Cirripedia having a flexible peduncle, provided with muscles: scuta and terga, when present, not furnished with depressor muscles: other valves, when present, not united into an immoveable ring.
This Family has been fully treated of in my former volume, published by the Ray Society,[141] and I should here only have alluded to its existence, had it not been for the genus Alcippe, which differs in so many important characters from the other members of the Lepadidæ, that formerly I did not even suspect that it could belong to this Family, and therefore deferred its examination. The genus Alcippe was discovered, well described and illustrated, in 1849, by Mr. Hancock; to whose very great kindness I am indebted for permission to dissect and examine his entire stock of this truly remarkable Cirripede. In the classification of the whole class I have not felt so much doubt, as whether I ought to institute a family for the reception of this genus. Alcippe differs from all other Cirripedes (putting on one side for the instant, the males and complemental males of Ibla and Scalpellum) in the very singular fact of being destitute of a rectum and anus;—in the three segments of the thorax, which usually support the second, third, and fourth pairs of cirri, being without any appendages;—in the fifth and sixth pairs of cirri having their inner or posterior rami metamorphosed into very singular roughened cushions or buttons, which apparently serve to triturate the food;—in the caudal appendages being muscular, and being used conjointly with the cirri;—and lastly, in the pupa having a lesser number of segments in its abdomen and caudal appendages than in (as far as I have seen) any other Cirripede. It will be thought that these characters are amply sufficient to justify the placing Alcippe in a separate family, more especially when the close general resemblance in the animal’s body in most of the other members of the Balanidæ, Verrucidæ, and Lepadidæ, is borne in mind. On the other hand, the males and complemental males of Scalpellum and Ibla must indisputably be considered as members of the Lepadidæ; yet the male of Scalpellum vulgare and ornatum has no stomach, anus, or mouth, which is a far more abnormal structure than the absence only of the anus in Alcippe: the cirri, also, in these same males, differ from the ordinary cirripedial type decidedly more than in Alcippe. Again, in the male of Ibla, all the cirri, excepting the fifth and sixth pairs, are aborted, and these two pairs are usually only uniramous; here, then, we have a decided resemblance to Alcippe. Hence, if we might assume that the female Alcippe had partially assumed characters confined to the males of the other genera, it would assuredly stand amongst the Lepadidæ. Independently of this comparison with the foregoing males, the affinities of Alcippe are so special to several genera amongst the Lepadidæ, that it seems unnatural to force it out of the position which it well occupies between Ibla and Anelasma, and place it in another family by itself: thus, in being bisexual, and in the general character of its very curious males, Alcippe shows an affinity to Ibla and Scalpellum; and to the former of these genera it is related in several particulars, such as in the body being lodged within the peduncle, and in the structure of the larval antennæ, &c.: to Anelasma and Alepas it is allied in the general character, and to a certain extent in the muscles, of the capitulum; Anelasma, also, has all its cirri to a certain degree rudimentary, and Alepas cornuta has the inner rami of the fifth and sixth pairs of cirri,—namely, the very same rami which are so curiously modified in Alcippe,—small, destitute of muscles, and functionless for their proper purpose: to Anelasma and Lithotrya it is allied in the peculiarity of the lower end of the peduncle becoming elongated by growth, and in being imbedded; and to Lithotrya by its powers of excavation and manner of attachment. Now, I believe it generally holds good that when a form is really distinct from another group, its affinities are general, or only in a slight degree special to the members of that group. Nor, indeed, can it be asserted that Alcippe differs much more, somewhat more it certainly does, from the other genera, than does Anelasma, with its more singular mouth, spineless rudimentary cirri, and fimbriated peduncle; and I have never regretted having included this genus amongst the Lepadidæ. Hence, after much consideration, I have resolved to consider Alcippe as one of the Lepadidæ, though so curiously modified,[142] and having characters confined to the males of the other genera. Perhaps I have been in some degree influenced by the difficulty of finding external characters by which to separate Alcippe as a family from the other Lepadidæ.
[141] The fossil species have been described in a separate Monograph published by the Palæontographical Society. Since its publication, M. Bosquet has produced an excellent memoir, containing descriptions, with the most beautiful illustrations, of several new Cretacean species of Pollicipes and Scalpellum. The memoir is entitled a ‘Monographie des Crustacés Fossiles du Terrain Crétacé, du D. de Limbourg.’
[142] Adrien de Jussieu, in his ‘Memoir on the Malpighiaceæ,’ ‘Archives du Museum,’ tom. 3, p. 86, when speaking of the characters afforded by the degraded flowers, which in certain genera are borne together with ordinary flowers, makes the following observations bearing on the question here discussed, viz., whether or not to include Alcippe amongst the Lepadidæ. “Ces exemples peut-être aideront à comprendre comment à des genres d’une organisation assez compliquée, viennent quelquefois s’en rattacher d’autres d’une organisation beaucoup trop simple en apparence, membres appauvris et dégradés d’une même famille, qui lui appartiennent sans la représenter; comment le type, s’y présente comme effacé, ne conservant plus pour se laisser reconnaître que quelque trait isolé, mais caractéristique, dont la valeur, essentiellement ordinale, peut être ainsi constatée.” Under the point of view, so strongly and admirably insisted on lately by Milne Edwards (‘Annales des Sciences Nat.,’ 3d series, tom. 17), of describing types without regarding whether the different members blend together on their confines, perhaps Alcippe should be raised to the rank of a Family: I feel quite unable to decide how properly to act.
But we shall presently find, when we come to Cryptophialus, that all the above difficulties, great as they are, are greatly enhanced, for Cryptophialus is certainly allied in a very direct and curious manner (in decided opposition to the remarks just made on special affinities) to Alcippe, and yet in all the more important parts of its organisation, and in its metamorphosis, it differs so fundamentally, that I have felt myself obliged to form not merely a Family, but a distinct Order for its reception.