Davidson in his Monograph on the British Fossil Brachiopoda states that the largest “recent Brachiopod which has come under my notice is a specimen of Waldheimia venosa Solander, measuring 3 inches 2 lines in length, by 2 inches in breadth, and 1 inch 11 lines in depth.” It was found in the outer harbour of Fort William, Falkland Islands, in 1843. A specimen of Terebratula grandis from the Tertiary deposits, however, exceeds this in all its dimensions. Its length was 4½ inches, its breadth 3 inches 2 lines, and its depth 2 inches 2 lines.
Distribution in Space
Brachiopods are very localised; they live in but few places, but when they are found they usually occur in great numbers. During the cruise of the Challenger, dredging was conducted at 361 stations; at only 38 or 39 of these were Brachiopoda brought up. Mr. Cuming, quoted by Davidson, records that after a great storm in the year 1836, he collected as many as 20 bushels of Lingula anatifera on the sea-shore at Manilla, where, he relates, they are used as an article of food. It has been suggested above that their abundance in certain localities is due to their limited powers of locomotion, which are effective but for a few hours, the larva being, moreover, so minute that unless borne by a current it could not travel far from its parent. When once settled down it has little to fear from the attacks of other animals. The size of its shell relative to its body would deter most animals from regarding it as a desirable article of food, and as far as is known at present the Brachiopoda suffer but little from internal parasites, the only case I know being a minute parasitic Copepod belonging to a new and as yet unnamed genus which I found within the mantle cavity of Cistella (Argiope) neapolitana in Naples. Their slight value as an article of diet has doubtless helped to preserve them through the long periods of geological time, through which they have existed apparently unchanged.
Two of the recent genera of the family Lingulidae, Lingula and Glottidia, are usually found between tide-marks or in shallow water not exceeding 17 fathoms. Discina is also found about the low-tide level, but one species at any rate, Discinisca atlantica, has been dredged, according to Davidson, “at depths ranging from 690 to nearly 2425 fathoms.” Their larvae frequently settle on the shells of their parents, and thus numbers of overlapping shells are found clustered together. Crania is usually dredged from moderate depths down to 808 fathoms, adhering to rocks, lumps of coral, stones, and shells.
Of the Testicardines, Terebratula Wyvillei has probably been found at the greatest depth, i.e. 2900 fathoms, in the North Pacific. It is interesting to note that its shell is glassy and extremely thin. The Brachiopoda are, however, as a rule, found in shallower water; they abound up to a depth of 500 or 600 fathoms, after which they rapidly diminish with increasing depth. About one-half the named species occur at a depth of less than 100 fathoms.
The vertical range of depth of certain species is great; Terebratula vitrea is recorded from 5 to 1456 fathoms, T. Wyvillei from 1035 to 2900 fathoms. This is to some extent explicable since, after a certain depth has been reached, many of the external conditions, such as absence of temperature and light, must remain constant even to the greatest depths of the ocean.
The area of the ocean explored by dredging forms such an infinitesimal fraction of the whole, that it seems superfluous to consider the horizontal distribution of Brachiopods. A few facts may, however, be mentioned. Certain species, as Terebratula vitrea, T. caput serpentis, Waldheimia cranium, Megerlia truncata, and Discinisca atlantica, have a very wide if not cosmopolitan distribution. The second of the above named extends as far north as Spitzbergen, and as far south as Kerguelen Island. Many species are, on the other hand, very localised, and have hitherto only been found in one place. A very considerable number of these have been dredged off Japan and Korea, and this region may be to some extent regarded as the headquarters of the group.
The following species have been obtained within the limits of the British Area, as defined by Canon Norman, who has been good enough to revise the list, which is founded on that drawn up by Davidson in his Challenger Report. Their range of bathymetric distribution is given in the column on the left.
| Depth in Fathoms | |||
| 0 to | 1180. | Terebratulina caput serpentis Lin. | Oban, and off Cumbrae Islands, Loch Torridon, Scotland, off Belfast |
| 8 to | 25. | Terebratula (Gwynia) capsula Jeff. | Belfast Bay, E. and S. coast of Ireland, Plymouth, Weymouth, and Guernsey |
| 5 to | 690. | Waldheimia cranium Müller | North British seas. Off Shetland |
| 75 to | 725. | Waldheimia septigera Lovén | North British seas. Off Shetland |
| 20 to | 600. | Terebratella spitzbergenensis Dav. | N.N.W. of Unst, Shetland |
| 18 to | 364. | Argiope decollata Chemnitz | Two miles east of Guernsey |
| 20 to | 45. | Cistella cistellula S. Wood | Shetland, near Weymouth, S. coast of England |
| 650 to | 1750. | Atretia gnomon Jeff. | W. of Donegal Bay in 1443 faths. Between Ireland and Rockall, in 1350 faths. |
| 10 to | 690. | Rhynchonella psittacea Gmelin. | Shetland and near Dogger Bank.This species is possibly fossil as well as recent |
| 3 to | 808. | Crania anomala Müller | Loch Fyne, North of Scotland |
| 690 to | 2425. | Discinisca atlantica King | W. of Donegal Bay in 1366 faths., W. of Ireland in 1240 faths., off Dingwall Bay |