna and some- 

 times special microscope techniques are required to 

 discern them. 



The organ by which the order is distinguished, the 

 ventral tube, arises on the ventral side of the first 

 abdominal segment. This is a bilobed appendage 

 with filaments capable of extrusion. Although its 

 purpose is not fully understood, this tube is pre- 

 sumably for adhesion or for some respiratory function. 



The "spring" or furca (furcula), when present, is 

 composed of a pair of whiplike appendages, the basal 

 parts (the manubrium) of which are fused together 

 and attached to the fourth, or occasionally the fifth, 



abdominal segment. A pair of dentes arises from the 

 manubrium and accounts for a major part of the spring. 

 Each dens is equipped with a hooklike, chitinous 

 tip of many variations (the mucro) by which certain 

 genera are separated. When retracted under the body, 



metarhorox 

 mesotnorax 

 prathorax 



- * J'?Ki^ anus 



^xgenital 

 opening 



manubrium 



praetorsus or transtarsus 



Fig. 2:1. Entomobrya laguna Bacon and onotomical 

 features (Essig, 1942.) 



74 



