XII. — CRUSTACEA AND LOWER INVERTEBRATA. 95 



2. OligOChaBta. — In this order are included the Earth- 



worms, which, in some parts of Australia, attain gigantic 

 proportions. Megascolides australis occurs in Gippsland, 

 and when extended is sometimes six feet in length ; in 

 New South Wales are found Notoscolex grandis, and iV. 

 camdenensis, the latter from eighteen inches to two feet, 

 and the former from two feet six inches to three feet six 

 inches in length. 



3. Ohaetopoda. — Marine worms usually provided with 



tubular setigerous feet termed " parapodia " ; external 

 branchiae on the dorsal surface, which, however, are often 

 absent or rudimentary ; head in most cases distinct and 

 provided with tentacles. Examples — Ai^hrodite austrcdis, or 

 Sea Mouse, Lepidonotus melanogratiwius, Syllis corruscans, 

 and Nereilejxts amhlyodonta. 



4. Cepholobranchia. — In this order the branchiae are 



on or near the head. The body has the regions well 

 defined and is protected by a tube, which is either mem- 

 branous, calcareous, or composed of sand grains cemented 

 together. Serjoida vasifera, Sahella velata, Vermilia ccBsjn- 

 tosa, and Sjoirogra^^his australiensis, are examples from 

 Sydney Harbour. 



Class v.— The POLYZOA. — This class consists of minute 

 marine animals forming colonies which either assume an erect 

 plant-like aspect or spread over stones, shells, &c., and are com- 

 posed of vast numbers of cells, in which the polypides reside ; the 

 mouth is surrounded by a circle of ciliated tentacles. There 

 are three sub-orders in this class : — (See Case I.) 



1. Chilostomata, is characterised by having the cell opening 



or mouth closed by a movable lip or operculum. 

 Examples — Catenicella ventricosa, Bugula neritina, Flustra 

 dissimilis, Adeona cellulosa, and Selenaria maculata. 



2. Cyclostomata, has the mouth or cell aperture round, 



and without a movable operculum. Idmonia milneaiia 

 and Mesentipora repens are examples. 



3. OtenOStomata, has the cell aperture closed by a series of 



marginal seta. Amathia hicornis. 



