“Sergestes arcticus Kröyer.
Oversigt Vidensk. Selsk. Forhandl. Kjöbenhaven, 1855, p. (6); Monograph. Sergostes, Vidensk. Selsk. Skr., V., Naturvidensk. mathem. Afh., IV. pp. 240, 276, Pl.III. figs. 7a -7g, Pl. V. fig. 16, 1856.
Smith, Proc. National Mus., Washington, III. p. 445, 1881.
Plate XVI. Fig. 4.
Station.
N. Lat.
W. Long.
Fathoms.
Specimens.
304
41°35’0”
65°57’30”
139
Fragments only.
309
40°11’40”
68°22’0”
304
1 ♀
326
33°42’15”
76°0’50”
464
1 ♂, 1 ♀
337
38°20’8”
73°23’20”
740
1 ♀, 55mm. in length.
In this species there is an epipod and a well-developed podobranchia at the base of the second maxilliped, and above its base a simple lamella in place of a pleurobranchia, a large anterior pleurobranchia with a simple lamella back of it on each of the three succeeding somites, a large anterior and a small posterior pleurobranchia on the antepenultimate somite, and on the penultimate somite two small branchiæ, of which the posterior is very much the smaller, while the last somite is without branchiæ; or, indicating the simple pleurolamellæ by accents, the branchial formula* may be indicated as follows : —
Somites.
VII.
VIII,
IX.
X.
XI.
XII.
XIII.
XIV.
Total.
Epipods
1
1
0
0
0
0
0
0
(2)
Podobranchiæ
0
1
0
0
0
0
0
0
1
Arthrobraniæ
0
0
0
0
0
0
0
0
0
Pleurobranchiæ
0
0’
1’
1’
1’
2
2
0
7
8+(2)
The structure of the branchiæ themselves, in this and in the two following species as well, is very different from that in Penæus, or any of the Penæidæ described in this paper. The branchiæ are pinnate in form, and each pinna is a complete phyllobranchiæ; that is, they are compound phyllobranchiæ, while those of Penæus are compound trichobranchiæ. The structure is more like that in Sicyonia (judging by Bate's description of the branchiæ of that genus) than that in Penæus.
The first pair of thoracic legs are subchelate, and the dactyli of the external maxillipeds and the propodi of the first, second, and third pairs of legs are multiarticulate, as in the next species, the articulations being more conspicuous than in that species. These structural characters of the thoracic legs are, however, undoubtedly characteristic of all the species of the genus.
* Boas (Studier over Decapodernes Stægtskabsforhold, Vidensk. Selsk. Skr., VI., Natuvidensk. mathem. Afh., I., 1880), for S. Frisii Kröyer, gives an epipod and a rudimentary arthrobranchia for the eighth somite and a single pleurobranchia for each of the succeeding somites including the last. Bate (Ann. Mag. Nat. Hist., 5th ser., VIII. p. 193, 1881 ), gives, for the genus Sergestes, a " mastibranchia" (epipod) and one pleurobranchia for the eighth somite, a single pleurobranchia for the ninth, a pleurobranchia and pleurolamella each for the tenth, eleventh, and twelfth, two pleurobranchiæ for the thirteenth, and nothing for the last; but under S. Kröyeri he says, "This species has two well-developed pleurobranchiæ attached to the penultimate somite of the pereion, two to the antepenultimate, one plume and a leaflike plate to the next three somites, and one plume and a rudimentary mastibranchial plate to the first pair of gnathopoda" (second maxillipeds). This last statement of Bate would apparently indicate an arrangement of the branchiæ much like that which I have given above, or even nearer to that of S. robustus described beyond, but it is very unlike the arrangement indicated by his formula for the genus.“
(Smith, 1882)
