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The sperm ultrastructure of some beetles of Tenebrionoidea was studied with particular attention to those of the Ripiphoridae, Mordellidae, and Meloidae. These three groups are often thought to form a clade, which is the sister group of the remaining Tenebrionoidea. The testes of the two former families have thinner but longer spermatic cysts containing fewer and longer sperm. Within each cyst all sperm cells have the same orientation, but cross sections showed that the orientation of the axonemes alternate between adjacent cysts, possibly due to the cysts bending on themselves. In both families the sperm has a bilayered acrosome and the flagellum, which shows mitochondrial derivatives starting laterally to the nuclear base, has a typical 9 + 9+2 axoneme with accessory tubules provided with 16 protofilaments in their wall, and well-structured triangular shaped accessory bodies. In Mordellistena sp (Mordellidae) sperm, both mitochondrial derivatives and accessory bodies are somewhat asymmetrical. Moreover, the flagellum shows a very thin and long tail end provided with only accessory tubules. Meloidae species have testes with thicker sperm cysts containing numerous shorter sperm. Within the individual cysts the sperm flagella exhibit an alternating orientation of their axonemes as consequence of a peculiar spermatogenetic process. The flagellar structure is similar to that of the above-mentioned species, but the accessory bodies are not well defined and constituted by fuzzy material. In Mylabris hieracii (Meloidae) sperm, the acrosome is flat with a conspicuous perforatorium and its nucleus has a peculiar quadrangular section. Berberomeloe majalis sperm has a large acrosome with an unusual pentagonal perforatorium. The centriolar structure of Mylabris variabilis shows a complex of dense radial links connecting the microtubular structures to the plasma membrane. These results suggest that Ripiphoridae have a closer relationship with Mordellidae than with Meloidae. These findings are in agreement with results obtained with molecular data.

In the present study, we describe the sperm morphology of 11 species of Elateriformia (9 elaterids, 1 lampyrid and 1 buprestid) using transmission electron microscopy. All species exhibited sperm that is not usually observed in insects in general. The most highlighted features are the displacement of the nucleus running parallel to the flagellar components, hitherto observed only in coccinellid and carabid beetles, and the presence of thin and dense structures along the nucleus, probably derived from the centriole adjunct, a feature that is so far exclusive to these insects. The other structures are a typical axoneme for insects with 9 + 9 + 2 microtubules, in a position diametrically opposite relative to the nucleus, two slender, symmetrical mitochondrial derivatives and a pair of discrete accessory bodies. This arrangement provides a bilaterally symmetrical flagellum, which favourably influences sperm hydrodynamics, as will be discussed. The occurrence of this unusual structural arrangement in the sperm of species from superfamilies that are phylogenetically as distant as Elateroidea and Buprestoidea support the monophyly of the infraorder Elateriformia, as proposed by some previous molecular studies.

The sperm structure of several species belonging to different tribes of the large Carabidae family is described. Some species of Nebriinae, such as Nebria brevicollis and Notiophilus biguttatus, have free conventional insect sperm. Their sperm type can be regarded as the ancestral model for Carabidae. All the other species examined, either with isolated sperm such as Calomera nemoralis, Scarites sp., Duvalius andreinii and Anillus florentinus or with spermatozeugmata and sperm associated to spermatostyles such as Typhloreicheia usslaubi, Brachinus italicus, Carabus convexus, Calathus fuscipes, Calathus montivagus, and Paraphorus mendax, showed sperm with long nucleus and a parallel axoneme running the length of the tail starting from the apical bell-like acrosome. C. nemoralis, like Cicindela campestris previously studied, has a sperm structure similar to that of several other Carabidae, confirming their correct assignment to the family. C. convexus has the same sperm structure as previously studied C. preslii and C. interstitialis, indicating that the spermatozeugmata of the group consist only of an apical cap in which the anterior sperm regions are embedded. Unlike other Carabidae with spermatozeugmata, Carabini have the typical sperm organization with acrosome, nucleus and flagellum in a regular sequence. A. florentinus, (Trechinae) shows major differences, such as the absence of an acrosome and an extremely long nucleus that reaches the end of the tail in close association with the axoneme. T. usslaubi (Scaritinae) has slender spermatozeugmata with orderly quartets of sperm. The posterior region of the sperm tail is also unusual, showing a perfect circular section and a plasma membrane reinforced by a dense underlying layer. The present observations confirm that spermatozeugmata, can vary in shape and size among different species of the Carabidae. Such diversity may be the result of the male reproductive strategy, different in each species, that enhances the efficiency of sperm transfer to the female.

The sperm ultrastructure of a few species of Limoniidae (Limonia nigropunctata; L. nubeculosa; Chionea n. sp.; C. alpina; C. lutescens) was studied. The two species of Limonia have a monolayered acrosome with crystallized material, a three-lobed nucleus in cross section, a ring of centriole adjunct material and a flagellum which consists of a 9 + 9 + 1 axoneme and a single mitochondrial derivative. The central axonemal tubule is provided with 15 protofilaments in its tubular wall, while the accessory tubules have 13 protofilaments and are flanked by the electron-dense intertubular material. The three species of Chionea share a monolayered acrosome, a nucleus with two longitudinal grooves, a centriole adjunct material which surrounds the centriole and the initial part of the axoneme. The axoneme is of conventional type, with 9 + 9 + 2 microtubular pattern, with accessory tubules provided with 13 protofilaments and intertubular material. However, in C. lutescens the accessory tubules start with 15 protofilaments and transform into a tubule with 13 protofilaments. These data are discussed in the light of the phylogenetic relationship between Limoniidae and Tipulidae. For this purpose, the sperm ultrastructure of Nephrotoma appendiculata was also considered comparatively.