The fine structure of the female reproductive system of Zorotypus caudelli Karny (Zoraptera) R. Dallai a, * , D. Mercati a , M. Gottardo a , R. Machida b , Y. Mashimo b , R.G. Beutel c a Department of Evolutionary Biology, Via A. Moro 2, I-53100 Siena, Italy b Sugadaira Montane Research Center, University of Tsukuba, Ueda, Nagano 386 2204, Japan c Institut für Spezielle Zoologie und Evolutionsbiologie mit Phyletischem Museum, Friedrich-Schiller-Universität Jena, Ebertstrasse 1, D-07743 Jena, Germany article info Article history: Received 18 April 2011 Received in revised form 2 August 2011 Accepted 13 August 2011 Keywords: Insect reproduction Spermatheca Insect phylogeny Ovary structure Electron microscopy abstract The general structure of the female genital system of Zorotypus caudelli is described. The ovarioles are of the panoistic type. Due to the reduction of the envelope (tunica externa) the ovarioles are in direct contact with the hemolymph like in some other insect groups, Plecoptera included. The calices are much larger in Z. caudelli then in Zorotypus hubbardi and their epithelial cells produce large amounts of secretions, probably protecting the surface of the eggs deposited on the substrate. Eggs taken from the calyx bear a series of long fringes, which are missing in the eggs found in the ovariole, and in other zorapteran species. The long sperm of Z. caudelli and the long spermathecal duct are likely related to a sexual isolating mechanism (cryptic female choice), impeding female re-mating. The apical receptacle and the spermathecal duct - both of ectodermal origin - consist of three cell types. In addition to the cells beneath the cuticle lining the lumen, two other cell types are visible: secretory and canal cells. The cytoplasm of the former is rich in rough endoplasmic reticulum cisterns and Golgi complexes, which produce numerous discrete dense secretory bodies. These products are released into the receiving canal crossing the extracellular cavity of secretory cells, extending over a series of long microvilli. The secretion is transported towards the lumen of the apical receptacle of the spermatheca or to that of the sper- mathecal duct by a connecting canal formed by the canal cells. It is enriched by material produced by the slender canal cells. Before mating, the sperm cells are enveloped by a thick glycocalyx produced at the level of the male accessory glands, but it is absent when they have reached the apical receptacle, and also in the spermathecal duct lumen. It is likely removed by secretions of the spermatheca. The eggs are fertilized at the level of the common oviduct where the spermathecal duct opens. Two micropyles at the dorsal side of the equator level possibly facilitate fertilization. The presence of these two micropyles is a presumably derived feature shared with Phasmatodea. The fine structure of the female reproductive system of Z. caudelli does not allow to assess the phylogenetic position at the present stage of knowledge. The enlarged calyx and the temporary presence of long fringes on the eggs are potential autapomorphies of Z. caudelli or may indicate relationships with other Zorotypus species. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Zoraptera is arguably the most enigmatic group of insects with respect to its systematic position. Whereas the “Strepsiptera problem” (Kristensen, 1999) appears to be largely solved (e.g., Wiegmann et al., 2009; Beutel et al., 2010), the systematic place- ment of Zoraptera is still an open question. As pointed out by Yoshizawa (2007), “more than 10 different systematic placements have been discussed” in Engel and Grimaldi (2002). The group is generally considered to belong to the hemimetabolous Neoptera, but there is, at present, an active debate and the expression “Zor- aptera problem” (Yoshizawa, 2007) underlines the difficulty of establishing a convincing phylogenetic hypothesis. Even though the available anatomical information has greatly increased in the last years (Beutel and Weide, 2005; Hünefeld, 2007; Yoshizawa, 2007; Friedrich and Beutel, 2008), the presently available morphological data are apparently still insufficient for a reliable placement. Like- wise, molecular studies failed to find an unambiguous result in this context (Carmean and Crespi, 1995; Huelsenbeck, 1998; Kjer, 2004; Maddison, 2004; Yoshizawa and Johnson, 2005). The results of a combined molecular and morphological analysis by Terry and * Corresponding author. Tel.: þ39 (0) 577 234412; fax: þ39 (0) 577 234476. E-mail address: romano.dallai@unisi.it (R. Dallai). Contents lists available at SciVerse ScienceDirect Arthropod Structure & Development journal homepage: www.elsevier.com/locate/asd 1467-8039/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.asd.2011.08.003 Arthropod Structure & Development 41 (2012) 51e63