ASTEROIDEA. 



ISO 



Order II. ETJASTEKIAE. 



With characters as above. 



Sub-Order 1. PHANEROZONIA. 



With large marginal plates. The supramarginal and inframarginal 

 plates are in contact. Papulae restricted to the abambulacral surface 

 within the area bounded by the supramarginal plates. Ambulacral plates 

 usually broad. Tube-feet in two rows in each arm. Oral adambulacrals 

 prominent. Pedicellariae when present sessile. 



Fam. 1. Archasteridae. Marginal plates thick, with spines or spini- 

 form papillae. Adambulacral plates large and not compressed. Ventro- 

 laterals and marginals with spines or paxilli. Superambulacral plates 

 absent. Pararchaster Slad. ; Pontaster Slad. ; Cheiraster Studer ; Pecti- 

 naster Perr. ; Lonchotaster, Dytaster, Plutonaster Slad. ; Archaster Miiller 

 and Troschel ; Grnathaster Slad. ; Asterodon Perr. ; Odontaster Verrill ; 

 Mimaster Slad. ; Goniopecten Perr. ; Leptogonaster Slad. ; Pseudar -chaster, 

 Aphroditaster Slad. British species : Pontaster tenuispiins, Scilly, 

 Faeroe Channel, etc. 90-60 fms. Plutonaster bifrons, Faeroe Channel, 

 etc., 200-1,300 fms. ; PI. bifrons, N. of Ireland, 1,360 fms. 



Fam. 2. Poreellanasteridae. Marginal plates well developed, but thin 

 and porcellanous in appearance, and apparently naked or covered only 

 with a thin epidermal layer. Abactinal area covered with membrane 

 and carrying in its centre an 

 epiproctal prominence (Fig. 

 137). Anus said to be absent. 

 Actinal surface of disc is 

 covered interradially with 

 squamiform plates. Cribriform 

 organs (1 to 14 in each inter- 

 radius) present. Adambulacral 

 plates large with simple mar- 

 ginal armature uniserially dis- 

 posed. Excepting Ctenodiscus 



all genera are exclusively from the deep sea. Cribriform organs are 

 situated on the marginal plates in the inter-brachial region of the disc, 

 and extend when numerous on to the base of the arms. They consist 

 of a number of parallel vertically arranged calcareous lamellae equal in 

 length to the height of the two series of marginal plates. 



Porcellanaster W. Thorns. (Fig. 137) ; Styracaster, Hyphalaster, and 

 Thoracaster Slad. ; Pseudaster Perr. ; Ctenodiscus Miill and Trosch. 

 British species : Ctenodiscus cristatus, Faeroe Channel, 312 fms. 



Fam. 3. Astro pectinidae. With large marginals bearing spines or 

 spiniform papillae. Actinal interradial areas small. Abactinal skeleton 

 with paxilli (Fig. 121). Tube-feet conical. Superambulacral plates 

 present. Anus absent. Pedicellariae rarely present. In Leptoptychaster 

 kerguelenensis the eggs pass into the spaces between the groups of paxilli and 

 there develop (W. Thomson, J. Lin. Soc. London, 1876, 13). 



Craspidaster Slad. ; Leptoptychaster Smith ; Moiraster Slad. ; Blaki- 

 aster Perr. ; Astropecten Linck ; Psilaster Slad. ; Phoxaster Slad. ; Bathy- 

 biaster Dan. and Kor. ; Ilyaster Dan. and Kor. ; Luidia Forbes ; Platas- 

 terias Gray. British species : Leptoptychaster arcticus, Faeroe Channel, 

 1,312 fms. Astropecten irregularis (aurantiacus) Atl. and Med., 10-1,000 



FIG. 137. Porcellanaster gracilis Sladen, side view, 

 showing three cribriform organs and the epiproctal 

 prominence. 



