NSS Convention 2026

Cryptic species are difficult to detect by conventional means of discerning species by morphological examination, but their presence can be revealed by DNA sequencing. Complexes of cryptic species can be discovered by sampling and performing sequencing of many populations across the breadth of a morphological species that occurs through a broad range. The isopod crustacean Caecidotea stygia is such a morphospecies, reported from caves and other groundwater habitats from six states in the midwestern United States.

A phylogenetic analysis resulting from sequencing 4-genes from almost 100 populations has resulted in the discovery of numerous molecular operational taxonomic units. Twelve of these are described as new species that occur in Indiana, Ohio and Illinois. Some of these populations, like the three known from a small area of Hardin County in southeastern Illinois, were long presumed to be distinct species due to their geographic isolation. Others, like the 10 new species described from southern Indiana, were less obvious.

Some of these species are endemic to individual stream basins, while others span low divides between adjacent basins. The most speciose area is the Blue River drainage, where five species occur. One species spans the Ohio River, having diverged millions of years prior to the formation of the river as a major stream. Perhaps the most interesting species is the most northerly of those occurring in Indiana. That species occurs in many caves north of the East Fork of White River and has also dispersed far into the glaciated region.