Molecular evidence for the gnathobasic derivation of arthropod mandibles and for the appendicular origin of the labrum and other structures.

Mandibles are feeding appendages functioning as "jaws" in the arthropod groups in which they occur. Which part of this appendage is involved in food manipulation (limb tip versus limb base), has been used to suggest phylogenetic relationships among some of the major taxa of arthropods (myriapods, crustaceans, and insects). As a way to independently verify the conclusions drawn from previous morphological analyses, we have studied the expression pattern of the gene Distal-less (Dll), which specifies the distal part of appendages. Our results show, in contrast to the traditional view, that both insect and crustacean adult mandibles are gnathobasic, handling food with the basal portion of the appendage. Furthermore, as is evident by the reduction in the number of Dll-expressing cells in the later developmental stages, adult diplopod jaws are also gnathobasic. Thus, jaws of all mandibulates (myriapods, crustaceans, and insects) seem to have a similar gnathobasic structure. We have also found that Dll is expressed in the labra of all arthropod taxa examined, suggesting that this structure is of appendicular derivation. Additionally, the spinnerets and book lungs of spiders, long considered on other grounds to be modified appendages, express Dll, confirming this interpretation. This study shows that, in addition to their use in phylogenetic and population genetic studies, molecular markers can be very useful for inferring the origins of a particular morphological feature.

Risk management alert: a summary of perinatal cases.

Connecticut Medical Insurance Company (CMIC) cases related to obstetrical care and the newborn represent the single most costly exposure to the Company. CMIC undertook the review of its perinatal cases, open and closed, to identify common elements that increased the liability exposure of individual physicians as well as the overall exposure to the Company.

A devonian spinneret: early evidence of spiders and silk use.

A nearly complete spider spinneret was found in Middle Devonian rocks (about 385 to 380 million years old) near Gilboa, New York. This is the earliest evidence yet discovered for silk production from opisthosomal spigots, and therefore for spiders. Two previously known Devonian fossils described as spiders lack any apomorphies of the order Araneae and are probably not spiders. The spigots of the Devonian spinneret resemble those of members of the living suborder Mesothelae, but the number of spigots and their distribution are like those of members of the suborder Opisthothelae, infraorder Mygalomorphae. The Devonian spider belonged to a clade that may be the sister group of all other spiders, of Mesothelae, or of Opisthothelae.

Early land animals in north america: evidence from devonian age arthropods from gilboa, new york.

A new fossil site near Gilboa, New York, is one of only three where fossils of terrestrial arthropods of Devonian age have been found. The new Gilboan fauna is younger than the other two but richer in taxa. Fragmentary remains and nearly whole specimens assigned to Eurypterida, Arachnida (Trigonotarbida, Araneae, Amblypygi, and Acari), Chilopoda [Craterostigmatomorpha(?) and Scuterigeromorpha(?)], and tentatively to Insecta (Archaeognatha) have been found. The centipedes and possible insects may represent the earliest records known for these groups.

Alkylphenols in the defensive secretion of the nearctic opilionid,Stygnomma spinifera (Arachnida: Opiliones).

The opilionid,Stygnomma spinifera, secretes from a pair of exocrine glands on the cephalothorax between the first and second pair of legs a major volatile component, 2-methyl-5-ethylphenol, and two minor components, 2,3-dimethylphenol and 2,3-dimethyl-5-ethylphenol. These alkylphenols are constituents of a defensive secretion and repel ants, a natural predator of opilionids. The probable significance of this secretion in the biology ofS. spinifera and in the defensive strategies of opilionids in general is discussed.