610 Haddon and Shackleton — A Revision of the British Actinice. 



Zoantliese themselves have, since the time of de Blaiuville, been recognized as a 

 well-marked division of the Actiniae. 



With the exception of the genus Sphenopus, and certain free varieties 

 of the genus Epizoanthus, all the members of this group are permanently 

 fixed, and with very few exceptions form colonies, the individuals of which 

 are united by the adhering base or coenenchyme. The coenenchyme extends 

 laterally, and from it new polyps arise, which remain permanently connected 

 with the colony. 



The coenenchyme may be band-like or form broad encrusting sheets ; usually 

 it is thin, but in the genus Palythoa it is so thick that the polyps are more or 

 less immersed within it. The polj^ps may be placed at considerable intervals 

 from each other, or they may be crowded together, the latter condition being 

 usually due to gemmation from the base of the polyps rather than from the 

 coenenchyme. 



It is characteristic of the group for the body- wall of the polyp and coenenchyme 

 to be incrusted with foreign particles — grains of sand, si^icules, foraminifera, and 

 such like. Some genera, such as Palythoa and Sphenopus, are always densel} 

 incrusted ; the incrustations in Parazoanthus vary according to the species from a 

 considerable amount to very few ; finally, the genera Zoanthus and Mammillifera 

 are unincrusted. 



The Zoanthese have the same body-regions as other Actiniae, with the excep- 

 tion of the basal disc, which must necessarily be absent in the colonial forms, and 

 of a physa in the free forms. In all the column is divisible into scapus and 

 capitulum ; the former is usually rigid. In nearly all preserved specimens the 

 capitulum is retracted, and this appears to be generally the case when living, for 

 these forms do not fully expand so frequently as most other sea-t emones. The 

 capitulum is usually thrown into triangular ridges. 



The tentacles are bicyclic, and may be very short or moderately long. When 

 fully expanded, the oral disc may be flat or projecting. The mouth is always 

 linear. Only one oesophageal groove is present. 



The colours are usually various shades of yellow, buff, and brown, due to the 

 sand incrustations ; some have varied colours — pink, green, violet, and so forth — 

 but it is very rare for the colours to be so vivid as is customary among other 

 Actiniae. 



Reproduction takes place by means of ova, by basal and coenenchymatous 

 gemmation, and by fission. 



The foregoing are all the characters which are available for the field 

 naturalist, and, until quite recently, were the only ones on which the definition 

 of species and their systematic arrangement were based. These purely external 

 characters are more than usually unsatisfactory for diagnostic purposes; hence 



