SEGMENTED SCHIZOCOELS 



235 



snakes, but these are tropical members of the group 

 and probably were not eating their regular food. 

 Spiders have specialized feeding behavior in that they 

 are structurally limited to liquids. Within the poison 

 injected into their prey are digestive juices. The 

 spider feeds by sucking body juices and digested 

 material. Spiders can go long periods without food; 

 some have been known to have gone without food for 

 as long as eighteen months. 



Spiders have different means of obtaining their 

 prey. The wandering spiders seek the animal and 

 pounce upon it. The ambushing spiders hide and 

 capture passing insects. The web-building spiders 

 form nets and wait for them to snare their prey. 

 Some spiders live in the webs of other spiders and 

 feed upon smaller prey neglected by the web maker. 



The webs of spiders are quite distinctive and can be 

 used to identify the spiders making them. Irregular 

 webs are mazes of threads extending in all directions 

 and are characteristic of the black widow and other 

 comb-footed spiders. Sheet webs are closely woven 

 sheets in a single plane with threads in all directions 

 in that plane and are made by the sheet web weavers. 

 Funnel webs, made by funnel web spiders, are sheet- 

 like in structure; but have a funnel extending from 

 one side to the spider's retreat. The orb weavers 

 make the most complex type, the orb web. The orb 

 weaver framework consists of lines radiating in a 

 single plane from the center. Sticky trapping silk 

 spirals from the center and is attached to the frame- 

 work. The spirals may be complete, incomplete, or 

 sparse. The orb web may also be modified by being 

 pulled into a dome-shaped structure. Some have a 

 trapline from the center to a retreat. The triangular 

 web is a pie-cut portion, a triangle, of an orb web 

 constructed by certain orb weavers. Irregular webs 

 with hackled bands, flat and more or less ribbon-like 

 combinations of threads, are made by many cribellate 

 spiders. The cribellum is a spinning device modified 

 from part of the spinnerets. The sheet and irregular 

 net webs are combinations of the two types and are 

 constructed by some spiders. The orb and irregular 

 net is another combination formed by some orb 

 weavers, the labyrinth spiders. 



Most spiders construct some type of nest. On the 

 ground spiders may construct tunnels and turrets, a 

 tunnel with a trap door, a silk-lined tunnel ("purse") 

 with a silk surface extension, or a simple silk retreat. 

 Some web makers have no nest; some make a silk 

 retreat near the web; others fold or roll leaves and line 



the enclosed space; and many use a portion of the 

 web, a crevice, or other natural retreat. 



Female spiders lay one or two to a few thousand 

 eggs. These are usually protected by an egg case that 

 will identify its maker. Development in the egg sac 

 is usually for a short period of time. In most species 

 the female dies right after laying the eggs, but in some 

 the females live and stay with the egg sac to protect 

 the developing young. Certain spiders carry the egg 

 sac around with them. 



Once hatched, some spiderlings leave the area by 

 ballooning. The young climb upward from the site of 

 the egg sac. From a high perch they let out long 

 strands of silk which soon catch the wind and so carry 

 the spiderlings away. The spiderlings usually travel 

 under 200 feet altitude but they have been found 200 

 miles from land. In this means of distributing the 

 species, which is not limited to spiderlings, individ- 

 uals may land and balloon many times. During the 

 hatching period when much ballooning is taking 

 place, the landing of many individuals can cause a 

 large accumulation of silk, producing the so-called 

 "gossamer showers." 



SubphylumPENTASTOMIDA( = LINGUATULIDA) 

 (Tongue Worms) 



Diagnosis: worm-like, unsegmented parasites, but 

 body constricted into rings that appear like segments; 

 cephalothorax short, without appendages except for 

 two pairs of ventral hooks on either side of the mouth; 

 arthropod characters shown by body covering 

 (chitinous cuticle), muscles, and nerve cord; without 

 jointed legs or circulatory, respiratory, and excretory 

 organs; vertebrate respiratory parasites; sexes sep- 

 arate, some with complex life histories and larval 

 stages involving a change of animal hosts; an example 

 of the fact that parasitic forms of any phylum usually 

 are difficult to classify from gross anatomy, because 

 adaptations often entail the loss of body parts (Figure 

 14.10). 



Subphylum TARDIGRADA (Water Bears) 



Diagnosis: unsegmented and worm-like, but with 

 four pairs of short and thick, unjointed legs termi- 

 nated by claws, last pair of legs are at end of body; 

 without antennae, circulatory or respiratory organs; 

 body covered by a cuticle that lacks chitin; sexes 

 separate; eggs laid or shed with molding of old cuti- 



