Invertebrata. Zoological Collections, 49 



Remarkable instances of the subserviency of one Animal to the formation of the 

 habitation of another. 



Without attempting to reason upon the causes of the admirable fitness of 

 things, or seeking to swell the list of final causes by more ridiculous conceits 

 than those which well-intentioned authors have devised, we collect the following 

 facts as remarkable instances of the adaptation of animals to each others' uses. 



The Actinia circiTieopadoSf Otto, {A. picta, Risso, Medusa palliata, Fabr.,) 

 has an extraordinary mode of life ; it is found fixed upon deserted univalve shells, 

 which are the habitations of a hermit crab ; the margin of the opening of the shell 

 is continued by a long horny greenish-coloured membrane, whereby the cavity 

 of the shell in which the crab lives is enlarged, and to this membrane the Actinea 

 is attached by its base around the orifice of the shell. 



Strom {^Beskriv. over fogderiet Sondmor. S. 164,) gives an imperfect notice 

 of this animal. He remarks that it is attached to the deserted shell of a Nerita, 

 which forms the habitation of a hermit-crab. Fabricius {Reise nach Norwegen, 

 S. 327.) also describes its peculiar habits, though he erroneously supposed it to 

 be a Medusa. 



On the west coast of Norway, where Strom and Fabricius made their observa-. 

 tions, Rapp found this Actinia on the shell of the Buccinum undatum, which was 

 inhabited by a hermit-crab. Fabricius also saw it attached to the shell of Turbo 

 littoreus, which had been occupied by a hermit-crab. Otto, who has given the 

 best description and figures of the Actinia carcineopados, {N'ov. Act. Acad. Cces. 

 fjcop. Carol. Nat. Cur. II. 288, PI. xl.) found it often at Naples on different 



shells of mollusca, which were the habitations of the Pagurus Bernhardus 



Rapp, Uber die Polypen, p. 58. Vide also Bohadsch, Anim. Marin, p. 135. 



Without being acquainted with the previous observations of the preceding 

 authors, our friend. Dr. Coldstream, has recently, in the Edin. New Phil. Jour- 

 nal, Oct. 1830, given the following account of the habits of another species of 

 Actinia, the A. maculata of Adams, (Linn. Trans. V. 8. ;) A. sulcata, Flem. 

 (Brit. An. 498;) and De Blainville, (Diet, des Sciences Nat. Ix. 294.)* 



" Base fixed to a thin horny expansion attached to the apertures of various dead 

 shells, such as Trochus cinerarius and T. Magus.-)- and forming, as it were, an 

 extension of the body-whorl of the shell in a spiral form. Over this, the Actinea 

 is spread entirely, and covers also more or less of the shell. Its oral disc is uni- 

 formly situated close to the inner lip of the horny case. The aperture of the case 

 is accurately surrounded by its body, the margins of the opposite sides of which 

 meet, and are closely applied to one another at the middle of the outer lip of the 

 aperture, whence they ruu upwards towards the old shell, where they generally 

 separate again, leaving its apex uncovered. 



" The horny membrane to which the Actinia is attached, covers, for the most 

 part, nearly the whole external surface of the old shell to which it is fixed, and, 

 from the circumstance of its aperture, is prolonged into a large hollow expansion, 

 resembling in form, and occupying, relatively to the shell, the place of a ventri- 

 cose body-whorl. Its substance is of uniform thickness throughout its whole 

 extent, of a greenish-brown colour, translucent, having both surfaces irregularly 



* Dr. Coldstream, however, remarks that the characters of the species described by, 

 him " do not correspond with those assigned to A. sulcata, while they agree closely 

 with the description of the maculata of Adams. In the A. sulcata, the tentacula are green- 

 ish, and longer than the body ; in the A. maculata, they are white, with a faint streak of 

 brown, and shorter than the body; the first has the oral disc dentated, the latter has it 

 plain. Lamarck (An. sans Vert. iii. 69,) gives the specific name of maculata to a species' 

 from the Red Sea, but neither the characters assigned to it, nor the figure m the Ency- 

 clopedie, (PI. 72, f. 10,) correspond with those of our animal. 



+ Adams found his specimens " surrounding the apertures of deserted shells of Murett, 

 despectus," . - 



VOL. III. Gr 



