A Monograph on the Sub-class Cirripedia · Charles Darwin
[F]
_Parietes and radii not permeated by pores. Basis sometimes permeated by pores, sometimes not, sometimes excessively thin and hardly distinguishable._[86] [86] The following species might, owing to variation, or to the obscurity of their structure, without care, be classed in the wrong sections:--in A, _Balanus Ajax_, from living attached to Milleporæ, is sometimes elongated in its rostro-carinal axis, and from having its radii only finely porose, it might be classed in B: on the other hand, _Bal. stultus_ is sometimes but little elongated, and the basis hardly boat-formed, and hence might be classed in A. The distinction between all the species in (B) and the sub-genus Acasta is artificial. In sections C and D, I have seen one specimen of _B. spongicola_ with a solid basis, and very young specimens of _B. improvisus_ are thus characterised, and therefore these species are liable to be placed in the wrong section, D: _Bal. nubilus_, also, has part of its base non-porose, and therefore likewise might be placed in D: on the other hand, the circumference of the basis in _B. patellaris_ is often porose, and hence this species, which belongs to D, might be placed in C. In _Bal. glandula_, in D, the parietes of the compartments, without several were examined, might be thought to be solid, and therefore this species might be wrongly placed in F; on the other hand, the fossil _B. unguiformis_, in F, often has porose parietes, and such specimens would naturally be placed in D. Lastly, without care, _B. flosculus_ might be thought to have a membranous basis, and so get placed in E.
The genus Pachylasma, without an examination of the animal's body, might easily get misplaced in the wrong genus, amongst the species in the last section (F) of Balanus, yet there can be no doubt that Pachylasma belongs to the Chthamalinæ. _Section_ A. 1. BALANUS TINTINNABULUM. Pl. 1, fig. _a_-_l_; Pl. 2, fig. 1 _a_-1 _o_. LEPAS TINTINNABULUM. _Linn._ Syst. Naturæ, 1767. ---- ---- _Ellis._ Phil. Transact., vol. 50, 1758, Tab. 34, figs. 8 and 9. ---- ---- _Chemnitz._ Neues. Syst. Conch., 8 B. (1785), Tab. 97, figs. 828-831. BALANUS TULIPA. _Bruguière._ Encyclop. Meth., 1789; sed non _B. tulipa alba_, in _Chemnitz_; neenon _B. tulipa_, _O. F. Müller_, Zoolog. Dan.; neenon _B. tulipa_, Poli, Test. ut. Siciliæ. ---- ---- _G. B. Sowerby._ Genera of Recent and Fossil Shells, Tab. Genus Balanus. LEPAS CRISPATA (_var._) _Schröter._ Einleitung Conch. vol. iii, Tab. 9, fig. 21. ---- SPINOSA (_var._) _Gmelin._ Linn. Syst. Nat. ---- TINTINNABULUM, SPINOSA, CRISPATA ET PORCATA. _W. Wood._ General Conchology, 1815, Pl. 6, figs. 1, 2. Pl. 7, figs. 4, 5. Pl. 8, figs. 1-5. BALANUS TINTINNABULUM. _Chenu._ Illust. Conch.[87] ---- D'ORBIGNII (_var._) _Chenu._ Illust. Conch., Tab. 6, fig. 10, sed non Tab. 4, fig. 13. ---- CRASSUS (Foss.) _Sowerby_ (!). Min. Conch., 1818. Tab. 84. [87] Chenu gives several admirable figures of this species; but he confounds some forms certainly distinct under this name, for instance the _B. tulipiformis_ of this work.
_Shell varying from pink to blackish purple, often striped and ribbed longitudinally: orifice generally entire, sometimes toothed. Scutum with the articular ridge broad and reflexed. Tergum with the basal margin generally forming a straight line on opposite sides of the spur._ _Var._ (1) communis (Pl. 1, figs. _a_, _b_, _f supra_; Pl. 2, figs. 1 _a_, 1 _c_, 1 _d_, 1 _e_, 1 _i_, 1 _k_): _conical or tubulo-conical; smooth or moderately ribbed longitudinally; colours varying from purplish-pink to blackish-purple; often in obscure longitudinal stripes; orifice of shell rounded-trigonal_. _Var._ (2) vesiculosus (_young_) (Pl. 2, fig. 1 _h_): _exterior surface of the scuta impressed with small square holes, arranged in two or more rows, radiating from the apex of the valve_. _Var._ (3) validus (Pl. 1, figs. _c_, _f infra_): _globulo-convex; coarsely ribbed, ribs flexuous; either smooth or rugged; pale chocolate purple or pink; shell extremely strong; orifice almost circular_. _Var._ (4) zebra (Pl. 1, fig. _g_): _conical; rich chocolate purple with broad snow-white ribs; sheath bright chesnut colour; summits of alæ oblique; orifice almost circular_. _Var._ (5) crispatus (_Schröter_) (Pl. 1, fig. _h_): _pale blueish or pinkish-purple, with irregular rough projections, or with short, sharp, needle-like points; scuta with their exterior surface either plain, or with radiating lines formed of hood-like projecting points_. _Var._ (6) spinosus (_Gmelin_) (Pl. 1, fig. _i_): _globulo-conical or cylindrical; shell rather thin, with long, upcurved, nearly cylindrical, very sharp points; colours very pale; attached to other specimens, and to Lepas anatifera_.
_Var._ (7) coccopoma (Pl. 1, fig. _d_; Pl. 2, fig. 1 _f_, 1 _l_, 1 _o_): _globulo-conical; orifice small, rounded; walls generally smooth, thick; intense rose-colour, sometimes most faintly striped longitudinally with varying shades of pink; radii tinged with purple; scutum sometimes as in_ var. communis, _sometimes with its basi-tergal corner much cut off, with the adductor ridge prominent, the pit for the depressor muscle deep, and the articular ridge broad and hooked; tergum sometimes as in_ var. communis, _sometimes with a broader spur, placed nearer to the basi-scutal corner of the valve_. _Var._ (8) concinnus (Pl. 1, fig. _e_; Pl. 2, fig. 1 _g_): _globulo-conical; walls finely ribbed; dull purple, tinged and freckled with white; scutum, with a broad, hooked, articular ridge, with an extremely sharp plate-like adductor ridge, and with a cavity, bordered by a plate, for the rostral depressor muscle; tergum as in_ var. 1. _Var._ (9) intermedius: _radii with their summits slightly oblique; parietes pale blueish purple, with narrow dark purplish-blue longitudinal lines; sheath with the internal surface of the rostrum and lateral compartments much darker colored than the internal surface of the carina and carino-lateral compartments; scuta and terga as in_ var. communis. _Var._ (10) occator (Pl. 1, fig. _k_; Pl. 2, 1 _b_): _radii with their summits slightly oblique; parietes smooth, or ribbed, or spinose; very pale blueish-purple, with narrow darker longitudinal lines; sheath with the internal surface of the rostrum and lateral compartments dull blue, whilst the corresponding parts of the carina and carino-lateral compartments are white; scuta with small, sharp, hood-formed points, arranged in straight radiating lines; terga with the spur placed at either its own width, or less than its own width, from the basi-scutal angle_.
_Var._ (11) d'Orbignii (_Chenu_) (Pl. 1, fig. _l_; Pl. 2, 1 _m_, 1 _n_): _radii with their summits oblique, and the orifice of the shell rather deeply toothed; shell conical or tubulo-conical, smooth, or rugged; colour dull purplish-lilac, with the tips of the parietes and a band along one side of the radii quite white; sheath rather darker at the rostral than at the carinal end; scuta as in_ var. 1; _terga as in_ var. occator. _Habitat._--West coast of Africa, on mytili; Madeira, on rocks; West Indies; Cape of Good Hope, on a patella and on kelp; mouth of the Indus; East Indian Archipelago; Sydney, Australia, attached to Lepas anserifera, adhering to a floating cane; Peru; Galapagos Islands; West Mexico; California. Extremely common on ships' bottoms arriving from West Africa, India, and China, often associated with _B. amphitrite_. _Fossil_ Red Crag, England; Mus. S. Wood and J. de C. Sowerby.--Touraine (?); Mus. Lyell. _General Remarks._--This, the first species of Balanus, is, perhaps with the exception of _B. amphitrite_, the most difficult and variable in the genus. There are some other species which vary quite as much in external appearance; for instance, _B. perforatus_; but _B. tintinnabulum_ also varies in far more important points, as in the proportions and structure of the opercular valves. The difficulty in determining whether or not the differences are specific, is wonderfully increased by whole groups of individuals varying in exactly the same manner. I have seen three most distinct varieties taken from the bottom of the same vessel, so that I did not at first entertain the least doubt that they were three distinct species.
I may mention, as showing the vacillations which I have experienced on this subject, that beginning with the impression, that the above three varieties were really distinct species, after going over the several immense collections of specimens placed at my disposal, I came to the conclusion that the above three, and several other forms presently to be described, were only varieties; yet after an interval of some months, having to look at some of these specimens again, I could not but think that I had come to a false conclusion, and so went into all the details again, and satisfied myself that I had followed a right course; after another interval, I had to repeat the same process, and even now I can never look at a group of the beautifully coloured shells with their small rounded orifices of _var. coccopoma_ attached to the _Avicula margaritifera_, or again at _var. d'Orbignii_, with its toothed orifice and white tips to the compartments, without thinking that they must be specifically distinct from the dull-coloured specimens with large entire orifices so common on ships' bottoms; yet I can produce a full series of intermediate forms, and I can further show, in each variety, that the several points of difference by which each is characterised, are variable. I may be permitted to add, in order to show that it has not been from indolence that I have combined so many forms, that I had named and already written out full descriptions of most of the varieties, before determining to sacrifice them.
Seeing that _B. tintinnabulum_ and _amphitrite_ are the two most variable species in the genus, more especially in the important characters derived from the opercular valves, and knowing that these species are attached so very frequently to ships' bottoms, one is led to suspect that their extreme tendency to vary may be due to their being exposed to varying and peculiar conditions, whilst transported to new and distant localities. It is even just possible, as may be inferred from the facts given in the Introduction (p. 102) in regard to certain monstrous specimens of _Bal. balanoides_ having been apparently impregnated by adjoining individuals, that the varieties may interbreed, and so produce numerous intermediate forms. Whether or not this could take place, I am inclined to look at these two species, as in an almost analogous condition with our domestic animals, which give rise to such infinitely numerous varieties. It appears to me probable, that several of the varieties keep true to their peculiarities, as long as they continue to breed in the same locality; but that when their larvæ become attached to ships' bottoms, and are thus transported and exposed to new conditions, they give rise to new and ever-varying varieties. I will first give a full description of the more common forms of _B. tintinnabulum_, which undoubtedly belong to the same species, only alluding to the less frequent points of difference, and then separately describe the more marked varieties.
_General Appearance._--Shape of shell generally tubulo-conical, or conical, or globulo-conical, rarely depressed. Orifice either large and rounded-trigonal, or small and oval, either entire or less frequently toothed. Surface quite smooth, or longitudinally ribbed; ribs of variable strength, not unfrequently flexuous or branching, sometimes roughened with blunt or sharp projecting, irregular points, or more rarely with almost cylindrical, upturned, long spines; the simple longitudinal ribs are generally most strongly marked in young specimens. _Colour_, generally varying from pink, to pink tinged with purple, to dark, inky purple, more or less striped, longitudinally, with white or pale tints; rarely the shell is of the brightest rose-colour, either uniform or longitudinally striped; sometimes it is pale purplish, or dark blue; and sometimes dark chocolate-purple: the ribs, when present, are generally more or less white, sometimes snow-white. That there is much variation in colour, and in the prominence of the longitudinal ribs, is quite certain, as the two sides of the same individual sometimes differ greatly in these respects. The radii are generally rather darker coloured than the parietes, but sometimes they are lighter, even in the darkest tinged specimens. The surfaces of the radii are occasionally finely plaited in lines parallel to the basis. In some infrequent varieties the radii have oblique summits, making the orifice of the shell to be toothed. The sheath is generally feebly coloured, but sometimes bright chesnut-brown, and sometimes blueish. The _strength_ of the shell varies considerably; some of the globulo-conical varieties are extremely massive. _Size_; basal diameter of largest specimen very nearly three inches; height of the highest specimen three inches.
Young specimens are apt to have a peculiar aspect; for their shell is often strongly ribbed longitudinally, and the summits of their radii are sometimes oblique. Their scuta are sometimes deeply pitted in radiating lines. Their colours are generally pale. I have seen specimens attached to kelp from the Cape of Good Hope, with their parietes white and ribbed, and their radii mottled with pinkish-purple; I have seen other young specimens from the Galapagos Archipelago, of a uniform grayish-blue. The _Scuta_ generally have their lines of growth moderately prominent; occasionally they are longitudinally striated, with the lines of growth flexuous and upturned at intervals into small, sharp, hood-liked projections, which are symmetrically arranged in straight lines radiating from the apex of the valve; I have seen this structure in some specimens of _var. crispatus_ and in _var. occator_ (Pl. 2, fig. 1 _b_); and I have noticed an intermediate state in _var. communis_. The degree to which the basi-tergal corner of the valve is rounded off varies much even in _var. communis_ (Pl. 2, fig. 1 _a_, 1 _d_, 1 _e_). The articular ridge (1 _c_, 1 _e_) is broad and much reflexed; and often, but not always, distinctly hooked (1 _f_). The adductor ridge is confluent with the articular ridge, and runs straight down the valve, bounding the cavity for the depressor muscle; generally the adductor ridge is blunt, and so little prominent as barely to deserve notice; but I have seen it sharp and prominent in one specimen of _var. communis_, and it is generally prominent in _var. coccopoma_ (1 _f_), and most remarkably so in _var. concinnus_ (1 _g_). The cavity for the lateral depressor muscle is generally very slight; but in the two vars. just mentioned, and sometimes in _var. communis_, it is deep. In _var. concinnus_ (1 _g_) there is a remarkable plate developed for the attachment of the rostral depressor muscle. The scuta are coloured either dull-purple or reddish, or striped longitudinally white and blue. The surface is sometimes externally depressed in the line of the adductor ridge; and in young specimens there is sometimes, along this line, a chain of pits (1 _h_), as in full-grown specimens of _B. trigonus_ and _lævis_.
The _Tergum_ (Pl. 2, figs. 1 _i_ to 1 _o_) is broad, with a generally closed longitudinal furrow; this furrow is open in young specimens, and it is often, but not always, open in rather large specimens of _var. occator_; it is always open in _var. d'Orbignii_ (Pl. 2, fig. 1 _m_), and sometimes in _var. concinnus_. Apex barely beaked, except in _var. spinosus_, in which it is sensibly produced. Spur placed either very nearly in the middle of the basal margin, or when least medial, it stands at above its own width from the basi-scutal angle; yet in some specimens of _var. occator_ the spur is less than its own width from this angle. The basal margin (1 _i_), on opposite sides of the spur, either forms a nearly straight line, or the scutal portion descends lower than the carinal portion, and curves very regularly towards the spur; this is the case in _var. d'Orbignii_ (1 _n_), and in some specimens of _var. occator_. The carinal half of the basal margin generally forms an angle with the spur of only a little above a rectangle. The spur varies a little in length and breadth, but never exceeds one fourth of the greatest breadth of the valve. The scutal margin is broadly inflected, the inflected portion forming either a right angle, or somewhat less than a right angle, with the exterior surface of the valve. Internally the articular ridge is prominent, and is either considerably or slightly curved; it extends down either about half, or three fourths, of the length of the valve. The spur is produced for a considerable distance up the internal surface of the valve as a prominence. The crests for the tergal depressor muscle are very feeble. In one specimen, in which both the shell and operculum had undergone much disintegration, the scuta and terga were calcified together.
_Compartments_: their exterior appearance has been already described. The parietal tubes are not large; they are generally crossed by transverse septa in their uppermost part; but they are sometimes almost solidly filled up by dark shelly layers. The internal surface of the parietes is more or less plainly ribbed; in old specimens, however, it generally becomes smooth. The _radii_ have their septa denticulated on both sides; and they are porose, that is, the interspaces between the septa are not filled up solidly. The radii generally extend from tip to tip of the adjoining compartments, that is, their summits are parallel to the basis; but in three not common varieties, viz., _vars. intermedius_, _occator_, and _d'Orbignii_ (the former of which at least must, without the smallest doubt, be ranked as a mere variety), their summits are oblique. I have occasionally met with specimens of _var. communis_ with oblique radii; and this is not very infrequent in young shells. Exteriorly the radii are generally smooth, but sometimes finely ribbed horizontally, owing to the projection of the septa. The _alæ_ have their sutural edges smooth; their summits are usually parallel to the basis, but they are often much broken; in _var. zebra_, however, in every specimen which I examined, the summits were oblique. The sheath varies much in colour: in _var. occator_, and in a less degree in _var. intermedius_ and _var. d'Orbignii_, the portion lining the rostrum and lateral compartments is much darker than the other parts of the sheath. The _Basis_ generally has a thick, underlying, cancellated layer. Sometimes the basis (Pl. 1, fig. _b_) is irregularly cup-formed.
_Mouth_: labrum with four or six minute teeth: mandibles with five graduated teeth; inferior point more or less spinose. Maxillæ, either with or without a small notch, beneath the upper pair of spines; in the lower part there are two spines longer than those immediately above them. _Cirri_, the first pair has the rami unequal, in the proportion of about 19 segments in the longer ramus, to 16 in the shorter. The segments in the latter have their anterior surfaces very protuberant. The second pair is short, with the anterior surfaces of the segments protuberant. On the thorax (Pl. 25, fig. 1), on each side, at the bases of third pair of cirri, there is a projecting membranous plate fringed with fine bristles. The three posterior pairs have their segments shield-shaped in front, generally bearing four pairs of spines, of which the lower pair is minute; between these pairs there are some minute spines. In some young specimens from the Cape of Good Hope, and in _var. concinnus_, I found six pairs of spines on the segments of the posterior cirri.
_Geographical Distribution._--This species is extremely common over the whole of the warmer seas. It ranges from the Island of Madeira to the Cape of Good Hope, and on the west coast of America, from Monterey, in lat. 37° N., in California, to Peru. It is attached to rocks and sub-littoral shells, to floating timber, to kelp, and to _Lepas anatifera_. It is attached in wonderful numbers to ships' bottoms arriving at our ports, from West Africa, the West Indies, the East Indian Archipelago, and China. It is generally associated with _B. amphitrite_ and _amaryllis_. I have already stated that, on the bottoms of vessels, the different varieties are generally grouped together; and this makes me believe that they are local. In Mr. Stutchbury's collection there are numerous specimens taken from a ship which first went to the west coast of Africa for guano, and then to Patagonia for the same object, and it was interesting to see the manner in which numbers of _B. psittacus_, a Patagonian species, had become attached on the African _B. tintinnabulum_. The varieties from the west coast of America seem eminently peculiar; we there find _var. coccopoma_ and _concinnus_; and a blueish, rugged variety, with peculiar opercular valves. _Geological History._--I have seen specimens in Mr. S. Wood's collection from the Red Crag of England, which, though not accompanied by opercular valves, I cannot doubt belong to this species. The specimens named by Mr. Sowerby, in the 'Mineral Conchology,' as _B. crassus_, and which I have seen through the kindness of Mr. J. de C. Sowerby, also belong to this species. I further believe that a specimen in Sir C. Lyell's collection, given to him by M. Dujardin under the name of _B. fasciatus_ from Touraine, is likewise _B. tintinnabulum_.
_Varieties._ With respect to _var. communis_, I have nothing to remark. The second, _var. vesiculosus_ (Pl. 2, fig. 1 _h_), is confined to young specimens, and may, perhaps, be due to a want of calcareous matter. With respect to _var. validus_ (Pl. 1, figs. 1 _c_, 1 _f infra_), I may observe that some of the coarsest and strongest specimens which I have seen were said to have been attached to a surface of iron. I have seen two large lots of _var. zebra_ (1 _g_), taken by Mr. Stutchbury, from the bottoms of ships, arriving from Bengal and China, and in both cases associated with _var. communis_, and in one case with _var. coccopoma_. I at first thought that this variety, _zebra_, was specifically distinct, but now I feel no doubt, that it is a mere variety; its body was in every respect identical with that of _var. communis_.
Nor have I any doubt that _var. crispatus_, of Schröter (Pl. 1, fig. _h_), is only a variety, although the scuta in some specimens have a peculiar appearance, externally like these valves in _var. occator_ (Pl. 2, fig. 1 _b_): the scutum is here broader and flatter than in _var. communis_, and the adductor ridge is very feebly developed, but we shall see how variable this ridge is in all the varieties: externally, the sharp, hood-like points formed by the upturned lines of growth, have a very remarkable appearance, from being arranged in quite straight radiating lines. This structure is evidently caused by the same tendency which produces on the walls the sharp, upturned, irregular points; but it is singular that the scuta are smooth in some specimens with very rough parietes; and, on the other hand, bristling with the symmetrically arranged, hood-like projections, in other specimens on which I could with difficulty detect only a few exceedingly minute points on the walls. In _var. communis_ I have seen a few specimens with a slight tendency in the scuta to become striated longitudinally. The tergum in _var. crispatus_ presents no difference from that in _var. communis_. Some of the roughest and best characterised specimens of _var. crispatus_ appear to have come off copper-sheathed vessels.
I believe _var. spinosus_ of Gmelin (Pl. 1, fig. _i_), has been correctly considered by me as a variety, but I have unfortunately seen only one set of specimens with their opercular valves preserved: these were attached to _Lepas anatifera_. The colour of the shell varies from reddish-purple to nearly white; the radii are sometimes quite white; the walls are slightly ribbed. The scuta in the above specimens, externally were smooth; the adductor ridge was rather more distinct from the articular ridge than in any other variety; and the terga rather more plainly beaked. The tubular, up-curved, calcareous spines sometimes occur only on one side of the shell, and often only in the lower part. These spines are often coloured brighter than the walls. Their presence cannot be accounted for (any more than the state of the scuta in the foregoing _var. crispatus_) by the nature of the surface to which they are attached; for I have seen one set attached to a large rugged specimen of _B. tintinnabulum_, and another to the very smooth valves of _Lepas anatifera_. I believe that this form is almost always associated with _var. communis_, which is an argument that it is only a variety.
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