Subkingdom VI. Arthropoda. —Metazoa, with definite number of segments; jointed legs. 
§ 1. Water-breathing. 
Class I. Crustacea. —Having gills and more than eight jointed legs; four antennte. 
Order 1. Cireipedia. —Fixed; shelly covering; feathery arms: Balanus. 
Order 2. Entomostraoa.— Chitinous shell; joints of abdomen and thorax more or less than fourteen: Cyclops. 
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