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Astigmatans are a large group of mites living in nearly every environment and exhibiting very diverse reproductive strategies. In spite of an uniform anatomical organization of their reproductive systems, gametogenesis in each sex is highly variable, leading to gamete formation showing many peculiar features and emphasizing the distinct position of Astigmata. This review summarizes the contemporary knowledge on the structure of ovaries and testes in astigmatic mites, the peculiarities of oogenesis and spermatogenesis, as well as provides new data on several species not studied previously. New questions are discussed and approaches for future studies are proposed. [ABSTRACT FROM AUTHOR]

Abstract: Testes, spermatogenesis and spermatozoa are described in the mite Carpoglyphus lactis (L.), the first representative of the Hemisarcoptoidea superfamily studied ultrastructurally. Paired testes are located posteriorly in the idiosoma, with germaria situated dorsolaterally. The germarium consists of a compact group of spermatogonia; no testicular central cell was found. The remainder of the gonad is occupied by germ cells in different stages of spermatogenesis, distributed separately rather than in cysts, and embedded in a few large somatic cells filling the remaining space. Spermatocytes are covered by a spongy layer, a product of the Golgi apparatus. Spermatids are anucleate. Their chromatin condenses into granular and then tubular threads. As spermiogenesis progresses, the spongy layer assembles at a single site and forms a structure termed the spongy body; mitochondria become electron dense, elongate and gather forming a bundle; a narrow ER cistern, promptly transforming into a dense lamella, appears between the mitochondria and chromatin. Mature spermatozoa are small, highly electron-dense cells interdigitating with others via superficial protrusions. They possess chromatin threads, electron-dense lamella and mitochondria, but do not have an acrosome. Our results support the monophyly of Astigmata, but do not explain the phylogenetic affinities of Hemisarcoptoidea to other superfamilies of astigmatic mites. [Copyright &y& Elsevier]

The development of male and female gonads in arrhenotokous and thelytokous species of Histiostoma was studied using transmission electron microscopy (TEM). All instars were examined: larvae, protonymphs, facultative heteromorphic deutonymphs (=hypopi), tritonymphs, and adults. In testis primordium, spermatogonia surrounding a testicular central cell (TCC) with a gradually enlarging, branched nucleus are present already at the larval stage. Spermatogonia and the TCC are connected via narrow, tubular intercellular bridges revealing that the TCC is a germline cell. Spermatocytes appear at the protonymphal stage. At the heteromorphic deutonymph stage, the testis primordium is similar to that of the protonymph, but in the tritonymph it is much larger and composed as in the adult: spermatids as well as sperm cells are present. The latter are congregated ventrally in the testis at the entrance of the deferent duct. In the larval ovary, an eccentrically located ovarian nutritive cell (ONC) is surrounded by oogonia which are connected with the ONC via tubular intercellular bridges. In later stages, the ovary grows and oocytes appear in the protonymph. Meiotic synaptonemal complexes in oocytes occur from the tritonymph stage. At about the time of the final molting, tubular intercellular bridges transform into peculiar diaphragm-crossed bridges known only in Histiostoma mites. In the adult female, growing oocytes at the end of previtellogenesis lose intercellular bridges and move ventro-laterally to the ovarian periphery towards the oviduct entrance. Vitellogenesis occurs in oviducts. Germinal cells in both the testis and ovary are embedded in a few somatic stroma cells which may be well discernible already in the larval ovary; in the testis, somatic stroma cells are evident not earlier than the end of the tritonymphal stage. The ovary has a thin wall of flat somatic cells, whereas the testis is covered by a basal lamina only. The obtained results suggest that gonads in Histiostoma and other Astigmata originate from two primordial cells only., (Copyright © 2014 Elsevier Ltd. All rights reserved.)