.\\THO\IUH s ]: STYI.AI TIS. 



1 10 



Genus STYLACTIS Allman, 1864. 



Slylaclis, ALLMAN, 1864, Annals anil Mag. Nat. Hist., scr. 3, vol. 13, p. 353; 1871, Monograph TubuUnan Hy>lroi,l;,, p. 301. 

 CLARKF., 1882, Mem. Boston Sue. Nat. Hist., vol. 3, p. IjS. SH.IKHIOS, iSSi), American Naturalist, vol. 33, p. 801. 



These are Margelinae in which the medusa is degenerate, and indeed in the European 

 species of Stylactis no medusae are set free, mere sporosacs being developed on the hydranths. 

 The two American forms, however, produce free-swimming, although degenerate medusae. 



The medusa has 8 rudimentary tentacle-bulbs, 4 radial and 4 interradial ; 4 simple radial- 

 canals and a ring-canal. The manuhiium is sac-like without a mouth, and without oral 

 tentacles. The gonad encircles the sac-like manubrium, and the mature eggs or spurn arc- 

 found in the ectoderm. The sexes are separate. 



The hydroid, Stylactis, hears a resemblance to hoth HyJractinia and Podocoryne, hut 

 unlike the two last named the hydrorhi/.a is not covered with a fleshy layer of cu-nosarc 



c 



Fl<i. 8|. Oceania urtnuta, from life, liv tlie author. Viplr /.ML,!,,,-]! .il Station, December |S, H/O-. 

 A. Mature female. 



M. Basal part of tentacle showing ectodermal ocelli^ on its velar sule. 

 C. Part <>f lip, '<lin\\m^ m\\ of nettling-warts. 



(hydrocaulus). The hydrorhiza of Stylactis is formed of a network of anastomosing stolons 

 invested with a chitinOUS pensarc, hut are without a superficial layer of naked ccenosarc. 

 The hydranths are simple, claviform, or cylindrical, with one or two circles ot tilitorni ten- 

 tacles around the oral /one. The hydranths arise singly from the hydrorhi/a and are of 

 two sorts, reproductive and nutritive. Spines also arise from the hydrorhi/a. The spor- 

 osacs, or medusa-huds, are borne upon the sides ot the reproductive hydranths m an irregular 

 circlet helow the tentacles. 



The type species is Styl/ictis fuciola of the Mediterranean (see Allman, 1864) which 

 was first described by M. Sars (1857, Nyt. Mag. Naturvid., ()), under the name Podocoryne 

 fuciola. Allman pointed out its peculiar characters and distinguished it from Podocoryne, 



One of the most remarkable species is St\ltiftii iniimi Alcock Il8t)2, Annals and Mag. 

 Nat. Hist., ser. 6, vol. 10, p. 207, I fig.). This is commensal upon a fish Minum in,-rtnn. 

 Sporosacs, but no medusa-buds, are produced by the hydroid ot this species. 



