ECHINODERMATA 



FAMILY 4. OREASTERIDAE. 



Thick-bodied starfishes with small marginal plates, and a reticulate 

 arrangement (Fig. 974 B) of aboral plates: 10 genera. 



OREASTER Miiller and Troschel (Pentaceros Linck). Body very 

 regularly star-shaped, with short arms and large central disc; plates 

 with tubercles: 40 species, which are all littoral and subtropical or 

 tropical. 



0. reticulatus (L.) (Fig. 974). Diameter 30 to 40 cm.; body very 

 thick: South Carolina and southwards, in shallow water. 



Fig. 974 Oreaster reticulatus (Tennent). A, outline of body ; B, aboral surface of arm. 



FAMILY 5. ASTEEOPIDAE. 



Starfishes whose body is covered by a thick, smooth skin, concealing 

 the underlying skeleton : 7 genera. 



DERMASTERIAS Perrier. Body stellate and thick; no spines on the 

 marginal or aboral plates: 1 species. 



D. imbricata (Grube). Size 15 to 20 cm. : on rocks in shallow water: 

 Alaska to Monterey, California; common. 



ORDER 2. SPINULOSA. 



Arms usually long and without prominent marginal plates; aboral 

 body wall spiny and usually with a more or less reticular or imbricated 

 skeleton; ambulacral feet with sucking discs; pedicellariae rare or absent 

 and not pedunculate: 5 families. 



Key to the families of Spinulosa here described: 



di Mouth plates small ; ambulacral groove narrow. 



&! Aboral skeleton composed of imbricating scales 1. ASTERINIDAE 



& 2 Aboral skeleton reticular 2. ECHINASTEBIDAE 



o, Mouth plates large ; ambulacral groove wide. 



& x Usually more than 5 arms 3. SOLASTERIDAE 



& a Five arms present 4. PTEBASTEBIDAE 



