(“Challenger” Reports, “Cirripedia,” 1883, viii. 8-11), gives a brief
geological summary down to 1882. In that year J. M. Clarke
(Amer. Journ. Sci. and Arts, 3rd series, vol. xxiv., p. 55) added
a new species to Plumulites (Barrande, 1872), remarking that the
species in question, P. devonicus, “is interesting in being the first
representative of fossil barnacles from the Devonian, Barrande's
species of Plumulites and Anatifopsis, as well as the Turrilepis of
Woodward, being from the Upper and Lower Silurian, and Plumulites
jamesi (Hall and Whitf., Pal. Ohio, vol. ii.) from the Hudson
River group.” Since Plumulites appears to be a synonym of Turrilepas
(not Turrilepis), the species Turrilepas wrightii (Woodward,
1865), from the Upper Silurian of Dudley, did not long enjoy an
isolated eminence as the oldest known cirripede. As pointed out
by Dr Bather (Geol. Mag. 1901, decade 4, vol. viii. p. 521),
palaeontologists themselves have in this branch not very closely followed
the progress of their own science, since Dr Ruedemann, in regard
to his new Pollicipes siluricus, 1901, speaks of “the enormous gap
existing between the appearance of this Lower Siluric type and the
next Upper Triassic (Rhaetic) representatives of the genera Pollicipes
and Scalpellum.” Many species of Scalpellum from the Wenlock
shale of Gotland were described in 1892 by C. W. S. Aurivillius,
who at the same time founded the species Pollicipes signatus on an
almost perfect specimen from the Lower Ludlow of Wisby in Sweden.
Aurivillius considered that Pollicipes signatus showed a closer
approach to the Balanidae than any other of the Lepadidae, but
he, too, in ignorance of the Devonian Protobalanus (Whitf.),
discoursed needlessly about the gap in the distribution. Dr Bather
justifiably anticipates further discoveries, but if, already in Silurian
as in modern times, the members of these families had to pass
through nauplius and cypris stages to maturity, there is one
“enormous gap” between them and the common ancestor of the crustacean
class that will not be easily filled.
To later phylogenetic links an
addition is offered by Dr Woodward
(Geol. Mag., 1901, p. 145),
who transfers his Pyrgoma
cretaceum, 1865, to a new genus
Brachylepas (fig. 1), and a new
family Brachylepadidae, intermediate
between the Rhaetic Pollicipes
and the modern Balanus. Among
other fossil genera of recent
institution, Archaeolepas, Lepidocoleus,
Squama, Stramentum can only be
mentioned as incentives to
research. Among living forms, added
since Weltner's catalogue, may be
noticed Koleolepas willeyi, from the Loyalty Islands (Stebbing, in
Wil1ey's Zool. Results (1900) pt. v., p. 677. This was found in
a Turbo shell, occupied also by a Pagurid, and coated with
Actinians. The cirripede, which has an
elastic peduncle, a crested capitulum, but
no valves, and the first cirrhi longer than
the rest, should stand near Eremolepos, the
name given by Weltner in place of the
preoccupied Gymnolepas (Aurivillius). In
the genus Scalpellum, S. giganteum, Gruvel
(Trans. Linn. Soc., 1901) disputes with S.
stearnsii (fig. 2), Pilsbury, 1890, which shall
be accounted the greater. The latter is
threatened with a new generic name (Chun,
Aus den Tiefen des Weltmeeres, 1900,
p. 502).
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Fig. 1.—Brachylepas cretacea (Woodward), from Margate chalk. |
The horizontal distribution of barnacles over all seas is fully explained by Darwin. The bathymetric range of sessile as well as pedunculate forms down to such depths as twelve or eighteen thousand feet—Verruca quadrangularis, Hoek, 1900 fathoms; Scalpellum regium, Wyville Thomson, 2850 fathoms—is a more recent discovery. Gruvel (Contribution à l'étude des Cirrhipèdes, 1894) found that the species frequenting sea surface or shallow water, notwithstanding their feeble powers of vision, cannot live long when entirely debarred from light. It must, therefore, be supposed that abyssal forms have gradually acquired such tolerance of darkness as makes their health independent of the sun. Among other singularities of habitat, not the least curious is the freedom with which some small species, especially in the genus Dichelaspis, occupy the very jaws of large crustaceans. It is generally stated that cirripedes are confined to salt water, and, generally speaking, that is true. But Platylepas bissexlobata (De Blainville), from the west coast of Africa, is sometimes found entirely buried, except its operculum, in the skin of the manatee. Now, since it seems this Manatus senegalensis ascends rivers, we may infer that its parasite travels with it. Studer (Crustacea of the Gazelle, 1882) records Balanus amphitrite (Darwin?) from roots and stems of mangroves in the Congo, where, he says, “it follows the mangroves as far as their vegetation extends along the stream, to six sea-miles from the mouth.” Darwin notes B. improvisus as quite tolerant of water not saline. Why the Thyrostraca, so hardy, so widely dispersed and multitudinous, and with a history so prolonged, should not have made more extended and more independent incursions into fresh water remains a problem. Though the Ornitholepas australis (Targioni Tozzetti, 1872), found on the tail feathers of a bird, represents only the cypris-larva of a cirripede, it still shows one of the many facilities for dispersion which these creatures enjoy. A striking instance of their abundance is cited by Aurivillius (1894) from a report by Captain G. C. Eckman, who late in the summer observed great masses of Lepas fascicularis forming broad belts in the North Sea. Aurivillius himself examined a humpback whale which had as many as fifty specimens of Coronula diadema on each side of its head. He believes that the cetacean approaches not only rocks, but ships, in the hope of freeing itself from its lodgers. Yet the fact that the long, soft Conchoderma auritum stands exposed on the Coronula, sometimes ten on one, indicates that the whale can have little chance of evicting its tenants, even at the expense of rubbing off the eighteen flattened horns of its own skin embedded in cavities round the domed base of the Coronula shell. The fecundity in the genus Lepas has struck many observers. Hoek (“Challenger” Reports, “Cirripedia,” 1884, vol. x.) notes that, while in Scalpellum the number of eggs may be less than a hundred, “in Lepas anatifera it amounts, on the contrary, to many thousands and tens of thousands.” In the same treatise Dr Hoek has useful chapters on the anatomy, development and sexes of the group, with references to the important researches since Darwin by Krohn, Claus, Kossmann and others. Francis Darwin, in the life of his father (1888, iii. 2), says, “Krohn stated that the structures described by my father as ovaries were in reality salivary glands, also that the oviduct runs down to the orifice described in the Monograph of the Cirripedia as the auditory meatus.” Hoek, however, observes that the interpretation of the glands as salivary is not given by Krohn as his own opinion, but only quoted from Cuvier. Hoek himself proposes to -call them pancreatic glands.
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Fig. 2.—Scalpellum stearnsii. |
On the absorbing question of the development, T. T. Groom (Phil. Trans., 1894, vol. clxxxv.) supplies a full bibliography, beginning with the pioneers Slabber (1778; properly 1769) and J. Vaughan Thomson (1830). Groom's monograph was almost immediately supplemented by Chun's chapters on the same subject (Bibliotheca Zoologica, 1895, Heft 19, Lieferung 2), to which an important discussion is contributed by H. J. Hansen (Die Cirripedien der Plankton-Exp., 1899). He insists on the value of the upper lip or labrum for generic distinction, and as an aid in affiliating larval forms of different stages to their several species. He cites Groom's evidence that larvae obtained from the egg readily go through one moult in the aquarium, and the known fact that the last larval stage is marked by a longitudinal series of six pairs of immovable spines or processes. He considers, then, that by a judicious comparison of larval forms with these two easily determinable stages the poverty of existing information on the subject may be gradually, if laboriously, diminished. The large and peculiar Archizoea gigas of Dohrn must, he thinks, belong to the Lepadidae as a larva in the last stage, but not, as v. Willemoes Suhm supposed, to Lepas australis, or even to the genus Lepas at all.
Thyrostraca anomala.—This section comprises Darwin's Apoda, the footless, Lilljeborg's Suctoria, called by Fritz Müller the Rhizocephala or rootlet-headed, and the group to which Lacaze-Duthiers gave the alternative names Ascothoracida, sac-bodied or Rhizothoracida, rootlet-bodied. For the present these names may be dispensed with in favour of their equivalents, the three families Proteolepadidae, Sacculinidae and Lauridae. The first is still limited to the single genus and species Proteolepas bivincta (Darwin), parasitic within the sac of another cirripede. Nothing is certainly known of its development, except that the ova are extremely small, but H. J. Hansen (Die Cirripedien der Plankton-Exp., 1899, p. 53) argues that various nauplii of a type not previously described may probably be referred to this group or family. The second family, discussed by Delage, Giard, Kossmann and others, has no dearth of genera and species, though about several of them the information is scanty. Almost all of them are parasitic on other crustaceans. Sphaerothylacus polycarpus (Sluiter, 1884) has an ascidian for its host. Sarcotaces (Olsson, 1872) has two species parasitic in fishes. But these exceptional and dubious forms do not obtain nutriment by sending rootlets in a rhizocephalous manner into their patrons. The family Peltogastridae is sometimes separated from the Sacculinidae, and sometimes made to do duty for both, the latter course being improper, since Saeculina (J. Vaughan Thompson, 1836) is not, as has been supposed, preoccupied, and must, therefore, take precedence of Peltogaster (Rathke, 1843). In the same family stands the genus Sylon, noted by Kröyer without a name in 1842, named by him without a description in 1855, described by Michael Sars in 1869, and published by G. O. Sars in 1870. Hoek (“Challenger” Reports, 1888, vol. xxiv. app. A) will orientate the English reader on this genus. For the complicated parasitism of isopods and Sacculinidae on the same hosts Giard and Bonnier (Bopyriens, 1887, p. 197) should be consulted.
The remaining family may, till further knowledge, be allowed to cover four remarkable species, three of them resident on Anthozoa, one on an echinoderm. Only the first, the celebrated Laura
