Spermatheca

In the stem-species pattern of the Chloropidae family-group, as represented in the stem-species pattern of the Carnidae, there are sclerotised spermathecal capsules with spherical surrounding tissue. Sclerotised spermathecal capsules are considered plesiomorphic for the Chloropidae family-group because they are present in the stem-species pattern of the Acalyptratae.
Within the Carnidae, the stem-species pattern is represented in Neomeoneurites and Hemeromyia. However, in Meoneura, the capsules are reduced in size and can be found as small, sclerotised, pointed tips at the end of the distally slightly enlarged spermathecal ducts.
In Acartophthalmus nigrinus (Acartophthalmidae), the spermathecal capsules are completely reduced and the spermathecal ducts end with slight ramifications in the surrounding tissue.
In the Chloropidae, a spermathecal capsule is sometimes present and the shape of the spermathecae differs: the tissue surrounding the end of the spermathecal ducts is always spherical in the Siphonellopsinae and Oscinellinae that I studied, while it is spherical or unevenly shaped in the Chloropinae. In the Oscinellinae the tips of the spermathecal ducts are slightly enlarged and are connected to the mostly very small, lightly sclerotised spermathecal capsule via a short and slender duct. In the Siphonellopsinae, the tips of the spermathecal ducts are also slightly enlarged, but there is no capsule. In these cases the short and slender duct opens into a lumen surrounded by gland tissue. In the species of the subfamily Chloropinae that I examined, the spermathecal ducts end without an enlargement, but also with a short, slender duct which opens into a lumen within the surrounding gland tissue. A small spermathecal capsule, as is present in the Oscinellinae, probably represents the stem-species pattern of the Chloropidae because the presence of a capsule is the plesiomorphic character state for the Chloropidae family-group and for the Acalyptratae. As a result, the capsule must have been reduced several times within the Chloropidae. The short and slender duct at the end of the spermathecal duct is probably an apomorphy of the Chloropidae.
In the stem-species pattern of the Milichiidae, there is no sclerotised spermathecal capsule. The distal end of the spermathecal ducts projects slightly out of the coil and is surrounded by epithelial gland cells. There is only slight variation in the shape of the spermathecae within the Milichiidae: the spermathecae may be rather long or more spherical. In some species the distal end of the spermathecae is pointed. In Desmometopa the distal end of the ducts is slightly enlarged.
The shape of the spermathecae may be useful for phylogenetic studies. However, as yet not enough species have been studied, because unsclerotised spermathecae are very difficult to detect in preserved material.
Since spermathecal capsules are present in the stem-species pattern of the Chloropidae family-group and in the stem-species pattern of the Carnidae and Chloropidae, the capsule must have been reduced in the Acartophthalmidae, in the stem-species of the Milichiidae, and at least twice within the Chloropidae. A complete reduction of the spermathecal capsule also occurs convergently in several acalyptrate families, for example in the Ephydridae and Fergusoninidae. (ex Brake 2000)