Variety Of Body Form

Although the generally considered primitive Collembola (Fig. 2) display most of the features described above, most genera differ from this. All families have some forms with reduced numbers of eyes, and Neanuridae, Hypogastruridae, and Isotomidae (Figs. 1E and 1G) often have reduced or no furcula. The Neanuridae (Fig. 1D) often have large spines on the body as well as spectacularly complex mouthparts. Indeed these are so complex and varied (Fig. 3) that species can be identified by their mouthparts alone. The Onychi-uridae (Fig. 1C) all lack eyes and almost all lack pigment and a furcula. They are characterized by the presence of pseudocelli through which defensive toxic and/or repulsive fluids are secreted. These along with the Hypogastruridae, Poduridae, and Neanuridae have well developed, seta bearing, first thoracic segments; the remaining families all have greatly reduced, nonsetaceous, first thoracic segments (Fig. 2), and some families have fusion of abdominal segments. The Neelidae and Sminthuridae have the first four abdominal segments fused and more or less fused with thoracic segments. Some Entomobryidae and Sminthuridae (as well as most Tomoceridae) have antennal subsegmentation, giving the appearance of more than four antennal segments. The largest species are found in the Neanuridae, Entomobryidae, and Tomoceridae, often reaching 5 mm and occasionally over

10 mm in length, but the Neelidae and Mackenziellidae rarely reach 1 mm.

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