A Monograph on the Sub-class Cirripedia · Charles Darwin
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_Parietes_, not porose; internally, the ribs are smooth, with their basal edges very finely or barely denticulated. The _radii_ (as already stated) are of variable breadth; they have their upper margins either very slightly or highly oblique, but always smooth and rounded: their sutural edges are quite smooth, or sometimes, with a strong lens, traces of transverse striæ, representing septa, can just be discovered. The _alæ_ have their upper margins very oblique; their sutural edges are, in the large specimens, quite smooth; in the younger ones, plainly crenated; the recipient furrow being clearly marked with these teeth. _Basis_ plainly porose. _Varieties._--It is certain that there are longitudinally plicated specimens of this species, and that the obliquity of the upper margins of the radii also varies a little: nevertheless some of the deeply plicated specimens undoubtedly have a very different aspect from the ordinary varieties, and do really differ in the sutural edges of the alæ being crenated, and in the greater narrowness and obliquity of the radii; but these points are all commonly variable. I have not seen any large specimens of the variety, _plicatus_, so as to compare them with the large specimens of the normal form, yet I can hardly entertain any doubt, considering their agreement in so many important points, that I have rightly treated these forms as mere varieties; it is unfortunate that none of the specimens of the _var. plicatus_ seen by me have had opercular valves, as their presence would have removed all shadow of doubt.
_Affinities_: this is a strongly characterised species, and nearly allied only to the following species, _B. dolosus_. The furrows on the scuta in some degree resemble those on _B. lævis_, but there is no alliance with that species. It is certain that amongst recent species, the chief affinity is with _B. Hameri_ and _amaryllis_. 42. BALANUS DOLOSUS. Pl. 8, fig. 7. _Radii with their upper margins oblique and smooth; sutural edges smooth: basis permeated by large pores. Tergum with the spur not very short, broad as one third of valve._ _Fossil_ in Red and Mammaliferous Crag, England; Mus. S. Wood, Bowerbank, Lyell, J. de C. Sowerby, Henslow, &c. Mammaliferous Crag, Postwick, near Norwich, Mus. Lyell. This species so closely resembles _B. bisulcatus_, both externally and in all the essential characters of the parietes, radii, and basis, that it is quite superfluous to describe over again these parts. The specific characters are derived from the opercular valves, which present well defined distinctions, found by me constant in several specimens of both species. _B. dolosus_, like _B. bisulcatus_, has quite smooth and deeply plicated varieties, often adhering to the same univalve. The ribs on the inner surfaces of the parietes are remarkably prominent. I think the upper margins of the radii are in this species rather more oblique than in _B. bisulcatus_. The sutural edges of the radii are marked by the finest striæ, representing septa. The sutural edges of the alæ are generally distinctly crenated. The basis is often slightly cup-formed, and very plainly porose: its surface is marked by radiating ridges. The orifice of the shell is large, and elongated, especially in young specimens. The basal diameter of the largest specimen is .4 of an inch.
The _Scuta_ have no trace of the two or three longitudinal furrows so conspicuous on these valves in _B. bisulcatus_, and which, in that species, run down from the apex of the valve; this fact showing that the furrows occur in quite young individuals. The whole valve is not quite so narrow as in _B. bisulcatus_, but otherwise agrees with it in shape: internally, there is hardly any difference: the articular furrow is not so wide: the articular ridge is very prominent, and abruptly truncated at its lower end: the adductor ridge is also prominent; it here runs a little higher up the valve than in _B. bisulcatus_. The _Tergum_ differs more in the two species: the spur is not so broad; measured in its upper part, it is only about one third of the entire width of the valve, instead of being half as wide as the valve: it is considerably longer, depending beneath the basi-scutal angle more than half its own width: the basal margin of the valve on the carinal side, does not slope so gradually into the spur: the occludent and carinal margins are slightly arched, as in _B. bisulcatus_. Internally, the surface is rough, the articular ridge is prominent, and the crests for the tergal depressores are well developed,--all as in _B. bisulcatus_. It is remarkable, how generally the opercular valves have been preserved in this species in its fossil condition, as compared with most other species of the genus.
It is not easy to distinguish by external characters the rugged varieties of this species from _B. crenatus_; indeed, the only difference is that the furrows receiving the edges of the radii, generally, exhibit in _B. crenatus_ a slight impression of the septa, which are entirely absent in _B. dolosus_. By internal characters, such as the non-porose parietes, and porose basis, our present species widely differs from _B. crenatus_. 43. BALANUS UNGUIFORMIS. Pl. 8, fig. 8 _a_-8 _b_. BALANUS UNGUIFORMIS. _J. de C. Sowerby_ (!). Mineral Conchology (sine descriptione) Tab. 648, fig. 1, (Jan. 1846). ---- ERISMA. _J. de C. Sowerby_ (!). Ib., fig. 2. ---- PERPLEXUS. _Nyst_, apud D'Omalius (Sine descript. vel Tab.), Geologie de la Belgique, 1853.[101] [101] I am much indebted to M. Bosquet for specimens bearing this title, from Klein Spauwen, which certainly appear to me, as far as can be judged by the separated compartments, without the opercular valves, to belong to our present species. _Parietes thin, sometimes permeated by pores; radii with their upper margins oblique; sutural edges very finely crenated: basis solid. Tergum with the spur narrow, bluntly pointed._ _Var._ erisma, _with the walls longitudinally folded or ribbed_. _Fossil_ in the Eocene formation, Isle of Wight, Colwell Bay; Hordwell; Barton, (Chama Bed); Headon; Bembridge. Bergh, near Klein Spauwen, Belgium (?). Attached to various shells and wood. Mus. J. de C. Sowerby, E. Forbes, F. Edwards, Charlsworth, T. Wright, Bowerbank, Tennant, Bosquet.
This species, the most ancient one as yet well known in the genus, presents to the systematist a most unfortunate peculiarity, in the parietes being almost as often as not permeated by small pores: I have seen no other instance, except to a limited degree in _B. glandula_, of this character being variable, and hence it must be still considered of high classificatory value, in so varying genus as Balanus. Owing to this varying condition of the parietes, together with the basis being quite solid, our present species has as good a claim to be ranked in the last as in the present section; indeed, I think it has more affinity to _B. crenatus_ and _glandula_ in the last section, than to any other recent forms: I have placed it in its present place, owing to its intimate affinity to _B. varians_, in which the parietes seem always to be solid; and partly, I believe, because all the first specimens examined by me exhibited no traces of parietal pores. Owing to the kindness of Mr. F. Edwards, I have seen the original specimens, excellently figured by Mr. J. de C. Sowerby in the 'Mineral Conchology:' I can perceive no difference between _B. unguiformis_ and _erisma_, excepting that the walls in the latter are longitudinally folded,--a character we know to be variable in so many species. In both varieties, the parietes are sometimes porose and sometimes solid. The smaller specimens, however, figured in the 'Mineral Conchology' to the right hand, may possibly be a distinct species, as I infer from the narrowness of their radii.
_General Appearance._--Shell, tubulo-conical, sometimes considerably elongated and sub-cylindrical: surface either very smooth, or slightly folded, or deeply folded so as to be strongly ribbed longitudinally: orifice rather large, rhomboidal, narrow at the carinal end, toothed, but not deeply: walls rather thin and fragile: radii of moderate width, with their summits oblique, not quite smooth. Basal diameter of largest specimen, about three quarters of an inch. _Scuta_, with the external surface smooth: there is a trace of a furrow running down the valve from the apex, near to the occludent margin, and this is only worth mentioning from the analogous furrows in _B. bisulcatus_. Internally, the upper surface of the valve is roughened: the articular ridge is very prominent, and slightly reflexed: there is no distinct adductor ridge; there is a slight but variable depression for the lateral depressor. _Tergum_, with the longitudinal furrow shallow; spur moderately long, about one fourth or one fifth of the width of the valve; placed at about its own width from the basi-scutal angle; basal end bluntly pointed; the basal margin on the opposite sides of the spur forms a nearly straight line; the carinal margin has an extremely narrow border formed by upturned lines of growth. Internally, the surface is roughened with little points: the articular ridge is prominent: the crests for the tergal depressores moderately prominent.
_Parietes_: the longitudinal ribs on the internal surface are either feebly, or, in the lower part, strongly developed; their basal ends are only just perceptibly denticulated. As already stated, in about half the specimens, there were no traces of parietal pores; in the other half there were either distinct or obscure pores; the pores are circular, generally of unequal sizes, and never large; in the same individual they would sometimes be almost wholly absent in some of the compartments, and quite plain in the other compartments. The Radii are either moderately wide or rather narrow, and have their upper margins very oblique, and not distinctly arched, and not quite smooth: their sutural edges are very finely crenated, the teeth or septa not being denticulated. The upper margins of the _alæ_ are rather less oblique than those of the radii: their sutural edges are barely crenated. The _basis_ is thin, and without any trace of pores; the upper surface is sometimes furrowed in radiating lines. 44. BALANUS VARIANS. Pl. 8, fig. 9. B. VARIANS. _G. B. Sowerby_, in Darwin's Geolog. Observ. on South America, (Sept. 1846), Tab. 2, fig. 4, 5, 6. _Parietes moderately thick: radii with their upper margins very oblique; sutural edges almost smooth, or finely crenated: basis finely porose. Tergum with the spur small, narrow, bluntly pointed._ _Hab._--Port St. Julians, Patagonia; ancient Tertiary formation. Eastern plain of Tierra del Fuego (?).
This species comes so close to _B. unguiformis_, that I have some doubt whether they ought to be specifically separated: the whole shell is stronger, and the basis can be seen to be porose when a polished section is made: the spur of the tergum is smaller, more pointed and more medial, but these latter differences may be due to mere variation. Should _B. varians_ and _unguiformis_ prove to be the same species, the latter name has the priority. _General Appearance._--Shell moderately strong and thick; shape conical or tubular, or even inverted conical; orifice moderately toothed, large, sub-trigonal; walls either smooth or longitudinally folded; the elongated specimens are most apt to be smooth. The Radii are narrow and oblique. Diameter of largest specimen above three-quarters of an inch. _Scuta_, with the lines of growth moderately prominent; the internal surface of the valve has been ill preserved; but a very prominent, hardly reflexed, articular ridge, can be distinguished, as well as the absence of an adductor ridge. _Terga_, with no distinct longitudinal furrow running down the valve: spur short, bluntly pointed, narrow, about one fifth or one sixth of width of valve; placed at above its own with from the basi-scutal angle; the basal margin, on each side close to the spur, curves towards it. Internally, all that can be distinguished, is that the articular ridge is prominent.
_Parietes_; their inner surfaces appear to have been nearly smooth; the absence of parietal pores could be made out only by polishing a transverse section. The Radii are narrow, and have their upper margins very oblique and rather smooth: in the elongated varieties the sutural edge appears to be almost absolutely smooth; in the conical specimens it is slightly crenated, the septa being apparently not denticulated. In living species we have a similar variation in the state of the sutural edges of the radii, in _B. balanoides_ and _crenatus_ the edges being much smoother in much elongated specimens than in other varieties. The _alæ_ have their upper margins less oblique than those of the radii, with their sutural edges barely crenated. The _basis_ is either flat, or, in the elongated specimens, deeply cup-formed; in section it can be seen to be finely and irregularly porose. 45. BALANUS INCLUSUS. Pl. 8, fig. 10 _a_-10 _c_. _Shell reddish-brown: radii broad, with their upper margins not oblique, or only moderately oblique; sutural edges with plainly denticulated septa: basis porose. Scutum without an adductor ridge; tergum with the spur rather narrow._ _Var._ (_a_) (Pl. 8, fig. 10 _b_, 10 _c_), _with the shell elongated in its rostro-carinal axis; basis narrow, clasping the stem of a zoophyte; lateral compartments much broader than the almost linear rostrum, carina, and carino-lateral compartments_.
_Var._ (_b_), _with rough longitudinally folded walls, and with the summits of the radii forming an angle of about 45° with the basis_. _Fossil_ in Coralline Crag, Sutton and Gedgrave; attached to foliaceous Bryozoa; Mus. S. Wood, Bowerbank. _Var. a_, Coralline Crag, Sutton, attached to cylindrical branches of corals; Mus. S. Wood. _Var. b_, attached to shells, Osnabruck, Hanover, Mus. Lyell; Bünde, Westphalia, Mus. Krantz. My materials consist of a beautiful series of specimens in Messrs. Wood and Bowerbank's collections; but unfortunately only a single young specimen had its opercular valves preserved. Not one specimen of the very curious variety (_a_) had opercular valves, yet I cannot feel any doubt about its being only a variety, caused by its attachment to a thin cylindrical branch of a coral, instead of to a foliaceous Bryozoon; it will, however, be convenient to give a separate description of this very remarkable form. With respect to var. (_b_), both sets of specimens came to me with the name _B. stellaris_, of Bronn; but as Bronn distinctly states, that in his species the parietes are porose, and as such is not here the case, this cannot possibly be that species: these specimens did not possess their opercular valves, and therefore cannot be identified with certainty. _General Appearance._--Shell conical, with the orifice rather large, and rhomboidal. The surface is very smooth, except in var. (_b._) from the Continent, in which it is rugged and longitudinally folded. The colour is ochreous-brown (chiefly no doubt derived from the imbedding substance) tinged with red. The radii often have a much darker and more distinct red tint; they are sometimes longitudinally striped with dirty white. The radii are broad, with their summits straight, and very slightly oblique; in _var. b_, however, they slope at an angle of about 45°. Basal diameter of largest specimens .6 of an inch; but this is an unusual size.
_Scuta_ (from a young individual), with the growth ridges little prominent. Internally the articular ridge is moderately prominent, with its lower end very obliquely rounded off; there is no adductor ridge; there is a minute pit for the lateral depressor muscle. _Terga_, with a slight longitudinal depression extending down to the spur: spur short, with its lower end almost square or truncated, about one fourth of width of valve, and placed at about half its own width from the basi-scutal angle. Internally, the articular ridge is prominent; the crests for the tergal depressores are feebly developed. _Parietes_, moderately thick and generally strongly ribbed internally, without parietal pores. _Radii_, wide, with their upper margins straight, not smooth or rounded, and very slightly (or, in _var. b_ moderately) oblique; their sutural edges have well-developed septa, which are denticulated: the interspaces between the septa are filled up solidly. The _alæ_ have their upper margins oblique: they are only slightly, and sometimes not at all, added to above the level of the opercular membrane: their sutural edges are smooth. The _basis_ is thin, but plainly porose.
_Var._ (_a_).--With respect to this remarkable variety, any one would at first think it specifically distinct. The shell is much compressed, or elongated in the rostro-carinal axis, sometimes to a great degree; I have seen a specimen .25 of an inch in this axis and only .1 in its broadest part; but this is a very unusual degree of elongation. The most remarkable character is the extraordinary narrowness of the carina, the carino-lateral compartments, and of the rostrum, compared with the great breadth, especially along the basal margin (Pl. 8, fig. 10 _b_, 10 _c_), of the lateral compartments. The radii are of unusual breadth. The tips of the rostrum and of the lateral compartments are a little arched in, tending to make the shell somewhat globular. The true basis is extremely narrow (fig. 10 _c_): it is deeply grooved, from clasping the thin, cylindrical stem of the coral to which it had adhered; and I have seen specimens in which the opposite edges of the groove had met, a tube having been thus actually formed.
From the grooved basis, and from the elongation of the shell in the rostro-carinal axis, this species presents so close a general resemblance to _Balanus calceolus_, and its allies, that I have seen it in a collection arranged on the same tablet with a fossil specimen of _B. calceolus_. Notwithstanding the above several strongly-marked characters, by which this variety differs from the ordinary form, there is a resemblance in colour and aspect, which though difficult to be described, made me from the first suspect that the two were specifically identical. In no point of real structure is there any difference, excepting that, perhaps, the pores in the basis are here rather smaller; but this might arise from the little development of the peculiar basis. Having come to this conclusion, I was interested by finding a specimen in Mr. Wood's collection, which had originally fixed itself (judging from the form of the basis) on a cylindrical stem, but which had subsequently grown on to an adjoining flat surface; consequently, one side of the shell presented all the peculiar characters of the present variety, whereas the other side, at the rostral end, was undistinguishable from the ordinary form. The unequal development of the rostrum on the two sides was very striking, and clearly showed how great an effect could be produced by the nature of the surface of attachment.
This singular variety cannot be considered accidental, in the sense in which this term may be applied to some varieties: the larva evidently fixes itself intentionally, in a certain definite position, on the branch of the coral (when a branch is chosen), exactly as in the case of _Balanus calceolus_, or _Scalpellum vulgare_. But when other species of Balani occasionally fix themselves on branched corals, their position seems to be accidental and unsymmetrical; thus among the symmetrically elongated specimens of the present species, I found one specimen of _Balanus bisulcatus_, which had evidently been attached in an almost transverse position to a branch, and had thus become much distorted; so, again, I have seen specimens of the recent _B. amaryllis_ attached irregularly to a Gorgonia, in the midst of the symmetrically elongated shells of _Balanus navicula_, an ally of _B. calceolus_. This variety does not seem to attain so large a size as the ordinary form. _Affinities._--This species is allied to the two last described fossils, namely, _B. varians_ and _unguiformis_, but is perhaps more nearly related to the recent _B. allium_, an inhabitant of the Barrier Reef of Australia. The longitudinally folded variety (_b_) can hardly be distinguished by external aspect, or even by the opercular valves, from _B. crenatus_; but when the shell is disarticulated, the porose walls and non-porose basis of _B. crenatus_, allow of no mistake in the diagnosis of the two species.
2. _Sub-Genus_--ACASTA. Pl. 9. ACASTA. _Leach._ Journal de Physique, tom. lxxxv, 1817. _Compartments six; parietes and basis non-porose: basis calcareous, cup-formed, not elongated, attached to sponges, or rarely to the bark of Isis._ Distribution mundane; imbedded in sponges and the sponge-like bark of Isis. This sub-genus, in one sense, is a very natural one, inasmuch as all the species are closely allied in essential structure, in general appearance, and in habit. On the other hand, in the structure of the shell, in all the characters derived from the opercular valves and animal's body, Acasta cannot properly be distinguished generically from some species of Balanus; thus _B. navicula_ and _cymbiformis_ agree in the parietes and basis not being porose and in all other essential respects, differing only in the shell being more elongated in the rostro-carinal axis and in being attached to Gorgoniæ instead of to sponges; yet we shall see that _Acasta purpurata_ lives imbedded in the bark of Isis, so that even the habit of being imbedded in sponges fails. _Balanus terebratus_ would have been ranked as an Acasta had it inhabited sponges. On the other hand, some species of Balanus inhabit sponges, as is often the case with _B. spongicola_, and always with _B. declivis_: but both these species are distinguished easily from Acasta, the former by its porose walls and basis, and the latter by its membranous basis; it may, however, be reasonably doubted whether such differences ought to be considered as even sub-generic. The most important character of Acasta probably consists in the anterior ramus of the fourth pair of cirri, differing slightly in the arrangement of its spines, and in some other points, from the rami of the two posterior pairs of cirri,--a character not as yet observed in any other cirripede. Had not the genus Acasta been already founded and extensively admitted, certainly I should not have formed it; but considering the close similarity in habits, aspect, and structure, of the nine species of Acasta, and considering the already large size of the genus Balanus, I hope I may stand excused for admitting Acasta as a sub-genus.
_General Appearance._--The shape varies from nearly globular to that of a somewhat flattened acorn, the orifice being often a little contracted from the inward curvature of the tips of the parietes. In _A. spongites_, however, the orifice is generally widely open; and, on the other hand, in _A. sporillus_, the orifice is reduced to a mere pore. The usual tint is pale reddish, but _A. purpurata_ is purple, and _A. sporillus_ purplish-brown. The surface is either smooth, or is shagreened with minute points, as in _A. sporillus_, and _fenestrata_, and in some specimens of _A. sulcata_; and in all the species, except _A. sporillus_ and _fenestrata_, many individuals are furnished with elongated, curved, sharp, shelly points, like those in _var. spinosus_ of _Balanus tintinnabulum_. The summits of the radii, which are generally of moderate breadth, are more or less oblique; their surface is often marked by lines parallel to the basis, instead of by vertical lines corresponding with the lines of growth, as in most species of Balanus. The carino-lateral compartments vary in proportional breadth in the different species: in _A. sporillus_, they tend to become rudimentary, and in this species (Pl. 9, fig. 9 _b_) their basal margins, or rather points, do not reach down to the basis. The species are all small, _A. glans_ and _undulata_ are the largest, being sometimes .55 of an inch in basal diameter.
_Opercular Valves._--These differ in no generic respect from those of Balanus. The _Scuta_ are striated longitudinally in several of the species: the adductor ridge is barely developed in any, being most prominent in _A. cyathus_. The articular ridge is prominent in _A. fenestrata_ and _purpurata_. In the _Terga_, the spur is either truncated and very broad, or moderately narrow and bluntly pointed: the surface of the valve is often depressed, and in _A. spongites_ and _fenestrata_ it is furrowed in the line of the spur. The articular ridge and furrow are well developed in _A. fenestrata_ and _purpurata_. The crests for the tergal depressor muscles are either absent or very feebly developed. _Structure of the Parietes and Radii._--The parietes are not porose; internally, they are either smooth, or slightly, or strongly ribbed in longitudinal lines; the presence of these ribs, which are homologous with the parietal septa in Balanus, is variable even in the same species. In _A. sporillus_ the inner surface is curiously reticulated. The sutural edges of the radii are either smooth, or very slightly crenated by the septa, in lines parallel to the basis. The upper margins of both radii and alæ are always more or less oblique. The radii sometimes do not extend down to the basis; and in this case, as will presently be described, apertures are left in the lower half, between the compartments. In _A. glans_ and _lævigata_ the internal margin of the wall of each compartment, from the sheath to the basis, projects inwards, forming inside the shell as many double ridges (Pl. 9, fig. 5 _b_), as there are compartments, namely, six: a nearly analogous structure occurs in certain species of Balanus. The basal edge of the sheath, in most of the species (5 _b_, 9 _b_), depends freely, and is hollow beneath, but this is always a variable point.
Text from Project Gutenberg, public domain in the United States.