Air motion sensing hairs of arthropods detect high frequencies at near-maximal mechanical efficiency

Using measurements based on particle image velocimetry in combination with a novel compact theoretical framework to describe hair mechanics, we found that spider and cricket air motion sensing hairs work close to the physical limit of sensitivity and energy transmission in a broad range of relatively high frequencies. In this range, the hairs closely follow the motion of the incoming flow because a minimum of energy is dissipated by forces acting in their basal articulation. This frequency band is located beyond the frequency at which the angular displacement of the hair is maximum which is between about 40 and 600 Hz, depending on hair length (Barth et al . [ 1 ] Phil. Trans. R. Soc. Lond. B 340 , 445–461 ( doi:10.1098/rstb.1993.0084 )). Given that the magnitude of natural airborne signals is known to decrease with frequency, our results point towards the possible existence of spectral signatures in the higher frequency range that may be weak but of biological significance.

Silvanerpeton miripedes, a new anthracosauroid from the Viséan of East Kirkton, West Lothian, Scotland

ABSTRACTSilvanerpeton miripedes gen. et sp. nov. is a small gracile anthracosauroid. The holotype is an almost complete articulated specimen in black shale. Its anthracosaur characters include tabular-parietial contact, with a tabular horn and a moderate surangular crest indicating relationship with the embolomeres. It has gastrocentrous vertebrae with poorly ossified centra and neural arches, and the presacral vertebral count is estimated to be over 30. There are a number of apparently primitive characters as found in other anthracosauroids include a closed palate, mobile basal articulation, and an intertemporal. It differs from the other recognised species of anthracosaur at East Kirkton, Eldeceeon rolfei, in vertebral count, number of ribs, interclavicle shape, relative limb length, and in having an unossified tarsus, and a pedal phalangeal count of 23455.Disarticulated bones from East Kirkton including large limb and vertebral elements may belong to this taxon, to Eldeceeon rolfei or to as yet unidentified taxa.

The feeding mechanism of Antarcturus and a redescription of A. spinacoronatus Schultz, 1978 (Crustacea: Isopoda: Valvifera)

The behaviour and feeding mechanism of valviferan isopods of the genus Antarcturus , exemplified by A. spinacoronatus , have been studied for the first time. This poorly known species is redescribed and details of its morphology, studied by light and scanning electron microscopy, are reported. Adaptations to its special habits include: cuticular spines on trunk segments and limbs which protect it from predators and conceal its outlines; first pereopods with brushes of setae, the most important of which are the medio-ventral and dorsal setae of the propodus used for cleansing the filter combs of pereopods 2-4; long rows of setae on pereopods 2-4 used in passive sieving of phytoplankton; and stout pereopods 5-7 with their spines that are used for climbing. The long setae of the filtering limbs are moved by a hydraulic mechanism. The structure of the basal articulation of these setae is described. The most conspicuous movements of the anterior limbs during feeding are recorded. A comparison with Arcturella sawayae reveals the functional adaptations of the more specialized Arcturella . It is suspected that the family Arcturidae evolved in the Antarctic or Subantarctic Oceans.

Cranial morphology of the Loxommatidae (Amphibia: Labyrinthodontia)

The labyrinthodont superfamily Loxommatoidea is now divided into two families. The highly aberrant Spathicephalus is placed in a new family, the Spathicephalidae, to be described elsewhere. The family Loxommatidae is retained for the remaining genera, Loxomma, Megalocephalus and Baphetes . Additional material and further preparation has made possible a redescription of the three loxommatid genera and new skull restorations have been produced for most species. In particular the loxommatid braincase and palatoquadrate are reconstructed for the first time; in many features their structure is more primitive than that hitherto described for any temnospondyl. Since an intertemporal bone is found to be a feature of Baphetes as well as Loxomma , these two genera have been separated on the basis of skull shape and on stratigraphical grounds. A specimen from the Communis zone, Westphalian A, is attributed to Loxomma , as L. rankini sp.nov., while ‘ Loxomma bohemicum ’ has been transferred to the genus Baphetes as B. bohemicus (Fritsch). A further specimen, originally associated with Macrerpeton , has also been referred to this genus as B. lintonensis sp.nov. The skull of Megalocephalus pachycephalus can be described in greater detail than that of any other loxommatid species and thus forms the basis for discussion of the functional morphology. Jaw muscles are reconstructed for this species and it is concluded that the antorbital vacuity, which characterizes the Loxommatoidea, evolved as a bulging hole for a large pterygoideus muscle associated with a piscivorous habit and a kinetic inertial system of jaw closure. Consideration of the mechanics of jaw closure sheds light on a further enigma, i.e. the function of the basipterygoid articulation in the primitive temnospondyl skull. The loxommatid skull is considered divisible into two units. The presence of a specialized cranial joint between the quadrate and quadratojugal allows potential for any movement at the basal articulation to be accommodated in the main at this site. It is suggested that the system described for loxommatids represents an alternative design to the mobile cheek region of anthracosaurs and that the articulations represent zones of elasticity, which accommodate the stresses on the skull caused by a powerful jaw musculature.

Memoirs: Contributions to the Development of the Skull in Sturgeons

1. Acipenser stellata of the age of ten and a half days has a process which by its relations suggests that it is a basitrabecular process, and it may represent the vestige of the basal articulation of the palatoquadrate. 2. The so-called profundus is a ramus ophthalmicus superficialis trigemini, the profundus being absent.

NEW TACHINIDÆ WITH A SLENDER PROBOSCIS

The Tachinidæ described below have a slender, rigid proboscis, of which the portion beyond the basal articulation is at least one half longer than the height of the head. All are from the Pacific Coast, and, except where otherwise stated, were captured or bred by the writer.Siphona plusiœ,n. sp.—♂ ♀ Terminal section of proboscis—the part beyond the second geniculation—not more than three-fourths as long as height of head. Frontal vitta yellow, less than twice as wide as either side of the front next the antennæ; sides of front grayish pollinose, frontal bristles descending nearly to apex of second antennal joint, two pairs of orbital bristles; face whitish, the sides bare; vibrissæ inserted near the oral margin, only two or three small bristles above each; cheeks less than one-fourth as wide as height of eyes.