Filaments, five on each side; segments of the three posterior cirri with triangular brushes of spines.
Var. (_Donovani_, of Leach.) Carina with the upper part flat, spear-shaped, externally with a narrow central ridge.
Var. (_Villosa._ Pl. I, figs. 6 _b_, _c_.) Valves placed rather distant from each other; carina extremely narrow, with the upper part of nearly the same width throughout; terga with the lower part much ac.u.minated; body of animal finely villose.
Coasts of Great Britain and France; Baltic Sea, according to Montagu Southern United States (from Aga.s.siz); tropical Atlantic Ocean; East-Indian Archipelago, off Borneo and Celebes; Pacific Ocean, between the Sandwich and Mariana Archipelagos; New Zealand: attached to fuci, Spirulae Janthinae, Velellas, often to feathers and cork; often a.s.sociated with the young of _L.
anserifera_, (var. _dilatata_,) and _L. pectinata_.
_General Appearance._--Capitulum highly variable in all its characters; thick and broad in proportion to its length, but the breadth is variable,--in some specimens, the capitulum being longer by one-fifth of its total length than broad; in others, one-fifth broader than long.
Valves generally approximate; in some varieties, however, from the narrowness of the carina and terga, the valves stand far apart, there being an interval between the carina and scuta of nearly half the breadth of the latter. Valves excessively thin, brittle, transparent, colourless, smooth, but generally sinuous along the zones of growth, which are conspicuous: valves generally covered throughout by thin chitine membrane, which is thickly clothed, especially in the inters.p.a.ces between the valves, with minute spines, barely visible to the naked eye. _Scuta_ with the lower part of the tergo-carinal margin extremely protuberant; occludent margin, more or less, but slightly reflexed, with a depressed line running from the umbo to the apex; basal margin much reflexed, but to a variable extent and at a varying angle, even up to a right angle,--an external rim or collar being thus formed.
There are no distinct _internal_ teeth, but the basal margin under the umbones, is more or less distinctly produced into a rounded disc or projection, which is generally not so much outwardly reflexed as the rest of the basal margin: there is no distinct internal basal rim. The primordial valves are generally visible, but they do not lie, as in all other species, close to the basal margin, but a little above it,--the lower reflexed portion having been subsequently developed. _Terga_ flat, with the occludent margin slightly arched, and not, as in the foregoing species, formed of two sides; apex bent towards the carina; width of the lower half highly variable, owing to the varying extent to which the scutal margin is hollowed out; in some specimens, the whole lower half beneath the apex of the scuta is of nearly the same width throughout; in other specimens this lower part is spear-shaped. The widest part of the tergum either equals in width, or is only two-thirds of the width of the widest part of the carina beneath its umbo. _Carina_ (Pl. I, fig. 6 _a_) highly variable in shape, with the part above the umbo either spear-shaped and slightly concave within, or nearly flat and furnished with a central external ridge; or the upper part (fig. 6 _c_) is of equal and extreme narrowness throughout, and deeply concave within, appearing as if only the central ridge had been developed. The part below the umbo, (answering to the fork in the foregoing species,) is about one-third of the length of the whole valve, and generally twice as wide as the upper part, but in the variety with the upper part of the carina equally narrow throughout, the lower part is thrice as wide as the upper; the disc, or lower part, is generally slightly concave within, exteriorly either with or without a central ridge; basal margin rounded; lateral margin more or less curved, according to the form of the upper part. The disc is not more deeply imbedded in membrane than is the upper part of the valve. The heel or umbo is either angular and prominent, or rounded. In very young specimens the carina is simply bowed, instead of being rectangularly bent.
_Peduncle_,--short, narrow, being abruptly inflected all round under the basal edges of the capitulum; lower part of very variable shape, being often suddenly contracted into a mere thread (fig. 6 _b_), which sometimes widens again at the extreme end. The external membrane is very thin, and is penetrated by the usual fine tubuli leading to the corium; its surface is wrinkled and dest.i.tute of spines, or with extremely few.
The peduncle is often completely surrounded by a yellowish ball, (of which I have seen specimens from the coast of England, and from off Borneo,) sometimes half as wide as the capitulum, composed of very tender, vesicular, structureless membrane, and of a pulpy substance: perhaps the yellow colour may be owing to long immersion in spirits.
Some authors have supposed that the ball was the ovisac of the animal; and for the first few minutes, deceived by the numerous included spores of, as I believe, Bacillariae, I thought that this was the case; others have supposed that it consisted of some encrusting algae or other foreign organism; but it is, in reality, a most singular development of the cement-tissue, which ordinarily serves to attach Cirripedes by their bases to some extraneous object, but here surrounding that object and the peduncle, gives buoyancy, by its vesicular structure, to the whole.
The membrane of the ball falls to pieces in caustic potash, differently from the chitine membrane of the enclosed peduncle, and this shows that there is some difference in composition from ordinary cement. The ball, when cut in two, exhibits an obscure concentric structure. The whole is excreted by the two cement-ducts, through two rows of orifices, one on each side of the surrounded portion of the peduncle; and I actually traced, in one case, the yellow pulpy substance coming out of the cement-ducts. The upper apertures are in gradation larger than those below them, and they stand a little further apart from each other; these are figured as seen from the outside, much magnified, at Pl. I, fig. 6 _d_. I did not succeed in finding the cement-glands, but I followed the ducts, of rather large size, running for a considerable distance as usual along and within the longitudinal muscles of the peduncle. Nearly opposite the uppermost aperture, on each side, the duct pa.s.ses out through the corium, and becomes laterally attached to the outer membrane of the peduncle, at which point an aperture is formed (as in other cases, by some unknown process), thus giving exit to the contents of the duct. Beneath this upper aperture the duct runs down the peduncle, between the corium and the outer membrane, till it comes to the next aperture, to which it is also attached, and so on to all the lower ones; but I believe no cement tissue continues to pa.s.s out through these lower apertures. Beneath the lowest aperture the two ducts run into the two prehensile antennae of the larva, which, as usual, terminate the peduncle. The antennae are attached to some small foreign body in the centre of the vesicular ball, by the usual tough, light brown, transparent cement. The two upper apertures are nearly on a level with the outside surface of the ball; and it was evident that as the animal grows, new apertures are formed higher and higher up on the sides of the peduncle, and that out of these, fresh vesicular membrane proceeds, and grows over the old ball in a continuous layer. It appears that the growth of the vesicular ball is not regular,--that it is not always formed,--and that when formed the whole, or the lower part, sometimes disintegrates and is washed away. As that portion of the peduncle which is enclosed ceases to grow, and has its muscles absorbed, retaining only the underlying corium, whereas the upper unenclosed portion, and likewise, (as it appears) lower portions once enclosed but since denuded, continue to increase in diameter, the peduncle, when the vesicular ball is removed, often has the most irregular outline, contracting suddenly into a mere thread, and then occasionally expanding again at the basal point.
Frequently two or three specimens have their peduncles imbedded in one common ball, of which there is a fine specimen in the College of Surgeons (Pl. I, fig. 6), the ball being about one inch and a quarter in diameter, with a slice cut off. In this specimen, it is seen that the vesicular membrane proceeding from several individuals, unites to form one more or less symmetrical whole, and that the original common object of attachment is entirely hidden. Dr. Coates[29] gives a curious account of the infinite number of specimens, through which he sailed during several days, in the Southern Atlantic Ocean: the b.a.l.l.s appeared like bird"s eggs, and were mistaken for some fucus, which was supposed to have encrusted the scales of the Velellae, to which the Cirripede had originally become attached. Several individuals had their peduncles imbedded in the same ball, "which floated like a cork on the water." As this species grows into an unusually bulky animal, we here see a beautiful and unique contrivance, in the cement forming a vesicular membranous ma.s.s, serving as a buoy to float the individuals, which, when young and light, were supported on the small objects to which they originally had been cemented in the usual manner.
[29] Journal of the Acad. Nat. Sc., Philadelphia, vol. vi, p.
138, 1829.
_Filamentary Appendages._--Five on each side, of which four lie in pairs at the base of the first cirrus (of these, only three are sometimes developed), and one on the flank of the prosoma.
_Mouth._--Palpi much ac.u.minated. Mandibles with five teeth; the first not far remote from the second; inferior point rather broad and finely pectinated. Maxillae with two large, unequal, upper spines, and four regular steps.
_Cirri._--Posterior cirri, with the upper parts of the segments slightly protuberant; in young specimens, the spines can be seen to consist of five pairs, placed in two converging lines in the upper half of each segment, with numerous minute, latero-marginal, and intermediate little bristles: in large specimens, all these latter have so increased in number, that the normal five pair cannot be distinguished, and the front of each segment is covered by a triangular thick brush of bristles, all pointing in the same direction, thus giving a very unusual character to the posterior cirri: the dorsal tuft on each segment consists of six or seven large spines, with from one to three dozen fine ones. First cirrus and anterior ramus of second cirrus with broad brushes of bristles. The pedicels of all the cirri are thickly covered with bristles. _Caudal_ appendages smooth, with rounded summits.
_p.e.n.i.s_ very hairy: vesiculae seminales purple, much convoluted, lying within the prosoma; testes dendritic, scarcely enlarged at their terminal points, purplish; ovigerous fraena large with sinuous margins, the glandular beads being arranged in groups.
_Size._--The largest specimen (from the coast of Devonshire) had a capitulum 1.6 of an inch long, and 1.2 broad, and of unusual thickness.
_Colours_, after having been in spirits: front surfaces of the segments of the cirri and of the pedicels purple. In some specimens from off Borneo, parts of the sack and the inters.p.a.ces between the two scuta, were of a fine purple. Montagu states, that the whole sh.e.l.l and body of animal, when fresh, are pale blue, with the cirri spotted with brown.
_General Remarks._--The extreme variability of this species is remarkable. In the College of Surgeons, there is a group of specimens collected by Mr. Bennett, I believe, in the Atlantic, in which the extreme narrowness of the carina and of the terga (Pl. I, fig. 6, _b_, _c_) (with consequent wide s.p.a.ces of membrane left between these valves), led me, at first, to entertain no doubt, that it was quite a distinct species, which was strengthened by finding that the whole surface of the cirri were villose, with very minute spines; hence I called this variety, _villosa_. On the closest examination, however, I could detect no other differences, and the narrowness of the carina and terga varied very considerably: moreover, in one of the specimens, which was about intermediate in the form of its valves between this variety and the common form, the surfaces of the cirri were not in the least degree villose. Again, in some other specimens, the terga were as narrow as in Mr. Bennett"s, whilst the carina had its usual outline.
In a var. (called by Leach, _P. Donovani_,) from the Atlantic, under the Equator, the carina is remarkable from the extreme flatness of the upper part, and from the presence of an exterior, narrow, central ridge. In one specimen from Jersey, in the British Museum, the carina made an extremely near approach to this same form.
_Affinities._--This species is certainly much the most distinct of any in the genus, and Mr. Gray has proposed to separate it under the name of Dosima; but considering the close similarity of the whole organisation of the internal parts, together with the transitional characters afforded by _L. australis_, I think the grounds for this separation are not quite sufficient. I have remarked, under _L. australis_, on the affinity between that and the present species. In the carina terminating in a disc (though here not imbedded), there is some slight affinity to _Paecilasma eburnea_ and _cra.s.sa_, and markedly so in the arrangement of the bristles on the posterior cirri. In the valves being covered with villose membrane, and to a certain extent in the form of the carina and of the occludent margin of the terga, and especially in the two rows of cement-orifices in the peduncle, there is some affinity to Scalpellum.
PaeCILASMA. _Nov. Genus._[30] Plate II.
ANATIFA. _J. E. Gray._ Proc. Zoolog. Soc., 1848, p. 44.
TRILASMIS. _Hinds._ Voyage of the Sulphur. Mollusca, 1844.
[30] [Greek: Pokilos], various, and [Greek: elasma], plate or valve. I have not been able to adopt Mr. Hinds" name for this genus, as it would be too glaringly incorrect to call a five-valved species, a _Trilasmis_.
_Valvae, 3, 5, aut 7, approximatae: carina solum ad basales apices tergorum extensa, termino basali aut truncato aut in disc.u.m profunde infossum producto: scuta paene ovalia, umbonibus ad angulum rostralem positis._
Valves, 3, 5, or 7, approximate: carina extending only to the basal points of the terga; with its lower end either truncated or produced into a deeply imbedded disc. Scuta nearly oval, with their umbones at the rostral angle.
Mandibles with four teeth; maxillae notched, with the lower part of edge prominent; anterior ramus of the second cirrus not thicker than the posterior ramus; caudal appendages uniarticulate, spinose.
Generally attached to Crustacea.
I have already given my reasons for inst.i.tuting and separating this genus from Lepas; as far as the capitulum is concerned, the differences between these genera certainly appear trivial; they consist in the carina not extending up between the terga, and in the lower end being either truncated, or produced into an imbedded disc: the terga have a single occludent margin. The included animal"s body differs in more important respects; for both mandibles and maxillae are very distinct; the cirri of some of the species also differ; and the caudal appendages are here always spinose: there are no filamentary appendages: and lastly, the habits are different.
The genus may be divided into two sections, firstly, _P. Kaempferi_ and _P. aurantia_, which have their carinae basally truncated, the basal angles of their terga cut off, and the anterior rami of their second cirri shorter than the posterior rami; and, secondly, _P. cra.s.sa_, _P.
fissa_, and _P. eburnea_, which in these several respects are otherwise characterised. The _P. eburnea_, however, differs rather more from _P.
cra.s.sa_ and _P. fissa_, than these two do from each other; but certainly not enough to allow of the retention of Mr. Hinds" genus of Trilasmis.
_P. cra.s.sa_, in an especial degree, connects together all the forms.
_General Appearance._--Capitulum oval, more or less produced, flat or gibbous; formed of three, five, or seven approximate valves; the lesser number arising from the abortion of the terga, and the greater number from the scuta being divided into two segments. Valves moderately thick, either white or reddish, smooth or striated, and sometimes partly covered by membrane, bearing minute spines. _Scuta_ oval, of varying proportions; the basal margin is generally narrow, and blends into the carina-tergal margin; the internal basal rim generally is well developed, sometimes with, and sometimes without internal teeth beneath the umbones. In _P. eburnea_, and sometimes in _P. cra.s.sa_, there is a line of apparent fissure, and in _P. fissa_ of actual disseverment, running from the umbo to the apex of each scutum, nearly in the line in which a ridge extends in Lepas: the primordial valves of the scuta in these three species, are seated at the basal angles of the lateral and larger segments. The positions of the primordial valves, and the direction of growth in the calcified valves, are, in all the species, the same as in Lepas. In several of the species attached to Crustacea, the two scuta are unequally convex, which is caused, as was pointed out to me by Mr. Gray, by that valve which lies close and nearly parallel to the body of the crab, being least developed. The _Terga_ are either quite absent, or rudimentary as in _P. cra.s.sa_, or pretty well developed as in the other species: the occludent margin is single, and not double as generally in Lepas; the basal angle is either pointed or truncated.
The _Carina_ varies considerably in shape, but never extends up between the terga, nor ends downwards in a fork; in the first two species it is truncated; in the others, it terminates in a deeply-imbedded oblong disc, which in _P. eburnea_ seems almost entirely (but of course not quite) to separate the inside of the capitulum from the peduncle; a similar separation is effected in _P. fissa_, where the imbedded disc is small, by two large teeth on the internal basal rims of the two scuta.
The carina is always narrow, and either solid internally or very slightly concave.
_Peduncle_, is very short and narrow; the membrane is generally ringed with thicker, yellower portions, and often bears very minute spines.
_Size._--All the species are small, with a capitulum not exceeding half an inch in length.
_Filamentary Appendages._--None.
_Mouth._--Labrum generally considerably bullate in the upper part, with a row of teeth on the crest. The _mandibles_ have four teeth, with the inferior point narrow and spine-like, or rudimentary and absent. The _maxillae_ have, under the two or three upper great spines, a deep notch itself bearing spines; beneath this, the lower part is straight and considerably prominent, Pl. X, fig. 15. Outer maxillae are covered on their inner sides continuously with spines.
_Cirri._--The first pair is sometimes seated very distant from the second. The arrangement of the spines on the posterior cirri varies, to an unusual degree within the limits of the same genus. We have either the ordinary structure of anterior pairs, with single fine intermediate spines (as in _P. Kaempferi_ and _aurantia_), or we have the pairs increased by one or two additional longitudinal lateral rows, as in _P.
eburnea_; or we have the front spines forming a single transverse row, as in _P. cra.s.sa_ and _P. fissa_, Pl. X, fig. 29, _a_. The segments in none of the species are protuberant; the anterior ramus of the second cirrus does not seem to be thicker than the posterior ramus, as is usually the case. The rami of the second, and of most of the other cirri, are unequal in length,--the anterior ramus, contrary to the ordinary rule, being longer in _P. eburnea_, _P. fissa_, and _P.
cra.s.sa_, than the posterior ramus by several segments; I have hitherto observed this inequality only in the sessile genus Chthamalus.
The _Caudal Appendages_ are small, uniarticulate, and always furnished with bristles.
_Distribution._--Four out of the five species live attached to Crustacea in the European and Eastern warmer temperate and tropical oceans; the fifth species was found attached to the dead spines of an Echinus, off New Guinea. It is probable that several more species will be hereafter discovered.
1. PaeCILASMA KaeMPFERI. Pl. II, Fig. 1.
_P. valvis 5; carinae basi truncata et cristata: scutorum dentibus internis umbonalibus fortibus: tergorum ac.u.mine basali truncato, margini occludenti paene parallelo._
Valves 5; carina with a truncated and crested base; scuta with strong internal umbonal teeth; terga with the basal point truncated, almost parallel to the occludent margin.
Maxillae with short thick spines in the notch under the two upper great spines; caudal appendages with scattered bristles on their summits, and along their whole outer margins.
j.a.pan; attached, in great numbers, to the upper and under sides of the _Inachus Kaempferi_ of De Haan, a slow-moving brachyourous crab, probably from deep water. British Museum.
_General Appearance._--Capitulum rather compressed, narrow, and produced. Valves white, tinged with orange, smooth, moderately thin, occasionally with faint traces of striae radiating from the umbones.
_Scuta_, apex pointed, with a very slight ridge running to the umbo; basal margin equalling two thirds of the length of the terga, with an internal basal rim; on the under side of each valve, beneath the umbo, there is a strong tooth. Out of the numerous specimens, all excepting one had their scuta unequally convex, with their occludent margins unequally curved, that of the more convex valve at the umbo, curling beyond the medial line. The basal end of the carina is, likewise, slightly curved laterally, and always turns towards the more convex valve. This inequality, as Mr. Gray pointed out to me, depends on the position of the specimens; the flatter side lying close to the carapace of the crab. _Terga_, flat, oblong, nearly rectangular; occludent margin straight; basal angle, truncated, almost parallel to the occludent margin; in width, three or four times as wide as the carina. _Carina_, (fig. 1, _a_) short, narrow, slightly curved, upper part broadest, with the apex rounded, only just pa.s.sing up between the basal broad ends of the terga; externally carinated, internally very slightly concave; basal end abruptly truncated, crested, not deeply imbedded in the membrane of the peduncle.