A Monograph on the Sub-class Cirripedia Part 15

_Genus_--ALEPAS. Pl. III.

ALEPAS. _Sander Rang._ Manuel des Mollusques, 1829.

ANATIFA. _Quoy_ et _Gaimard_. Voyage de l'Astrolabe, 1834.

TRITON. _Lesson._ Voyage de la Coquille, 1830.

CINERAS. _Lesson._ Secundum Sander Rang.

_Capitulum aut sine valvis, aut scutis corneis, paene abditis._

Capitulum without valves,[41] or with h.o.r.n.y, almost hidden, scuta.

[41] Any one not attending to the characters derived from the softer parts of the Balanidae and Lepadidae, might easily confound with Alepas the genus Siphonicella (genus nov.), which, undoubtedly, though having the external appearance of a pedunculated cirripede, belongs to the Balaninae, and is closely related to Coronula.

Filaments seated beneath the basal articulations of the first pair of cirri; mandibles, with two or three teeth; maxillae notched, with the lower part irregular, projecting; caudal appendages multi-articulate.

Attached to various living objects, fixed or floating.

_Capitulum_ either entirely dest.i.tute of valves, or with transparent h.o.r.n.y scuta, not containing any calcareous matter, and almost hidden in membrane. These scuta are formed of a lower and a lateral lobe, placed at above right angles to each other; they are added to by successive layers, and closely resemble in shape the scuta of the _Conchoderma aurita_. The orifice in _A. tubulosa_ projects so much as to be almost tubular. In _A. parasita_ and _A. minuta_ it does not project, and is either moderately large, or very small in proportion to the length of the capitulum; from contraction it is much wrinkled. The membrane forming the capitulum is smooth and very transparent; it contains very few tubuli, except under certain irregular projections in _A. cornuta_.

The _Peduncle_ is rather short and narrow; it blends into the capitulum, and is not, in some of the species, separated from it by any distinct line; the surface of attachment is rather wide. Within the peduncle we have the three usual layers of striae-less muscles; namely, the innermost and longitudinal, which run lower down than the others; the middle and transverse; and, lastly, the exterior, oblique muscles, which cross each other (becoming transparent) on the rostral central line. These several muscles run up from the peduncle and surround the capitulum; from the transparency of the membranes they can be seen from the outside: they are particularly conspicuous round the orifice, which they probably serve to close. There is, in all cases, the usual adductor scutorum muscle (with transverse striae), which is attached under the h.o.r.n.y scuta, where such exist. The fact of the striae-less muscles of the peduncle surrounding the whole capitulum, has been observed only in one other genus, namely Anelasma. In consequence of this structure, the capitulum must possess considerable powers of contraction.

The antennae of the larva in the _Alepas cornuta_ and _A. minuta_ have the sucking disc nearly circular, with the spines unusually plain on the distal as well as proximal margin. Basal segment broad, much constricted where united to the disc. The ultimate segment has on the middle of the outer margin, in _A. cornuta_, two minute spines, which I have not observed in any other cirripede: on the summit there are the usual spines.

_Size._--Three of the species are small.

_Filamentary Appendages._--These are rather small; there is only one on each side, situated on the posterior margin of a slight swelling, beneath the basal articulation of the first cirrus; and therefore in the position in which the filaments are most constant in Lepas, and where they likewise occur in Conchoderma.

_Body._--The prosoma is either pretty well developed or is small, according as the first cirrus is placed near to, or far from the second cirrus.

_Mouth._--Labrum moderately bullate, with the lower part more or less produced; crest with blunt, bead-like teeth, and short hairs.

_Palpi_ (Pl. X, fig. 8), ac.u.minated and narrow to an unusual degree.

_Mandibles_, with two or three teeth, and the inferior angle ac.u.minated; the lateral bristles unusually strong, so as to give the main teeth the _appearance_ of being pectinated.

_Maxillae_, widely notched, with three great upper spines; the part beneath the notch projecting, and either straight or irregular.

_Outer Maxillae_, with the inner bristles either continuous or divided into two groups: exteriorly there is a smaller or larger prominence, with long bristles. The olfactory orifices are either slightly, or not at all protuberant.

_Cirri._--In the three posterior pair, the segments have their bristles arranged in a transverse row, either in the form of a narrow brush, or consisting only of a single pair with two or three minute, intermediate, and lateral marginal spines. The anterior ramus of the second cirrus is thicker, and more thickly clothed with spines than is the posterior ramus: this latter ramus, however, and both rami of the third cirrus, are rather more thickly clothed with spines than are the three posterior pair. The unique case in _A. cornuta_ of the inner rami of the fifth and sixth cirri being rudimentary (Pl. X, fig. 28) will be minutely described under that species.

_Caudal Appendages_, thin, tapering, multi-articulate, about as long as the pedicels of the sixth cirrus.

_Stomach._--The oesophagus runs in a somewhat sinuous course, and enters the top of the stomach obliquely. There are no caeca. The biliary envelope presents a reticulated structure, instead of the usual longitudinal folds.

_Generative System._--The p.e.n.i.s is hairy, not very long, and ringed or articulated in an unusually plain manner; the s.p.a.ce between each ring being about one fourth of the diameter of the p.e.n.i.s: the unarticulated basal portion or support is here remarkably long. The vesiculae seminales are long, tortuous, and enter the prosoma. The ovarian tubes are of wide diameter: in _A. cornuta_ they surround the whole capitulum. The ovigerous fraena are small, constricted at the base, and square on the free margin, which is studded with minute glandular beads, borne on the finest footstalks.

_Range._--Southern sh.o.r.es of England, Mediterranean, Atlantic, West Indies, New Zealand, attached to various objects. _A.

parasita_ has been always taken on Medusae.[42]

[42] It appears that Solander (Dillwyn Des. Cat., vol. i, p. 34) observed a species of this genus adhering to a Medusa on the coast of Brazil. Mr. c.o.c.ks informs me that an Alepas, apparently _A. parasita_, has been cast on sh.o.r.e near Falmouth, attached to a Cyanaea; and that two other specimens adhered to the bottom of a vessel arriving at that port from Odessa.

_Affinities._--This genus differs from all, except Anelasma, in the manner in which the striae-less muscles of the peduncle run up and surround the capitulum, and likewise in the reticulated character of the biliary envelope of the stomach. To Conchoderma, especially to _C.

aurita_, there is manifest affinity in the form of the h.o.r.n.y scuta: there is also some affinity to this same genus in the presence of filamentary appendages though here little developed, and in the circular form of the disc of the larval antennae, and, lastly, in the ovarian tubes in _A. cornuta_ surrounding the capitulum. There is quite as close, if not closer affinity to Ibla, in the following peculiarities,--in the curved oesophagus,--in the general character of the cirri and trophi, with the olfactory orifices in one species in some degree prominent,--in the multi-articulated caudal appendages,--and in the plainly-articulated p.e.n.i.s, with its elongated unarticulated support, though both these characters are exaggerated in Ibla. Lastly, the scuta in Ibla, though not at all resembling in shape those of _A. cornuta_, are formed without calcareous matter; and again, in Ibla, the muscles of the peduncle run up to the bases of the valves, and so almost surround the s.p.a.ce in which the animal's body is lodged.

The four species of Alepas appear to form two little groups; viz. _A.

parasita_ and _A. minuta_ on the one hand, and _A. cornuta_ and _A.

tubulosa_ on the other.

1. ALEPAS MINUTA. Tab. III, fig. 5.

ALEPAS MINUTA. _Philippi._ Enumeratio Mollusc. Siciliae, 1836, Tab. xii, fig. 23.

---- ---- _A. Costa._ Esercitazione Accadem., vol. ii, part I, Naples, 1840, Pl. iii, fig. 5 (secundum Guerin in Revue Zoolog., 1841, p. 250.)

---- ---- _Chenu._ Ill.u.s.t. Conch., Pl. iii, figs. 8-10.

_A. apertura non prominente, capituli longitudinis vix tertiam partem aequante: scutis corneis, paene absconditis: longitudine tota ad quartam unciae partem._

Orifice not protuberant, one third of the length of the capitulum: scuta h.o.r.n.y, almost hidden. Total length quarter of an inch.

Outer maxillae, with the spines in front continuous; posterior cirri, with several long spines arranged in a transverse row on each segment; caudal appendages longer than the pedicels of the sixth cirrus.

Sicily; attached to a Cidaris:[43] island of Capri (_A. Costa_).

[43] I am greatly indebted to Professor J. Muller, of Berlin, for kindly lending me specimens.

Capitulum oval, blending insensibly into the peduncle; moderately flattened; composed of thin structureless membrane, with the exception of two h.o.r.n.y, almost quite hidden scuta. Orifice situated near the summit, and in a line, which is oblique to the longitudinal axis of the peduncle; much wrinkled; barely one third of the length of the whole capitulum.

The _Scuta_, consist of yellowish, transparent, h.o.r.n.y, laminated chitine, without any calcareous matter; externally covered by the common integument of the capitulum; these valves are placed very near to each other, close under the orifice, and therefore high up on the capitulum; the membrane between them is smooth and unwrinkled; they are formed of two rather ac.u.minated lobes, joining each other at above a right angle; one lobe (the longer one) stretching nearly transversely across the capitulum, the other running down parallel to its rostral margin: in shape and position they resemble the scuta of _Conchoderma aurita_; and if another lobe had been developed it would have run along the orifice, and then these valves would have resembled the scuta of _Conchoderma virgata_. In a specimen with a capitulum 2/10ths of an inch long, the scuta from point to point were 1/20th of an inch in length.

_Peduncle_, much wrinkled, about one third in diameter of the capitulum, and shorter than it; at the base it is generally expanded into two or three finger-like projections. _Length_ of the largest specimen, about one fourth of an inch. _Colour_, according to A. Costa in the work above cited, "rufo-flava vittata;" but after spirits the whole becomes uniformly yellowish.

_Filamentary Appendages_, situated beneath the basal articulation of the first cirrus, on the posterior edge of the usual enlargement; ac.u.minated, about two thirds of the length of the shorter ramus of the first cirrus.

_Prosoma_ well developed.

_Mouth._--On each side there are two slight prominences; one under the mandibles, the other transverse nearer to the adductor muscle.

_Labrum_, placed near the adductor muscle, with the upper part not more bullate than the lower part; crest with a row of blunt teeth, and many fine bristles growing chiefly outside the teeth; there are many fine bristles on the inner or supra-oesophageal fold of the labrum.

_Palpi_ not nearly touching each other, pointing towards the adductor: much hollowed out on their inner sides, hence narrow and ac.u.minated, with doubly serrated bristles.

_Mandibles_, with three teeth and the inferior angle ending in a single sharp spine; whole inferior portion narrow; first tooth as far from the second, as the latter from the inferior angle; owing to the presence of short thick spines projecting from the sides of the jaw, the lower edges of the second and third teeth appear pectinated.