There are two ecdyses or moults during development, a partial moult, concerning only the ventral surface of the “pro-embryo” as it assumes the larval form, and a complete moult at the final stage, before emergence from the incubating sac.
At the end of winter the mother cuts a hole in the silken web, and the young brood issues forth.[[337]]
Classification.—The order Chernetidea consists of a single family, Cheliferidae. Nine genera are recognised by most authors, but their grouping has been the subject of a good deal of difference of opinion, largely dependent on the different systemic value allowed by various arachnologists to the absence or presence of eyes, and to their number when present. Simon takes the extreme view that the eyes are only of specific value, and he is thus led to suppress two ordinarily accepted genera, Chernes and Roncus, which are separated chiefly by eye-characters from Chelifer and Obisium respectively. He relies rather on such characters as the presence or absence of galea, epistome, and trochantin, and establishes three sub-families as follows:—
(i.) Cheliferinae.—Galea. No epistome. Trochantin on all legs. Eyes two or none. Sole genus, Chelifer (Chelifer + Chernes).
(ii.) Garypinae.—Galea. No epistome. Trochantin on legs 3 and 4 only. Eyes four or none. Genera Chiridium, Olpium, and Garypus.
(iii.) Obisiinae.—No galea. An epistome. No trochantin. Genera Chthonius and Obisium (which includes Roncus).
Whatever be the value of the eyes in the classification of this group—and Simon adduces strong arguments for his view—there can be no doubt of their convenience in practical identification. Moreover, as Pickard-Cambridge[[338]] points out, a grouping of the genera according to the eyes results, as regards British species, in pretty much the same linear arrangement as Simon’s classification, and it may therefore be convenient to mention that, of the six genera represented in this country, Chthonius and Obisium are four-eyed, Roncus and Chelifer two-eyed, while Chernes and Chiridium are eyeless.
Sub-Fam. 1. Cheliferinae.—These Chernetidea have the cephalothorax slightly narrowed in front, and generally marked dorsally with two transverse striae, while the abdominal plates are bisected by a dorsal longitudinal line. With the exception of Chelifer cancroides, which is always found in houses, all the species are to be sought under bark, though occasionally they are discovered under stones.
The two genera of this sub-family are Chelifer and Chernes, the species of Chelifer being two-eyed, and those of Chernes blind.
As already stated, Simon does not consider the possession of the two—often very feebly developed—eyes of generic importance, and admits only the genus Chelifer.