Just a passing observation about some species from the family Atyidae (freshwater “basket-handed” shrimps). The first shrimp is Caridina serratirostris (Japan: photo from this aquarium exhibit), the second Potimirim sp. (Puerto Rico: collected by yours truly), the third Atyopsis moluccensis (an aquarium-trade specimen from somewhere in southeast Asia), and the fourth Atya scabra (Panama). Notice anything?
Why this is so, I can only speculate.
Note that changes in coloration can be quite dramatic in Atyopsis moluccensis and are so pronounced in C. serratirostris that it’s known to aquarists as the “ninja shrimp” — don’t come away thinking that the striping is an immutable characteristic of these two species. From what I’ve seen in aquaria, the color-changing ability of Potimirim is more feeble (limited to stress-induced paling). And while I don’t have any direct experience with Atya scabra, it — one way or another — seems to exhibit a fair amount of color variation between locales.
Though the first two species are similar in size (around 1-1.5 cm), the last are comparatively massive (Atyopsis moluccensis and Atya scabra may both exceed 10 cm). This dichotomy is paralleled by functional morphology. Potimirim feeds on algae and detritus, primarily by sweeping (Fryer); in this respect, it resembles many Caridina spp. However, its bristle-bearing chelipeds can also be used (pers. obs.) for the kind of passive filtration that sees greatest development in Atyopsis and Atya. In the absence of strong current (e.g., during drought conditions), shrimp from these two genera may resort to sweeping food from the substrate like their smaller relatives (Covich et al.).
Given the name of this blog, I’m obligated to point out that the four species shown above are all amphidromous; their larvae require saline water to develop and presumably waft downstream to estuaries or the ocean from the freshwater habitats occupied by adults (Page et al. & Yakushiko et al.).
Covich, A., Crowl, T., & Scatena, F. (2003). Effects of extreme low flows on freshwater shrimps in a perennial tropical stream. Freshwater Biology, 48(7), 1199-1206. doi: 10.1046/j.1365-2427.2003.01093.x.
Fryer, G. (1977). Studies on the Functional Morphology and Ecology of the Atyid Prawns of Dominica. Royal Society of London Philosophical Transactions Series B, 277, 57-129.
Page, T. J., Baker, A. M., Cook, B. D., & Hughes, J. M. (2005). Historical transoceanic dispersal of a freshwater shrimp: the colonization of the South Pacific by the genus Paratya (Atyidae). Journal of Biogeography, 32(4), 581-593. doi: 10.1111/j.1365-2699.2004.01226.x.
Yasuhiko, N., Yasuhiko, N., Atsushi, H., Yasuhiko, M., & Kazutsugu, H. (2005). Larval Rearing of Three Amphidromous Shrimp Species (Atyidae) Under Different Feeding and Salinity Conditions. Suisan Zoshoku, 53(3), 305-310.