A Monograph on the Sub-class Cirripedia Part 24

_Scuta_ rather small, oval, with the upper end pointed; rather convex; basal and lateral margins blending into each other; the upper produced portion above the umbo is small; there is a deep pit for the adductor muscle, and there is a fold on the occludent margin in the usual position; occludent margin not straight.

_Terga_ large, one third of their own length longer than the scuta; fat, sub-triangular; the three margins are not quite straight; the carinal margin projects a little above the apex of the carina, and the scutal margin is excised to fit the upper part of the scuta.

_Carina_ bowed, internally deeply concave; upper portion above the umbo, about one fourth of the total length, extending between the terga for two thirds of their length, up to the slight prominences on their carinal margins: a ridge separates, on each side, the parietes from the tectum.

_Rostrum_ (fig. 7 _a_) unusually large, about two thirds of the length of the scuta, and twice as long as the rostral pair of latera; internally concave, externally carinated; outline of the upper portion acutely triangular, of the lower portion rounded; umbo seated at the upper end.

_Upper Latera_ pentagonal, with the apex rounded.

_Rostral Latera_ flat, four-sided, with the basal margin the longest, and the baso-carinal angle produced.

_Infra-median Latera_ nearly equalling in area the upper latera; not descending so low down as the rostral and carinal latera; outline of lower half semi-oval, of upper half rectangular.

_Carinal Latera_ flat, four-sided, with the basal margin the longest, and slightly protuberant; baso-rostral angle produced; whole valve larger than the rostral latus, but closely resembling it in form.

_Sub-carina_ minute, not above one third of the size of the rostral latera, which are the smallest of the other valves; internally deeply concave; externally solid, pyramidal, standing out beyond the surface of the carina, with the umbo at the apex.

The umbones of the four pair of latera are seated a little above the centre in each valve, on the summit of a raised triangular portion; this arises from the valve at first growing only downwards, and when added to at the upper end, the new part forms a ledge at a lower level round the old part, which had already acquired some thickness.

_Peduncle_, short, about half the length of the capitulum; narrow; thickly clothed with minute, longitudinally elongated, spindle-shaped, calcareous scales or beads, which project but little.

_Length_ of the capitulum, rather under 3/10ths of an inch.

In a _Young Specimen_, with its capitulum, together with the peduncle, only 1/10th of an inch long, the scuta, terga, and carina are very large in proportion to the valves of the lower whorl. The latter project more, and are externally more pointed, as in the genus Pollicipes. The rostrum is well developed; the infra-median latera, in proportion, are the least of all the valves. The carina is straight and pointed, and not, relatively to the scuta, quite so long. The scuta are rather broader in proportion to their length, which would naturally follow from less having been added to their apices,--these valves at first growing only downwards. The membrane covering and connecting the valves is furnished with long thin spines.

_Mouth._--Labrum placed far from the adductor scutorum muscle, with the upper part exceedingly prominent; apparently there are no teeth on the crest. Palpi blunt.

_Mandibles_, narrow, with four teeth, of which the second is not smaller than the others; inferior angle sharp and produced, barely pectinated.

_Maxillae._--Under the two or three great upper spines, there is a tuft of fine bristles; the inferior part of the edge is step-like, and much upraised.

_Outer Maxillae_, with the inner edge deeply notched, and the bristles arranged in two quite distinct tufts; the bristles on the outer surface are long. Olfactory orifices, thin, tubular, and projecting.

_Cirri._--The first pair is placed far from the second; the three posterior pair are long and straight, with their segments much elongated, not protuberant, bearing four or five pair of long spines, with little intermediate tufts of minute spines, and with the minutest spines on the lateral upper edges. Dorsal tufts with one spine extremely long, equalling a segment and a half in length; the others very short.

Spines all serrated. First cirrus not very short; rami nearly equal, with the four terminal segments of both tapering; all the basal segments much thicker, and thickly covered with bristles. Second cirrus (as well as the third in a less degree), with the anterior ramus thicker than the posterior ramus, and with all the lower segments in both rami thickly clothed with three or four longitudinal rows of spines.

_Caudal Appendages_, spinose, uni-articulate; but the specimen was injured, and I could not exactly make out their shape: I believe it was oval, and thickly fringed with fine spines.

_p.e.n.i.s_, very small, almost rudimentary, narrow, and hairy, scarcely exceeding in length the pedicel of the sixth cirrus.

COMPLEMENTAL MALE. Pl. VI, fig. 5.

Before describing the parasite of the present species, which departs entirely from the character of the males of the three preceding species, it is proper to state that I consider it to be a Complemental Male simply from a.n.a.logy, as will hereafter be more fully shown at the end of the genus. Had a specimen of the parasite been brought to me without any information, I should have concluded that it was an immature individual of a new genus of pedunculated Cirripedes, remarkable from the rudimentary condition of the valves, and exhibiting, in one important character, namely, in the form of the larval prehensile antennae, an alliance to Scalpellum. Had I been then told that three individuals in a group, had been found attached to _S. rostratum_, not outside the valves, but to the integument, in a central line, between the labrum and the adductor scutorum muscle, in such a position that when the Scalpellum closed its valves, these parasites were enclosed within the capitulum, my surprise would have been great; for it is very improbable that this singular and unparalleled position was accidental in this one group of specimens, inasmuch as there seems to be a relation between the naked condition of the capitulum of the parasite, and the protection afforded to it by the capitulum of the Scalpellum. It further becomes apparent on reflection, that these minute parasites, though having the appearance of immaturity, can not increase in size, or but little, for if they did grow, and acquired an ordinary size, they would either be killed by the pressure of the scuta of the Scalpellum, or they would destroy the latter, and in doing so soon lose their own support, and thus necessarily perish!

The one full-grown specimen of _S. rostratum_, in Mr. c.u.ming's collection, was in a good state of preservation, but dry. The three parasites were attached, as stated, close under the labrum, between it and the adductor muscle. They are constructed like ordinary Cirripedia, and have a mouth, thorax and cirri, enclosed in a capitulum, supported on a peduncle of moderate length and narrow. The entire length of the capitulum and peduncle, as far as could be ascertained in the shrivelled condition of the specimens, was 35/1000ths, and the greatest width of the capitulum 11/1000ths of an inch. Both capitulum and peduncle are hirsute with spines, nearly 1/1000th of an inch in length, mingled with shorter hairs in little rows of three and four together. The figure (5) in Pl. VI is merely a restoration, as accurate as could be made from the much shrivelled specimens. There are only three valves,--namely, an oval carina (_a_), seated rather high up on the capitulum, in a rudimentary condition and only 1/1000th of an inch in length, and a pair of scuta; these latter consist of a narrow, slightly curved plate, 8/1000ths in length, broadest at the lower end, where the breadth is 2/1000ths of an inch. The prehensile antennae, at the end of the peduncle, have pointed hoof-like discs: I was not able to make out the other parts. It deserves notice, that in the young specimen of the ordinary form of _S.

rostratum_, 1/10th of an inch in length, and therefore only thrice as long as the parasites, all the valves were perfect, and seemed to have followed the ordinary law of development.

_Mouth._--The largely bullate labrum is placed far from the adductor, in the same manner as in the hermaphrodite. The mandibles have three large sharp teeth, with the inferior point very sharp and small, so that there is one less tooth than in the hermaphrodite. The maxillae have two or three large upper spines, the others being very thin; I believe the lower part is upraised and step-like, as in the hermaphrodite. The outer maxillae are bilobed in front, with a few short bristles on the outer side near the bottom. I was not able, from the dried state of the specimens, to discover whether the olfactory orifices were tubular.

Altogether it was apparent, from this imperfect examination, that there was a close similarity between the mouth of the parasite and of the hermaphrodite.

The _Thorax_ is unusually elongated.

_Cirri._--The first pair is very short, and is distant from the second.

All have the appearance of immaturity, with their pedicels very long in proportion to their rami; the latter are slightly unequal in length, even in the sixth pair. There appeared to be six segments in the rami of the sixth pair, each segment bearing two or three pair of long spines.

_Caudal Appendages_, with two or three little spines on their summits.

_p.e.n.i.s_, short, blunt, thick at the apex, with one or two spines on it.

I did not see any ovaria, but this could hardly have been expected in specimens in a dried condition, without they had happened to have been in a gorged condition. Certainly there were no ova.

In the general summary at the end of the genus, I shall give my reasons for believing this parasite to be the Complemental Male of the _Scalpellum rostratum_.

5. SCALPELLUM PERONII. Pl. VI, fig. 6.

SMILIUM PERONII. _J. E. Gray._ Annals of Philosoph., new series, tom. x, 1825.

---- ---- ..... Spicilegia Zoologica, tab. iii, fig. 10, 1830.

ANATIFA OBLIQUA. _Quoy_ et _Gaimard_. Voyage de l'Astrolabe, Pl.

xciii, fig. 16, 1823-1834.

POLLICIPES OBLIQUA. _Lamarck._ An. sans Vertebres (2d edition).

_S. (Herm.) valvis 13: laterum paribus tribus; pari superiore multum elongato: pedunculi squamis calcareis nullis._

(Herm.) Capitulum with 13 valves: three pair of latera; upper latera much elongated: peduncle without calcareous scales.

Mandibles with 10 or 11 unequal teeth: maxillae with the edge nearly straight, bearing numerous spines.

COMPLEMENTAL MALE, attached externally, between the scuta and below the adductor muscle; pedunculated; capitulum formed of six valves, with the carina descending far beneath the basal angle of the terga; mouth and cirri prehensile.

Swan River, Australia, attached to a coralline; Mus. c.u.ming.

Port Western, Ba.s.s's Straits, as stated in the Voyage of the Astrolabe. Mus. Brit.

HERMAPHRODITE.

_Capitulum_ formed of 13 valves; namely, two scuta, two terga, a carina and sub-carina, a rostrum, a pair of upper latera, and two pair of lower latera; these latter valves, with the sub-carina and the rostrum, make a whorl of six pieces. The upper part of the capitulum is, as usual, produced. The upper valves are separated (in specimens which have not been dried) by rather wide inters.p.a.ces of membrane; they are covered (excepting, generally, their umbones,) by membrane, which in the inters.p.a.ces is clothed with fine spines. The spines, or the marks where they were once articulated, are visible over nearly the entire surface of the membrane covering the valves. The spines are particularly numerous round the orifice of the sack. The whole capitulum, (in a dried condition), is coloured dull purplish-red, which is only in part due to the underlying corium, for the valves themselves are pale red. After having been long kept in spirits, the whole capitulum becomes colourless. The valves are smooth, faintly marked by lines of growth.

The umbones of the lower valves project outwards, giving a denticulated appearance to the base of the capitulum.

_Scuta_, slightly convex, oblong, breadth about two thirds of the length, almost quadrilateral, with the upper portion produced into a flat projection; this projection is almost spear-shaped, being constricted a little on each side below the apex. There is a deep pit for the adductor muscle. The umbo is near the apex, the part above not being above one fifth of the whole length of the valve. As in _S.

vulgare_, the growth is at first downwards, and subsequently a little upwards and downwards, thus producing the upper, small, spear-like projection, which lies at a lower level than the umbo. There is a fold on the occludent margin.

_Terga_, large, flat, triangular; carinal margin slightly hollowed out; occludent margin slightly arched, with a small portion protuberant to a variable amount. The apex is slightly curved towards the carina.

_Carina_, long, internally deeply concave, angularly bent, the lower portion slightly longer and wider than the upper part; the two halves meet each other at about an angle of 135; the upper half is parallel to the longer axis of the terga, between which it extends for three fourths of their length. The external surface is rounded, except near the umbo, where the edge is carinated; growth almost equally upwards and downwards; the parietes and tectum are not separated by ridges.