224 



PORIFERA 



CHAI 



Fig. 110. Megascleres. a-l 

 and q-s, Modifications of 

 monaxon type, a, Stron- 

 gyle ; b, tylote ; c, oxea ; 

 d, tylotoxea ; e, tylostyle ; 

 /, style ; g, spined tylo- 

 style ; h, sagittal triod (a 

 triaxon form derived from 

 monaxon) ; j, oxytylote ; k, 

 anatriaene ; I, protriaene ; 

 m, sterraster (polyaxon) ; 

 n, radial section through 

 the outer part of m, show- 

 ing two actines soldered 

 together by intervening 

 silica ; o, desma of an 

 Anomocladine Lithistid 

 (polyaxon) ; q, crepidial 

 strongyle, basis of rhab- 

 docrepid Lithistid desma ; 

 r, young form of rhab- 



docrepid desma, showing crepidial strongyle coated with successive layers of silica ; s, 



rhabdocrepid desma. 



33. -I 



34. 



35. 

 36. 

 37. 



38. 

 39. 

 40. 



41. 



42. 

 43. 



Skeleton reticulate or fibrous . . . . .34 



Skeleton radiate or diffuse . . . . .37 



Skeleton with radiating fibres forming a reticulum with, others crossing 

 them at right angles .... Quasillina 



fNo microscleres . . . . . .35 



I Microscleres sigmata andV .,, .,, , . , , 



, r . t Vtoxa with or without trichodragmata 



(Microscleres sigmata or J n // 



(Sponge fan- or funnel-shaped . . . . .36 



\ Sponge not fan- or funnel-shaped . . Hymeniacidon 



("Megascleres slender and twisted . . . Phakellid 



y Megascleres somewhat stout, not twisted . . Tragosia 



(Sigmata present, skeleton diffuse . . . Biemma 



(Sigmata absent . ... . . . .38 



(Skeleton more or less radiate . . . . .39 



\ Skeleton diffuse ; sponge boring . . . Cliona 



(Sponge discoid with marginal fringe . . . Halicnemia 



\ Sponge massive or stipitate without marginal fringe . .40 



(Sponge body prolonged into mammiform projections . Polymastia 

 \Sponge body without mammiform projections . . .41 



TNo microscleres. Megascleres tylostyles with or without styles 

 -j Suberites 



[Microscleres centrotylote. Megascleres styles or tylostyles Ficulina 



(Choanosomal megascleres smooth . . . .43 



\Choanosomal megascleres spined . . . Dendoryx 



J Microscleres chelae and sigmata of about the same size .Lissodendoryx 

 (Chelae, if present, smaller than the sigmata . . Yvesia 



