IC)I5-] Fauna of the Chilka Lake : Coelenterates. 89 



Genus Halianthus, Kwietniewski. 



1896. Halianthus, Kwietniewski, Jena. Zeitsch. Naturwiss. XXX, p. 585. 



The species hitherto assigned to this genus are mainly Arctic, but McMurrich 

 (op. cit., 1905, p. 223) has described one from the Pacific coast of South America. 

 I can find no previous record from the Indian Ocean. 



Halianthus limnicola, sp. nov. 

 (Plate vi, fig. 2 ; plate vii, figs. 4, 4a, 4b.) 



When at rest the living animal has a conical shape, slightly swollen in the mid- 

 dle region and slightly constricted at the truncated end, i.e. just below the oral disk. 

 The aboral end is bluntly pointed and often not at all inflated ; externally there is no 

 apparent separation of capitulum, scaphus and physa, but the last is to some extent 

 retractile. The body can assume practically any shape from spherical to cylindrical 

 and sharp constrictions at one or more points are often a noticeable feature of pre- 

 served specimens ; when the tentacles are retracted the upper part of the column 

 assumes a subspherical form, while the aboral region is constricted into a cylindrical 

 peduncle ; or the whole organism may have an elegant vase-like outline. There is 

 no external cuticle or sheath. 



On the external surface there are twelve longitudinal rows of relatively large, 

 though not very prominent, solid tubercles, which correspond roughly in position 

 with the twelve mesenterial spaces; they are mainly due to thickenings of the 

 mesogloea. Towards the aboral extremity these rows, and also the individual 

 tubercles, tend to become obsolete. The whole of the body-wall and the wall of the 

 disk and tentacles is hyaline and practically colourless, but the tentacles are often 

 ornamented on the upper surface with V -S haped translucent bars and the disk is not 

 so transparent as the column. The mesenterial filaments and the gonads are of a 

 bright yellowish flesh-colour, which is communicated by reflection to the remainder of 

 the animal, especially in a state of contraction. Specimens in spirit or even formalin 

 become more or less opaque. 



The oral disk is ample, its outline in contraction is broadly oval, the longer axis 

 being that of the mouth, which occupies the greater part of the disk in this axis. 

 The lips are by no means prominent when the mouth is closed ; there are six low 

 transverse ridges at each side. The normal number of tentacles is twelve, but occa- 

 sionally one or more subsidiary tentacles are produced asymmetrically ; the normal 

 arrangement is that the tentacles form two concentric circles of equal numbers and 

 alternate round the margin. There is no structural difference between ordinary and 

 subsidiary tentacles; both when fully expanded are stout, cylindrical and blunt and 

 hardly longer than the longer diameter of the disk ; they can be contracted into little 

 wart-like projections. The disk is usually flat but can assume a conical or even a 

 clavate form. 



The aboral extremity is perforate, but the pore is always small. 



Our largest specimens, which have shrunk very little, are about 5 mm. long. 



