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In the present study, spermatozoon ultrastructure was documented in two species of hangingflies, Bittacus strigosus Hagen (Mecoptera: Bittacidae) and B. stigmaterus Say. Structures considered important to phylogenetic assessment that were observed in B. strigosus and B. stigmaterus included a short bilayered acrosome, elongated nucleus, tube-like glycocalyx, centriole adjunct material, accessory bodies, two mitochondrial derivatives, extra axonemal rods, globular units, and 9+2 arrangement of microtubules in the axoneme. Comparisons were made to Bittacus planus Cheng, which was previously examined by electron microscopy ( Xie and Hua 2010 ). Similarities among the ultrastructural characteristics of the three Bittacus species support the monophyly of this genus. Displacement of a mitochondrial derivative by an accessory body was documented for the first time. This paper includes clarifications on differences between accessory bodies and extra axonemal rods, which are issues important to phylogenetic placement.

The ultrastructure of spermiogenesis and spermatozoa is examined for the first time in the heterogastropod family Mathildidae (Mathilda brevicula Bavay and Mathilda sp.). Mathildid spermatozoa exhibit the following features: (1) an ovoid acrosomal vesicle showing curved dense layers basally and underlain by a thin curved plate; (2) a solid, rod-shaped nucleus showing a shallow basal invagination (nucleus helically keeled in Mathilda sp.); (3) a midpiece composed of a 9+2 axoneme, 9 thick and periodically banded coarse fibres (associated with the axonemal doublets) and a continuous mitochondrial derivative; (5) glyco-gen piece composed of the axoneme surrounded by dense granules; (6) and end piece (paddle-shaped terminally). Results of the study demonstrate that mathildids share the same key sperm and spermi-ogenic features observed in the Architectonicidae. The monophyly of the Architectonicoidea, established by previous authors on anatomical grounds, is therefore confirmed using sperm morphology. Spermatozoa of the two mathildids investigated lack the periodically banded midpiece structures seen in investigated species of Architectonica (A. pcrspectiva (Linnaeus), A. perdix (Hinds)), Heliacus (H. (Heliacus) variegatus (Gmelin)) and Pseudotorinia (P. laseronorum (Iredale)) thereby resembling most closely the spermatozoaof Philippia lutea (Lamarck) and Psilaxis oxytropis (A. Adams) which also lack suchbanded structures. Given the widely accepted primitive status of the Mathildidae within the Architectonicoidea, the genera Philippia and Psilaxis may prove to be relatively basal rather than advanced genera within the Architectonicidae. Thi: view needs to be tested by examination of sperm morphology in other genera of the Architectonicidae and also the basal mathildid genus Tuba sensu lato (= Gegania + Tubena). Such information will be vital in any future cladistic study of the Architectonicoidea.

Sperm ultrastructure is described for Pleurehdera haraldi Er. & Ev. Marcus, 1970 and contrasted with data from previously investigated members of the Notaspidea. The acrosomal vesicle is small (length 0.13 pm, breadth 0.09 pm) and supported basally by a short (0.37 pm) pedestal which overlaps extensively with the tapered nuclear apex. Nuclei are approxi-mately 15 pm long and sometimes exhibit a single helical keel. Absence of the keel in many of the observed spermatozoa suggests possible dimorphism with regard to this feature. A short basal invagination of the nucleus forms the point of attachment for the centriolar derivative and axoneme/coarse fibre com-plex. A single glycogen-filled helix is present within the mitochondrial derivative of the midpiece. Distally, an annulus occurs at the junction of the elongate (at least 160 pm) midpiece and short (1.5 pm) glycogen piece. Axonemal microtubules persist to the posterior tip of the spermatozoon. Comparison with other Notaspidea confirms that Pleurehdera is closest to Berthella and Berthellina within the Pleurobranchinae (of the family Pleurobranchidae). Sperm morphology supports the unity of the pleurobranchine tribe Berth- ellini.