Anna Z. Urbisz

Diversity of features of the female reproductive system and other morphological characters in leeches (Citellata, Hirudinida) in phylogenetic conception

An epistemological–evolutionary conception of leeches (Hirudinida) based on features of the female reproductive system in combination with other morphological characters is presented in the spirit of the cladistic school of taxonomy. Characters relating to the structure of the ovary and the course of oogenesis in leeches were interpreted in this manner, for the first time. Each study was conducted on type species of higher taxonomic groups of true leeches. Results of analyses using features of the reproductive system only as well as in combination with other morphological characters show Piscicolidae and Glossiphoniidae as sister clades making Rhynchobdellida a monophyletic group. Also, Hirudiniformes and Erpobdelliformes appeared to be sister clades within Arhynchobdellida. The relationship between the outgroup specimens and leeches remained unresolved, because both Acanthobdella peledina and branchiobdellidans appeared to be in an equivocal relationship to hirudinidans. Characters concerning the structure of the female reproductive system and course of oogenesis thus appeared to be useful, although conservative, for reconstruction of leech phylogeny, and they well reflect phylogenetic relationships of Hirudinida at the family level.

The ovary of Tubifex tubifex (Clitellata, Naididae, Tubificinae) Is composed of one, huge germ-line cyst that is enriched with cytoskeletal components

Recent studies on the ovary organization and oogenesis in Tubificinae have revealed that their ovaries are small polarized structures that are composed of germ cells in subsequent stages of oogenesis that are associated with somatic cells. In syncytial cysts, as a rule, each germ cell is connected to the central cytoplasmic mass, the cytophore, via only one stable intercellular bridge (ring canal). In this paper we present detailed data about the composition of germ-line cysts in Tubifex tubifex with special emphasis on the occurrence and distribution of the cytoskeletal elements. Using fixed material and live cell imaging techniques, we found that the entire ovary of T. tubifex is composed of only one, huge multicellular germ-line cyst, which may contain up to 2,600 cells. Its architecture is broadly similar to the cysts that are found in other clitellate annelids, i.e. a common, anuclear cytoplasmic mass in the center of the cyst and germ cells that are connected to it via intercellular bridges. The cytophore in the T. tubifex cyst extends along the long axis of the ovary in the form of elongated and branched cytoplasmic strands. Rhodamine-coupled phalloidin staining revealed that the prominent strands of actin filaments occur inside the cytophore. Similar to the cytophore, F-actin strands are branched and they are especially well developed in the middle and outermost parts of the ovary. Microfilaments are also present in the ring canals that connect the germ cells with the cytophore in the narrow end of the ovary. Using TubulinTracker, we found that the microtubules form a prominent network of loosely and evenly distributed tubules inside the cytophore as well as in every germ cell. The well-developed cytoskeletal elements in T. tubifex ovary seem to ensure the integrity of such a huge germ-line cyst of complex (germ cells - ring canals - cytophore) organization. A comparison between the cysts that are described here and other well-known female germ-line cysts is also made.

Barbronia weberi (Clitellata, Hirudinida, Salifidae) has ovary cords of the Erpobdella type.

The organization of the ovaries in representative of the Salifidae (Hirudinida, Erpobdelliformes) was studied at the ultrastructural level for the first time. Like in other leeches, the ovaries of Barbronia weberi are composed of an outer envelope (i.e., an ovisac made up of two coelomic epithelia, muscle cells, and connective tissue) and several internal units, which are broadly similar to the ovary cords found in representatives of the Erpobdellidae. There are usually 6–8 ovary cords that are twisted or cambered with a narrow apical part and a broader, irregularly shaped distal end in each ovisac of B. weberi. Each ovary cord is built from somatic and germ‐line cells and the latter tend to form multicellular cysts that are equipped with a central cytoplasmic core (cytophore). There are two morphologically different subpopulations of germ‐line cells: oocytes and more numerous nurse cells. Growing oocytes form protuberances on the ovary cord surface and eventually detach from the cord and float freely in the ovisac lumen, whereas the other components of germ‐line cysts (i.e., nurse cells and cytophore) degenerate. It should be pointed out that there is a prominent gradient of germ‐cell development along the long axis of the cord. The somatic cells form the ovary cord envelope (the so‐called spongiosa cells) and also penetrate the spaces between germ‐line cells. Both kinds of the somatic cells, that is, those forming the cord envelope and the somatic cells that are associated with oocytes (follicular cells) have a well‐developed system of intercellular channels. Additionally, one prominent somatic cell, the apical cell, was found at the apical tip of each ovary cord. Because the aforementioned features of ovary cords found in B. weberi are very similar (with a few minor exceptions) to the ovary cords that have been described in Erpobdella octoculata and E. johanssoni, we propose the term “ovary cords of the Erpobdella type” for them. Our results support a close phylogenetic relationship between Salifidae and Erpobdellidae. J. Morphol. 275:479–488, 2014.

Ultrastructural study of spermatogenesis and sperm in the African medicinal leech Hirudo troctina Johnson, 1816 (Annelida, Hirudinida)

This paper presents the process of spermatogenesis in the leech Hirudo troctina Johnson, 1816 using light, fluorescent and transmission electron microscopy. At the onset of spermatogenesis in testes, the pear-shaped spermatogonia divide mitotically without full cytokinesis and as a result isogenic groups are formed (clusters, clones) with 2, 4, 8, 16, 32, 64, 128 spermatogonia and, finally, 256 primary spermatocytes occur. The final meiotic divisions of spermatocytes give rise to clones with 1024 spermatids. There are hundreds of developing germ-line clones in each testis. In each clone, the male germ cells divide in full synchrony and they are in the same phase of spermatogenesis. During complex spermiogenesis each spermatid becomes a filiform spermatozoon with a helicoid nucleus, which is characterized by the presence of a long acrosome with two regions - anterior and posterior, which are followed by a helicoid nucleus, a midpiece with only one mitochondrion and a long flagellum. Our results were compared to those on other clitellate annelids that have been studied to date, especially to sperm formation in Hirudo medicinalis Linnaeus, 1785. Only minor differences were found in the length and the diameter of different organelles and the number of spermatids in germ-line clones.