Hooge MD 2003 (citation) - The arrangement of the copulatory organ is similar to copulatory organs found in the family Mecynostomidae. However, light microscopy of living specimens, confocal microscopy, and histological sections reveal that the wall of the seminal vesicle is more muscular and orderly than that of any known species in the Mecynostomidae. The seminal vesicle of mecynostomids is typically a thin, unorganized network of muscle fibers. The family Dakuidae is further distinguished from the Mecynostomidae in having sperm with 9 + 2 axonemes, instead of 9 + 1, and ventral body-wall musculature that has straight longitudinal muscles between the frontal pore and mouth, and lacking sigmoid-shaped anterior diagonal muscles positioned between outer circular and inner longitudinal muscles (Hooge 2001). It is likely that the Dakuidae is more closely related to other taxa that share similar sperm morphology and patterns of body-wall musculature, such as the Actinoposthiidae, Haploposthiidae, Otocelididae, and some species of the Convolutidae (see Hooge et al. 2002).
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