204 



PORIFERA 



CHAP. 



Fig. 97. Hyaloneraa thomsaii. A, 

 Whole specimen with rooting tuft 

 and Epizbanthus crust ; B, pinulus, 

 a spicule characteristic of but not 

 peculiar to the Amphidiscophora, 

 occurring in the dermal and gastral 

 membranes ; C, amphidisc with 

 axial cross ; D, distal end of root- 

 ing spicule with grapnel. (After 

 F. E. Schulze.) 



inserted in a sponge " ; next 



Ova have rarely been found, and 

 sexually produced larvae never ; but 

 Ijima has found archaeocyte clusters 

 in abundance, and his evidence is 

 in favour of the view that they 

 give rise asexually to larvae, described 

 by him in this class for the first 

 time (see p. 231). 



Both sub-classes are represented 

 in British waters : the Amphidisco- 

 phora by Hyalonema thomsoni and 

 Pheronema carpenteri ; the Hexas- 

 terophora by Euplectella suberea and 

 Asconema setubalense, and of course 

 possibly by others. 



Hyalonema thomsoni, one of the 

 glass -rope sponges, was dredged by 

 the Porcupine off the Shetland 

 Islands in water of about 550 

 fathoms. The spindle-shaped body 

 of the sponge is shown in Fig. 97. 

 Its long rooting tuft is continued 

 right up its axis, to end in a conical 

 projection, which is surrounded by 

 four apertures leading into corre- 

 sponding compartments of the 

 paragaster. 



The crust of Anthozoa of the 

 genus Epizoanthus (p. 406) on the 

 rooting tuft is a constant feature in 

 this as in other species of Hyalonema. 

 It contributed to make the sponge 

 a puzzle, which long defied inter- 

 pretation. The earliest diagnosis 

 the genus received was the " Glass 

 Plant." Then the root tuft was 

 thought to be part of the Upizo- 

 anthus, which was termed a " most 

 aberrant Alcyonarian with its base 

 we hear of the sponge as parasitic 



