Balanus amaryllis

Balanus amaryllis Darwin

Languages: English


Comprehensive Description

“Shell striped or clouded with pinkish-purple, or quite white; radii narrow, with their oblique summits smooth or arched: basis porose. Scutum plainly striated longitudinally: tergum with the spur narrow.

Var. (a):* bright rosy pink, not distinctly banded longitudinally. Hab. North-east coast of Australia.

Var. (b): snow white, glossy; orifice deeply toothed. Hab. — Mouth of the Indus; East Indian Archipelago; Philippine Archipelago; Moreton Bay, and the north-east coast of Australia. Attached frequently on ships' bottoms, associated with B. tintinnabulwm and amphitrite. Sometimes attached to Gorgoniae with B. calceolus.

General Appearance. — Shell steeply conical, with the orifice subrhomboidal, moderately large, very slightly, or deeply notched; surface very smooth; white, longitudinally banded with pinkish or leaden purple, with sometimes a purplish, sometimes a yellowish tint, the latter owing to the persistent epidermis; the bands are pale, and often fade away in the lower, and sometimes in other parts of the shell; the epidermis is generally more persistent on the narrow rounded radii than on the parietes, and hence the radii are generally yellowish. The opercular valves are pale dull purple; the sheath is darker purple, with the exception of the portions of the alee added during the diametric growth, which are of a dead white, and are externally conspicuous. The scuta are striated longitudinally. I may remark, that, excepting the narrowness of the radii, with their quite smooth, rounded and very oblique summits, some specimens are hardly distinguishable, in external aspect, from varieties of B. amphitrite. If the specimens from the north-east coast of Australia, of which I have seen many (but unfortunately only one small one had its opercular valves), form, as I fully believe, merely a variety; it is characterised by its nearly uniform beautiful rosy pink, without any distinct longitudinal bands; of these specimens I have seen one two inches in basal diameter, and three in height: of ordinary duller-coloured striped specimens, the largest was 1.7 in basal diameter. Of the perfectly white var. (b), I have seen several specimens, the largest being .6 of an inch in diameter: these have a somewhat peculiar aspect, but I have met with only one specimen with opercular valves, and that was extremely young; I at first considered this form as specifically distinct; but I can point out, after careful examination of the whole shell, operculum, and internal animal of the young specimen, no sufficient diagnostic characters.

Scutum, plainly striated longitudinally, with the striae dividing the prominent lines of growth into squarish beads; internally, the upper part of the valve is roughened; the articular ridge is short, remarkably little prominent, and not reflexed; the adductor ridge is blunt and little prominent; sometimes it is almost confluent with the articular ridge; there is a deep but variable depression for the lateral depressor muscle; and in young specimens of var. (a) it was almost absent. Tergum: the surface exhibits traces of longitudinal striae: there is a deep longitudinal furrow, with the sides folded in and quite closed in full grown specimens; the scutal margin is considerably curved towards the scutum. The spur is long and narrow, with the end bluntly pointed, placed at rather above its own width from the basiscutal angle; the basal margin slopes but little towards the spur: the crests for the depressores are feebly developed.

Parietes; their internal surfaces are strongly ribbed longitudinally, with the basal ends of the ribs coarsely denticulated, and with the denticuli extending close to the outer lamina. The radii are generally narrow, but their width varies; their summits are very oblique, smooth, rounded, and inflected, with the lines of growth, in the uppermost part, curving inwards; their sutural edges, in the upper inflected portion, are quite smooth, without septa; in the lower and larger portion, the edge is crenated with excessively fine teeth or septa, not denticulated; the radii, like the parietes, have no inner lamina; the recipient grooves in the opposed compartments are smooth, and are in the lower part of the shell of unusual depth. The alae, differently from the radii, generally have their summits very slightly oblique, but sometimes they are highly oblique; their sutural edges are most finely crenated. The basis is generally flat, sometimes cupformed; it is permeated by pores, crossed by transverse septa; and sometimes there is an underlying cancellated layer. Mouth: labrum with either six very small teeth, or with none. Mandibles (PL 26, fig. 5), with the third tooth a little thicker than the first; fourth and fifth teeth small, but quite distinct. Maxillae (PI. 26, fig. 7), with the inferior part forming a square step-formed projection, bearing, one behind the other, two spines as long as the upper pair; in a young specimen of var. (a) this step-formed projection was absent.

Cirri; first pair with the rami unequal by about four segments; the shorter ramus has the segments very protuberant in front, thickly clothed with strongly serrated spines; the second cirrus has segments moderately produced; the third has them produced only in a slight degree. The pedicels of the second and third cirri have dorsal tufts of spines, but not a hairy plate prolonged over the thorax. The posterior cirri have segments broader than long, bearing only two pairs of nearly equally long spines; and between each pair there is a small intermediate tuft. The penis has the usual basi-dorsal point.

B. amaryllis is a distinct and well-defined species, more nearly related to B. Hameri than to any other form.


* This variety perhaps is the B. roseus of Lamarck, as figured in Chenu, "Illust. Conch." Tab. 2, fig. 9; but as Lamarck does not even notice such conspicuous external characters as the longitudinal striae on the scuta, and the smooth rounded edges of the radii, it is impossible to identify his species.” (Darwin, 1851)

Author(s): Hammock, Jennifer

Ecology and Distribution


"...associated with B. tintinnabulwm and amphitrite. Sometimes attached to Gorgoniae with B. calceolus." (Darwin, 1851)

Author(s): Hammock, Jennifer


"North-east coast of Australia... Mouth of the Indus; East Indian Archipelago; Philippine Archipelago; Moreton Bay, and the north-east coast of Australia. " (Darwin, 1851)

Author(s): Hammock, Jennifer


"Attached frequently on ships' bottoms" (Darwin, 1851)

Author(s): Hammock, Jennifer


Darwin, C. (1851).  A monograph on the sub-class Cirripedia, with figures of all the species..