_Range._--This species, in the present state of our knowledge, seems to range further than any other of the genus, extending from Upper California, (lat. 32 to 35 N.,) across the Pacific, to at least 32 S., perhaps much farther south, for it was collected during the Antarctic expedition, and 32 was the highest lat.i.tude traversed by that expedition.
_Affinities._--This species is closely related to _P. cornucopia_ and _P. elegans_, but differs rather more from them, than these two do from each other. In the capitulum the chief distinctive characters are--the more perfect graduation in size, and the greater number, (taking equal-sized specimens,) of the whorls of latera--the darker colours--the central part of the basal margin of the carina in this species, being considerably excised--the peculiar form of the basal margin of the scuta--and lastly, the scutal margin of the terga being more hollowed out. In the animal"s body, the most obvious distinctive character is the uniarticulate caudal appendage. This species agrees with _P. elegans_, in the presence of the singular elbowed teeth, on some of the spines in the first three pairs of cirri.
4. POLLICIPES MITELLA. Pl. VII, fig. 3.
LEPAS MITELLA. _Linn._ Systema Naturae, 1767.
POLLICIPES MITELLA. _G. B. Sowerby._ Genera of Sh.e.l.ls, fig. 2.
POLYLEPAS MITELLA. _De Blainville._ Dict. Sc. Nat. (1824) Plate, fig. 5.
CAPITULUM MITELLA. _J. E. Gray._ Annals of Philosoph., new series, vol. x, 1825.
_P. capitulo valvarum unico sub-rostro verticillo instructo: laterum pari superiore (introrsum spectanti) inferiorum magnitudinem ter aut quater superante: lateribus inferioribus utrinque obtegentibus: pedunculi squarmarum verticillis densis, symmetrice dispositis._
Capitulum with only one whorl of valves under the rostrum: the upper pair of latera, viewed internally, are three or four times as large as the lower latera, which overlap each other laterally: scales of the peduncle symmetrically arranged in close whorls.
Maxillae, deeply notched: caudal appendages, multi-articulated: filamentary appendages, none.
Philippine Archipelago, Mus. c.u.ming: China Sea, Mus. Brit.: Amboyna and East Indian Archipelago, according to Rumphius and other authors: Madagascar, according to J. E. Gray.
_Capitulum_, compressed, consisting of the scuta, terga, carina, rostrum, and a large pair of upper latera, with a single lower whorl of smaller valves; these latter vary from 22 in very small specimens, to 26 in large specimens. The capitulum, therefore, is formed of at most 34 valves; but in the largest specimen seen by me, the capitulum being 2.3 of an inch in width, there were only 32 valves. In the smallest, namely, with a capitulum .15 of an inch in width, there were 30 valves. The valves are remarkably strong, and formed of white sh.e.l.ly matter; they are closely approximate, and overlap each other: the scuta and terga are articulated together by a fold; the apices of the valves are either worn and disintegrated, or they project freely like horns beyond the sack, to a much greater extent than in any other recent species of the genus: even a considerable portion of the scuta projects obliquely upwards. The exterior surfaces of the valves (when not worn) are covered by a strong yellow membrane, and the upper free parts are generally attached together for some little length by this same membrane. The valves are plainly marked by the zones of successive growth; and most of them are ribbed and furrowed slightly, from their umbones to their basal margins.
The yellow external membrane, examined microscopically, is marked by, or rather formed of, numerous growth-lines, crossed by longitudinal beaded ridges. The tubuli are not numerous, and of small diameter.
_Scuta_ (Pl. VII, fig. 3 _a"_, _a_) triangular, with the apex more or less produced, according to the state of its preservation, and a little curved towards the terga; basal margin, and in some degree the tergo-lateral margin, arched, and slightly protuberant; occludent margin thickened, slightly prominent, with the inner edge covered by the yellow membrane, like the exterior surface of the valve. The upper part of the tergo-lateral margin overlaps a little the edge of the tergum, and receives it in a furrow,--the two valves being thus locked together.
This furrow lies in the freely-projecting, membrane-covered portion, and extends up to the apex; it is of variable depth. Internally the scuta are concave, and in some old specimens to a high degree. In these latter, the basal margin, towards the tergo-lateral side, is strongly sinuous; the prominences are formed by the terminations of the external longitudinal ridges, and correspond to the inters.p.a.ces between the valves of the lower whorl. These ridges, which are interesting, from throwing light on similar ridges in some fossil species, are present, both on old and young specimens, and run from the apex of the valve, in a slightly curved line, to the tergo-lateral half of the basal margin, where, as we have just seen, they sometimes form prominences. They consist of three or even four obscure, almost confluent, ridges, of which the middle one is generally (but not always) the smallest: together they cover the whole of that part of the scutum, which is not overlapped along the basal margin by the rostrum and large upper latus; and they seem evidently due to the growth of the sh.e.l.l in this inters.p.a.ce having been freer. So, again, the three or four small, confluent, component ridges have the same relation to the inters.p.a.ces between the small latera of the lower whorl.
_Terga_ large, four-sided, with the internal growing surface (fig. 3 _a"_ _b_), almost diamond-shaped; basal angle blunt, rounded; exteriorly, from the apex to the basal angle there is a rather broad, very slight prominence, which bears the same relation to the carina and upper latus, as do the compound ridges on the scuta to the rostrum and upper latus. The upper part of the scutal margin forms a slightly-projecting, rounded shoulder, though variable in its degree of prominence, in relation to the variable depth of the recipient furrow in the scuta. Externally, parallel to the occludent margin, and close below the prominent shoulder, just mentioned, there is a slight and variable depression, extending up to the apex of the valve. This depression is due to the prominence, variable in degree, of the tergal edge of the recipient furrow in the scuta.
_Carina_, triangular, strong, inwardly bowed, generally with a large upper portion freely projecting; exteriorly with a narrow, sharp, central ridge or keel, which is solid, the interior concavity not reaching so deep; inner growing surface (fig. 3 _b"_, _b_) deeply concave, triangular. Basal margin square--that is, transverse to the longer axis of the carina, or it even rises (as is best seen in the growth-ridges) a little towards the exterior keel. On each side of the central exterior keel, there is a narrow longitudinal ridge, corresponding with the inters.p.a.ce between the sub-carina and the next-but-one latus of the lower whorl; the latus next to the sub-carina is very small, and overlies the ridge itself. In a very large specimen, these lateral longitudinal ridges formed (as they likewise did on the rostrum) slight prominences on the basal margin. In one specimen the carina was straight.
_Rostrum_ closely similar, in almost every respect, to the carina, even to the exterior, lateral, longitudinal ridges, and in their relation to the inters.p.a.ces in the lower whorl. The valve is generally not so long, but rather wider, more inwardly bowed, and with the exterior solid keel less prominent than in the carina. The inner growing surface (fig. 3 _b"_ _d_) is less ac.u.minated at its upper end.
_Upper pair of Latera._--These are much larger than the remaining valves of the lower whorl; they are straight, triangular, and much ac.u.minated, with their apices, when well preserved, extending far up, for fully three fourths of the height of the scuta. They nearly equal in length the carina. The growing surface (fig. 3 _b"_, _a_) is flat, triangular, in well-preserved specimens forming only a third or a quarter of the entire length of the valve. In the middle of the basal margin there is a very slight prominence, corresponding with a slight external central ridge, formed as heretofore by the overlapping of two of the valves of the lower whorl. Basal margin nearly on a level with that of the scuta and with the basal points of the terga. The foregoing eight larger valves form the main cavity, in which the body of the animal is lodged.
_Valves of the Lower Whorl._--These, seen externally, seem to belong to more than one whorl, but internally their basal margins stand on a level. They vary in number, as already stated, from 22 to 26. I have seen an individual with a valve more on one side than on the other. They are of unequal sizes, but they are rather variable in this respect: the largest are not above half the size of the upper latera: three or four pairs, together with the sub-rostrum (_e_) and sub-carina (_c_), are always larger than the others: these two latter valves differ from the others only in being more concave. Seen externally, all these valves project considerably, and curl a little inwards, with their apices generally worn and truncated. Viewed internally (fig. 3 _b"_), whilst the valves are in their proper places, the inner and growing surfaces of the smallest are seen to be triangular,--of the larger, some are rhomboidal, and others quadrilateral with the upper side much longer than the lower. These latter valves overlap the upper parts of the little valves on both sides of them; the rhomboidal valves overlap a valve on one side, and are overlapped on the other; the triangular valves are overlapped on both sides.
The corium lining the capitulum is produced into narrow purple crests, which enter the interstices between the valves, more especially along the line separating the upper and lower whorls. There is, also, a distinct flattened, tapering, free projection of corium, which enters between the carina and sub-carina; and another between the rostrum and sub-rostrum.
_Peduncle_, much compressed, short, rarely as long as the capitulum; in one very large specimen it was extremely short, barely one fifth of the length of the capitulum. The attached portion, which is moderately pointed in young specimens, becomes extremely broad in old specimens.
The calcified scales sometimes differ a little in size, in specimens of the same age: they are always compactly and symmetrically arranged: in old specimens they are much larger than in young ones: each scale has, at first, a transversely elliptic growing base, which ultimately becomes nearly circular. Exteriorly the tips of the scales are always disintegrated; they are sometimes club-shaped, owing to the scales having been re-added to after a period of reduced growth. The scales are fringed with brown disintegrating membrane.
_Attachment._--At the base of the peduncle, the two cement-ducts running together, twist about in a singular manner, and at their bends pour forth cement. According to the age of the specimen, the ducts vary in diameter from 1/2000th to 5/2000ths of an inch. The two cement glands are small and difficult to find; they are retort-shaped, with two ovarian tubes entering each. They lie close together, in nearly the centre of the peduncle, and less than half-way down it. This proximity of the two cement-glands, and their position low down the peduncle, are of interest in relation to the position of these same glands in the sessile Cirripedes.
_Size and Colours._--This is the largest and most ma.s.sive species in the family. I have seen one specimen in the British Museum, from the Coast of China, 2.3 inches across the capitulum, and 1.5 in length, with the valves surprisingly thick. The relative width and length of the capitulum varies. The sack (in specimens long kept in spirits) is dirty purple, and exteriorly between the scuta, dark purple. The cirri, trophi, p.e.n.i.s, caudal appendages, three posterior segments of the thorax, and the abdominal surface are dark-brownish purple.
_Body._--Thorax remarkably compressed and carinated; prosoma pretty well developed. Extending from the base of the second cirrus, to nearly a central line on the thorax, there is on each side a rounded ridge: there is a second transverse ridge, running from the base of the first cirrus to near the adductor scutorum muscle: these ridges seem formed merely to allow of the larger development of the testes.
_Mouth._--Labrum highly bullate; crest without any teeth, but with a few minute hairs. The inner fold of the labrum forming the supra-oesophageal cavity, is thickened, and shows a trace of a central line of junction, as in Sessile Cirripedes.
_Palpi_ (Pl. X, fig. 7), small; of a singular club-like shape, owing to the convexity of the outer margin; exterior spines long, all doubly serrated.
_Mandibles_ (Pl. X. fig. 1), with five teeth, of which the second is very small; inferior angle coa.r.s.ely pectinated.
_Maxillae_ (fig. 14), with a deep narrow notch (bearing some fine spines) beneath the two upper great spines, which stand on a prominence; edge straight, bearing fourteen or fifteen pairs of spines: on the inferior angle there is an obscure tuft of shorter and finer spines: apodeme long, sinuous, and slender.
_Outer Maxillae_ (fig. 17), with the inner margin divided by a deep notch into two lobes, of which the upper one is rather short; both are clothed with a compact row of short bristles; exterior margin with longer bristles.
_Olfactory Orifices_, large and prominent to an unusual degree.
_Cirri_, moderately long and curled; the four posterior pair are alike; each segment has its anterior face somewhat protuberant, and bears six pairs of long spines, with a rather large, narrow tuft of intermediate spines, some of which are finely and doubly serrated. The dorsal tufts consist of short, thick spines, with some fine longer ones. The first cirrus is seated near the second; its rami are slightly unequal in length; lower segments paved with bristles; one ramus is thicker than the other, and some of its segments have coa.r.s.ely pectinated spines.
Second cirrus has the five basal segments of its anterior ramus highly protuberant, and paved with bristles, of which some are coa.r.s.ely pectinated; the basal segments of the posterior ramus are rather more thickly clothed with bristles than are the posterior cirri, but otherwise resemble them. The third cirrus, as already stated, is exactly like the three posterior pairs; and this is a very unusual circ.u.mstance.
On the dorsal surfaces and sides of the pedicels of the posterior cirri, there are some scattered, short, thick, minute spines.
_Caudal Appendages_, multi-articulate: in a medium-sized specimen, each contained eight segments, which reached half-way up the upper segment of the pedicel of the sixth cirrus. Lower segments flattened; the upper, tapering, and cylindrical; all have their upper margins furnished with stiff, little spines. In a young specimen (only .3 of an inch in length, including the peduncle), the caudal appendage contained only four segments, and the tip did not reach to the upper edge of the lower segment of the pedicel of the sixth cirrus.
_Stomach_, without caeca.
_Generative System._--Vesiculae seminales not reflexed at their broad ends; white, spotted with black. Testes, pear-shaped, borne on long footstalks: p.e.n.i.s covered with minute bristles, in little tufts arranged in straight lines. The ovarian tubes fill up the peduncle to its base, but do not surround the sack; they are of small diameter, and simply branched. There is a very narrow ovigerous fraenum, with a straight edge, lying on each side under the line of junction between the scutum and upper latus.
_Affinities._--This species differs from all the others of the genus, in the third cirrus resembling exactly the three posterior pairs. In most of its characters--namely, in the symmetrical arrangement of the scales on the peduncle, in the considerable size of the valves of the lower whorl, in the general approximation of the valves, in the multi-articulated caudal appendages, in the form of the outer maxillae, in the prominent olfactory orifices, in the basal segments of the anterior ramus alone of the second cirrus being paved with bristles, there is more affinity to _P. cornucopia_, _P. elegans_, and _P.
polymerus_ than to _P. sertus_ and _P. spinosus_.
In the scuta and terga being articulated together, in the union of all the valves by stiff membrane, in the peculiar manner in which the valves of the lower whorl overlap each other, in the corium entering between some of the valves in filiformed appendages, in the near equality of size of the rostrum and carina, in the shortness of the peduncle in old specimens, in the position of the cement-glands, and lastly in the characters of the third pair of cirri, this species presents a closer affinity to the sessile Cirripedes, more especially to the Chthamalinae, than does any other species of any other genus amongst the Lepadidae. The movements, however, of the four opercular valves are not at all more independent of the other valves, than in the other Pedunculated Cirripedes; and the peduncle is furnished with all its characteristic muscles.
5. POLLICIPES SPINOSUS. Pl. VII, fig. 4.
ANATIFA SPINOSA. _Quoy_ et _Gaimard_. Voyage de l"Astrolabe. Pl.
xciii, fig. 17.
_P. capitulo valvarum uno aut pluribus sub-rostro verticillis instructo: laterum pari superiore vix inferioribus longiore: membrana valvas tegente (post desiccationem) subfusca flavescente: pedunculi squamis inaequalibus, non symmetricis: verticillis longiuscule distantibus._
Capitulum with one or more whorls of valves under the rostrum: upper pair of latera only slightly larger than the lower latera: membrane covering the valves (when dried) light yellowish-brown: scales of the peduncle of unequal sizes, unsymmetrical, arranged in rather distant whorls.
Maxillae, with the edge square and straight: caudal appendages uniarticulate: filamentary appendages, none.
New Zealand. Mus. Jardin des Plantes, Paris: Mus. c.u.ming.
_Capitulum_, flattened, triangular, broad, with the valves varying in number, in full-grown specimens of the same size, from 30 to above 60; the scuta, terga, and carina are very much larger than the other valves; the rostrum, however, is nearly half the size of the carina; the remaining valves are exceedingly small. In some specimens there is only one whorl under the carina; in other specimens there are distinctly two whorls. The scuta, terga, and carina stand pretty close together; they are moderately thick, and are covered, in chief part, by yellowish-brown membrane, which is dest.i.tute of spines.
_Scuta_, triangular, broad, basal margin slightly protuberant.
_Terga_, as large as the scuta, flat, regularly oval, basal point blunt and rounded.
_Carina_ very slightly curved, triangular, internally rather deeply concave, basal margin straight. The inner and growing surface is four fifths of the entire length of the valve. In half-grown specimens the apex projects a little outwards.