The type species of Benthastelena and Tristichotrochus are essentially similar in gross shell facies, sharing convex whorls, umbilicus, thin shell, exsert protoconch, late-developing P1, relatively strong P2 and P3, high, narrow sharply angulate spiral cords, and sharply pointed nodules. Unfortunately, well preserved animals of T. aculeatus were unavailable to me, though isolated teeth from a decayed dry animal are very similar to those in B. katherina, the external anatomy, radula and jaws of which are similar to those in Calliostoma (.v. str.) and subgenus Fautor. Since I am unable to find a single character or combination of character states that would justify placement of B. katherina and T. aculeatus in discrete genera or subgenera, Tristichotrochus is synonymised with the prior Benthastelena.
Benthastelena appears to be restricted to the tropical and subtropical western Pacific. Apart from the species recorded herein, typical members include the Japanese species C. (T.) soyoae Ikebe, 1942. as well as several undescribed species from off the Philippine Islands (NMNZ, MNHN). Benthastelena also seems to be an appropriate position for a second group with similar sculpture but in which P2 is not significantly enlarged, the spire is more narrowly conical with flatter whorls, and with or without a narrow umbilicus. This group includes such species as T. tosaensis Kuroda & Habe, 1961 (western Pacific), C. (T.) gendalli Marshall, 1979 (Kermadec Islands), and C. (T.) paucicostatum Kosuge, 1984 (Philippine Islands). As already discussed herein, adults of such typical Benthastelena species as B. katherina resemble their own juvenile stages in whorl convexity and in the relatively large size of P2 and P3.
Benthastelena is thus separated from Calliostoma (.v. str.) (and other genus-group taxa) primarily on the basis of the high narrow, widely spaced, angulate spiral cords and the (generally) prickly nodules on the spire whorls. In the apparent absence of other significant differences, it is possible to interpret Benthastelena as a subgenus of Calliostoma, as some do.
Most species that have been referred to Tristichotrochus other than those already mentioned fall into three groups on the basis of distinctive shell morphology. These groups, typified by Trochus unicus Dunker, 1860 (Japan), Ziziphinus haliarchus Melvill, 1889 (Japan), and Calliostoma formosense E.A. Smith, 1907 (South China Sea) are each probably worthy of at least subgeneric status within Calliostoma, though resolution of these problems is beyond the scope of the present contribution.