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.
Basis.—The base is either saucer or cup-shaped, but in A. cyathus it is almost flat; it is generally symmetrical and smooth, with the lines of growth closely approximate. In A. fenestrata the basis is commonly as deep, as the shell is high. The edge, in several of the species, is crenated with minute teeth or notches; and these are so large in some specimens of A. sulcata and cyathus, as to make the edge almost pectinated. In A. glans, and in a lesser degree in A. lævigata, there are six knob-like teeth (fig. 5 a), corresponding with the points of junction, between the basal edges of the inwardly prominent margins of the six compartments, and the basis: in those specimens, in which the six teeth are largely developed, six ridges produced by their successive development, extend down towards the centre of the basal cup. When the basal cup is dissolved in acid, there is but a little animalised tissue and an external membrane, formed as usual in slips, and furnished with blunt little external points (apparently representing spines), each of which has a short tubulus extending to the corium. Although I dissolved the basis of three specimens, I could not distinctly make out any cement; nor did I see any cement-ducts; yet these are readily distinguished, after the dissolution of the basis in acid, in Balanus, Elminius and Tetraclita. There can be no doubt that the young shell must at first be cemented to a fibre of the sponge; but I suspect that the cementing-tissue is not subsequently formed, owing to the support afforded by the growth of the enveloping sponge. As some species of Balanus are habitually or occasionally imbedded in sponges, it is important to observe, that the species of Acasta are not only imbedded, but are attached to the fibres of the sponge: but even this character, as we have already seen, is not sufficient to distinguish the genus Acasta from Balanus, for B. declivis is attached exclusively to sponge.
Perforations in the Shell.—Calcification seems often to fail to a certain extent in this genus: the basal cup in most specimens of A. spongites, and in some of A. glans and other species, is irregularly perforated by numerous minute orifices, closed only by the external membrane, and filled up inside by pulpy corium. In some specimens of A. spongites, from the Cape of Good Hope, parts of the basis were riddled like a sieve. I have seen similar perforations in the parietes of a few specimens of A. glans. In some specimens of A. sulcata, the radii do not extend quite down to the basal edge of the walls (Pl. 9, fig. 2 a), and in consequence a small cleft, closed only by membrane, is left between the compartments, for a little space above the basal cup. In A. fenestrata (fig. 7 a), and in a lesser degree in A. purpurata (8 a), not only do the radii not extend to the basal cup, but the parietes either on one or both sides of each suture are hollowed out, so that six, large or small, elongated, membrane-covered openings are formed, which extend from beneath the sheath down to the basal cup. These openings, which I have not seen in any other genus, will be more fully described under the respective species.
Mouth.—The parts of the mouth are identical in the several species, and present no generic differences from those in Balanus. The outer maxillæ and palpi appear unusually prominent: the labrum is deeply notched, with no teeth, or very obscure teeth on each side. The mandibles have five teeth, but the fifth is sometimes confluent with the inferior angle. The maxillæ are not notched; and carry one or two spines, near their inferior angle, nearly as large as the upper pair. The outer maxillæ are bilobed.
Cirri: in the first pair, the rami are very unequal in length, the one ramus being from half to one-third of the length of the other. The segments in the second and third pairs, are not so much broader, or so much more crowded with bristles, in comparison with the three posterior pairs, as is the case with most species of Balanus. The three posterior pairs, except in A. purpurata, are much elongated, and the long thin segments bear four, and sometimes only three, pairs of spines, which are generally doubly and finely serrated, or even feathered. The most remarkable fact respecting the cirri, is, that in A. spongites, sulcata, cyathus, and glans, the fourth pair, instead of being identical in structure, as in all other genera, with the fifth and sixth pairs, has, on its anterior ramus, the pairs of spines more crowded together, with the little intermediate spines, and those in the dorsal tufts, a little longer than in the sixth cirrus; and between the pairs of spines, there occur some straight, upwardly pointed, very minute, and very thick spines or teeth. And, what is still more remarkable (as will hereafter be described in detail), in certain specimens, but not in all, of A. sulcata, the front surfaces of the lower segments on the anterior ramus, are developed into thick, small, downwardly curved, hook-like teeth; this likewise is the case with the upper segment of the pedicel (Pl. 29, fig. 2),—a most elegant, mandible-like organ for the prehension of prey being thus formed. The variability of such beautifully contrived teeth is very surprising. Some similar teeth occur on the segments of the anterior ramus of the fourth cirrus, but not on the pedicel, in A. cyathus. A few teeth resembling the above, but thicker, occur on the segments of the anterior ramus of the same cirrus, in A. purpurata.
Branchiæ, &c.—In A. spongites, I found the branchiæ rather small, with transverse plications. The muscles of the sack, which run to the opercular valves, seemed rather feeble in most of the species. The penis in several species was remarkably long, and in A. spongites I noticed the straight projecting point at its dorsal base, as is common in Balanus.
Affinities, &c.—At the commencement of the description of the genus, I gave my reasons for keeping Acasta distinct as a sub-genus from Balanus. The species are particularly troublesome to identify, not only from the great variability of the most obvious characters, but from the very close general external appearance of most of the species, and the consequent necessity for cleaning and disarticulating at least one specimen in every group. The shape, however, of the shell and basis, and the state of their disarticulated edges, whether smooth, crenated, or toothed, here offer more serviceable, though still very variable, characters for the identification of the species, than is usual with sessile cirripedes; and this, probably, is in part due to the almost free or unattached condition of the whole shell, suspended, as it were, in the midst of sponges, which they inhabit. The opercular valves, on the other hand, are less serviceable than usual.
Range, Habitats, &c.—The species are found all over the world, excepting in the very cold latitudes.[102] Acasta lævigata ranges from the Red Sea to the Philippines; A. spongites from the south of England and Wales to the Cape of Good Hope; and A. cyathus from Madeira to the West Indies; most of the other species seem to have rather confined ranges. The East Indian Archipelago seems to be the metropolis of the genus, for here A. lævigata, fenestrata, purpurata, and sporillus, are all found. Of these four species, A. purpurata lives imbedded, not in sponges, but in the sponge-like bark of an Isis; and I think it probable, that A. sporillus may have somewhat analogous habits. The same species often lives imbedded in different kinds of sponge; thus, I have seen A. lævigata and cyathus in apparently three kinds, and A. spongites in, as I believe, four kinds. The genus existed during the miocene period, in the Coralline Crag, under a form closely allied to A. spongites.
[102] I am greatly indebted to Mr. Bowerbank for his great kindness, in looking over his immense collection of sponges from all parts of the world, and sending to me all the specimens of Acasta he could find imbedded in them.
LEPAS SPONGITES. Poli. Testacea utriusque Siciliæ, 1795, Tab. 6, fig. 3-6.
BALANUS SPONGEOSUS. Montagu. Test. Brit. Suppl., 1808.
------ SPONGITES. De Blainville. Dict. Sc. Nat., Pl. 116, fig. 3.
LEPAS SPONGIOSA. Wood’s General Conchology, p. 47.
ACASTA MONTAGUI. Leach, in Lamarck, Animaux sans Vertèbres, 1818, et in Encyclop. Brit., Supplement, 1824, vol. 3, Pl. 57.[103]
------ ------ J. E. Gray. Annals of Philosophy, New Series, vol. 10, Aug. 1825.
------ SPONGITES. Philippi. Enum. Mollus. Siciliæ, vol. 2, p. 211, 1844.
BALANUS MONTAGUI. Brown’s Illustrations of Conchology (2d edit. 1844), Pl. 53, fig. 24-26.
[103] As the plate to the Supplement to the ‘Encyclop. Brit.’ is marked as engraved in 1817, I presume Dr. Leach gave a proof to Lamarck, thus enabling him to publish this species four years before the Supplement itself appeared.
Carino-lateral parietes about one sixth of width of lateral parietes: inner surface of the parietes generally ribbed feebly: scutum with the articular ridge abruptly cut off at its lower end: tergum with the spur rounded-truncated, about one third of width of valve.
Hab.—South coast of England; South Wales, (Tenby); Portugal; Naples; Sicily; Cape of Good Hope.
This species and the three following, have caused me much doubt and trouble. At first I took the view here adopted, namely, that they were distinct: more careful examination made me run them altogether under one name. Finally, after still further deliberation, and the examination of a few additional specimens, I concluded there was the least chance of error in classing them separately. I may here mention, that in some sponge from the Cape of Good Hope, this species was mingled with Balanus spongicola.
General Appearance.—The shape is usually that of a cup, the orifice being, in most cases, rather large, and deeply notched, owing to the great obliquity of the radii and alæ. The surface is generally smooth, but furnished with sharp calcareous projections. The colour is pinkish, and chiefly in the upper part of the shell; the lower part is often yellowish from the preserved epidermis. The parietes in the carino-lateral compartments are always narrow, being only one sixth or one seventh of the width of the parietes in the lateral compartments. The radii are not very wide, never equalling in width the parietes. The basis is moderately deep, and sometimes very deep, being even occasionally curled like a horn on one side. The specimens from Lisbon and Naples are a little larger than any British specimen which I have seen; the former being .3 of an inch in basal diameter.
Scuta: these are striated longitudinally in close lines, generally plainly, but to a variable degree. The whole valve is flat, thin, and rather elongated, with barely a trace of an adductor ridge: the articular ridge is short and rather prominent: it terminates downwards abruptly, and this does not appear to be the case in the two following species. Terga: these are small compared with the scuta, they are slightly beaked: the spur is truncated but rounded, more especially on the carinal side; it is rather more than one third of the width of the whole valve. The articular ridge and crests for the depressor muscles are feebly developed.
Structure of the Parietes and Radii.—The state of the inner surface of the parietes varies much; generally they are slightly ribbed close to the basis, the ribs sometimes extending up to the sheath; rarely the surface is quite smooth. The edges of the radii are slightly crenated. The upper internal surfaces of the radii, where overlying the alæ, are usually marked by feeble undulating lines, nearly parallel to the basis. The alæ have very oblique summits.
Basis: this is generally of a regular cup-like form, and about two thirds as deep as the shell is high; sometimes it is pointed at the bottom and distorted. The edge is feebly crenated, and rarely quite smooth. It is often penetrated by small rounded irregular holes; and I have seen specimens from the Cape of Good Hope with parts like a sieve.
Cirri: in the first pair, the anterior ramus is nearly thrice as long as the posterior ramus. The second cirrus is short, with one ramus longer by three or four segments than the other ramus; the terminal segments are truncated. The third cirrus is about one third longer than the second cirrus. In the anterior ramus of the fourth pair, the regular pairs of spines are rather crowded together in the upper part of each segment, and the intermediate little spines and dorsal tufts are rather long in comparison with those of the fifth and sixth pairs of cirri: moreover, amongst the regular pairs, a few very minute and thick spines, pointing upwards, could be perceived. So that we here have the very unusual case of the fourth cirrus not exactly resembling the fifth and sixth pairs; and we shall see, in the following species, that this same anterior ramus of the fourth cirrus presents in addition another very extraordinary character. In the sixth cirrus there are on each segment four pairs of spines.
ACASTA SULCATA. Lamarck. Animaux sans Vertèbres, 1818.
------ ---- Deshayes, in Guerin, Magasin de Zoologie, 1831, Tab. 24.
Carino-lateral parietes about one sixth of width of lateral parietes: inner surface of the parietes generally ribbed strongly: basis with the edge strongly crenated: orifice of shell rather small: tergum with the spur generally truncated and nearly half as wide as valve.
Var. (a) (fig. 2 b): with the walls externally ribbed.
Var. (b) (fig. 2 a): with small membrane-covered clefts between the edges of the walls, close above the basal cup.
Hab.—Sydney, Port Fairy, Moreton Bay in lat. 27° S., New South Wales; Southern Australia; and, according to Lamarck, Western Australia, in lat. 25° S. Mus. Brit., Cuming, Bowerbank, &c.
I am almost ashamed to admit this species, so small are its differences compared with A. spongites; yet I think that it probably is a distinct form.
In general appearance and character this species comes very near to A. spongites. As in the latter, the parietes of the carino-lateral compartments are narrow.[104] The orifice seems always to be smaller. Internally, the parietes are generally much more strongly ribbed, and the edges of the basal cup more plainly crenated. The sheath is generally coloured of a brighter pink, sometimes tinged with orange. The average largest specimens (from .3 to .5 of an inch in basal diameter) are a little larger than the largest European specimens: I have seen one specimen from Moreton Bay .4 in basal diameter, and from the basal cup being very deep, actually .75 in height. The scutum has the articular ridge not so prominent and not so abruptly cut off at the lower end, as in A. spongites: on the other hand, the adductor ridge seems rather more prominent; but these differences are trifling. In the tergum the breadth of the spur (fig. 2 c, 2 d) varies in specimens taken out of the same branch of sponge; some can hardly be distinguished from the same valves in A. spongites, but generally the spur is broader and squarer.
[104] In Mr. Cuming’s collection there is a specimen, from Sydney, which I fully believe to be the present species, but cannot be positively sure, as the opercular valves have been lost, which is very remarkable from the walls of the carino-lateral compartments being reduced to the thickness of a mere thread, not one twentieth of the width of the lateral compartments; we here see the structure of Acasta sporillus prefigured.
This species presents some remarkable varieties: in one specimen, from Sydney, the parietes were externally ribbed longitudinally (fig. 2 b), the ribs being roughened with minute points, giving to the shell an elegant appearance; and this without doubt is the A. sulcata of Lamarck, procured by Peron at Shark’s Bay, lat. 25° S., on the opposite of the Australian continent: some specimens from Port Lincoln, in South Australia, were not ribbed, only smoothly striated in longitudinal lines; although both sets of specimens had almost smooth scuta, and were thus different from common specimens, yet there could be no doubt, from their similarity in all other points, that they did not differ specifically from them, though the latter had their scuta striated, but not their parietes. Hence we see that there is no relation between the striæ on the parietes and on the scuta. The Port Lincoln specimens, and some others, were remarkable from the radii not extending down to the basal cup, a minute cleft, covered only by membrane, being thus left along the sutures, low down between the parietes (fig. 2 a); we shall see this singular structure strongly developed in A. perforata. Owing apparently to these clefts, the edge of the basal cup, exhibited traces of six knob-like teeth, like those characteristic of A. glans.
Cirri.—The cirri resemble those of A. spongites, with the exception that the segments on the posterior pairs bear only three main pairs of spines. With respect to the anterior ramus of the fourth pair of cirri, the following very singular facts were observed:—in a specimen from New South Wales (var. with the tergum having a narrow spur), on two or three of the lower, but not on the lowest, segments, the front margin was produced or developed into two or three minute, thick teeth, slightly curved like hooks downwards: in other specimens from New South Wales (var. with the tergum having a broad spur, and inhabiting the same branch of sponge with the last-mentioned variety), there was no trace of these teeth. But again, in two other specimens with the tergum having a broad spur (collected by different persons, near Sydney), and in another from South Australia, this structure was carried to an extreme, for in these (as represented, Pl. 29, fig. 2) there were beautifully formed teeth on the fourteen lower segments (the twelve upper being without them), and likewise on the upper segment of the pedicel. These teeth are graduated in size on each segment; they are admirably adapted for securing any prey; and, in fact, they convert each segment into a mandible-like organ. On the segments, on which these teeth are well developed, some of the regular pairs of spines are aborted.
Diagnosis.—Finally, this species, if it be, as I believe, distinct, differs from A. spongites only in the internal surface of the parietes being more strongly ribbed and brighter coloured,—in the edge of the basal cup being more plainly crenated,—in the articular ridge of the scutum being of a different shape,—in the spur of the tergum being often broader,—in the segments of the posterior cirri having only three pairs of main spines,—and, lastly, in the occasional presence of the hook-like teeth on the anterior ramus of the fourth cirrus.
Carino-lateral parietes about one fourth of width of lateral parietes: radii wider than the parietes: basis nearly flat, small: tergum with the spur truncated, half as wide as valve.
Hab.—Madeira, Mus. Lowe, and Bowerbank. West Indies, Mus. Stutchbury. Hab. unknown, Mus. Brit.
I feel more confidence in this case, than in that of A. sulcata, that we here have a distinct species, though at one time I treated it only as a marked variety of A. spongites. I rely chiefly on the great proportional width of the radii of all the compartments, and on the width of the carino-lateral compartments, compared with the lateral compartments, and on the general shape of the shell, which differs considerably from that of the two previous forms: in consequence of Acasta being attached to and imbedded in a yielding substance, such as sponge, I believe external form to be of more value as a specific character in this genus, than in most sessile cirripedes. I have examined specimens taken out of the yielding Spongia officinalis and out of an unusually compact sponge, and they resembled each other in every respect.
General Appearance.—Colour pale pink, or that of flesh: basis remarkably flat and rather small, with the walls above bulging out a little. The radii are very wide, being wider than the parietes to which they belong: the orifice is generally rather large. The parietes of the carino-lateral compartments vary from one third to one fourth of the width of the parietes of the lateral compartments. Basal diameter of largest specimen .35 of an inch. Internally, the parietes are generally more strongly ribbed than in A. spongites.
The Opercular Valves are large, owing to the form of the shell. The Scuta present no particular character, and are not distinguishable from those of A. sulcata; but the adductor ridge is perhaps rather more developed. The Terga (Pl. 9, fig. 3 c) are nearly as large as the scuta, and this is an unusual circumstance; the spur is more than half as wide as the valve; it is placed not quite close to the basi-scutal angle; on the carinal side, the basal margin of the valve slopes a little towards the spur. I may mention, that in several specimens from Madeira, the scuta and terga, on one side, had grown to a monstrous thickness.
Cirri: these resemble, in every respect, those of A. spongites, with the remarkable exception that on the anterior ramus of the fourth cirrus, several segments were furnished with the beautiful downward curved, mandible-like teeth, as in A. sulcata; but differently from in that species, there were none on the upper segment of the pedicel. I should have thought this an excellent specific character, had not these teeth been so extremely variable in A. sulcata.
Finally, I think this species is more nearly related to A. sulcata than to A. spongites.
Shell, apparently, as in A. spongites, but larger: scutum marked by longitudinal ridges, often in pairs, with the intermediate furrows rather wide: spur of tergum nearly half as wide as valve.
Fossil in Coralline Crag (Sutton), Mus. S. Wood.
I owe to Mr. Wood the inspection of a fine suite of separate valves. Owing to the shell never having been found entire, its general shape is not known, and, what is of more consequence, the relative proportional width of the parietes of the carino-lateral compartment is unknown. I have (but with doubt) given it a distinct specific name, owing to the peculiar character of the furrows on the scuta, and to the large size of the whole shell. In its other characters it comes nearest to A. spongites, excepting in the spur of the tergum, which resembles that of A. sulcata.
The compartments appear to have been rather smooth externally. The radii are not wide, as in A. cyathus; and the basis is cup-formed. Internally, the parietes are feebly ribbed, as in A. spongites. Judging from the dimensions of the separated valves, this species must have equalled and perhaps exceeded the size of the largest living species, namely, A. glans, from Australia. Hence we may infer, that the basal diameter probably exceeded .55 of an inch: I may add, that the largest European specimens of A. spongites, from Naples and Portugal, are only .3 of an inch in basal diameter.
Scuta.—These seem to resemble the scuta of A. spongites in all respects, except in the longitudinal ridges standing much further apart, and, consequently, in the furrows being much wider: each ridge is generally double. Although there is a good deal of variability in the character of these ridges in A. undulata, and likewise in A. spongites, I have not seen any form intermediate between them. It must, however, be confessed, that this is an extremely variable character in many sessile cirripedes. In the Terga, the spur is about half the width of the whole valve, and therefore rather wider than in A. spongites.
ACASTA GLANS. Lamarck. Animaux sans Vertèbres, 1818.
Parietes internally quite smooth, with the lateral margins of each compartment inwardly prominent: basis with the edge rarely crenated, but furnished with six inwardly prominent teeth: scutum strongly striated longitudinally.
Var. (a) with the edge of the basal cup finely crenated.
Hab.—New South Wales, Southern Australia; Mus. Brit., Stutchbury, &c.
This fine species seems to be extremely common, imbedded in an open porose sponge on the eastern and southern shores of Australia. It is very distinct from the other species, with the exception of the following A. lævigata, which, with some hesitation, I have allowed to remain specifically separated.
General Appearance.—Excepting in its larger size, this species differs in external appearance but little from A. spongites; its colour is pale dirty reddish. The surface is generally studded with small calcareous points. The parietes of the carino-lateral compartments are about one fourth of the width of the parietes of the lateral compartments, and therefore proportionally of the same width as in A. cyathus. The largest specimen which I have seen, was .55 of an inch in basal diameter.
Scuta.—These are slightly narrower, thicker, and more convex than in A. spongites: they are strongly striated in longitudinal lines. The articular ridge is very feebly developed. Terga: in full-grown specimens, the spur is half the width of the whole valve, and is truncated; its basal edge being parallel to the basal margin of the valve. The articular ridge and crests for the depressor muscles are very feebly developed.
Internal structure of the parietes.—The inner surface of the parietes is quite smooth, without even a trace of ribs or teeth. But the most important character is that the internal lateral margins on both sides of each compartment, from the sheath to the basis, project inwards and form a rim; so that when the shell is viewed from within (Pl. 9, fig. 5 b, representing the lateral and carino-lateral compartments, and part of the carina), the six sutures are seen to be strengthened by six double columns.
Basis.—This is moderately cup-formed. The edge, in order to meet the basal points of the inwardly projecting lateral margins of the six compartments, has six knob-like teeth. These are placed at unequal distances, for two on each side stand near each other, owing to the narrowness of the carino-lateral compartments. The degree of their development varies extremely; when most developed, as in the specimen figured (Pl. 9, fig. 5 a), each tooth is bifid and a little hollowed out, so as to receive the points of the two inwardly projecting margins which form each suture. Ridges, more or less prominent, running from each of the six marginal teeth, extend towards the centre of the cup. These six teeth cannot be seen from the outside. The edge of the cup is rarely crenated; but I have seen two instances in which this was the case.
Cirri.—In the first pair, the rami are not quite so unequal as in A. spongites; the longer ramus being about twice as long as the shorter. In the third pair, there are some very minute, thick, upwardly-pointing spines, which I did not notice in A. spongites. In the fourth pair, the spines are a little more crowded, with longer dorsal tufts, than in the sixth pair; and they are mingled with some very minute, thick, upwardly pointing spines. In young individuals, there are only three pairs of main spines on the segments of the sixth pair, instead of four pairs.
ACASTA LÆVIGATA. J. E. Gray (!). Annals of Philosophy, (new series), vol. 10, Aug. 1825.
Parietes internally quite smooth, with the lateral margins of each compartment inwardly prominent: basis with the edge strongly crenated, and furnished with six inwardly prominent teeth: scutum feebly striated longitudinally, or smooth.
Var. (a), epidermis coloured dull orange.—Red Sea.
Hab.—Red Sea, Philippine Archipelago; Mus. Brit., Cuming, &c.
This species, of which I have examined many specimens from the above two and other unknown localities, agrees in all essential points of structure with A. glans, and consequently I for some time classed them together; but the characters, though usually of small value, by which this form differs from A. glans being apparently constant, I have with some doubt allowed it to remain specifically distinct. These characters are, firstly, the much smaller size of the whole shell in A. lævigata; secondly, the edge of its basal cup being always crenated, which seems to be a rare accident in A. glans; thirdly, though of secondary importance, the scutum being here less plainly striated; and, lastly, the spur of the tergum being of less breadth, and of a more rounded outline; on the other hand, it must be confessed, that when small specimens of A. glans are taken, there is hardly any difference in the spurs of the terga.
General Appearance and Structure of Shell.—The surface of the shell is often very smooth, but is sometimes studded with some small sharp calcareous points. The colour is white, or pale reddish-brown; but in the specimens from the Red Sea, the tint is more orange, with the upper part of the shell white. The orifice of the shell is unusually small. The largest specimen which I have seen was only .25 of an inch in basal diameter, and therefore less than half the size of A. glans. The internal surfaces of the parietes are smooth, with the two lateral margins inflected, as in A. glans. The edge of the basal cup has six knob-like teeth, like those in A. glans, but smaller; and, in addition, it is finely crenated.
Scuta: these differ only in being less plainly striated in longitudinal lines; indeed, some specimens show hardly a trace of this structure. Terga; these valves, in some varieties (Pl. 9, fig. 6 b) can hardly be distinguished from those of equal size from young individuals of A. glans; other varieties have the spur (Pl. 9, fig. 6 a) not truncated, but broadly pointed, and therefore of considerably different shape.
Neither in the mouth, nor cirri could I detect any difference with A. glans.
Shell reddish, with six large, membrane-covered apertures between the sutures, above the basal cup: carino-lateral parietes half as broad as lateral parietes; internally, parietes and edge of basis smooth; tergum with the articular ridge short and prominent; spur pointed.
Hab.—Philippine Archipelago, Mus. Cuming.
General Appearance.—Shell rather elongated or tubular; with the upper part reddish, and the surface roughened with very minute points. The basal cup is generally as deep as the shell is high, ending downwards in a blunt point, often curved to one side. The summits of the radii, as usual, are oblique. The parietes of the carino-lateral compartments are about half as wide as the parietes of the lateral compartments, and are therefore of greater proportional width than in the foregoing or any other species of the genus. The large membrane-covered openings, or, as they may be called, windows, presently to be described, between the lower halves of the compartments, is much the most remarkable character of this species. The largest specimen which I have seen was only .23 in diameter, and .6 of an inch in height, measured from the basal point of the cup to the tips of the compartments.
Scuta.—These barely exhibit a trace of longitudinal striæ. The valve is rather thick and convex. The basi-tergal angle is much rounded off. Internally, the articular ridge is thick and rather prominent. Terga: the valve is furrowed in the line of the spur: the spur is pointed and rather long; it is distinctly separated from the basi-scutal angle of the valve, and the basal margin on the two sides of the spur forms a straight line. The articular ridge is prominent, and short.
Structure of the Parietes, Radii, and Basis.—The parietes are internally quite smooth down to its basis. The edges of the radii are also smooth, as is the edge of the basal cup. The alæ project less than usual. The radii are of moderate breadth, they extend downwards only a little below the sheath, namely, about half way down the shell, where they terminate, as usual, in a point. The increase in width, during growth, of the radii, and their not extending down to the basis, would necessarily cause a gap between the opposed edges of the walls, in the portion beneath the radii; but besides this, the edges of the walls themselves, beneath the radii, and on the opposed side beneath the alæ, are hollowed out, but on the latter side or beneath the alæ sometimes in a lesser degree. The result of this is, that the compartments, in their lower halves, are separated from each other by membrane-covered windows or apertures, arched at their upper ends, and of considerable size, namely, about as wide as the parietes of the carino-lateral compartments. I have only further to remark, that during the downward growth of the parietes, the apertures increase in size, but at the same time become closed up at their upper ends; and the arched layers of shell added at these upper ends, assume a very different aspect from the rest of the parietal surface,—appearing like two wedges, with their points upwards, let in, on one side of the suture, between the ordinary parietal surface and the radius, and, on the other side of the suture, between the ordinary parietal surface and the recipient furrow of the radius.
The animal’s body was in a bad state of preservation; but, as far as I could make out, the cirri resembled those of A. glans.
Affinities.—This species differs from A. glans in not having the internal margins of the compartments projecting inwards. It differs from all the ordinary varieties of A. spongites, in the smoothness of the basal edges of the parietes and of the edge of the cup; in the greater width of the carino-lateral compartment, though this is a variable point in A. spongites; slightly in the shape of the scuta and terga; and, lastly, in the large, membrane-covered openings between the compartments.
Shell dull blueish-purple, with six small, membrane-covered apertures between the sutures, close above the basis: tergum with the articular ridge very short and prominent; spur very broad and rounded.
Hab.—Sumatra; Philippine Archipelago; imbedded in the bark of an Isis; Mus. Cuming, Stutchbury, Brit.
This species is perfectly distinct from the others, as shown by its general appearance, its habits, and the structure of its opercular valves: it is allied to A. fenestrata, in having membrane-covered apertures between the compartments, and in some respects in its opercular valves: it is also allied to A. sulcata and cyathus in the parietes being often internally ribbed, in the basal cup having a crenated edge, and in the anterior ramus of the fourth cirrus being furnished with the minute hook-like spines.
General Appearance.—Sub-globular, slightly compressed, with a rather small orifice; smooth, but sometimes furnished with sharp shelly points; dull purple, more or less dark, with the upper parts of the walls often white. The radii are rather narrow, and generally white, with their summits only slightly oblique, but variable in this latter respect. The parietes of the carino-lateral compartments are narrow, being only one sixth of the width of the parietes of the lateral compartments. In some specimens there are membrane-covered apertures of considerable size, in others mere narrow clefts, between the basal halves of the compartments. The basal cup is moderately deep. The largest specimen was only .16 of an inch in basal diameter.
Scuta, rather broad, externally convex, not longitudinally striated: articular ridge prominent, short, not extending down above one third of the length of the valve. Depression for the adductor muscle deep. On the internal surface, near to the rostral angle, a rather large purple spot of corium adhered to the valve. Terga, broad, externally rather convex: scutal margin protuberant: carinal margin slightly inflected, or furnished internally with a rim: articular ridge prominent, very short, not extending down above one fourth of the valve. Spur very broad, rounded, confluent with the basi-scutal angle of the valve.
Internal Structure of the Parietes, Radii, and Basis.—The parietes, internally, are either quite smooth, or more commonly ribbed, with the basal edge in consequence crenated; the ribs are either placed at an unusual distance from each other, and consequently are few in number, or are pretty close together. The edge of the basal cup is either quite smooth, or closely crenated, or distantly toothed, in conformity with the state of the internal surface of the parietes. The radii have nearly smooth edges, with their summits more or less oblique. They sometimes extend down only three fourths, or only two thirds, of the length of the shell, and the margins of the parietes under the radii being a little hollowed out, the sutures are converted into clefts or apertures (of course covered by membrane) like, but not so large as, those in A. fenestrata. The margins of the parietes are hollowed out only on the side of the radius, and not on both sides of the sutures, as is most usual in A. fenestrata. In some specimens the radii extended down close to the basal cup, and only very minute clefts were left between the opposed edges of the parietes.
In the animal’s body the only noticeable character was, that on the anterior ramus of the fourth pair of cirri, some of the segments were furnished with very broad and thick, small, downwardly curved, teeth or hooks, like those described in certain varieties of A. sulcata; but they are here stronger and thicker. The segments in the three posterior pairs of cirri are not so much elongated, as in the other species.
Shell purplish-brown, with the parietes internally strongly ribbed and reticulated: carino-lateral compartments extremely narrow, not extending down to the basis.
Hab.—Sooloo Islands, East Indian Archipelago; Mus. Dana.
I am indebted to Mr. Dana, the distinguished naturalist of the United States Antarctic Expedition, for two specimens of this interesting species, which, in the singular reticulated structure of the inner surface of the walls, and in the almost rudimentary condition of the carino-lateral compartments, not extending down to the basal cup, is very distinct from the foregoing species. I have used Mr. Dana’s very appropriate MS. name of sporillus. The specimens were dredged up, lying quite loose and unattached at the bottom of the Sooloo sea; the one which I opened, must have long lain dead; but Mr. Dana assures me that some were living, and he has sent me drawings of parts of the mouth and cirri: I am much surprised at this circumstance; for analogy would have made me believe that this species must have been imbedded in some sponge-like body, such as the bark of a zoophyte, and that it could not have lived unattached. I may add that a small fragment of a brown leathery substance adhered to the upper end of one of the two specimens, and this seems to indicate attachment.
General Appearance.—Shell shaped like a pointed acorn; slightly flattened; orifice extremely small; surface very finely punctured, covered by a purplish-brown epidermis, with transverse stripes of different shades, and with the apex dark; according to Mr. Dana, when fresh, the colour was purplish-carmine. Radii narrow, white. The carino-lateral compartments are extremely narrow; the wall-portion (fig. 9 b) forming a mere linear rib, terminating downwards in a sharp point, which does not reach the basal cup: hence this compartment evidently tends to become rudimentary. The basal cup is moderately deep and pointed. Basal diameter .16; height, from the bottom of the cup to the top of the shell, .24 of an inch.
Scuta: narrow, with the upper part produced; not striated longitudinally; coloured by a pale purple, longitudinal band. Internally, there is scarcely a trace of an articular ridge, which, in the other species, is always more or less developed. Terga with the spur bluntly pointed; nearly the whole basal margin, on the carinal side, slopes towards the spur.
Internal Structure of the Parietes, Radii, and Basal Cup.—The parietes are strongly ribbed internally; and these ribs are connected by very narrow, less prominent, transverse, slightly branched ridges, giving a reticulated structure to the inner surface. Between several of the main longitudinal ribs, in the lower part of the shell, new ribs may be seen in process of formation, and these tend to convert the reticulated structure into a double row of minute cells. I have not met with an exactly similar structure in any other cirripede; but I have no doubt that the little transverse ridges are homologous with the transverse calcareous septa in the parietal pores of many Balani, in the same manner as the internal longitudinal ribs, in this and other species of Acasta, are homologous with the longitudinal septa forming the above pores. The edge of the basal cup is pectinated with teeth, which lock into the teeth formed by the ends of the internal parietal ribs. The radii are narrow, and have smooth edges. The alæ project beyond the parietes to a remarkably small extent. The sheath is free, or hollow beneath. I have already described the almost rudimentary condition of the carino-lateral compartments; this is best exhibited in an internal view of the two compartments, as given in Pl. 9, fig. 9 b.
Animal’s body unknown to me: from Mr. Dana’s drawing the three posterior pairs of cirri seem to have been much elongated: and the rami of the first pair, as usual, unequal in length.
M. Deshayes has given an indifferent figure and imperfect description of ACASTA TUBULOSA (Guerin, Magasin de Zoologie, 1831, Tab. 39; and Guerin, Iconographie du Règne Animal, Mollusques, Tab. 38, fig. 4, but here by a misprint called A. spinulosa); it is utterly impossible to recognise the species of this genus from such materials.