A Monograph on the Sub-class Cirripedia Part 28

_Description._ The number of valves in the capitulum has in this genus acquired its maximum. The number varies considerably in the same species, and even on opposite sides of the same individual, and generally increases with age. It is more important, that the number of the whorls in _P. cornucopia_, and in the two following closely-allied forms, also increases with age. In _P. sertus_ and _P. spinosus_, even the number of the whorls varies in different individuals, independently of age. The valves are arranged alternately with those above and below; they are generally thick and strong, making the capitulum somewhat ma.s.sive; in some species they are subject to much disintegration; but in others, the apices of the several valves, especially of the carina and rostrum, are well preserved, and project freely: they are covered with membrane, which, differently from in most species of Scalpellum, either does not bear any spines, or only exceedingly minute points. In all the species there is a sub-rostrum and sub-carina, and often beneath these a second sub-rostrum and sub-carina. In medium-sized specimens there are at least 20 valves in the lowermost whorl. The carina is either straight or curved, but never rectangularly bent, and is always of considerable breadth. None of the valves are added to at their upper ends. The scuta have a deep pit for the adductor muscle. The valves lie either some little way apart, or more commonly close together. In _P. mitella_ the scuta and terga are locked together by a fold, and the valves of the lower whorl overlap each other in a peculiar manner, resembling that in which the compartments in the sh.e.l.ls of Sessile Cirripedes fold over each other.

The _Peduncle_ is of considerable length in some of the species, and rather short in others; it is, in every case, clothed with calcified scales. The scales in the first four species are placed alternately and symmetrically; they are formed and added to in the same manner as in Scalpellum; they differ in size according to the size of the individual, and consequently the lower scales on the peduncle, formed when the specimen was young, are smaller than the upper scales; the lower scales are separated from each other by wide inters.p.a.ces of membrane, owing to the continued growth of the peduncle by the formation of new layers of membrane, and the disintegration of the old outer layers. Each scale is invested by tough membrane (or has been, for it is often abraded off), in the same manner as the valves; each is furnished with one or more tubuli, in connection with the underlying corium. In _P. sertus_ and _P.

spinosus_, the scales are small, spindle-shaped, and not of equal sizes, and the rows are distant from each other, so that their alternate arrangement is not distinguishable; in these two species, new scales are formed round the summit of the peduncle, and the growth of each is completed whilst remaining in the uppermost row; but, besides these normal scales, such as exist in the other species of Pollicipes and in Scalpellum, new scales are formed in the lower part of the peduncle, which are generally of very irregular shapes, are often larger than the upper ones, are crowded together, and sometimes do not reach the outer surface of the membrane. This formation of scales in the lower part of the peduncle, independently of the regular rows round the uppermost part, is perhaps a feeble representation of the calcareous cup at the bottom of the peduncle in the genus Lithotrya. The prehensile antennae will be described under _P. cornucopia_.

_Size._--Most of the species are large: and _P. mitella_ is the most ma.s.sive of the Pedunculated Cirripedes.

The _Mouth_ is not placed far from the adductor muscle. The labrum is highly bullate. The mandibles have either three or four main teeth (Pl.

X, fig. 1), with often either one or two smaller teeth inserted between the first and second. The maxillae (Pl. X, figs. 13, 14), have their edges either straight and square, or notched, or more commonly with two or three prominences bearing tufts of finer spines. The outer maxillae (fig. 17) generally have a deep notch on their inner edges, but this is not invariable. The olfactory orifices in most of the species are highly prominent.

_Cirri._--The first pair is never placed far distant from the second.

The posterior cirri have strong, somewhat protuberant segments; and between each of the four or five pair of main spines (Pl. X, fig. 27), there is a rather large tuft of straight, fine, short bristles. The second and third pair have the basal segments, either of the anterior rami, or of both rami, so thickly clothed with spines (fig. 25), as to be brush-like: in _P. mitella_, however, the third pair is like the three posterior pair in the arrangement of its spines, in this respect resembling the sessile Chthamalinae. The caudal appendages are either uni-articulate and spinose, or multi-articulate: it is remarkable that there should be this difference in such closely allied species as _P.

cornucopia_ and _P. polymerus_: the short, obtuse, obscurely-articulated caudal appendage of the former species (fig. 22) makes an excellent pa.s.sage from the uni-articulate (fig. 19) to the multi-articulate form, as in _P. mitella_.

The stomach, in those species which I opened, is dest.i.tute of caeca; the hepatic glands are arranged in straight lines; the r.e.c.t.u.m is unusually short. The prosoma is well developed.

In _P. cornucopia_, _P. elegans_, and _P. polymerus_, there are numerous filamentary appendages both on the prosoma, and at the bases of the first pair of cirri: these appendages are occupied by testes, and I suspect stand in relation to the length of the peduncle and consequent great development of the ovaria. In order to give s.p.a.ce for the filamentary appendages, the sack (generally roughened by small inwardly-pointing papillae) penetrates more deeply than usual into the upper part of the peduncle. There are small ovigerous fraena in _P.

sertus_, _P. spinosus_, and _P. mitella_: in the three other species, the fraenum or fold occupies the usual position on each side, and is large; but in one specimen carefully examined by me, I was unable to see any glands; and in another specimen, the ovigerous lamellae were not attached to the fraena; hence I conclude that the fraena are functionless in these three species.

_Affinities._--I have already remarked on the close relations.h.i.+p between this genus and Scalpellum; there is also some affinity with Lithotrya.

_Distribution._--All over the world. The _P. cornucopia_ ranges from Scotland to Teneriffe: the _P. polymerus_ is found in opposite hemispheres in the Pacific Ocean, extending from California to at least as far as 32 south of the Equator.

_Geological History._--Having so lately given, in the 'Memoirs of the Palaeontographical Society,' a full account of all the fossil species known, I will not repeat here the conclusions there arrived at. I will only state, that species of Pollicipes are found in all the formations, extending from the Lower Oolite to the Upper Tertiary beds.

1. POLLICIPES CORNUCOPIA. Pl. VII, fig. 1.

POLLICIPES CORNUCOPIA. _Leach._ Encyclop. Brit. Supp., vol. iii, 1824.

---- SMYTHII, var. _Leach_. Ibid.

LEPAS POLLICIPES. _Gmelin._ Systema Naturae, 1789.

---- GALLORUM. _Spengler._ Skrivter Naturhist. Selskabet, Bd. i, Tab. vi, fig. 9, 1790.

_P. capitulo, valvarum duobus aut pluribus sub-rostro verticillis instructo: valvis albis, aut glaucis: pedunculo, squamarum densis verticillis symmetrice dispositis._

Capitulum with two or more whorls of valves under the rostrum; valves white or gray; scales on the peduncle symmetrically arranged in close whorls.

Maxillae with three tufts of fine bristles, separated by larger spines: segments in the first cirrus less than half the number of those in the sixth cirrus: caudal appendages multi-articulate: filamentary appendages attached to the prosoma.

Coast of Portugal; mouth of the Tagus. England,[64] Ireland, and the Frith of Forth in Scotland. Mediterranean (according to Brugiere): Teneriffe: Mogador, Africa.

[64] This species is said by Montagu ('Test. Brit. Supplement') to have been found attached to drift timber in the Frith of Forth, and to the bottom of a wrecked vessel towed into Dartmouth. According to Mr. W. Thompson ('Annals of Nat. Hist.'

vol. xiii, p. 436), it has been found attached to wood-work near Dublin.

Capitulum, obtusely triangular, ma.s.sive: valves close together, rather thick, with their exterior surfaces convex, naked, except in the lower parts, where united together by tough, greenish-brown membrane, dest.i.tute of spines. The edges of the orifice are widely bordered by membrane, coloured fine crimson red. The valves, in a specimen with a capitulum above three quarters of an inch long, were 52 in number; in a specimen one fifth of an inch long, only between 20 and 30. Two whorls of valves are distinct beneath the carina and rostrum. In one specimen in Mr. c.u.ming's collection, with a capitulum 1.4 of an inch long, there were three whorls beneath the rostrum, and four beneath the carina. The scuta, terga, and carina are much larger than the other valves.

_Scuta_, oval, the basal and tergo-lateral margins sweeping into each other, and the apex pointed; internally (Pl. VII, fig. 1 _a_) the pit for the adductor muscle is deep.

_Terga_, larger than the scuta, internally (fig. 1 _a_) slightly concave; carinal margin much curved and protuberant; basal angle blunt; scutal margin either curved with the upper part straight, or formed of two almost distinct lines, corresponding with the tergal margin of the scutum, and with one of the sides of the upper latus.

_Carina_, much curved, extending far up between the terga, internally deeply concave, widening much from the top to the bottom; basal margin highly protuberant, with a central portion either truncated and very slightly hollowed out, or bluntly and rectangularly pointed, with the apex itself rounded.

_Rostrum_, not one third of the length of the carina, concave, triangular, with the basal margin slightly protuberant. Of the other valves, including the sub-carina and sub-rostrum, the shape of their inner surfaces is sub-triangular, with the basal margin convex; externally the umbones are pointed, and slightly curled inwards, so as to overlap each other like tiles: the smaller valves, however, of the lower whorls (fig. 1 _a_) are more or less transversely elongated, so as to become almost elliptic instead of triangular. Of the latera, the upper pair, which corresponds to the inters.p.a.ce between the scuta and terga, is the largest, but barely exceeds in size the pair answering to the carinal latera in Scalpellum, which lie between the terga and carina: the next largest pair is the rostral, or that between the scuta and rostrum. Some, however, of the lower latera are of nearly equal size.

_Peduncle_, narrower, but generally longer than the capitulum; upper part encased with small calcareous scales, with their apices curved inwards, and overlapping each other. The inner surface of each scale is triangular, with the basal margin protuberant. The scales continue to grow or be added to, only in about the ten upper whorls, which form but a small part of the whole peduncle; in the lower part, the scales become further and further separated from each other. The surface of attachment, in full-grown specimens, is broad; but in two very young specimens, which I removed with great care after the action of potash, I found the peduncle ending in a filiform prolongation, such as often occurs in _Scalpellum vulgare_ and in _Lepas fascicularis_. At the extremity of the pointed peduncle, there were seated the larval prehensile antennae, of which the following measurements are given to show how minute they are.

_Inch._ Length, from apex of disc, to the further edge of the basal articulation 20/6000 Breadth of basal segment, in broadest part 6/6000 Hoof-like disc, length of 6/6000 Ultimate segment, entire length of 6/6000 " " breadth, in broadest part 6/20000

The disc resembles a broad, rounded hoof, very little longer than broad, and narrowed in at the heel; the apex is not at all pointed, and bears some minute and thin spines. There is one large spine on the under side of the disc; and another on the basal segment, on the outside, in the usual position. The ultimate segment is long and thin; it has a notch on the inner side (the segment supposed to be stretched forward), bearing two or three long flexuous spines; and there are three or four other spines on the summit: altogether there is a close resemblance with the antennae in Scalpellum, excepting that the hoof-like disc is not here pointed.

_Colours._--Valves internally tinted, in parts, grey; peduncle, brown; corium of sack, purplish-brown, of peduncle, rich coppery brown; cirri, banded dorsally, and with the front surfaces of the segments, purplish-brown. Edge of the orifice of sack, fine crimson red. The specimen here described had been dried for a few weeks, and was then moistened.

_Dimensions._--The largest specimen which I have seen, in Mr. c.u.ming's collection, had a capitulum 1 and 4/10ths of an inch long; a fine specimen, from Teneriffe, was 9/10ths in length. In a specimen with a capitulum 1/20th of an inch long, and about the same in breadth, there were eighteen valves; so that, besides the princ.i.p.al valves, five pair of latera, the sub-carina, and sub-rostrum, were already developed, and on the upper part of the peduncle, there were many calcareous scales.

_Filamentary Appendages._--The prosoma is well-developed, with thirteen or fourteen pair of short, blunt filaments, placed close together in two longitudinal rows; those nearest the thorax are the longest; outside this double row, on each side, there is a row of papillae, indicating a tendency to the formation of two other rows of filaments. There is a pair of longer filaments, one on each side of the mouth, pointing upwards, and thinly clothed with long spines; at the bases of the first pair of cirri there is a second pair of filaments, shorter and bearing a few minute spines. The bottom of the sack is studded with small rounded papillae, with roughened summits.

_Mouth_, not placed very far from the adductor muscle.

_Labrum_, highly bullate, equalling, in its longitudinal diameter, the rest of the mouth; upper part square, not overhanging the lower part; there are some small teeth on the crest.

_Palpi_, oval, outer and inner margins nearly alike, thickly clothed with spines.

_Mandibles_, with three very strong, yellow teeth; inferior point broad, coa.r.s.ely pectinated. In one specimen, on one side, the third tooth was represented by two smaller teeth.

The _Maxillae_ bear three conspicuous tufts of fine bristles, separated by larger spines; the first tuft is placed close to the two, upper, large, but unequally-sized spines; the second tuft is placed in the middle, and the third at the inferior angle. The two latter tufts stand on prominences; between the two upper tufts there are three pair, and between the two lower tufts four or more pair of rather strong spines: (see the figure, 13, Pl. X, in the allied _P. polymerus_.)

_Outer Maxillae_, with the inner edge divided in the middle by a conspicuous notch, and with the bristles above and below short, making two _equal_ combs. On the exterior surface, the bristles are longer and more spread out. Olfactory orifices prominent, protected by a punctured swelling between the bases of the first pair of cirri.

_Cirri_, short and rather thick; the first pair is not far removed from the second. The segments of the three posterior pair are somewhat protuberant, bearing six pair of short, strong spines, graduated in length, between which there is a very thick, longitudinal brush of short, fine, straight bristles, of which the lower ones are the longest; some thick, minute spines arise from the upper lateral edges of the segments. The spines in the dorsal tufts are short, much crowded, and of nearly equal length; see figure, 27, Pl. X, in the allied _P.

polymerus_. In a specimen in which the sixth cirrus had seventeen segments, the first cirrus had, in the shorter ramus, eight segments, of which the lower four were thick and protuberant, with the spines doubly serrated. In this same specimen, the anterior ramus of the second cirrus had twelve segments, of which the five basal ones were highly protuberant, and thickly clothed with non-serrated spines. In the third cirrus the basal segments of the anterior ramus are highly protuberant.

The basal segments in the posterior rami of both these cirri, are slightly protuberant, but otherwise resemble the segments in the three posterior pair.

The _Caudal Appendages_ (Pl. X, fig. 22), in full-grown specimens, just exceed in length the lower segments of the pedicels of the sixth cirrus; they are nearly cylindrical, bluntly pointed, with five oblique imperfect articulations; the lower or basal articulations cannot be traced all round, being distinct only on the ventral surface. There is a row of short spines round the upper edge of each segment, with a little, short tuft on the point of the terminal segment. In a rather young specimen, however, with its capitulum one fifth of an inch long, each appendage certainly consisted of a single segment, with spines only on the summit.

_p.e.n.i.s_ purple, with excessively short and fine spines in tufts, chiefly near the extremity. In a specimen with a capitulum only one fifth of an inch long, the p.e.n.i.s consisted of a mere pointed papilla, not so long as the caudal appendage, and therefore equalling in length only the lower segment of the pedicel of the sixth cirrus.

_Ovigerous fraena._--I could see none, though there were two large lamellae in the sack. The ova were flesh-coloured, but they had been dried and then placed in spirits. The ova were wonderfully numerous, oval, much elongated, and 1/100th of an inch in length.

2. POLLICIPES ELEGANS.

POLLICIPES ELEGANS. _Lesson._ Voyage de la Coquille, tom. ii, p.

441, 1830, et Ill.u.s.t. Zool., Pl. x.x.xix, 1831.

---- RUBER. _G. B. Sowerby._ Zoolog. Proc., 1833, p. 74.