Madagasikara johnsoni is a species of tropical freshwater snail with a gill and an operculum, an aquatic gastropod mollusc in the family Pachychilidae.[2]
This species is endemic to Madagascar.[2] The only precisely known locality is in Ankara Sontsitra National Park, West Madagaskar.[2]
The type locality was given as "River Kamony, in the north-west of the island",[1] but the thereabouts of this locality has not been exactly determined.[2] The most detailed version of the type locality is that of the Kamoro River drainage in Mahajanga Province, north-west Madagascar.[2]
Madagasikara johnsoni was originally discovered and described (under the name Melanatria johnsoni) by Edgar Albert Smith in 1882.[1]
The shell is large, elongate-pyramidal, turreted, thick, covered with an olive epidermis.[1] It is closely lineated or strigate with longitudinal lines of a darker tint.[1] The shell has nine whorls.[1][2] Whorls are very slightly convex beneath, strongly spirally ribbed and grooved.[1] The ribs are six in number on the upper whorls and rounded; the two above are much more slender than the four beneath; the uppermost borders the suture; the next lies in the concavity at the top of the whorls; and the rest surround the slight convexity, and are three times as broad as the sulci separating them.[1] All the whorls, with the exception of the last four, are coronated at the slight angle below the excavation with very short, hollow, oblique spinules.[1] Some of the spiral grooves exhibit rows of fine granules.[1] The last whorl descends somewhat, giving the shell a slightly distorted appearance.[1] It is girded with about twelve transverse costae, a few at the base being smaller than five principal ones around the middle.[1]
The aperture is bluish within, faintly stained with olive-brown near the margins.[1] The peristome widely and deeply sinuated on the outer lip in the concavity of the whorl, arcuate and prominent in the middle, then shallowly sinuated again.[1] Columellar margin is thickened, free, arcuate, reflexed, ending in a distinct basal sinus.[1]
The width of the shell is 24-28.9 mm.[1][2] The height of the shell is 69.9-77.7 mm.[2] The width of the aperture is 14.0-14.2 mm.[2] The height of the aperture is 20.5-21.0 mm.[2]
There is not known description of operculum.[2] There is also not known anatomy of this species.[2] Reproduction strategy is also unknown.[2]
This article incorporates public domain text from the reference[1]
Madagasikara johnsoni is a species of tropical freshwater snail with a gill and an operculum, an aquatic gastropod mollusc in the family Pachychilidae.
