Aktedrilus, Knollner, 1935

Rodriguez, Pilar & Fend, Steven V., 2018, On spermatophore-producing aquatic microdrile oligochaetes (Annelida: Clitellata), Zootaxa 4497 (1), pp. 41-60 : 50

Aktedrilus species producing spermatophores

( Figure 4 )

Among phallodrilines, only a few Aktedrilus species, with or without spermathecae, transfer sperm by attaching spermatophores to the partner's body wall. These species were initially classified in the genus Bacescuella Hrabě, 1973 , but that genus was placed in synonymy with Aktedrilus by Erséus (1987). At present, six Aktedrilus species produce spermatophores; these are dome-shaped, on short stalks or directly attached to the body wall ( Fig. 4A ). Placement is either on the dorsal or ventral sides of the body wall, in the clitellar region. The single, dorsal spermatheca is absent in four of these species, but a small spermatheca is present in A. arcticus and A. parvithecatus , and can be full of sperm. Erséus (1978) suggested that this has little or no functional relevance; some specimens can bear up to 3 or 4 spermatophores, and the author suggests that the presence of spermathecae can be just a relic of ancestral forms, in which spermatophores had not evolved.

Aktedrilus species producing spermatophores show a different degree of development of glandular tissues in the ectal part of the male duct. The conspicuous, glandular, pendant organ in the ectal section of the atrium may function both in the formation of spermatophores and as copulatory organ related to the attachment of spermatophores during mating ( Fig. 4B–F ). Although referred to as a 'penis' in some species, this organ is not associated with conspicuous musculature. The copulatory organ is enclosed in a bulbous male sac (usually described as a "penial sac"), which is the ental section of the copulatory bursa. In A. labeosus and A. mediterraneus , the copulatory organ is encircled by a large glandular ring or a pair of lips ( Fig. 4D–F ). In other species, such as A. arcticus , a very thick epithelium of the so-called 'penis' ( Fig. 4B,C ) also suggests a glandular function. Most Aktedrilus species have some form of male sac, but in the species producing spermatophores, the ectal end of atrium is joined to a more or less enlarged and folded copulatory bursa (long in A. labeosus , Fig. 4D ).

Figures

FIGURE 4. Aktedrilus species forming spermatophores (from Swedish Museum of Natural History collection). A. A. mediterraneus (Erséus, 1980), spermatophore in segment XI. B–C. A. arcticus (Erséus, 1978), histological sections of the male duct. D. A. labeosus (Baker & Erséus, 1982), copulatory bursa and glandular organ. E,F. A. mediterraneus, histological sections of the male duct. Abbreviations: a atrium, cb copulatory bursa, go glandular organ, gr glandular ring, ms male sac, o ovary, sf sperm funnel, sph spermatophore, vd vas deferens.