I feel compelled to form an Order for the one genus and species, namely, [Cryptophialus minutus], to be here described. We must, I conceive, attribute much greater value, in classification, to internal parts and organs, at least where such are not known to vary, than to external structure. Now in [Cryptophialus], the body consists of eight segments, of which the first two are not developed in any cirripede hitherto described. Of the eight, the seven posterior or thoracic segments are quite free, or detached from the carapace, and do not bear any appendages; whereas in all the foregoing cirripedes of the order Thoracica there are (at least in the normal sex) six pairs of cirri; [Alcippe] alone must be excepted, in which there are only two pairs. Again, in the [Thoracica] there are no abdominal appendages, excepting the terminal or caudal, whereas in [Cryptophialus] the abdomen bears three pairs of biramous cirri. In the crest of the labrum, being produced into a special, lancet-formed organ, articulated at its base and capable of movement, and in the palpi projecting straight upwards, we have a great difference from all other cirripedes; and these organs, we have every reason to believe, possess a high classificatory importance. The œsophagus in [Cryptophialus], where it enters the stomach, is armed with teeth and hairs, moved by muscles, forming a beautiful structure, of which we have not a trace in any other cirripede. Lastly, and perhaps most importantly of all, the metamorphosis is different; for the early larval stages are passed under an egg-like condition within the sack of the parent; and the pupa differs from the pupæ of all other cirripedes, in not having natatory thoracic limbs, and is therefore only able to crawl about by the aid of its great prehensile antennæ.
Thus far the evidence is decisive in favour of [Cryptophialus] being placed in a separate Order; but if we were to trust to the characters derived from the external covering or carapace,—and such characters are of high importance, as we may safely infer from the natural arrangement of the foregoing families which depends on the structure of the carapace,—we should place [Cryptophialus] close to [Alcippe] amongst the Lepadidæ. These genera agree in their burrowing habits,—in their attachment by a horny rostral disc,—in the external membrane being covered with triturating points,—in the spinose and notched orifice, with an external lateral bar on each side, and in the inner tunic of the sack being protected by hairs and spines. They agree to a considerable extent in shape, and in the peculiar arrangement of the muscles of the whole external covering of the animal: they agree, also, in their manner of growth, and in the sack extending down to their basal extremity. Some of these resemblances may possibly be analogical, and due to similarity of habits, and not to affinity; and we must attribute to mere similarity in function, a certain amount of resemblance in their labrums, for this part is essentially different in the two genera; and to the same cause, the resemblance between the brush formed by the two pairs of thoracic cirri and caudal appendages at the end of part of the thorax in [Alcippe], with the three pairs of abdominal cirri at the end of the whole thorax in [Cryptophialus]. I allude to this latter resemblance, for it was owing to it, and to the similarity in the habits of [Cryptophialus] and [Alcippe], that I stated, in the introduction to my former volume on the Lepadidæ, that the two genera would probably fall into the same order. In the structure of all the parts of the mouth and of the cirri, in the digestive organs and in the metamorphoses, [Cryptophialus] is not more closely related to [Alcippe] than to any other genus whatever amongst the Lepadidæ.
Nevertheless I am confirmed in the view that the external resemblances between these two genera are due to some real affinity, and are not merely analogical, by a very remarkable fact,—namely, that [Alcippe] and [Cryptophialus] are both bisexual, and have males, several in number, attached exactly in the same position, and which males are so closely similar that, considered by themselves, they might absolutely be almost classed as species of the same genus! For they agree in the absence of all internal organs and parts, excepting the single testis, vesicula seminalis, and immensely long probosciformed penis; and they agree, also in manner of growth, in the arrangement of the muscles, and even in shape. The whole case seems to me very singular, and, as far as my knowledge extends, unique: we have two animals, of which the females, if classed by their external parts (homologically consisting of the three anterior segments of the head), would be placed alongside each other in the same family; but when classed by the whole rest of their organisation, certainly must be ranked in distinct orders;[150] yet the males of these very same animals might almost stand in the same genus. If it be asked why the position of [Cryptophialus] in the system should not be determined by the male, instead of by the female, the answer would be that the male is here abnormal and rudimentary in its whole structure; and I believe systematists are agreed that less perfect parts (and therefore a less perfect whole) offer less valuable characters than the more perfect parts or whole. We see this conclusion plainly verified in the case of the hermaphrodite Scalpellum vulgare and Ibla quadrivalvis, for there can be no doubt where these species should be arranged, yet if we attempted to place them by their complemental males, we should utterly fail: exactly in the same manner, if Ibla Cumingii and Scalpellum ornatum were ranked by their males, they would be quite misplaced. So again, if we were to attempt to class the six species of Scalpellum by their males and complemental males, undoubtedly the first three and last three species of the genus would have to stand in distinct orders! Hence we may reject the males as a foundation for classification, but no doubt they serve to show that the resemblances in the carapaces of [Alcippe] and [Cryptophialus], are not merely analogical or functional, but evince a true affinity, though these genera differ so greatly, in mouth, body, œsophagus, cirri, and especially in their metamorphoses.
[150] M. Milne Edwards would, perhaps, in accordance with the profound views lately propounded by him on classification, consider [Cryptophialus] as an extremely modified, and, to a certain extent, degraded member or satellite of the type of the Lepadidæ; but I do not myself feel able to draw a line of distinction between the being a very abnormal member of one group, and belonging to a distinct group. I may add that I have several times tried to persuade myself, with no success, into the belief that I have somehow misunderstood the homologies of the thoracic segments and cirri of [Alcippe] and [Cryptophialus]; for if this were so, the two genera could be brought into much closer relationship; but with any conceivable amount of error on my part, there remains the great difference in the metamorphosis, not to mention the palpable differences in the cirri, the parts of the mouth, and in the whole course of the alimentary canal.
CRYPTOPHIALUS MINUTUS. Pl. [23], [24], fig. [1] to [19].
Hab.—Chonos Archipelago, Southern Chile; imbedded in the Concholepas Peruviana.
FEMALE. [Fig. 1-18.]
General Appearance.[151]—This, the smallest known cirripede, is flask-shaped and compressed, with a small orifice, on a more or less produced neck, placed at one corner: one of the narrow sides of this carapace is somewhat flattened or depressed, with its superior edge prolonged a little upwards; by this side, the animal is attached to the cavity in the shell, within which it is lodged. There is here no distinction between a peduncle and capitulum, that is between the lower or anterior, and the upper or posterior end of the animal, as seen externally. The small orifice is toothed and hairy: it is coloured purple, as is likewise the projecting labrum; the rest of the animal being tinted only by the muscles and internal parts seen through the outer integuments. The largest specimen (fig. [2]) which I have measured did not quite attain the length of one tenth of an inch. This cirripede inhabits, in vast numbers, the shells of the living Concholepas Peruviana, amongst the Chonos islands; the whole outside of the shell being sometimes completely drilled by its cavities, almost touching each other, as happens in the case of [Alcippe] with the shells of Buccinum. The oval aperture leading into the shell-cavity, in full-sized specimens, is between (2-3)/100 of an inch in length: it is generally surrounded by a narrow, internal, calcareous rim, which apparently has the same inorganic origin, as in [Alcippe]. The toothed orifice of the carapace leading into the sack, fills up the orifice of the shell-cavity; but it can be voluntarily withdrawn a little: when opened, and the animal is in action, the lancet-formed, moveable crest of the labrum, and the abdominal cirri, are exserted.
[151] I am greatly indebted to Dr. Hooker, for having several years ago, when I examined this my first cirripede, aided me in many ways, and shown me how to dissect the more difficult parts, and for having made for me several very correct drawings, which, with some subsequent alterations, are now engraved.
Integuments.—The external membrane is colourless, thin, but strong; it is studded with minute bifid, trifid, and quadrifid points of hard chitine, which are the agents of excavation: they are directed upwards, except towards the lower end, where they are directed from the disc or surface of attachment. These points beneath the orifice, and on each side close along the lateral bar, are larger than elsewhere. There are no points on the disc or surface of attachment, which is formed of somewhat thickened, yellowish membrane, and is not moulted, like the rest of the external membrane, but is formed of successive layers extending beyond each other; the lines of growth, however, being obscure, and only occasionally distinguishable. The disc is oval, not extending to the lower end of the animal, and with the upper edge thinning out and produced upwards (fig. [1]). The animal, during its growth, moves a little downwards in its cavity, by means of the new layers of the attached disc being formed, not symmetrically with respect to the old layers, but beyond them or at a greater depth in the shell; hence when the animal is removed quite perfect, by the Concholepas being dissolved in acid, the upper and deserted margin of the disc or surface of attachment generally projects as a free edge, but in a tattered and worn condition. In full grown specimens, which have ceased burrowing downwards, nearly the whole disc, though occupying the same position relatively to the animal, becomes in fact deserted, and is lined by membrane continuous with, and like that, investing the rest of the body, but furnished only with simple blunt points, instead of with the sharp bifid and trifid triturating points.