The origin and evolution of the euarthropod labrum

A widely (although not universally) accepted model of arthropod head evolution postulates that the problematic labrum, a structure seen in almost all living euarthropods, evolved from an anterior pair of appendages homologous to the frontal appendages of onychophorans. However, the implications of this model for the interpretation of fossil arthropods have not been fully integrated into reconstructions of the euarthropod stem group, which remains in a state of some disorder. Here I review the evidence for the evolution of the labrum from living taxa, and reconsider how fossils should be interpreted in the light of this. Identification of the segmental identity of head appendage in fossil arthropods remains problematic, and often rests ultimately on unproven assertions. New evidence from Parapeytoia is presented to suggest that the labral appendage persisted well up into the upper stem-group of the euarthropods, which prompts a re-evaluation of widely-accepted segmental homologies and the interpretation of fossil central nervous systems. Only a protocerebral brain was present in large part of the euarthropod stem group, and the modern deutocerebrum must have been a relatively late addition.

Molecular phylogeny confirms the placement of enigmatic Stachys persepolitana in Lamium (Lamiaceae; subfam. Lamioideae)

The main purpose of this study was to test the hypothesis that Stachys persepolitana is extraneous in Stachys (tribe Stachydeae, subfam. Lamioideae, Lamiaceae) and instead belongs to the genus Lamium (Lamieae, Lamioideae). We investigated the phylogenetic position of S. persepolitana using plastid (rps16 intron, trnL-F and matK regions) and nuclear (nrITS) DNA sequence data with both parsimony and Bayesian phylogenetic approaches. Plastid and nuclear data strongly support that S. persepolitana is extraneous in Stachys and belongs in fact to the genus Lamium. Morphological characters also corroborate its placement in Lamium. Most of the morphological features used to distinguish S. persepolitana from the rest of Stachys fit with Lamium. Anterior pair of stamens bending outward after pollination, anthers hairy and mericarps triquetrous are the most important characters correlating S. persepolitana to Lamium.

Four new species of Heth Cobb, 1898 (Rhigonematida: Hethidae) from Vietnamese diplopods

Four new species of Heth are described from diplopods collected in different parts of Viet Nam: Heth vietnamensis sp. n. and H. tonkinensis sp. n. in Ba Vi National Park, Ha Tay Province; H. taybaci sp. n. in Lai Chau Province and H. taynguyeni sp. n. in Chu Yang Sin National Park, Dak Lak Province. The new species are morphologically related to those described from Papua New Guinea, but are differentiated by the form of the female cuticular armature. Heth vietnamensis sp. n. is characterised by the posterior end of the lappets overhanging the anterior pair of the lateral spines, the similar size of spines in both pairs and the presence of two pairs of small papillae on the anterior lip of the cloacal aperture. Heth tonkinensis sp. n. can be differentiated from the other species by having the longest lappets, lateral spines with fused bases and the unequal-sized spicule heads. Heth taybaci sp. n. has the shortest lappets of the described Vietnamese species, has gaps between the lateral spines that are wider than the spine base and the presence of a bursa-like cuticular fold at cloacal aperture level. Heth taynguyeni sp. n. males also have a bursa-like cuticular fold but, unlike H. taybaci sp. n., this species is characterised by the bifurcate distal tips of the spicule and the undulating inner margin of the lappets.

Transepithelial potential differences and Na+ flux in isolated perfused gills of the crabChasmagnathus granulatus(Grapsidae) acclimated to hyper- and hypo-salinity

SUMMARYWe studied the transepithelial potential difference (TEPD) and 22Na flux across isolated perfused gills (anterior pair 5 and posterior pairs 6–8) of the crab Chasmagnathus granulatus acclimated to either hypo- or hyper-osmotic conditions.The gills of crabs acclimated to low salinity, perfused and bathed with 10 ‰ saline solutions, produced the following TEPDs (hemolymph side with respect to bath side): 0.4±0.7, –10.2±1.6, –10.8±1.3 and –6.7±1.3 mV for gills 5, 6, 7 and 8, respectively. Gills 6, 7 and 8 did not differ significantly. Reducing the saline concentration of bath and perfusate from 30 ‰ to 20 ‰ or 10 ‰ increased significantly the TEPDs of these gills. TEPDs of gill 6 (representative of posterior gills) were reduced by 69±5 % and 60±5 % after perfusion with ouabain or BaCl2 (5 mmol l–1 each), respectively. The same gill showed a net ouabain-sensitive Na+ influx of 1150±290 μequiv g–1 h–1.Gill 6 of crabs acclimated to high salinity produced TEPDs of –1.5±0.1 and –1.3±0.09 mV after perfusion with 30 ‰ or 40 ‰ salines, respectively. Perfusion with ouabain or BaCl2 reduced TEPDs by 76±7 % and 86±4 %, respectively. A net ouabain-sensitive Na+ efflux of 2282±337 μequiv g–1 h–1 was recorded in gill 6 perfused with 38 ‰ saline.

Chilenomyia paradoxa gen. n., sp. n. and Chilenomyiinae, a new subfamily among the Chironomidae (Diptera)

Male and female of Chilenomyia paradoxa are described. An outstanding autplesiomorphy of the male hypopygium, even as compared to Diptera in general, is apparently the presence of two pairs of well developed gonocoxites. The anterior pair of large, simple lobes is homologous with laterosternite IX of other chironomid males and with gonocoxite IX of the females. The posterior pair, consisting of gonocoxites + gonostyli, is enclosed between the anterior lobes and corresponds to the clasper apparatus of other Chironomidae. The male clasper of Chironomidae is hence evidently a derivative of sternite X and not of sternite IX as hitherto assumed. A further indication of this is the wellknown intimate connection between the claspergonocoxites and sternapodeme X. However, in Chilenomyia the sternapodeme forms a simple semicircular arch ending in sharp points deep into the cavity of the gonocoxites, while in other chironomids the sternapodeme is firmly connected with the anterodorsal margin of the gonocoxites. The Chilenomyia pattern is probably an autapomorphy. Another autapomorphy is displayed by the subapically inserted gonostyli which have rotated through 90° so that the normally frontal surface becomes directed dorsad, meaning that each gonostylus forms a clasper together with the apical end of the gonocoxite. This and supporting evidence lead to the conclusion that Chilenomyia deserves a new subfamily, Chilenomyiinae, which forms the sister group of a monophyletic group comprising all other chironomid subfamilies except Telmatogetoninae.

Neuromuscular Physiology of the Longitudinal Muscle of the Earthworm, Lumbricus Terrestris

1. The motor fields of individual segmental nerves have been mapped electrophysiologically in the longitudinal muscle of the earthworm, Lumbricus terrestris. 2. The anterior pair of segmental nerves (SNI) innervates approximately the anterior two-thirds of its segment and a small portion of the segment just anterior to it. 3. The posterior pair of segmental nerves (SNII-III) innervates approximately the posterior two-thirds of its segment and a small portion of the segment just posterior to it. 4. Adjacent nerves (both intrasegmental and intersegmental) have partially overlapping motor fields; that is, adjacent segmental nerves innervate some of the same longitudinal muscle fibres.