46 



ZOANTHARIA 



oval-shaped and with granular contents of close-lying grains (PI. 7. fig. 1). The whole mesoglcea with 

 exception of the very innermost part is incrusted. The entoderm is moderately developed, sometimes 

 darkly pigmented. 



The sphincter is long and strong, in the distal part it forms a few deep folds, in the proximal 

 numerous but small folds. 



The ectoderm of the tentacles contains numerous spirocysts, whereas the thick-walled capsules 

 (length about 22//), are very scarce. The mesoglcea is richly incrusted. 



The ectoderm of the a\sophagus is very high and contains numerous uematocysts 24— 26/i long 

 and thick-walled; further, there is a sparse occurrence of larger or smaller uematocysts with coiled 

 thread as in the filaments. The mesoglcea is thin though however thickened in the siphonoglyphe. 



The number of mesenteries varied in the two specimens examined 

 between 34 and 38. In both specimens the one side had one mesentery 

 more than the other. 



The macro-mesenteries are rather thick even in specimens with ex- 

 panded mesenteries, whereas the micro-mesenteries are weak and in the 

 lower part of the oesophageal region extend a little over the main part 

 of the entoderm of the body-wall. In specimens having the mesenteries 

 contracted broadwise the longitudinal musculature lies iu deej) folds even 

 extending below the oesophagus (Text-fig. 6). The parieto-basilar muscles 

 are very weak. The distribution of the longitudinal musculature on the 

 body-wall is fairly considerable, whereas hardly any parieto-basilar muscles 

 occur. Below the oesophagus extend the mesenteries, which contain the 



phagus oi Isozoanthns davisi. Meso- 

 glcea and muscles black, ectoderm undeveloped sexual organs reaching some way into the gastrovascular 

 of the oesophagus shaded, ento- 



Tcxt-fig. 6. Transverse section 

 through a portion of the body- 

 wall with mesenteries and <ieso- 



derin dotted. The light parts in 

 and outside the mesoglcea of the 

 body-wall represent incrustations. 

 Ectoderm of the body-wall absent. 



cavity. 



The filaments have the usual structure. Two kinds of uematocysts 



with greatly twisted thread and often of a somewhat curved shape occur, 



the one kind larger 37—53// long and 10—12// broad, the other smaller 



elongated, egg-shaped, .somewhat broader at the one end (length 15— 22 //, largest breadth 6—7//). 



Further, the filaments contain thick-walled uematocysts broader at the one end than at the other 



(length 22—24//, breadth 5—6//). 



One of the specimens investigated had undeveloped testes. 



Isozoanthus islandicus. 



PI. 2. fig. 20. PI. 7 fig. 2. 



Occurrence: 64^45' N., 29° 06' W. 568 Dan. fms. Bott. temp. 4-4°. Ingolf Exp. St. 90. i colony. 



Dimensions: Length of the largest polyp 0-9 cm., greatest breadth about 0-2 cm. 



Colour in alcohol: dark. 



External appearance. The only colony of this species was attached to a couple of .spicules 

 of a Hexactinellida. The thin ccenenchyme was very large encircling the spicules almost entirely, so 

 that it formed a tube round these. In fig. 20 PL 2 we see very little of the spicules. The polyps. 



