Comparative reproductive morphology of two species of Macrobdella (Hirudinea: Arhynchobdellida: Macrobdellidae)

Abstract

Leech internal morphology has historically been examined through dissection, serial sectioning, or whole mounts, techniques that are irreversibly destructive to the specimen. Micro-computed tomography (microCT) is a powerful tool for studying the internal morphology of soft-bodied invertebrates, such as leeches, and has advantages over destructive techniques. Here, we examined the reproductive morphology of two morphologically similar and closely related species of macrobdellid leech, Macrobdella decora (n = 6) and Macrobdella mimicus (n = 7). We found the oviducts external and internal to the vagina to be longer and more convoluted in specimens of M. decora than in specimens of M. mimicus and the junction of the oviducts into the common oviduct was outside the vaginal tissue of specimens of M. decora rather than inside as in M. mimicus specimens. The ejaculatory ducts external and internal to the male terminal organ were longer and more convoluted in specimens of M. decora than in M. mimicus specimens. Measurements of the accessory organ using 2D images and volume measurements of the 3D reconstructions of the ovaries and epididymes were compared using a Student t-test to estimate significant differences between the species, although none were found. A new character, the maximum diameter of the ejaculatory duct, was measured using 2D images and was found to be significantly different between the two species (p = 0.038). Although the sample size here was low, this character could potentially be taxonomically informative at the species level for macrobdellid leeches and other arhynchobdellid leeches with similar morphology (e.g. Hirudinidae, Praobdellidae, Semiscolecidae).