A Monograph on the Sub-class Cirripedia Part 23

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, sh.e.l.ly valve of the female; in the same way as the valves in certain Paecilasmas; 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.

_Antennae._--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 laminae 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 antennae 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 antennae 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 h.o.m.ologous 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 sh.e.l.l; _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.[57] 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 larvae, 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 exuviae of the former occupant: certainly, the males are less firmly attached to their pouches, though some small quant.i.ty 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 sh.e.l.l 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?

[57] It is possible, though opposed to all a.n.a.logy, that the females may be short-lived, and breed only once, in which case the males would not have to be periodically replaced.

3. SCALPELLUM RUTILUM. Pl. VI, fig. 2.

_S. (Foem. an Herm.) valvis 14 sub-rufis: carinae tecto plano, utrinque crista rotundata instructo; margine basali truncato: lateribus superioribus lat.i.tudine duplo longioribus._

(Fem. or Herm.) Capitulum with 14 reddish valves: carina with the roof flat, bordered on each side by a rounded ridge; basal margin truncated: upper latera twice as long as broad.

Mandibles with three teeth: maxillae narrow, bearing only four or five pair of spines: segments of the second and third pair of cirri with one side wholly covered with spines.

MALES, two, lodged in hollows, on the under sides of the scuta; pouch-formed, with four (?) rudimentary valves; no mouth; cirri not prehensile.

Hab. unknown; a.s.sociated with _Dichelaspis orthogonia_. British Museum.

FEMALE OR HERMAPHRODITE.

There is only a single specimen in the British Museum, and this had nearly all its valves separated, and many of them in fragments: from its state of decay, I think the specimen must have been dead, when originally collected.

_Description._--The capitulum consists of fourteen valves, including from a.n.a.logy a rostrum.[58] Valves, apparently covered with membrane, bearing some thin spines on the margins; clouded with a fine, though pale, orange tint; surfaces plainly marked with lines of growth.

[58] In my first, and as I thought careful examination of the separated valves (my only materials) of this species, I mistook one of the triangular rostral latera for the rostrum, and hence was unfortunately led into an error in my 'Monograph on the Fossil Lepadidae of Great Britain,' in which I state that the present species has only twelve valves in the capitulum; and I inferred from this, that _S. quadratum_, _S. fossula_, &c., had only twelve valves; I still believe this to be correct, but the existence of fourteen valves in _S. rutilum_ and _S. ornatum_, the recent species to which the above fossils are most closely allied, no doubt is a strong argument in favour of this higher number.

_Scuta_, elongated, nearly three times as long as broad; apex, pointed; basal margin extremely oblique, forming an acute angle with the occludent margin; the lateral margin is slightly hollowed out, and is separated from the tergal margin by a large rectangular projection or shoulder. The occludent margin is nearly straight; externally, there is a slight ridge running down the middle of the valve, from the apex to the baso-lateral angle; and a second ridge running from the apex to the tergo-lateral angle. The lines of growth do not end abruptly at the tergo-lateral angle, as is the case with _S. ornatum_ and several fossil species, but run up a little way along the tergal margin. The umbo is seated at the uppermost point, and, therefore, the main growth is downwards. There is a large rounded depression for the adductor muscle (_a_, fig. 2 _a'_), and higher up, opposite the tergo-lateral angle, there is another hollow (_b_), for the lodgment of the males; this latter is of nearly the same shape as the hollow for the adductor muscle, but rather more conspicuous than it. From the appearance of the under surface of the scuta, it might readily have been thought, that there had been two adductor muscles.

_Terga_, of large size, longer than the scuta, flat, triangular, with the whole inferior part much produced and spear-like. A portion of the apex, must have projected freely above the sack.

_Carina_ (Pl. VI, fig. 2 _b'_), simply bowed (_i. e._, not rectangularly bent), with the umbo (and primordial valve) seated at the upper point; rather ma.s.sive, narrow, only slightly increasing in width from the upper to the lower end; the two sides are flat, and at right angles to the roof, which is bordered on each side by a rather broad, square-topped ridge (_see section_ fig. 2 _c'_), or the roof may be said to have a square-edged furrow running from the apex to the basal margin, and widening downwards; these two ridges have their lines of growth oblique, and hence have a twisted appearance; the central depressed portion of the basal margin, which is square or truncated, descends lower down than the two ridges. The sides of the valve close to the apex are broad, and consist, as I believe, of intra-parietes, as well as of parietes, but these parts are not separated from each other by ridges, as is commonly the case, more especially with the fossil species. I have described the carina in some detail, on account of its resemblance to that of the cretaceous _S. fossula_, _S. trilineatum_, and _S. quadricarinatum_.

_Rostrum_, unknown; but one probably existed.

_Upper Latera_, of large size, elongated, quadrilateral, approaching to diamond-shaped, with the angles rounded, nearly twice as long as broad; almost flat; upper half ac.u.minated, lying between the scuta and terga; the lower half broad, forming a rectangular projection lying between two latera of the lower whorl. The umbo is near the apex, the greater part of the growth being downwards, but the valve is added to a little, round the two sides of the apex; these additions do not take place in the early stages of growth, (as explained under _S. vulgare_,) and, therefore, they form a depressed rim.

_Rostral Latera_, almost exactly triangular, curved; basal margin furnished with a just perceptible rim.

_Infra-median Latera_, quadrilateral, sides unequal in length; the carino-basal margin being the longest; in area not quite twice double the rostral latera; directed obliquely upwards.

_Carinal Latera_, sub-triangular, produced upwards, with the apex rounded, and the two lateral margins hollowed out; the basal margin exceeds a little in length the basal margin of the rostral latera. The umbones of these two latera are seated at their basal outer angles, so that the growth of the valves is towards each other and upwards. The umbo of the infra-median latus is seated at the baso-rostral angle, and hence the growth is obliquely upwards. The umbones of the rostral latera must have been close together, over the unknown rostrum.

_Length_ of capitulum about 4/10th of an inch.

_Peduncle_, only small fragments are preserved; the calcified scales are small, closely imbricated, several of them together only equalling in length the basal margin of the rostral latera. Each scale is thin, transversely elongated; basal imbedded portion straight; upper margin rounded.

_Mouth._--Labrum with the upper part highly bullate, forming an overhanging projection; palpi apparently small and narrow.

_Mandibles_, narrow, produced, with three teeth; inferior angle pectinated, as is sometimes the third tooth; the distance between the tips of the first and second teeth equals that between the second tooth and the inferior angle.

_Maxillae_, extremely narrow, produced, without any notch; spinose edge exactly one third of the length of the mandibles: beneath the two upper great spines there are only three or four pair of spines; on the convex upper margin there are some minute tufts of the smallest hairs.

_Outer Maxillae_, rounded with the inner margins very sparingly but continuously covered with bristles. I could not ascertain whether the olfactory orifices were tubular.

_Cirri._--These consisted, in the one specimen, of merely small fragments. The segments of the posterior cirri are elongated, not protuberant, and support, I believe, five pair of non-serrated spines, and an exterior row of very minute spines: dorsal spines fine and long.

Either the second or third cirri, or probably both, are remarkable for having the whole of one side of each segment covered with irregular rows of long spines. Moreover, in the upper segments of these same cirri, between each separate dorsal tuft, there is placed one or two long bristles. The first cirrus appears to have had very broad segments, and these are singular from the spines in the dorsal rows, being extremely long. In some of the cirri, several of the basal segments are soldered together.

_Caudal Appendages_, lost.

From the state of the specimen, it was quite impossible to ascertain whether the individual here described was an hermaphrodite or female; from the a.n.a.logy of its nearest congener, _S. ornatum_, the latter is the most probable; but the genus Ibla shows how the s.e.xes may differ in the most closely-allied forms.

_Affinities._--From the hollows on the under sides of the scuta, for the lodgment of the males; from the umbones of the scuta and of the carina being situated on the apices of these valves; and from all the characters of the mouth, _S. rutilum_ is much more closely allied to _S.

ornatum_ than to any other species.

MALE, OR COMPLEMENTAL MALE.

In the concavity or hollow above the depression for the adductor muscle (Pl. VI, fig. 2 _a'_), I found males, but in so extremely decayed a condition, that they could hardly be examined. On one side, however, I distinctly saw the larval prehensile antennae, with pointed, hoof-like discs; and part of the thorax, with its small limbs and long spines, as in _S. vulgare_ or _S. ornatum_. I also saw clearly the eye. The four calcified beads or rudimentary valves, I believe, were present; but in removing the specimen, the whole fell to pieces and was lost. The outer integument was covered with rather thick, very minute bristles, each about, 2/10,000th of an inch in length, and therefore only half the length of those on the complemental males of _S. vulgare_. The cavities for the males are not formed, as in _S. ornatum_, by the thickening of the internal surface of the valve round a defined s.p.a.ce, but by the scutum being externally convex and internally concave down the middle, hollows being thus produced both for the lodgment of the males and for the attachment of the adductor muscle. These hollows are separated from each other by a slight transverse ridge. I do not know at which point of the margin of the valve, the orifice of the male is situated, but I presume close under the apex. In this species, as in _S. ornatum_, there can be no question that the scuta of the female are specially modified by their own growth for the reception of the males. It must be added that, as it was not possible to ascertain whether the ordinary form of _S. rutilum_ was hermaphrodite or female, so it must remain doubtful whether the parasites are males or complemental males; but the former, I think, is most probable.

[=TT= SUB-CARINa PRESENTE.]

4. SCALPELLUM ROSTRATUM. Pl. VI, fig. 7.

_S. (Herm.) valvis 15: rostro permagno: laterum paribus quatuor: pari superiore pentagono._

(Herm.) Capitulum with 15 valves: rostrum very large: four pair of latera; upper latera pentagonal.

Mandibles with four teeth; maxillae with the inferior angle prominent.

_Complemental Male_, attached between the mouth and adductor scutorum muscle; pedunculated; capitulum bearing a pair of elongated scuta and a rudimentary carina; mouth and cirri prehensile.

Philippine Archipelago; Island of Bantayan. Attached to a h.o.r.n.y coralline: 20 fathoms. Mus. c.u.ming.

HERMAPHRODITE.

_Capitulum_, with the upper part narrow and produced.

_Valves_, 15 in number, placed close together, clouded pale red, covered with membrane, which is thickly clothed with minute points.