236 



ANNELIDA AND ARTHROPODA: 



-1 



Figure 14.10 Sjbphylum Pentastomida, Porocepho/us, a tongue 

 worm. 



cle; larval stages usually present, but normally are 

 much like the adults in appearance (Figure 14.11). 



The Tardigrada might not even be arthropods. 

 They are included here because they show some 

 resemblance to the Onychophora. Other than that, 

 they really have few characteristics that might suggest 

 a joint-legged animal. 



Water bears probably will not be encountered by 

 the reader. Although they are found in the ocean, in 

 fresh water, and in damp terrestrial habitats, they 

 grow no longer than 1/25-inch. However, they pos- 

 sess one amazing capability — they have a remarkable 

 ability to withstand dessication. They can survive 

 after long periods in a shriveled, dried, apparently 

 lifeless state. 



Figure 14.11 Subphylum Tardigrada, Mocrobiotus, a water bear 

 (X 50). 



Subphylum MANDIBULATA ( = ANTENNATA) 



Diagnosis: body consists of head plus trunk or plus 

 thorax and abdomen; head with one or two pairs of 

 antennae (first two appendage pairs), one pair of 

 mandibles (jaws, the third pair of appendages), one 

 or more maxillae pairs, and three or more pairs of 

 walking legs; sexes usually separate; eggs are laid or 

 kept by the female until hatching; larval stages typ- 

 ically present. 



CLASS CRUSTACEA (Crustaceans) 



Diagnosis: head with two pairs of antennae, and 

 two pairs of maxillae; body typically with a shell; 

 shell usually with a single, extensive anterior portion. 



the carapace; exoskeleton, or shell, hard as a result of 

 calcareous deposits; appendages often with two, 

 sometimes pincer-like, terminal segments modified 

 for walking, swimming, capturing food, respiration, 

 and reproduction; sexes usually separate; eggs mostly 

 carried by female; development typically with larval 

 stages; mostly aquatic. 



The crustaceans include quite different-looking 

 creatures. The modification of the first two pairs of 

 appendages as antennae serves to identify most of 

 them. This class contains the marine crabs, lobsters, 

 shrimps and barnacles, and a few land forms, for 

 instance the sowbugs. 



Many of the crabs, shrimp.s, and lobsters are uti- 

 lized as human food. Others are an indirect source of 

 our food, because many of the game and commercial 

 fish eat crustaceans. The barnacles are often a nui- 

 sance because they grow on wharf pilings and boat 

 bottoms. Other crustaceans are grown in aquaria as 

 a ready source of fish food or for purely aesthetic 

 reasons. Some parasites of man must spend part of 

 their life in crustaceans. Sowbugs sometimes cause 

 considerable damage to cultivated plants. And a 

 wood-boring isopod can cause considerable damage 

 to wharf pilings. 



Crustacean sexes are usually separate. In nearly 

 all there are means for an aduh to carry the eggs. 

 These structures include egg sacs, brood pouches, 

 and specializations of the abdominal appendages. As 

 many as six larval stages are found. The number and 

 modifications of larval stages are characteristic for 

 each group of crustaceans. 



Subclass BRANCHIOPODA (Branchiopods) 



Diagnosis: free-living; thoracic appendages leaf- 

 like, four or more pairs, and with marginal gills; no 

 abdominal appendages; reproduction from unferti- 

 lized eggs is typical; mostly fresh-water; include the 

 following orders (Figure 14.12): 



ORDER ANOSTRACA (Anosiracans) 



Diagnosis: include brine shrimp of saline and fairy 

 shrimp of fresh waters; eyes stalked; no carapace. 



ORDER NOTOSTRACA (Tadpole Shrimps) 



Diagnosis: eyes sessile; carapace a broad and low 

 oval shield, somewhat king crab-like; tail with ter- 

 minal, jointed, forked, whip-like appendages. 



