LEODICIDAE. 231 



Most of the leodicids secrete tubes of varied consistence, many of these 

 being hyahne or papyraceous and composed exclusively of the secretion of the 

 worm, while in other cases fragments of shells, frustules of diatoms, shells of 

 Foraminifera and Radiolaria, tubules of serpulids, fragments of sea-weeds, and 

 other materials may be made use of in the construction of the walls. The tubes 

 are commonly simple, but may be branched. The mucus forming the sub- 

 stance or the matrix of the tubes is secreted by glands at the bases of the neuro- 

 cirri of the anterior region. Some species inhabit cavities or burrows in rocks, 

 calcareous Algae, coral reefs, or in the mud, the retreats being lined ordinarily 

 with a thin layer of transparent material. 



They are frequent in all parts of the world, though apparently more abun- 

 dant in the warmer seas. They occur often between tide-marks or near low 

 tide, in crevices of rocks, in mud, as among the growths of Zostera, among shells, 

 or in madrepores. In removing them from their retreats autotomy is fre- 

 quent. On the other hand some species may occur at depths approaching the 

 thousand fathom mark, though they do not attain depths as great as in the 

 closely related forms of the Onuphididae. 



Many species exhibit phosphorescence. Thus Crossland found Lysidice 

 afra (Peters) to be strongly phosphorescent during removal from the mud, a 

 blue light being given out from the mucus secreting pads adjacent to the neu- 

 ropodia and the mucus itself remaining luminous. 



Key to Genera. 



a. Branchiae present. 



b. Tentacles and eyes none Iphilime Marenzcllor. 



bb. Tentacles and eyes present or the latter indistinguishable. 

 c. Tentacles five. 



d. Tentacular cirri present Leodice Savigny. 



dd. No tentacular cirri. 



e. Composite setae present Marphysn Quatrefages. 



ee. Setae all simple Aphclothrix, gen. nov.^ 



cc. Tentacles three or less; tentacular cirri none. 



d. Tentacles three Amphiron Kinborg. 



dd. Tentacles two Coelobranchus Izuka. 



aa. Branchiae none. 

 6. Tentacles five. 



c. Tentacular cirri present Nicidion Ivinberg. 



cc. No tentacular cirri Paramarphysa Ehlers. 



bb. Tentacles three or less; no tentacular cirri. 



c. Tentacles three Lysidice Savigny. 



cc. Tentacle one Nematonereis Schmarda. 



' Marphysa mossambica Peters, genotype. &<p€\iis, simple, and Opi^, bristle. 



