THOMPSON: Humboldtiana from Chihuahua and Texas
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ITCV Institute- Tecnologico de Ciudad Victoria, Tamaulipas, Mexico.
UF Florida Museum of Natural History, University of Florida, Gainesville, FL.
USNM National Museum of Natural History, Washington, D.C.
Genus Humboldtiana Von Ihering, 1892
The genus Humboldtiana is in a state of systematic flux. This is, in part, because the genus is very widely distributed through central and northern Mexico and southwestern Texas. Throughout this range the genus has undergone extensive evolution in shell characters and soft anatomy. Thirty-seven species and two subspecies have been described up to now. Almost all are known only from a single locality, and those localities are widely scattered with great distances separating them. From the available data it is apparent that few if any species occur in a geographic area of more than a few km2. Thus, the known species are isolated both geographically and phyletically. Except for those species from southwestern Texas, geographic patterns of speciation are difficult to discern because of this isolation.
Most helminthoglytoid genera consist of species that are geographically separated by short distances from their nearest relative. Subgenera and species-groups are tightly associated with specific mountain ranges and other physiographic features. Apparent relationships are easily discerned because of anatomical similarities coupled with geographic proximity. Similar local patterns of speciation appear to be the case in Humboldtiana, but extensive local field collections that are needed to substantiate these patterns are not available from throughout most of the range of the genus. This has led to major underestimates of species diversity within Humboldtiana.
Papers dealing with the anatomy of Humboldtiana are Pilsbry 1927, Pilsbry 1939, Pilsbry 1948, Burch & Thompson 1957, Thompson 1967, Pratt 1971, Solem 1974, Fullington & Zimmerman 1977, Metcalf 1983, Thompson & Brewer 2000, Thompson 2006, and Thompson and Mejia 2006. Current investigations of DNA sequencing by Omar Mejia, Instituto Politecnico Nacional, Cd. Mexico, will provide new insight into phylogeny within the genus.
This study recognizes six subgenera of Humboldtiana: Humboldtiana s. s., Oreades Thompson & Brewer, 2000, and Polyomphala Thompson & Brewer, 2000, Gymnopallax new subgenus, Clydonacme, new subgenus, and Aglotrochus new sub-
genus. The subgenera are separated by differences of the shell and of the reproductive anatomy.
Key to the subgenera of Humboldtiana.
la. Dart-glands absent. Dart-sacs absent. Penis without a verge. Vagina undifferentiated into lower, middle
and upper segments....................................
........................Oreadne Thompson & Brewer, 2000.
Other characters. Shell without granular sculpture. Embryonic whorls smooth. Shell shape depressed-helicoid. Color pattern banded. Mantle color-pattern uniform. Penis retractor muscle inserting on apex of penis. Genital atrium long. Spermathecal duct short, less than length of uterus. Spermathecal duct without a caecum. Type species: Humboldtiana porterae Thompson & Brewer, 2000.
lb. Dart-sacs present. Dart-glands present. Penis with a verge. Vagina differentiated into lower, middle and upper (free) segments.....................................2a
2a. Mantle mottled with dark-gray spots. Apex of shell denuded; pitted due to erosion. Spermathecal duct without a caecum...................Gymnopallax n. subgen.
Other characters. Shell without granular sculpture. Apical sculpture smooth. Shell helico-globose. Banding on shell obsolete. Verge long, length of penis. Penis retractor muscle inserting on apex of penis. Genital atrium abbreviated. Middle vagina long, widely separating dart-glands from dart sacs. Dart-glands present; Dart-sacs present. Dart-bulbs at base of dart-sacs externally visible. Spermathecal duct longer than uterus. Type species: Humboldtiana cicatricosa n. sp.
2b. Mantle uniform in color. Apex of shell not denuded. Spermathecal duct with a caecum ..........................3a
3a. Shell without granular sculpture............................
..........................................Aglotrochus n.subgen.
Other characters. Embryonic sculpture consisting of straight, very fine transverse striations. Shell shape depressed-helicoid. Color pattern banded with numerous transverse dark streaks, Penis with a large verge. Penis retractor muscle inserting on apex of penis. Genital atrium long. Free vagina short. Middle vagina abbreviated so that the dart-glands are separated from the dart-sacs by a short gap. Dart-bulbs