Tidesmus Chamberlin, 1943

Shear, William A. & Shelley, Rowland M., 2007, The milliped genus Tidesmus Chamberlin, 1943 (Polydesmida: Macrosternodesmidae), Zootaxa 1656, pp. 51-68 : 55

Tidesmus Chamberlin, 1943

Tidesmus Chamberlin, 1943:35 . Chamberlin and Hoffman, 1958: 74. Loomis, 1960:68. Buckett, 1964:12. Shear, 1969:134. Jeekel, 1971:356. Hoffman, 1980:179. Shelley, 2002b:107.

Oodedesmus Loomis, 1960:60 . Hoffman, 1980:179; 1999:469. Shelley et al., 2000:116. NEW SYNONYMY. Phreatodesmus Loomis, 1960:62 . Buckett, 1964:12. Hoffman, 1980:179; 1999:470. Shelley et al., 2000:122. Shelley, 2002b:107. NEW SYNONYMY.

Type species: Of Tidesmus , T. episcopus Chamberlin, 1943 , by original designation; of Oodedesmus , O. variabilis Loomis, 1960 , by original designation; of Phreatodesmus , P. torreyanus Loomis, 1960 , by original designation.

Diagnosis: Pallid to light yellowish Macrosternodesmidae , lengths ca. 6.0–12.0 mm, widths ca. 0.8–2.5 mm. Gonopods with femoral setae, process B (see Shelley 1994) broad, curving strongly mediad, with or without basal subbranch; acropodite short and "blocky," distal zone clearly present or folded, flattened, and apparently absent, with distal, dentate shelf and transparent lamina bent caudad, mediad, or laterad; solenomere arising centrally from acropodal mass, extending generally ventrad.

Distribution. Coastal southern California, USA, and adjacent Baja California Norté, Mexico, to central and southeastern Arizona; potentially present in southwestern New Mexico, USA, and northern Sonora, Mexico. Potential presence in the former is indicated by occurrence 50 mi (80 km) to the west in Cochise County (Co.) , Arizona; that in Sonora is implied by occurrence 35 & 50 mi (56 & 80 km) to the north in Cochise and Pima cos ., Arizona.

Etymology. In addition to his biological work, R. V. Chamberlin studied native North American languages and compiled dictionaries of several of them. Tida means "small" in the Gosiute language and was combined with the traditional “… desmus ” suffix to form the generic name ( Chamberlin 1943).

Remarks. Aside from a 1976 collection of T. variabilis , all of the material we saw was collected in the early 1920s. After more than 85 years, these specimens are in poor condition; they may have been preserved for years in vials stoppered with cork or rubber, resulting in stained, brittle, and decalcified cuticles, and accumulated deposits that cannot be safely removed. Because of decalcification, which we did not anticipate from the appearances of the specimens, they tended to collapse during preparation for SEM examination. In the future, old, suspect specimens should be dehydrated in methanol, hexamethyldisilazane ( Nation 1983) or xylene before drying, or be subjected to critical point drying. However, we are confident that the heavily sclerotized gonopods were not distorted, based on comparisons of the SEM micrographs with drawings made before SEM preparation.

Because of the better condition of the specimens, we base our detailed description of somatic features of T. variabilis , which in all respects is as representative of the genus as the generotype T. episcopus .

The only habitat information, either on vial labels or in published accounts, is the statement, "under stones," for the types of T. episcopus . Little is therefore known about preferred environments, although one can plausibly suggest very close to water. The collection dates show a decided seasonality and a marked preference for cool-weather seasons of the year. As shown in the ensuing table, 15 (75%) of the samples were collected from November through March, in winter, late autumn, and early spring, whereas only 2 were taken in April and 3 in summer. Future collecting efforts should coincide with this seasonality pattern.

Seasonality of western macrosternodesmids; number of samples collected per month.

Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec. 6 4 1 2 - 1 1 1 - - 4 - Tidesmus hubbsi , the second species originally assigned to the genus, was based on a single female; Chamberlin's accounts (1943) provide no differences except size (at 9 mm T. episcopus is about twice as long as the 5 mm T. hubbsi ), and it is also geographically disjunct. We cannot address the species or present a meaningful diagnosis, and therefore remove hubbsi from Tidesmus and leave it unassigned.