Asellus hilgendorfii call for observations

oops here I am again with another isopod call for observations.

The invasive waterslater A. hilgendorfii has been reported from the Sacremento-San Joquin Delta of CA and may eventually spread further across California. Knowing the head pattern of this species could make it much easier to track this species’ spread in North America, but there’s a minor problem: the head patterns of this species is well recorded in Eurasia, but the issue is that there’s multiple subspecies with different head patterns. The subspecies in CA isn’t known, it could easily be the nominate, the Amur subspecies or some other subspecies, so learning what subspecies made it to the Americas could help with figuring out what the head pattern looks like and therefore help track it.

There are no observations of any Asellid in the Sacramento-San Joquin delta yet, so if anyone’s in the region’s willing to look for these there some shots you need to get:

  • a shot of the head for the pattern (since it differentiates the subspecies in A. hilgendorfii)
  • a shot of the first set of claws to see if there’s a large tooth in the center of the “palm” (no tooth = A. hilgendorfii, large tooth = C. racovitzai or possibly C. communis)
  • a shot of the underside of the telson to record if the individual’s a male or female

Even if the individuals you find aren’t A. hilgendorfii, it still could help track the other Asellid known from the delta: the also invasive Caecidotea racovitzai. Caecidotea communis, yet another invasive in the west, could also pop up in the delta, so taking a photo of the underside of the telson could help confirm one species of Caecidotea over the other if they’re found.


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