A BOX OF BRANCHIE

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CHAPTER XXIII

TRIBE III.-VALVIFERA

HERE the uropods undergo a remarkable metamorphosis, and assume a function distinct from any that they have elsewhere, for like a pair of folding doors they form a great part of the ventral surface of the pleon, these valves closing over the five pairs of branchial pleopods or opening to admit the water to them.

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In the History of the British Sessile-eyed Crustacea,' vol. ii. pp. 358, 368, 375, 378, the uropods are successively spoken of as the first or anterior pair of pleopoda,' as pertaining to 'the first segment of the tail,' as being absent in the Idoteida, where there is said to be a 'conversion of the fifth pair of pleopoda into a continuous operculum for the protection of the branchial organs,' and lastly, in the genus Idotea, as a strong outer pair (which are the terminal uropoda), forming an operculum' over the 'five pairs of very delicate branchial appendages.' Of these four statements the first two are consistent but erroneous, the last two are inconsistent with the first and with one another; only the final one is correct. All the four, as it happens, appeared in the same number of the work, namely, Part 19, published October 1, 1867, so that the confusion is difficult to account for, even as an accident of dual authorship.

The tribe includes two well-separated families, the Arcturida and Idoteidæ.

Family 1.-Arcturida.

The form of the animal is elongate and sometimes cylindrical; the segments of the pleon are more or less

coalesced. The second antennæ are large and long; the mandibles have a molar tubercle but no 'palp;' the outer plate of the first maxillæ and the inner plate of the second are broad; the maxillipeds have an oval epipod, a broadly expanded plate to the second joint, and the five joints of the 'palp' not very large; the first four pairs of limbs of the peræon are directed forwards, slender, ciliated, with the terminal joint minute; the last three pairs are stouter, ambulatory, with the terminal joint bifid. The. opercular uropods have the inner branch much shorter than the peduncle, the outer branch rudimentary or sometimes entirely wanting. When the valves are closed the branch of the uropods which is homologically the outer is shut up inside, even when present.

Arctūrus, Latreille, 1804, has the flagellum of the second antennæ more than four-jointed, the fourth segment of the peræon not greatly longer than the others, the marsupium of the female composed of four pairs of plates. The arctic Arcturus Baffini (Sabine) grows to a length of three inches. Mr. F. E. Beddard has described thirteen new species brought from various parts of the world by the Challenger. Others have been described by Miers, Sars, and Studer. Almost all have a striking appearance from the armature of spines or tubercles. In their clinging habit and general appearance they have some resemblance to the amphipod group, the Caprellidæ, some of which are also very spinose. It is interesting to observe that in creatures which are structurally very distinct a similar mode of life goes with a similar general appearance, so that the similarity of life may be supposed to have produced the similarity of look.

Astacilla, Cordiner, 1795 (=Leacia, Johnston, 1825), has the flagellum of the second antennæ not more than fourjointed, the fourth segment of the peræon much longer than any of the others, and the marsupium of the female consisting of two plates affixed to this segment. There is no reason for discarding Johnston's Leacia, on the ground that the different name Leachia was preoccupied. It is a common and quite justifiable practice to form generic names by

CORDINER'S LITTLE LOBSTER

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variations on the same theme, as Darwinia and Darwinella. Harger points out that Fleming's reference of Astacilla to the Rev. Charles Cordiner, 1784, is no proof that it was published or described at that date. But in a work entitled Remarkable Ruins and Romantic Prospects of North Britain with Ancient Monuments and Singular Subjects of Natural History by the Rev. Charles Cordiner of Banff. London, 1795,' there is a section headed' Astacillæ, Purple Doris, &c.,' containing the interesting passage which follows:

'One very lively species of little lobsters, which had taken up their dwelling among these coralines, seemed on account of its novelty to merit the attention of a particular drawing.

"Their general form and appearance in their natural state, and the size of life, are carefully represented at a, a, a; an elaborate delineation of the microscope, after a minute investigation of the particular structure of its several parts, is inserted above at A. That will more distinctly express to the curious the peculiarities of the animal than any specific distinctions which could be narrated. The eye appeared as a regular arrangement of bright specks, in circular rows, as at the figure I.

The diminutive ASTACILLE, of the general name of lobsters, is applied at present, as a common characteristic, until one more particularly appropriate may be fixed on to distinguish it by; for these are a species that do not appear to have been yet recognized among the varieties of British insects.'

Seeing that this account is accompanied by an unmistakable figure of Astacilla longicornis (Sowerby), it seems only proper to uphold the priority of Cordiner's generic name, and perhaps the name of the family ought to become Astacillida. The British species are Astacilla longicornis (Sowerby), Astacilla intermedia (Goodsir), Astacilla gracilis (Goodsir), Astacilla damnoniensis, Stebbing, Astacilla Deshayesii (Lucas), and Astacilla dilatata, Sars. This last and others of the genus named by the same author are found on the coasts of Norway. Astacilla granulata, Sars,

occurs in the North Atlantic, Astacilla marionis, Beddard, in the Southern Ocean. The young of this genus sometimes, if not always, have the fourth segment of the peræon not elongate, just as in Arcturus.

Family 2.-Idoteido.

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The body is ovate or oblong, or more or less oblongovate. The mouth-organs and pleon and its appendages are nearly as in the preceding family, but the maxillipeds sometimes have the palp' become three-jointed by coalescence. The second antennæ are not as a rule greatly elongate; the flagellum may be rudimentary, singlejointed, or more usually multiarticulate. The limbs of the peræon are usually nearly alike, but the first three pairs are sometimes subchelate, and the last two may be 'multiarticulate.'

Glyptonotus, Eights, 1852, has the maxilliped-' palp' three-jointed, the two terminal joints being fused and also the two that precede them. The first three pairs of limbs of the peræon have the sixth joint dilated and are subchelate. The pleon has three or four complete sutures; the stilets on the second pair of pleopods in the male are very elongate; the outer branch of the uropods is minute. Glyptonotus antarcticus, Eights, being 'dorsally sculptured,' corresponds with the generic name. It attains a length of three inches and a half by a breadth of an inch and threequarters, and is, therefore, one of the monster Isopods. The Arctic species, which also occurs in the Baltic and the depths of the Swedish Lakes, Glyptonotus entomin (Linn.), is not much smaller than the preceding. Chiridotea, Harger, 1878, is regarded by Miers as a synonym of Glyptonotus.

Chatilia, Dana, 1852. Mr. Miers, in his elaborate ‘Revision of the Idoteidæ,' says:-'The multiarticulate character of the sixth and seventh thoracic legs is probably not a character of the importance assigned to it by Dana. In its ovate form, four-segmented postabdomen [pleon], and elongated antennules, the relationship of Chatilia to Glyp

tonotus is obvious; but the antennules in Chatilia are placed immediately above the antennæ, as in Edotia.' In Chatilia ovata, Dana, the sixth pair of legs are described as being 'twice as long as the entire animal, terminating in a very long bristle-like extremity, which consists of numerous joints. The seventh pair has also a multiarticulate extremity, which is, however, quite short.' Dana thought a separate family Chatiliidae necessary for this genus.

Arcturides, Studer, 1882, in general appearance and in the length of the second antennæ approaches Arcturus, but the short-jointed limbs are all very nearly alike, though the first are shortest, and the three following pairs a little more prehensile than those to the rear. In the southern Arcturides cornutus, Studer, the head has a pair of frontal horns, and is not articulated with the first peræon-segment though divided from it by a suture.

Idotea, Fabricius, 1798, has the second antennæ moderately elongate; the maxilliped-' palp' four-jointed, only the last two joints being fused; the limbs of the peræon all nearly alike, with the sixth joint not or not much expanded, but the seventh prehensile. The uropods have on the basal plates a raised line near and almost parallel to the inner margin, and an apical plumose seta, which is concealed under the terminal plate. The species are very numerous, and several additional genera have been proposed which Mr. Miers does not think worthy to be upheld.

Idotea marina (Linn.) is the name he adopts for that which Bate and Westwood describe as Idotea tricuspidata, Desmarest, and Idotea pelagica, Leach, and which has also been called by a dozen other names. It is very abundant. Its distribution appears to be almost cosmopolitan. In size and colour it is extremely variable. Idotea metallica, Bosc, which seems to have as great a range over the world, is, however, not recorded from British coasts. Idotea emarginata, Fabricius, is common in British waters, but not like marina on the shore, and the same may be said of Idotea linearis (Linn.), with which Mr. Miers combines the curiously striped Idotea sexlineata of Kröyer.