Amphidromus perversus

Appearance

''Amphidromus perversus'' are amphidromine .

In ''Amphidromus perversus'' and most other thick-shelled ''Amphidromus'' species, the lip is internally thickened, forms a "roll" in its expansion, and has a very heavy parietal callus.

The shell is solid, polished, amphidromine, moderately large high, usually with a dark varix. Lip and callus white; ground color white, orange, yellow, or yellowish-green. Many specimens with interrupted or continuous radial brownish streaks covering part or all of the whorls on the lower spire and body whorl.

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''Amphidromus perversus'' undoubtedly offers the greatest array of discretely variable color combinations of any species of ''Amphidromus''.


Color variation of ''Amphidromus perversus perversus'' include 12 forms:
# ''Amphidromus perversus perversus'' f. ''aurea'' Dillwyn, 1817 , is usable for the orange-colored monochrome shells found on Java and Celebes. Apparently an individual variation.
# ''Amphidromus perversus perversus'' f. ''aureus'' Martyn, 1784 — It still have not been reported from a precise locality. It was based on three shells collected by Sir Joseph Banks, supposedly on Pulau Panaitan. The only ''Amphidromus'' found there, ''Amphidromus banksi'' Butot, is quite different and the actual locahty of aureus is still unknown. The shells have a wide, white zone below the suture as in the ''Amphidromus atricallosus'' complex and the lower parts of the whorls are yellow, with or without narrow, wavy, reddish-brown flammulations. The original specimens in the Natural History Museum appear to be a form of ''Amphidromus perversus'', but the locality remains a mystery. Note: Martyn's work was invalidated by action of the International Commission on Zoological Nomenclature, varietal names are not accorded legal status and the use of ''aureus'' is as a convenient term of reference.
# ''Amphidromus perversus perversus'' f. ''borneensis'' Pilsbry, 1900, is based on a stout variant of the interruptus pattern, whitish in background color, and rather similar to the Javanese subspecies, ''emaciatus''. It was described from South Borneo in the Bandjermassin District , but there are specimens in the Naturalis, Leiden from East Borneo. The flammulations above the periphery are reduced in number. Possibly this may prove to be a subspecies, but not enough data are available.
# ''Amphidromus perversus perversus'' f. ''infrapictus'' von Martens, 1867, was considered by Pilsbry to be identical with ''interruptus'' Müller, 1774. At best it might be considered a slightly different stage in an almost continuous series of variations.
# ''Amphidromus perversus perversus'' f. ''infraviridis'' von Martens, 1867, probably is a derivative of the Celebesian ''infrapictus''. Instead of flammulations and a basal purplish zone it has a pale green or greenish-yellow base which is only slightly darker than the greenish-yellow or citron-colored spire. It is most similar to typical ''perversus'' but differs in the darker basal portion.
# ''Amphidromus perversus perversus'' f. ''interruptus'' Müller, 1774, has a purplish or brownish zone on the base, a yellow or whitish patch near the columella, and brownish flammulations that are somewhat interrupted on the periphery and do not reach the suture above.
# ''Amphidromus perversus perversus'' f. ''mitra'' von Martens, 1867, is an unfigured variety from Bali and seems to be intermediate between ''interruptus'' and ''sultanus''.
# ''Amphidromus perversus perversus'' f. ''niveus'' P. & F. Sarasin, 1899 is snow-white with a black varix and black mark behind the peristome. It is an "albino" ''perversus'' which is common in the Celebes and sporadically seen from Java and Borneo.
# ''Amphidromus perversus perversus'' f. ''obesus'' von Martens, 1867, is an unfigured variety which probably can be equated with squat individuals of the typical ''perversus'' pattern.
# ''Amphidromus perversus perversus'' f. ''perversus'' Linnaeus, 1758, is a solid yellow shell with black varix and narrow black band behind the peristome. It is known from the whole range of the species.
# ''Amphidromus perversus perversus'' f. ''strigosus'' von Martens, 1867, has continuous, rather narrow, straight brown bands running from the suture to the bottom of the whorl. It is known from Bali, Borneo, and Celebes.
# ''Amphidromus perversus perversus'' f. ''sultanus'' Lamarck, 1822, has wavy brown bands running over the entire whorl. The bands are interrupted in the middle of the whorl by a narrow spiral band of the ground color. This variation is found in all parts of the species range.

Naming

There are six subspecies of ''Amphidromus perversus'':
⤷  ''Amphidromus perversus perversus''
⤷  ''Amphidromus perversus butoti'' Laidlaw & Solem, 1961
⤷  ''Amphidromus perversus emaciatus''
⤷  ''Amphidromus perversus melanomma''
⤷  ''Amphidromus perversus natunensis'' Fulton, 1896
⤷  ''Amphidromus perversus rufocinctus'' Fruhstorfer, 1905
⤷  ''Amphidromus perversus siglerae'' Thach, 2018

Distribution

Distribution of ''Amphidromus perversus'' include Sumatra and Java to Borneo, Sulawesi and Bali.

Absent from the Mentawi Chain and Panaitan Island. Its occurrence on Sumbawa needs confirmation. Probably it has been introduced into Singapore. Subspecies recognized here are from Great Natuna, Bawean, Kangean Islands and Riau Islands.