When I get time again, I will try to take better photos that illustrate this character. So the fusion of the sternites is a character of Pimeliines that also go with their lack of abdominal defensive glands. However, in dried specimens that do have membrane between the sternites, depending on how they dry when that are preserved, the membrane may shrink and the sternites may appear to be fused. Unfortunately this means that often, telling the difference between species having the membrane and those that don't just comes to experience gained from examining lots of Tenebs. In live specimens, this difference is more clear.