120 



COELENTERATA— HYDEOZOA 



PHYLUM II 



Stylaster Gray. Branching polyparia composed of a network of fibrous, 

 rose-coloured coenenchyma, in which are situated calicular depressions that are 

 provided with pseudosepta and columellae, and communicate with the zooid 

 tubes and vermiform canals. Recent, and occurring sparsely in the Tertiary. 



Order 3. TUBULARIAB AUman. 



Polyp Stocks which are either nahed or covered with chitinous outer layer (periderm). 

 Both the polypoid nutritive zooids, and also the medusoid reproductive animals are 

 without cup-shaped hydrothecae surrounding the polyp head. A chitinous or calcareous 

 skeleton (hydrophyton) is frequently secreted at the hase. 



Hydractinia v. Bened. (Fig. 186). Hydrophyton in the form of encrusting, 

 chitinous, rarely calcareous expansion, frequently investing gastropod shells. 

 The crust consists of successive, slightly separated, horizontal laminae, which 



l 



^- 





are supported by num- 

 erous vertical rods or 

 columns {radial pillars). 

 The surface is covered 

 with projecting hollow 

 spines and tubercles, 

 and is also traversed 

 by shallow, branching 

 grooves {astrorhizae). 

 Interlaminar spaces 

 communicating with 

 the surface by means 

 of rounded tubes. 

 Tertiary and Recent. 



Ellipsactinia Steinm. 

 Hydrophyton irregu- 

 larly ellipsoidal, com- 

 posed of thick, con- 

 centric, slightly separ- 

 ated, calcareous lam- 

 ellae, which are united 

 by sparsely distributed 

 vertical columns. 

 Lamellae are formed by the anastomosis of exceedingly delicate calcareous 

 fibres, punctured by numerous fine radial tubes, and furnished on both sides 

 with pits, tubercles and branching furrows. Upper Jurassic (Tithonian) ; 

 Alps, Carpathians and Apennines. 



Sphaeractinia Steinm. Like the preceding, but composed of thin, widely 

 separated lamellae, which are supported by numerous radial pillars. Centre 

 frequently occupied by a foreign body. Upper Jurassic (Tithonian). 



Loftusia Brady (Fig. 187). Ellipsoidal or fusiform bodies, composed of 

 thin, concentric or spirally rolled calcareous lamellae. Interlaminar spaces 

 wide, intersected by numerous radial pillars, and often secondarily filled with 

 calcareous mud. Eocene ; Persia. 



Parkeria Carp. Globular or walnut - shaped organisms with nodulated 



Fig. 186. 



A, Hydractinia echinata F\em. Recent; North Sea. Portion of commensal 

 colony, greatly enlarged ; hy, Polyps (hydranths) ; go, Generative buds (gono- 

 phores) ; hph, Hydrophyton adherent to shell of Buccinium undatum, and 

 showing reticulated structure in vertical section. B, Hydractinia calcarea 

 Gart. Vertical section of hydrophyton, greatly enlarged (after Carter) ; a, 

 Primary basal lainella ; h, Interlaminar space ; c, Second lamella ; d, Radial 

 pillars between the lamellae ; e, f, Tubercles and spines projecting on upper 

 snrface. C, Hydractinia pliocaena Allm. Pliocene ; Asti, Italy. Hydro- 

 phyton encrusting on Nassa shell (natural size). D, Portion of magnified 

 surface of the latter, showing branching grooves and wart-like tubercles. 



