Trilasma Goodnight & Goodnight, 1942

Shear, William A., 2010, New species and records of ortholasmatine harvestmen from Mexico, Honduras, and the western United States (Opiliones, Nemastomatidae, Ortholasmatinae), ZooKeys 52, pp. 9-46 : 20-24

Trilasma Goodnight & Goodnight, 1942

Trilasma Goodnight and Goodnight 1942, p. 7.

Ortholasma Shear and Gruber 1983, p. 14 (in part; only the species bolivari and sbordonii; see for complete references before 1983).

Ruaxphilos Goodnight & Goodnight 1945a, p. 299. First synonymized with Ortholasma by Shear and Gruber (1983).

Type species.

Trilasma bolivari Goodnight & Goodnight, 1942, by monotypy. Of Ruaxphilos, Ruaxphilos petrunkevitchou Goodnight & Goodnight, 1945, by monotypy.

Emended diagnosis.

Ortholasmatines in which the median hood process arises dorsally, projects anteriorly in a shallow curve, and is parallel-sided or nearly so, with a dorsal row or rows of tubercles (spoon-shaped and lacking dorsal tubercles in Ortholasma ); two or three lateral hood processes; males without cheliceral glands (cheliceral glands present in Ortholasma ); male first cheliceromere with distal inner tooth, dorsal tooth or sharp tubercle present or absent, curved mediobasal tooth on second cheliceromere (not verified for species known only from females); palpal patella with only two seta-bearing tubercles ( Ortholasma with several); large keel cells separated by transverse rows of much smaller keel cells ( Ortholasma lacks rows of smaller cells; Dendrolasma has either large or small cells but not both).

Notes.

Trilasma consists of seven species extending from Nuevo León, México, in the north to Honduras in the south. Not much ecological information is available. One species, sbordonii, is troglomorphic, but while other cave collections exist, none of the other species seems especially adapted for life underground (although both petersprousei sp. n. and tempestado sp. n. have unusually long, thin legs and palpi) and probably are at most troglophilic. Surface collections are from cloud forest litter, and from under the bark of pines. Except for chipinquensis, collected at an altitude of about 1525 m (5000'), all species come from altitudes ranging from 2100-3050 m (7000 –10000’) asl.

Trilasma species are immediately separable from Ortholasma species due to the presence of areas of small keel cells on the abdominal scutum (compare Figs 42, 45, and 54 with 1, 2). It appears that the small cell groups are at the anterior borders of the scute areas because in some species the first group is to be found at the very anterior margin of the scute (of area 1) and succeeding groups appear anterior to the paired median spines of the succeeding areas. The maximum number of groups is thus five, but the anteriormost is absent in some species, and the posteriormost is generally broken up into two groups on either side of the midline and consists of just two or three small cells on each side, or may be absent as well. The small cell groups of areas 2, 3 and 4 are the most marked and are successively wider, with the group of area 4 occupying about two-thirds the width of the scute and consisting of up to 20 small cells. In addition, Trilasma species have dorsal tubercles on the median hood process of the eye tubercle; these may be few (trispinosum sp. n., Fig. 43) or very numerous (tempestado sp. n., Fig. 44) and bearing branches that connect complexly with each other and with the usual lateral tubercles. Instead of the typically spatulate dorsal hood processes of Ortholasma species, Trilasma species have dorsal hood processes with nearly parallel sides that are obviously longer and narrower than in the former genus, reaching an extreme in the very narrow hood of Trilasma trispinosum sp. n. (Fig. 43). In several species the process tapers apically to a point.

Trilasma species are on average significantly smaller than Ortholasma species, ranging from a minimum of 2.1 mm in length to just 3.4 mm, including the hood. As in other members of the subfamily, the order of legs in length is 2, 4, 3, 1. In some species false articulations are present in at least some femora and metatarsi, but sometimes only in males. The detailed ornamentation of the leg femora, of taxonomic value in Ortholasma , because it differs between species, is quite uniform in Trilasma , consisting of numerous, short, club-shaped setae, among which are dispersed a few blunt, rod-shaped setae on elevated sockets. This character was studied for all species using scanning electron microscopy. The short, club-shaped setae are clearly seen to be hollow in some of the photomicrographs, but there appear not to be any pores communicating with the outside. In species of both Ortholasma and Dendrolasma , the longer setae on elevated sockets are acute and tapered, not blunt and rod-shaped.

Sexual dimorphism in Trilasma species is more pronounced than in Ortholasma species. Males are significantly smaller than females, with relatively longer legs, especially legs 2 and 4, which may also have increased numbers of tarsal segments, and in some species the males have false articulations in the fourth leg femora that are not present in the females. In addition to the basal, median tooth on the second cheliceral segment and the glands in the patellae and tibiae of the palpi, males of Trilasma species may have somewhat reduced dorsal ornamentation when compared to females, expressed in fewer small cells and lower paired tubercles of the dorsal areas. This dimorphism is especially notable at the posterior margin of the scute, where in females there is an obvious "post and rail fence" with long “posts” (Shear and Gruber, 1983); in males of the same species, this feature may be hardly noticeable.

The following characters seem to be useful in defining and separating the species of Trilasma : the relative length and robustness of the legs, the presence or absence and the number (if present) of false articulations in the femora and metatarsi of the legs (this may be sexually dimorphic in some species), the range of numbers of tarsal articles (difficult to evaluate because of small sample size; the counts given should be taken as variable by one or two articles in either direction), the relative prominence of the ocular keels, the patterns of small keel cells on the scute, the height of the paired area tubercles, and the shape and size of the dorsal hood process. In addition, there are autapomorphies of single species, such as the very narrow dorsal hood process and three lateral hood processes in Trilasma trispinosum sp. n.

While I am still certain that Ruaxphilos is a synonym of Trilasma , it is no longer clear that Ruaxphilos petrunkevitchou Goodnight & Goodnight, 1945 is a synonym of Trilasma bolivari , as placed by Shear and Gruber (1983). The type specimen of the former species came from Veracruz, whereas the latter is known from several localities in the transverse volcanic belt of central México.

Key to species of Trilasma