Geographical Range and Habits.
With respect to range, the results arrived at have no particular interest, for the species are not sufficiently numerous; and, what is still more adverse, the genera, with unimportant exceptions, range over the world; so that there is no scale of differences, and it cannot be said that these two regions differ in their genera, and these two only in their species. In all the following remarks, I have trusted exclusively to my own specific identification; and have rejected all assigned localities which appeared from any cause to be doubtful. Sessile cirripedes are found in every sea, from lat. 74° 18′ north to Cape Horn. The area included between the north point of the Philippine Archipelago and the south point of Australia, extending on the right hand to New Zealand, and on the left to Sumatra,—an area, which, though including two distinct Cirripedial regions, is small compared with the surface of the globe, yet includes a greater number of species, especially of peculiar species, than the whole rest of the known world. This is, probably, in chief part due to the broken nature of the land, affording diversified habitats, and to much of the coast being rocky. Cirripedes, from requiring to be attached, cannot live where the shores and adjoining bottom are sandy or muddy or formed of moving shingle; hence, no doubt, it arises, that there is such a remarkable contrast in the great number of the species inhabiting the bold rocky western coast of South America, and the few species living on the sloping, and often sandy or muddy or shingly, eastern shores of this continent. Hence, also, I believe, it is that not many species have been brought from India. Coral-reefs are not favorable to Cirripedes, consequently but few are known to inhabit the islands of the Pacific Ocean. Where Cirripedes can live, though the species in no district are numerous, the individuals abound in infinite numbers: I have walked over the coast-rocks of the Falkland and Chonos Islands, of Chile and Van Diemen’s Land, fairly encrusted over wide spaces with a continuous layer of Cirripedes, consisting of only two or three species; in the same manner as may be observed on many parts of the shores of Great Britain, and, I believe, of North America.
With respect to the effects of temperature on the range of Cirripedes, no genus (having more than one species) is confined to the torrid zones. [Pyrgoma], from being always attached to corals, is, of course, ordinarily found in the hotter seas; but one species ranges from the Cape de Verde Islands in the torrid zone to the southern shores of England and Ireland. [Tetraclita] is not found in the colder seas, but is numerous in species and in individuals, on the southern shores of Australia and at the Cape of Good Hope. I may here add, that the two genera with the most confined ranges, are [Chamæsipho] and [Elminius]; the former has only two species, one inhabiting Australia, and the other the East Indian Archipelago; [Elminius] has four species, confined to the southern hemisphere, and inhabiting Australia, New Zealand, and South America. To return to the effects of temperature; in Mr. Dana’s great work on Crustacea, an excellent chart is given, in which the isocrymal lines, or those exhibiting the mean temperature of the waters along their course, for the coldest thirty consecutive days in any season of the year, are given; and which lines Mr. Dana has shown are the most influential in governing the distribution of marine animals. At the isocryme of 68°, Mr. Dana divides the torrid and sub-torrid zones from the several temperate zones; and at 44°, the temperate from the sub-frigid and frigid zones; but as no Cirripedes are exclusively confined to these frigid zones, we may here disregard them. From Mr. Dana’s[76] table of the areas of the torrid and temperate ocean-zones, on both sides of the equator, it seems that they are nearly as 337 to 278, in relative area; and consequently, he remarks, that the marine species in any class, if distributed equally over the two, would be one fifth more numerous in the torrid than in the temperate zones. Now of Cirripedes, taking all the orders, there are at present known 147 species; of these, 7 have doubtful habitats, leaving 140 for comparison. Of these 140, nearly one quarter, or 37, inhabit both the torrid and temperate zones, as above defined; 46 are found exclusively in the torrid, and 57 exclusively in the temperate zones; so that the temperate zones, though less in area, and having, proportionally, even a considerably lesser length of coastline, nevertheless have a preponderance in the number of species. But it should be borne in mind, that there are two great temperate districts, separated from each other by one great torrid district; and, inasmuch as the number of species in any region seems to depend in some degree on the isolation of the sub-regions, we might have expected (the other conditions now being, and the past conditions having been alike), that the two great temperate areas would have contained more species, perhaps doubly more, than the single great torrid area.
[76] ‘Crustacea: United States Exploring Expedition,’ p. 1476 (corrected).
The proportional numbers, above given, are not very widely different, whether we take separately the [Balanidæ], the Lepadidæ, or all together. Mr. Dana has shown[77] at length, that generally amongst the Crustacea, the species which he considers of highest rank, belong to the extra-torrid zones: there seems to me in all such cases to be some degree of vagueness in the attempt to determine which are highest or lowest, but I have already elsewhere stated that [Balanus] is, probably, the most eminently Cirripedial form, and exhibits in the strongest manner all the characters by which Cirripedes differ from other Crustacea; as this genus is the largest, containing 36 species, of which the habitats are known, I may state that of these, exactly one third, or 12, inhabit both zones; 9 exclusively inhabiting the torrid, and 15 exclusively the temperate zones. According to the proportions of the whole class, the numbers should have been 9 torrid, to only 11.11 temperate; so that evidently the genus [Balanus] (in one sense typical) inclines towards the temperate regions more strongly than does either the family or the sub-class to which it belongs.
[77] Ibid., p. 1528.
With respect to the relation between the size acquired by the different species of sessile cirripedes, and the temperature of the localities inhabited by them, the genera [Chthamalus], [Tetraclita], and [Balanus], alone can serve for comparison: in [Chthamalus] much the largest species is found in the temperate zone: on the other hand, the two largest species of [Tetraclita] are from the torrid zone, though one of them also sometimes ranges into the temperate seas: in [Balanus], the largest species, and six other species having a basal diameter sometimes over two inches, inhabit the temperate regions; and two out of these seven species, flourish even in the Arctic seas; whereas, within the torrid zone, there are only three species with a diameter sometimes exceeding two inches, but two of these frequently become very large and massive; so that [Balanus], judging from the size of the species, as well as from their range, does not require for its highest development the temperature of the torrid zones.
The greater number of the species of the [Balanidæ] have wide ranges, as might be inferred from the fact of between one third and one fourth of the total number inhabiting both the torrid and temperate zones; but it should not be overlooked, that those species, as [Balanus tintinnabulum], [amphitrite], [improvisus], and, in a lesser degree, [B. trigonus] and [Tetraclita radiata], which seem to range over nearly the whole world (excepting the colder seas), are species which are habitually attached to ships, and which could hardly fail to be widely transported. Indeed, it appears to me surprising, that such species as [Balanus psittacus] and [eburneus], which often become attached to vessels, should still be confined, the one to Southern, and the other to Northern America. But some other Cirripedes, which I have never seen attached to vessels, have likewise immense ranges: thus [Tetraclita porosa] is found in every tropical and warmer sea, and [Chthamalus stellatus] ranges round the world in the northern hemisphere, and, along the eastern side of America, far south of the equator: [Balanus spongicola], and [Acasta spongites], extend from the shores of Britain to the Cape of Good Hope: [Balanus lævis] ranges from Tierra del Fuego to California. I may further remark, that the only two other species of [Balanus], and the one [Chthamalus], inhabiting Tierra del Fuego, are, also, found on the shores of Peru. But to show the powers of endurance in some species, I may specify the case of [Balanus improvisus], which flourishes on the coast of Nova Scotia, amongst the West Indian Islands, in Southern Patagonia, and near Guayaquil. Even more striking is the case of [B. crenatus], of which I have seen specimens from latitude 74° 48′ north, from the West Indies, and the Cape of Good Hope! In these two latter localities, however, it seems to be rare, and may have been first transported to them from the shores of Europe, on the bottoms of vessels, to which it sometimes adheres.
The several species of [Balanidæ] live attached either to coast-rocks, or to objects at various depths, down to, as in the case of [Balanus crenatus], 50 fathoms. [Balanus balanoides] sometimes adheres to rocks or wood so high up, that it is not covered by water during the neap tides. Mr. Thompson has informed me, that he once accidentally kept some specimens of this species out of water for seven days in a warm room, and that they were then quite lively. This species, is very easily killed by brackish water, as are some other species, whilst [B. improvisus] and [eburneus] can flourish in it; and at the Falkland Islands, I saw [Elminius Kingii] attached to rocks at the mouth of a fresh-water brook, so as to be covered by pure water during the ebb of each tide. Sessile cirripedes adhere to all sorts of objects, floating and fixed, animal and vegetable, living and dead, organic and inorganic. [Chthamalus] is, perhaps, more commonly attached to rocks than are the other genera. Living Mollusca are, I think, the most frequent objects of attachment: Mr. Cuming has remarked to me, that shells covered by an epidermis, as Patella, Haliotis, and Mytilus, are the greatest favorites. [Acasta] is always imbedded in sponges, or in the sponge-like bark of Isis; [Pyrgoma] and [Creusia] in corals; [Chelonobia] is attached to turtles, and one species to crabs or very smooth shells; [Coronula], [Tubicinella], and [Xenobalanus], are imbedded in the skin of Cetaceans; and [Platylepas] in that of manatee, turtles, or sea-snakes.
If we attempt, with our present not very imperfect materials, to divide the globe into provinces, according to the amount of difference in their Cirripedial inhabitants, including all orders and families, and disregarding entirely, as I think we ought, all probabilities or conclusions deduced from the distribution of other tribes of animals, we find that the globe may be divided into the four following great provinces and one sub-province. I should premise, that in the following remarks and tables,[78] the species of Lepas, Conchoderma, [Chelonobia], [Coronula], [Platylepas], and [Tubicinella], are excluded, owing to their being attached to floating or swimming objects, and being consequently widely and irregularly distributed.