One Australian kind (Ooperipatus) lays large 

 yolk-filled eggs. Most other velvet worms retain the 

 embryos inside the mother's body until the young are 

 ready to be born as '/2-inch facsimiles of the parents. 

 Some South American peripatuses develop a connec- 

 tion between mother and unborn offspring that is 

 analogous to the placenta of mammals. Across this 

 bridge the parent furnishes her young v\ith food and 

 oxygen and attends to the disposal of wastes, includ- 

 ing carbon dioxide. 



Pregnancy in peripatuses may last for more than a 

 year, and a female may even be carrying two differ- 

 ent generations of young at a time. Often the mild 

 excitement of being caught and placed in captivity is 

 enough stimulus to cause a pregnant mother peripa- 

 tus to expel her babies. For several weeks they may 

 remain with her, and then wander off on their own — 

 quite capable of feeding themselves. 



The Crustaceans 



{Class Crustacea) 



People who enjoy seafood are likely to think of 

 crustaceans as lobsters and crabs and shrimps. A 

 whaler is prone to regard the class Crustacea as 

 chiefly krill — the shrimplike denizens of the open 

 oceans upon which whales feed so extensively. In- 

 landers may be more familiar with the crayfishes or 

 crawfishes that resemble lobsters in body plan but 

 thrive in fresh waters. The twenty-five thousand dif- 

 ferent members of class Crustacea include not only 

 these animals — obviously "crusty" ones — but also an 

 astonishing array of others, from water fleas to bar- 

 nacles and fish parasites. Many are delicate micro- 

 scopic creatures that drift in the waters of ocean and 

 lake as plankton. 



When the lobster and its many relatives are viewed 

 as a group, the chief feature in common beyond their 

 arthropod nature seems to be possession of two pairs 

 of antennae. Other generalizations are subject to 

 many exceptions. Most crustaceans are marine ani- 

 mals, but some live in rivers and lakes. A few inhabit 

 the land, their gills modified in ways that require no 

 wetting to be useful in respiration. The majority of 

 crustaceans walk or creep or swim with their feet 

 downward; a few regularly swim inverted. Most crus- 

 taceans live out their lives in waters illuminated by 

 the sun. Yet others burrow in the bottom, and a sur- 

 prising number inhabit the lightless abysses of the 

 oceans. 



PHYLLOPODS 



Those crustaceans that regularly swim inverted 

 are best known from the fairy shrimp Eiibraiuhipus 

 and the brine shrimp Anemia. Both are members of 



Brine shrimps {Atieinia salina) swim inverted in brine 

 so concentrated that crystals form on their undersides. 

 These phyllopods are found only in salty lakes, where 

 they reach a length of a little under '/a inch. (Great 

 Salt Lake. Fritz Goro: Life Magazine) 



the order Phyllopoda. They drive themselves along 

 in shallow water by successive waves of motion in the 

 leafiike gill-feet, which are combined respiratory and 

 swimming organs. They manipulate food with their 

 leg bases, chewing it a little before swallowing it. Yet 

 phyllopods have a clearly defined head with a pair 

 of compound eyes, and a slender abdominal tail pro- 

 jecting behind the thorax with its paired gill-feet. 



Fairy shrimps appear and disappear so suddenly 

 that magic seems the only explanation. They occupy 

 very temporary pools, such as meitwater from snow 

 banks, and go through their growth stages so rapidly 

 by feeding on microscopic algae that suddenly a clear 

 new pond is occupied with inch-long swimming ani- 

 mals of iridescent colors — red, flesh-colored, green- 

 ish, bronze, or bluish. 



Male phyllopods pursue the females, reaching for 

 them with relatively huge claspers that extend from 

 one pair of antennae. Mated pairs swim in tandem, 

 the female often with dark spherical eggs filling a 

 pair of large brood pouches at the base of her ab- 



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