Thaliella ornata. J. E. Gray. Proc. Zoolog. Soc., 1848, , Annulosa, Plate.
S. (Fœm.) valvis 14, sub-rufis: lateribus superioribus quadranti-formibus, arcu crenâ profundâ notato.
(Fem.) Capitulum with 14 reddish valves: upper latera quadrant-shaped, with the arched side deeply notched.
Mandibles with three teeth; maxillæ narrow, bearing only four or five pair of spines.
Males, two, lodged in cavities on the under sides of the scuta; pouch-formed, with four unequal, rudimentary valves: no mouth: cirri not prehensile.
Algoa Bay, South Africa. Attached to Sertularia and Plumularia. British Museum.
I am greatly indebted to Mr. Bowerbank for specimens of this extremely interesting species; also to Mr. Morris, to whom Mr. Bowerbank had given some of the original specimens.
FEMALE.
Capitulum oblong, with the upper portion much produced; valves, 14, thick, naked, closely locked together, irregularly clouded with pale crimson; the membrane connecting the valves is not furnished with spines. On most of the valves there are furrows and ridges diverging from the umbones, and the lines of growth are plainly marked: in the valves of the lower whorl, the umbones are slightly protuberant.
Scuta, convex, unusually thick, oblong, quadrilateral, with the occludent margin the longest; lateral margin slightly hollowed out. The umbo (and primordial valve) is situated at the uppermost point of the valve, and consequently the growth is exclusively downwards. On the under side (Pl. VI, figs. 1 b´ and 1 c´), in about the middle of the valve, there is a pit (a) for the adductor scutorum muscle, the depth and distinctness of which varies a little; above the pit, and between it and the apex, there is a transverse, oblong, deeper depression (b), within which, the male is lodged. A small portion of the apex of the valve projects over the terga.
Terga, large, nearly equalling the scuta in area, flat and sub-triangular; the scutal margin is not quite straight. The apex of the valve is thick and solid, and must have projected freely for a length equalling one third of the occludent margin.
Carina, laterally broad, angularly bent; slightly widening from the apex to the base; internally, deeply concave. The position of the umbo varies, in young specimens it is seated at the uppermost point, and consequently in such there is no upward growth; in older specimens, from the junction and upward production of that part on each side of the valve, which I have called in fossil specimens the intra-parietes, the valve is added to above the umbo, but to a lesser degree than in S. vulgare. Slight ridges separate the roof from the parietes, and the parietes from the intra-parietes.
Rostrum, minute, narrow, widening a little from the apex downwards, inserted like a wedge between the umbones of the rostral latera, and hardly projecting above their upper margins, so as to be easily overlooked: internally concave.
Upper Latera (fig. 1 á), quadrant-shaped, with a deep square notch cut out of the arched margin, which notch receives the upper point of the carinal latera; the surface of the valve between the notch and the umbo is depressed.
Rostral Latera, small, gradually widening from the umbo to the opposite end, which is obliquely rounded.
Infra-median Latera, approaching to diamond-shaped, placed obliquely to the longer axis of the capitulum; or the upper part may be described as spear-shaped.
The only valve which I have seen at all like this, is a fossil specimen from the Upper Chalk of Scania; this is described in my memoir on the Fossil Lepadidæ (Palæontographical Society), under the name of Scalpellum solidulum (Tab. 1, fig. 8, e, f), and is perhaps erroneously there considered as a carinal latus.
Carinal Latera: these appear as if formed of two valves united together; the upper portion, widening as it ascends in a curved line, terminates in a rounded margin, which enters the deep notch in the upper latera; the other and lower portion is shorter, and terminates in a square margin abutting against the infra-median latera; the umbones of the carinal latera project beyond the line of the carina.
Direction of the Lines of Growth in the Valves. — This should always be carefully observed, on account of the great diversity there is in this respect between the different species, especially when the recent are compared with the older fossil species; moreover one of the chief characters between the genus Scalpellum and Pollicipes, depends on the direction of the lines of growth. In the scuta, terga, rostrum, and upper latera of the present species, the chief growth is downwards; in the carina, in mature specimens, it is both upwards and downwards; in the carinal latera, both upwards and towards the infra-median latera; in the infra-median latera chiefly upwards; and, lastly, in the rostral latera, towards the infra-median latera.
Peduncle, short, not half as long as the capitulum; calcareous scales imbricated as usual, tinged red, almost crescent-shaped, acuminated at both ends, of remarkable length, so that in each whorl there are only four scales: a full-sized scale equals in length one of the rostral latera. The tips of two scales, in one whorl, lie under the middle points of the carina and rostrum; and in the whorl, both above and below, a single much curved scale occupies this same medial position. The peduncle does not seem to have been attached in any definite position to the horny coralline, as is the case with S. vulgare.
Length of capitulum in the largest specimen .2 of an inch.
The Mouth is directed towards the ventral surface of the thorax. The Labrum is far removed from the adductor muscle, with the upper part forming an overhanging projection; I believe there are some very minute bead-like teeth on the crest. Palpi, small, narrow, thinly clothed with bristles.
Mandibles, with three teeth, of which the first is distant from the second; inferior angle not much acuminated, pectinated on both edges.
Maxillæ, small, narrow, produced, without any notch, with two large upper spines, of which one is much thicker than the other; on the convex upper margin there are some minute tufts of very small hairs.
Outer Maxillæ, with few bristles, arranged in a continuous line on the anterior surface; on the external surface there is a tuft of long bristles. Olfactory orifices situated laterally, forming two flattened, tubular projections.
Cirri. — First pair placed not far from the second; the three posterior pair not very long, with their segments elongated, not protuberant, bearing four pair of non-serrated spines, with a single short bristle between each pair; dorsal tufts small, with one spine longer than the others. First cirrus rather short, segments not very broad; second cirrus with the rami nearly equal in length, anterior ramus rather thicker than the posterior ramus, with three longitudinal rows of spines.
Caudal Appendages. — These are minute, rather broad, not half as long as the lower segments of the pedicels of the sixth cirrus, with four very long spines at the tip.
Penis. — There is no trace of a probosciformed penis in the four specimens examined; and as this organ is present in every ordinary cirripede, with the exception of Ibla Cumingii which we know to be exclusively female, so we may infer with some confidence that the form here described is female, although it is impossible in specimens once dried to demonstrate the absence of the vesiculæ seminales and testes.
Affinities. — This is a very distinct species; it is, however, much more nearly related to S. rutilum, than to any other species; and next to this, to S. vulgare; from this latter species it chiefly differs in the large scales of the peduncle, in the scuta not being added to at their upper ends, and in the membrane covering and connecting the valves being spineless; but there is a greater difference in the trophi and in the cirri. The peduncle of S. ornatum presents some resemblance to that of the singular cretaceous genus, Loricula.
MALE.
All the specimens, as already stated, were dry, but in an excellent state of preservation, so that after having been soaked in spirits, they could be minutely examined. In the four which I opened, I found, in a transverse pouch on the under side of each scutum, a male lodged; in a fifth dead and bleached specimen, the cavities in the shell for the reception of the males, were present; and in a sixth young specimen, also dead, cavities were in process of formation. As compared with plants, the relation of the sexes in this species may be briefly given, by saying that it belongs to the class Diandria monogynia. I will first describe the males themselves, and then the cavities in the shell of the female. The males differ in every point of detail, from the complemental males of S. vulgare, but yet present so close a general resemblance, that a comparative description will be most convenient.
The general shape of the whole animal is rather more elongated, and I suspect flatter, but this latter point could not be positively ascertained in dry specimens. The entire length is greater, being in the largest specimen 13/400 (instead of at most 11/400), and the width, 7/400 of an inch. The orifice is not fimbriated; the four bristly points over the calcareous beads are absent. The whole outer integument is much thinner, owing evidently to its protected position, and is not covered by little bristles, but with an extremely high power, minute points arranged in transverse lines can be distinguished. The calcareous beads, or rudimentary valves, are thin and regularly oval. It is remarkable that in all the specimens, two on one side were smaller than the two on the other side, — the smaller beads being 16/6000, and the larger, 22/6000 of an inch in diameter; therefore more than twice the size of one of the beads in S. vulgare, which are only 9/6000 externally in diameter. From the position of the eye, close to one margin, near the upper end of the flattened animal, and from the manner in which the little limbs and spines lay between two of the beads at the opposite end, it was manifest that these latter, one large and one small, corresponded with the terga of the other cirripedes, and that the other two, near the eye, answered to the scuta. The valves being of unequal sizes on the right and left-hand sides of the animal, is probably connected with one side being pressed against the hard, shelly valve of the female; in the same way as the valves in certain Pæcilasmas; are smaller and flatter on the side nearest to the crustacean to which they are attached. The eye, in being slightly notched on the upper and lower edge, shows signs of really consisting of two eyes, which I believe is always normally the case; it is rather larger, in the proportion of 13 to 11, being 13/12,000 of an inch in diameter, than in S. vulgare; and from the almost perfect transparency of the integuments, is far more conspicuous than in that species. Hence when the valves of the female are opened, the black little eye is the first part of the male which catches the attention. No vestige of a mouth could be discovered.
Thorax and Abdomen. — The thorax, as in S. vulgare, is highly extensible, and when stretched exhibits the same five transverse folds or articulations; when contracted, it is broader, so that even the truncated end of the abdomen is wider than the lower (properly anterior) end of the thorax in S. vulgare. Its thin outer integument is studded with excessively minute points in transverse rows. The four pair of limbs are longer than in S. vulgare, but the spines on them much shorter and thicker; each limb (including the first) supports three spines, of which one is seated on a notch low down on the outside, and is longer than the other two; of these two, the one on the same side with the notch, is a little longer than the other. The spines on the first and second pair of limbs are considerably shorter than those on the third pair, and these latter, are a little shorter than those on the fourth or posterior pair. Hence, the spines on the thoracic limbs, compared with those of S. vulgare, present considerable differences, both in their relative and absolute dimensions. The abdominal lobe is in proportion rather shorter; its end is less abruptly truncated, and supports a row of, I believe, six moderately long, and basally thick spines; these spines are not so long as those surmounting the fourth pair of limbs. On both lateral margins of the abdomen, rather on the ventral face, there is a row of, I believe, seven long spines, but it is very difficult to count the spines in specimens which have been once dried. I was able to distinguish that the two lower pair of spines on the ventral surface, are seated a little way one below and within the other, as in S. vulgare. The abdominal spines altogether form quite a brush, and there are certainly several more than in S. vulgare, and those on the two sides are much longer.
Antennæ. — The disc is hoof-like, with the upper surface forming a straight line with the upper edge of the basal segment; the apex is pointed and clothed with some fine down; there is a single spine pointing backwards, which rises from the lower flat surface. The ultimate segment was hidden in laminæ of cement; and I was not able to make out its structure. There is a single spine on the outer edge of the basal segment, in the usual position. The entire length of the limb, measured from the end of the disc to the further margin of the basal articulation, is 36/6000ths of an inch; measured to the inner margin, it is; 21/6000ths of an inch; the disc itself is 12/6000ths of an inch long; these measurements differ a little both absolutely ad proportionally, compared with those of the antennæ of S. vulgare.
Cavities in the Scuta of the Female for the reception of the Males. — These extend nearly parallel to the tergal margin, transversely across the valves, for three fourths of their width; they are seated above the depression for the adductor muscle, and are more conspicuous than it; they are deep and well defined, and each exactly contains one male. The males are placed with their orifices in a little notch in the occludent margin, and their prehensile antennæ at the further end. The distance to which the cavities extend across the valve, and their distance from the upper or tergal margin, varies a little, but chiefly in accordance with the age of the specimens; for the valve continues to increase in width, whilst the size of the cavity remains the same. The occludent margin of the scutum in the largest female, was .1 of an inch in length; of another, in which there was a fully developed cavity, .084; of a third, in which there was no cavity, only a slight concavity, with a preparatory impression, the length of the occludent margin was .062. The larger and smaller of these three valves, are drawn of their proper proportional sizes, in Pl. VI, figs. 1 b´, 1 c´. The preparatory impression (fig. 1 c´, b), consists of a narrow, not quite straight, extremely slight furrow, of slightly irregular width, bordered on each side by a very minute ridge, which is distinctly continuous with the inner edge of the occludent margin, both above and below the cavity. The furrow appears to have been formed by calcareous matter not having been deposited along this line, during the thickening or growth of the internal surface of the valve: I suspect, that it originates at a single period of growth, for I could see no signs of successively-formed transverse lines. I believe that it is strictly homologous with the fold, over which the complemental male is attached in S. vulgare, but carried, for a special purpose, much further across the valve and rectangularly inwards, for in structure and position both are identical. In comparing the internal views of the scuta in S. vulgare and S. ornatum (Pl. V, fig. 15 a´, and Pl. VI, fig. 1 c´), it must be borne in mind, that the latter should be compared, as clearly shown by the lines of growth, with that portion alone of the scutum in S. vulgare, which lies under the curved ridge connecting the umbo and tergo-lateral angle. The deep cavity in which the male is lodged, is formed subsequently to the preparatory furrow, simply by the gradual thickening of the surrounding surface of the valve, more especially of a ridge just above the pit for the adductor muscle, and of another broad ridge just beneath the tergal margin. The deepest part of the cavity lies parallel to the tergal margin along the upper side, and here, in the older valves, the preparatory furrow can by care be distinctly traced. In conformity with the shape of the cavity, the orifice or notch in the occludent margin of the scutum, is situated at the point where the preparatory furrow sweeps round and enters. I believe that the cavity is lined by membrane, and that between the cavity and the body of the female, there is a complex membranous layer, — a pouch or bag being thus formed. An imaginary section of this pouch (with the thickness of all the parts extremely exaggerated and in a reversed position) is given in Pl. VI, fig. 1 d´: a is the shell; x the cavity, converted, as I believe, into a pouch by, firstly, the delicate tunic (c) lining the sack of the female; secondly, a double layer (d) of corium; and, thirdly, by a special, rather thick membranous layer (b), which thinning out round the cavity coats only part of the under surface of the scutum. This latter membrane I have not seen in any other Cirripede, and I believe it is nothing but the tissue, here not calcified, which, in a calcified condition, ordinarily forms the valves. On this view, the males may be said to be lodged in pouches, formed in the thickness of the valves.
Concluding Remarks. — The males from the absence of a mouth (and no doubt of a stomach), must necessarily be short-lived, and, I suppose, are periodically replaced by fresh males. In one instance, the remnants of the two great compound eyes of the larva, could be seen at the end of the pouch, opposite the orifice. The larvæ, I conclude, crawl in at the orifice, one side of which is formed, as we have seen, of yielding membrane, and scratch out the dead exuviæ of the former occupant: certainly, the males are less firmly attached to their pouches, though some small quantity of cement is excreted, than are other Cirripedes to the objects to which they are attached. The small size of the female, and her valves not being thickly edged with chitine, accounts for the males having pouches specially formed for them, instead of being, as in S. vulgare, laterally imbedded in the chitine-border of the scuta. In hereafter weighing the evidence on the nature of the parasites in Ibla and in Scalpellum, the fact of the valves of the supposed female being here modified for the special purpose of lodging the males, will be seen to be important. If we imagine the male parasites to be extraneous animals, and that by adhering to the sack of the Scalpellum, they injure the corium and thus prevent the growth of the shell over an area exactly corresponding to their own size, and so form for themselves cavities; yet what can be said regarding the preparatory furrows? surely these narrow lines cannot have been produced by the pressure of the much broader parasites. Must we not see in the furrows, the first marking out, if such an expression may be used, of the habitation for the male, which has to be specially formed by the independent laws of growth of the female?
It is possible, though opposed to all analogy, that the females may be short-lived, and breed only once, in which case the males would not have to be periodically replaced.