REPORT ON THE DEEP-SEA MEDUSA. 49 



Family, Tesserid^e, Hseckel, 1877. 



TESSERiDiE, Hreckel, System der Medusen, 1879, p. 371, taf. xxi. 



Stauromedusae with simple, undivided umbrella margin, without hollow marginal 

 lobes or " arms." Eight principal tentacles (four perradial and four interradial) always 

 present, not transformed into marginal anchors or sense clubs ; besides these, sometimes 

 numerous secondary tentacles. Coronal muscle of the umbrella margin circular, not 

 divided into eight isolated marginal muscles. Either an apical process or an umbrella 

 peduncle on the apex of the umbrella. 



Sub-family, Tesseranthid.e, Haackel, 1879. 



Free-swimming Tesseridaa, without a stalk, but with an apical process on the cone of 

 the umbrella ; with simple solid tentacles without terminal urticating knob. 



Tesserantha, 1 Hseckel, 1879. 



Tesseridaa, without peduncle, with an apical process and with sixteen simple solid 

 tentacles without terminal urticating knob (four perradial, four interradial and eight 

 adradial). The genus Tesserantha is one of the simplest and oldest Medusae forms of that 

 important family the Tesseridse, which are to be regarded as the general ancestral 

 group of all Acraspedaa. This primitive Acraspeda form is essentially merely a Scy- 

 phostoma with sixteen tentacles which, in adapting itself to a free-swimming mode of life, 

 changed its oral disc into a subumbrella, and its basal peduncle into an apical process, 

 divided the peripheric gastral space into four radial pouches by four interradial fused 

 knobs, and became sexually mature in this form. Tesserantha is distinguished from the 

 octonemal closely related Tessera by the addition of eight new adradial tentacles (of the 

 third order) to the eight principal tentacles (four perradial and four interradial). More- 

 over, whilst in Tessera only four simple gastral filaments run out from the four septal 

 knobs, as terminal free processes of the four interradial tamiola, the septal knobs in 

 Tesserantha are beset with a double row of filaments throughout the greater part of their 

 iength (the proximal basal part alone excepted). In this and other respects, namely in the 

 formation of four perradial mesogonial folds and four interradial funnel cavities alternating 

 with these, Tesserantha comes nearer De'pastrella, and therefore forms an interesting- 

 transition gradation between Tessera and Depastrella. At present there is only one 

 known species of this genus, the deep-sea Medusa described below. 



1 Tesserantha, four-sided flower. 



(ZOOL. CIIALL. EXP. PART XII. 1881.) M 7 



