Planorbis intermixtus was first described as Planorbis (Gyraulus) intermixtus in 1874 by Albert Mousson.[1] It was described again in 1900 as Planorbis persicus by C. F. Ancey.[8] It was moved from the subgenusGyraulus to the subgenus Planorbis in 1976, where it remains today.[9] It may be alternatively referred to as Planorbis (Planorbis) intermixtus.[2]
Planorbis intermixtus shares several characteristics in common with other Planorbis species, and therefore cannot be distinguished by the shell alone.[9][10]
Shell
The shell of Planorbis intermixtus is similar to those of Planorbis planorbis and Planorbis atticus. As an adult, the shell of P. intermixtus measures between 6 to 7mm (0.24 to 0.28in) in width on average, and about 1.8mm (0.071in) in height. Under the right conditions, however, this species may grow up to 11.5mm (0.45in) in width. There are between 4–5 body whorls.[9] The aperture is weakly or moderately angled (distinct from the strongly angled shell of Planorbis philippii).[8][9] The final whorl may be rounded or keeled near the suture.[10][11]
Sexual Characteristics
Many sexual characteristics of Planorbis intermixtus are distinct from P. planorbis and P. atticus, but may overlap with those of Planorbis carinatus and Planorbis presbensis. The number of prostate diverticules range from 20–36, with an average of about 30 (± 2.8 for 1 standard deviation).[9] The number of diverticules increases with more western populations.[10] The preputium is pigmented, unlike the penis sheath. The penis sheath is relatively long (about 1.8 mm), is about the same length as the penis, is 75% of the length of the preputium, and is between 25–33% of the length of the vas deferens. The seminal vesicles have spiny projections. The bursa copulatrix is highly variable in shape. It may resemble a tadpole with a large bursa and skinny duct, elongated with a poorly defined bursa, or have intermediate characteristics. Most specimens have more elongate forms.[9]
Other Characteristics
The head and foot of Planorbis intermixtus are light grey or black in color, with the mantle being dark grey or black. It is diploid, with 18 pairs of (36 total) chromosomes. The radula of P. intermixtus is indistinguishable from P. planorbis.[9]
Planorbis intermixtus may be found alongside other mollusk species, including Physella acuta, Pseudobithynia zagrosia, Pisidium casertanum, and Radix persica.[4][13] It inhabits a similar variety of habitats as other planorbids, from small streams to rivers, and from temporary ponds to lakes. It inhabits primarily rocky environments, sometimes with aquatic vegetation.[5][13] It may be found at depths of up to 70cm (2.3ft), though usually it stays shallower at around 33cm (1.08ft) on average.[13]
Several fossils of this species have been discovered from the uppermost deposits in the Hammar Formation in Iraq (ancient Mesopotamia).[5][17] These deposits date back to the early Holocene.[5] At this point in time, this area was likely a freshwater lake or swamp, and may have been connected to the estuary formed by the Euphrates and Tigris rivers. Some fossils of Planorbis intermixtus are attached to fossilized aquatic plants.[5]
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