244 



ANNELIDA AND ARTHROPODA: 







Figure 14.19 Simple metamorphosis in on insect, o squash bug 

 (Hemiptera). From left to right, egg, nymph, and adult. 



simple eyes, and increased wing size. In forms hav- 

 ing complete metamorphosis (Figure 14.20) the im- 

 mature and adults are usually quite diflerent and, un- 

 like those with simple metamorphosis, often live in 

 difTerent habitats and have different habits. The 

 early instars are worm-like and are called larvae. The 

 different larval instars are usually similar in form, 

 their main change being increase in size. Transfor- 

 mation to pupa occurs after the last larval molt. The 

 pupa is usually inactive, does not feed, and is often 

 covered by a cocoon (many insects overwinter as 

 pupae). The final molt produces the adult. Finally, 

 there is a type of complete metamorphosis called 

 hypermetamorphosis in parasitic insects. Here the 

 different larval instars are unlike in appearance. 



Figure 14.20 Complex metamorphosis in an insect, a fly (Diptera). 

 From left to right, egg, larva, pupa, and adult. 



Subclass APTERYGOTA 



Diagnosis: primitive; wingless and not derived 

 from winged ancestors; little or no metamorphosis; 

 underside of abdomen with bristle-like appendages 

 (Figure 14.21). 



Figure 14.21 Subclass Apterygota. Order Proturo: 1, Eosen/omon 

 (x 30). Order Thysanura: 2, Thermobia, the fire brat (x 1); 3, Cam- 

 podea (x 3). Order CoNembolo: 4, Isotoma (x 6); 5, Entomobrya 

 {x 10). (After various sources.) 



ORDER PROTURA (Telsontails) 



Diagnosis: uncommon; considered most primitive; 

 minute, to 1/15 inch long; without eyes, wings, or 

 antennae; development direct; scavengers in moist 

 places, under and among surface objects and in soil 

 (Figure 14.21). 



ORDER THYSANURA (Bristletails) 



Diagnosis: mostly under 3/5 inch to two inches, 

 wingless, with two or three bristles on end of abdo- 

 men; development direct; scavengers, causing dam- 

 age to books, clothing, and foods; in human dwell- 

 ings, grassy and wooded areas, and damp places 

 under objects (Figure 14.21). 



ORDER COLLEMBOLA (Springtails) 



Diagnosis: mostly minute, to about 1/3 inch; 

 wingless, with a unique springing organ on ventral 

 abdomen; jump to more than 15 times their length; 

 development direct; scavengers or herbivores; in de- 

 caying matter under damp objects, sometimes on 

 fresh-water surface or along seashore; usually appear 

 in great numbers during the winter breeding season; 

 may congregate on sidewalks, lawns, pools, or even 



