A Monograph on the Sub-class Cirripedia · Charles Darwin
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LEPAS TESTUDINARIA. _Linn._ Syst. Naturæ, 1767. VERRUCA TESTUDINARIA. _Ellis._ Phil. Transact., vol. 50, 1758, Pl. 34, fig. 12. BALANUS POLYTHALAMIUS. _Bock._ Naturforscher, Stuch. 12, 1778, fig. 9. LEPAS TESTUDINARIA. _Poli._ Testacea Utriusque Siciliæ (1795) Tab. 5, fig. 9-11. CORONULA TESTUDINARIA. _Ranzani._ Memoire di Storia Naturale, Decade 1, (1820). ---- ---- _De Blainville._ Dict. des Sciences Nat., (1824), Tab. 117, fig. 2. CHELONOBIA SAVIGNII (?) _Leach._ Encyclop. Brit. Suppl., vol. 3, 1824. ASTROLEPAS ROTUNDARIUS. _J. E. Gray._ Annals of Philosoph. (new series), vol. 10, 1825. _Shell conical, depressed, heavy: radii rather narrow, depressed, generally notched on both sides._ _Hab._--Mediterranean; west coast of Africa; north-east coast of Australia; Low Archipelago, Pacific Ocean; west coast of Mexico, 23° N. Attached to turtles. It is impossible to feel sure which of the three species of the genus Linnæus had in view, when describing his _Lepas testudinaria_; but as Spengler has well discriminated the following species under the specific name of _caretta_,[123] and Ranzani the third species under _patula_, the present name may, without question, be retained for the following species. In several respects this species is intermediate between _C. caretta_ and _patula_, but it can most conveniently be described first. [123] I am indebted to Dr. J. E. Gray for having guided me to this identification.
_General Appearance._--Shell strong, globulo-conical, depressed; outline broadly oval; surface smooth, generally well preserved, but when disintegrated, upper part finely striated; colour dead white; orifice oval elongated, rather exceeding in length one third of the longer basal diameter of the shell. The radii are rather narrow, and deeply depressed; they have their summits square: their outer lamina, as explained under the genus, on both sides of each suture is in most specimens divided into teeth, the points of which face and touch each other. These teeth or notches give quite a peculiar appearance to the shell, and alone suffice to discriminate this species; they are sometimes blunt and partially obliterated, but it is rare to find a specimen in which some few teeth do not occur in some one of the six radii. I have, however, seen two or three specimens with all six radii perfectly smooth; in one of these the general shape of the shell, without the aid of any internal characters, almost sufficed to show that it belonged to the present species; but in another specimen, which had unusually narrow radii, and the whole surface of which had undergone considerable disintegration, and was consequently striated, could only be distinguished from _C. caretta_ by internal characters. I have seen several specimens having very irregularly shaped compartments, but generally the appearance of the whole shell is highly symmetrical, like a star; and the genus was appropriately named by old Klein, _Astrolepas_. In some specimens, in Mr. Cuming's collection, from the Low Archipelago, in the Pacific, taken off the toe-nail of a turtle, the shape was almost cylindrical; the shell almost resembling that of _Coronula diadema_. The largest specimen which I have seen was 2.3 of an inch in basal diameter, but only .55 in height.
_Structure of Shell and Radii._--After the full generic description, the only point to which I need allude is, that the radiating, parietal septa, as well as the descending sheath, are much thicker than in _C. patula_, and that their basal edges can be plainly seen by the naked eye to be dentated with numerous points. The thickness of these plates and of the sheath varies considerably. In _C. caretta_, I may add, the plates are broken up into many separate points, and in this species the descending sheath is not generally perforated, excepting at the sutures, by loop-holes for the entrance of ribbons of corium. The sheath and inner lamina of the parietes in _C. testudinaria_, taken together, fully equal one third of the entire thickness of the walls. Flattened cavities or tubes run up between the parietal septa for about two thirds of the height of the inside of the shell. With respect to the radii, I have only to add, that the thickness of the inner portion relatively to the generally notched outer lamina, varies considerably. _Opercular Valves_ (fig. 1 _b_-1 _d_).--These closely resemble each other in all three species, and have been almost sufficiently described under the genus. The scutum has its occludent margin always sinuous, but to a variable degree. In one specimen there was a deep little pit at the rostral end for the rostral depressor muscle. The terga vary considerably in shape, according as the basi-carinal corner is more or less truncated. The external furrow, marking the position of the rudimentary spur, varies much in distinctness, chiefly depending upon its nearness to the carinal margin of the valve.
_Mouth and Cirri._--The labrum sometimes has its teeth worn away. The second pair of cirri, relatively to the others, is shorter and thicker than in the two following species. 2. CHELONOBIA CARETTA. Pl. 14, fig. 2. LEPAS CARETTA. _Spengler._ Skrifter, Naturhist. Selbskabet, Bd. 1, 1790, Tab. 6, fig. 4. BALANUS CHELYTRYPETES. _Hincks_ (!) sine descript., Annals of Nat. Hist., vol. 5, p. 333. CORONULA SULCATA. _Chenu._ Illust. Conch., Tab. 1, fig. 1. _Shell globulo-convex, extremely massive and heavy; upper part worn, sub-striated: radii either not developed or very narrow: parietes without cavities extending up between the interrupted, radiating septa._ _Hab._--West coast of Africa; northern Australia; common. Attached to, and generally imbedded in, the carapaces of turtles. _General Appearance._--Shell extremely strong, massive, heavy, broadly oval, globulo-convex, though sometimes depressed; dirty white: surface in the upper part always worn and disintegrated, hence finely striated; in the lower part a little rugged, slightly folded, and occasionally, in deeply imbedded specimens, much folded or ribbed. Orifice oval, not at all angular, rather exceeding in length one third of the basal diameter of the shell. Radii either not at all developed, or very narrow; but even in the former case the six lines of suture are plain; and in the latter case the radii lie at some depth beneath the surface of the shell. It is remarkable that the compartments are hardly ever arranged symmetrically, the rostrum and carina not facing each other exactly; and this holds good in specimens attached separately, without any apparent cause for this want of symmetry. The largest specimen which I have seen was 2.1 in basal diameter; and this, which was a steeply conical individual, was 1.1 in height; and therefore nearly twice as high as an ordinary large specimen of _C. testudinaria_.
_Structure of Shell and Radii._--The descending sheath and radiating septa are of very variable thickness, and have their basal edges finely dentated. The septa are not continuous, from the circumference to the sheath, in unbroken plates, but are irregularly divided into separate, often short portions, and even occasionally into mere points. The sheath differs from that of the other two species in having loopholes for the entrance of ribbons of corium only on the eight lines of suture, and not (with rare exceptions) in the middle of each compartment: this is evidently due to fewer filaments of corium being here sufficient to supply the less deep interspaces between the radiating septa; for in this species there are no flattened cavities or tubes running far up the shell. The inner lamina of the walls cannot be here distinguished, for a solid, flat, calcareous surface extends from the circumference, between the radiating septa, to the sheath. The sheath, had it not been from the light thrown on this part by the other species, would have certainly been mistaken for the inner lamina of the walls. The absence of the flattened cavities or tubes extending up the parietes, seems to be the least varying character; and serves to distinguish this species from those worn and massive specimens of _C. testudinaria_, which have narrow and not-notched radii.
In specimens in which the radii are not developed, no vestige of the outer lamina can be detected, the lateral faces of the adjoining compartments being closely pressed together; but in specimens in which the radii have been developed and have grown, the outer lamina of course is present, and is extremely thick, with the growing edge having a branched and mammilated surface, as in _C. testudinaria_, but with the external surface not pitted or notched as in that species. The inner portion of the radius, whether or not developed, has nearly the same appearance, consisting of rather thick transverse septa, branching from a central ridge, which is sometimes obscure. The _Alæ_ are remarkably little prominent, as least in those specimens in which the radii are not developed, so that Spengler seems to have thought that the structure of the shell was essentially different from that of Balanus, which certainly is by no means the case. The edges of the alæ are very thick, nearly as thick as the inner portion of the radius. The _Opercular Valves_ hardly present any essential difference, compared with those of the other species; but the occludent margin of the scutum is apt to be more sinuous, and its rostral end blunter and squarer. The carinal end of the tergum is also squarer than in any common variety of _C. testudinaria_; the external furrow or spur, near the carinal margin, is very indistinct, and even sometimes is quite absent.
Neither the mouth nor cirri present any deviations from the generic character. 3. CHELONOBIA PATULA. Pl. 14, fig. 3 _a_, 3 _b_, 4. CORONULA PATULA. _Ranzani._ Memoire di Storia Naturale (1820), Tab. 3, fig. 25-28. ASTROLEPAS LÆVIS. _J. E. Gray_ (!). Annals of Philosophy (new series), vol. 10, 1825. VERRUCA CANCRI AMERICANI. _Ellis._ Phil. Trans., vol. 50, 1758, Pl. 34, fig. 13. _Shell steeply conical, very smooth and light; orifice large, generally exceeding half the basal diameter of the shell: radii broad, smooth, only slightly depressed._ _Hab._--Mediterranean; Gambia, West Africa; Charlestown; Jamaica; Honduras; Brazil; Australia. Attached to Crustacea, smooth univalve shells, and apparently to ships' bottoms. _General Appearance._--Shell white, very smooth, of little specific gravity, steeply conical, but not high; orifice broadly oval, polygonal, very large, namely, generally exceeding half the basal diameter of the shell. The summits of the compartments are usually perfectly preserved, pointed, and often a little recurved. The radii are rather broad, very smooth, with their summits slightly oblique and arched: they are seated only a little below the general level of the parietes. I have seen one specimen rather more than one and a half inch in basal diameter, but this is an unusual size; this species not growing to so large a size as the two foregoing forms.
_Structure of Shell and Radii._--The walls are here thinner than in the two foregoing species; and the basal surface of a compartment rarely equals half the basal diameter of the internal cavity of the shell, measured transversely to its longer axis. The radiating septa are also much thinner, generally sinuous, and so finely dentated along their basal edges, that the teeth can be clearly perceived only by the aid of a lens. The interspaces between the septa run up to nearly the summits of the compartments, and hence the lightness of the whole shell. The inner lamina of the parietes is here not so thick (fig. 4), and is more distinct from the descending sheath than in the foregoing species. The sheath is thin, like the radiating septa; the medial loophole in each compartment, for the entrance of a filament of corium, is much wider than in _C. testudinaria_, for it is generally as wide as the bordering plate on either hand; and in not a few specimens, the medial loophole is so wide as hardly any longer to deserve being so called, for the descending sheath is reduced to mere flattened pillars or legs on the sides of the sutures. Although the parietes are here not nearly so thick as in the two foregoing species, yet as the radii stand but little beneath the level of the parietes, the outer lamina of the radius has a considerable thickness, and is sometimes separated from the inner portion of the radius by an interval, in the same manner as in _C. testudinaria_; and the growing edges of the outer lamina exhibit traces of the same mamillated structure as figured in that species.
The _Opercular Valves_ are apt to be rather narrower and more elongated than in the foregoing species, with the occludent margin of the scutum generally, but not always, only slightly sinuous: externally the scutum is sometimes feebly striated longitudinally. In the tergum (Pl. 14, fig. 3 _b_) the longitudinal furrow is generally plainer, from being more distant from the carinal margin, and the rudimentary spur itself is more prominent. The mandibles usually have five narrow teeth; but I have seen one specimen having only four teeth, and with the inferior angle truncated. The cirri present no particular character.
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