18 INTRODUCTION. 



Sub-clasa V. Geaptolitid^ (extinct). 

 Class B. Aotinozoa. — Stomach opening below into the body-cavity, 

 which is diyided into a number of compartments by a series of vertical 

 partitions or "mesenteries." Reproductive organs iutemal. 



Order 1. Zoardlmria. — Tentacles simply rounded, in multiples of five 

 or six. — JEx. Sea-Anemones (Actinidse), Star-corals 

 (Astraaidae), Brain-corals (Meandrina), Madrepores (Ma- 

 dreporidie). 

 Order 2. Alcyonaria. — Tentacles fringed, in multiples of four. — Ex. 

 Dead-man's-toes (Alcyonium), Organ-pipe Coral (Tubi- 

 pora), Sea-rods (Virgularia), Sea-pens (Pennatula), Red 

 Coral (Corallium). 

 Order 3. Rugosa (extinct). 



Order 4. Ctenophora. — Animal oceanic, swimming by means of 

 bands of cilia or " ctenophores." — Jiisc. Pleurobrachia, 

 Venus' s Girdle (Cestum). 



SUB-KINGDOM IIL—AWNULOIDA. 



Animals in which the alimentary canal is completely shut ofiT from the 

 general cavity of the body, and in which there is a distinct nervous system. 

 A true blood-circulatory system may or may not be present. In all there is 

 a peculiar system of canals, which usually communicate with the exterior, 

 and which constitute what is called the " water-vascular system." The body 

 of the adult is never composed of a succession of definite rings, or provided 

 with successive pairs of appendage.^! disposed symmetrically on the two sides 

 of the body. 



The Annuloida are divided into two great classes : 



A. EcHiNonERMATA. — Integument composed of numerous calcareous plates 

 jointed together, or leathery and having grains, spines, or tubercles of cal- 

 careous matter developed in it. Water-vascular system (ambulacral system) 

 mostly employed in locomotion, and generally communicating with the ex- 

 terior. Adult generally more or less starlike or " radiate " in shape ; young 

 mostly showing more or less complete " bilateral symmetry," that is, show- 

 ing similar parts on the two sides of the body. Nervous system radiate. 



Order 1. Crinoidea. — (Sea-lilies). — Ex. Feather-star (Comatula). 

 Medusa-head Crinoid (Pentacrinus), Stone-lily (Encri- 

 nus.) 



Order 2. Mastoidea (extinct). 



Order 3. Cijstoidea (extinct). 



Order 4. Ophiuroidea (Brittle-stars). — Ex.. Sand-stars (Ophiura), 

 Brittle-stars (Ophiocoma). 



Order 6. Asteroidea (Star-fishes). — Ex. Cross-fish (Uraster), Sun- 

 star (Solaster), Cushion-star (Goniaster). 



Order 6. -Ec/«'«oi&a (Sea-urchins). — Ex. Sea-eggs (Echinus), Heart- 

 urchins (Spatangus). 



Order 7. Holothurmdea (Sea-cucumbers). — Ex. Trepangs (Holo- 

 thuria). 



B. ScOLECiDA. — ^Body usually flattened, or cylindrical and worm-like ; in- 

 tegument soft, without lime. Water-vascular system not assisting in loco- 

 motion. Nervous system consisting of one or two ganglia or little masses, 

 and not disposed in a radiate manner. 



Order 1. Tcmiada. — Ex. Tape- worm (Ttenia). 



Order 2. JrematoJa (Suctorial worms). — Ex. Liver-iluke (Distoma). 



