Fam. 5. Rhynchothoracidae.—The animal identified by Dohrn as Rhynchothorax mediterraneus, Costa (1861), is a minute and very remarkable form, without chelophores, with large 8–jointed palps, reduced by fusion to five joints, and 10–jointed, clawed ovigerous legs, which last are provided on the last five joints with peculiar toothed tubercles. The general aspect of the body is somewhat like that of an Ammothea, which genus it resembles in the ventral insertion of the ovigerous legs and the somewhat imperfect segmentation of the body. It differs from Ammotheidae in the possession of a claw on appendage III. It is highly peculiar in the structure of the mouth, in having a long forward extension of the oculiferous tubercle jutting out over the proboscis, in the extreme shortness of the intestinal caeca and ovaries which scarcely extend into the legs, and in the absence of cement-glands from the fourth joint of the legs; these last are present only in the third joint of the penultimate legs. A single pair of generative orifices are found on the last legs. A second species, R. australis, Hodgson, comes from the Antarctic.
Fig. [284].—Rhynchothorax mediterraneus, Costa. A, Body and bases of legs; B, terminal joints of palp. (After Dohrn.)
Fam. 6. Nymphonidae.—Appendage I. well-developed, chelate; II. well-developed, usually 5–jointed; III. well-developed in both sexes, usually 10–jointed, the terminal joints with one row of denticulated spines.
Nymphon, Fabr. (1794), about forty-five recognised species, of which some are but narrowly defined. Closely allied are Chaetonymphon, G. O. Sars (1888), including thick-set, hairy species, about eight in number, from the North Atlantic, Arctic, and Antarctic; and Boreonymphon, G. O. Sars (1888), with one species (B. robustum, Bell, Fig. [276]), also northern, in which the auxiliary claws are almost absent. Nymphon brevicaudatum, Miers (= N. horridum, Böhm), an extraordinary hispid form from Kerguelen,[[437]] is also peculiar. Pentanymphon, Hodgson (1904), from the Antarctic (circumpolar), differs in no respect save in the presence of a fifth pair of legs; one species.
The only other genus is Paranymphon, Caullery (1896) (one species, Gulf of Gascony, West of Ireland, Greenland), in which the palp is (6–)7–jointed, the ovigerous leg 8–jointed, and the auxiliary claws are absent.
Fam. 7. Pallenidae.—As in Nymphon, but appendage II. absent or rudimentary.
Fig. [285].—Pallene brevirostris, Johnston, ♀, Plymouth.
Pallene, Johnston (1837): about ten species (Mediterranean, North Atlantic, Arctic, Australia). P. languida, Hoek, Australia, lacks auxiliary claws, and is otherwise distinct; but P. novaezealandiae, G. M. Thomson, is typical. Pseudopallene, Wilson (1878):[[438]] appendage III. clawed; auxiliary claws absent; four (or more) species (North Atlantic, Arctic, Antarctic). P. (Phoxichilus) pygmaea, Costa (1836), and P. spinosa, Quatref., seem to belong to this genus or to Pallene. Cordylochele, G. O. Sars (1888): closely allied, but with front of cephalic segment much expanded and chelae remarkably swollen, includes three very smooth, elongated, northern species, to which Bouvier has added one from the Antarctic; Pallene laevis, Hoek, from Bass’s Straits, is somewhat similar. Neopallene, Dohrn (1881): as in Pallene, but with a rudimentary second appendage in the female, and no generative aperture on the last leg in the male (one species, Mediterranean). Parapallene, Carpenter (1892): as in Pallene, but without auxiliary claws, and with the two last segments of the trunk (which in Pallene are coalesced) independent (about ten species, East Indies and Australia); Pallene grubii, Hoek (Phoxichilidium sp., Grube, 1869), is probably congeneric. Pallenopsis, Wilson (1881): appendage I. 2–jointed; appendage II. rudimentary, 1–jointed; appendage III. clawless; auxiliary claws present; slender forms, including some formerly referred to Phoxichilidium; about fifteen species, world-wide. Pallene dimorpha, Hoek, from Kerguelen, with 4–jointed palps, deserves a new generic appellation. P. longiceps, Böhm, from Japan, with rudimentary 2–jointed palps in the male, is also peculiar.