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Pedipalps – chelate 'pincers' as the second pair of prosomal appendages – are a striking feature of scorpions and are employed in varied biological functions. Despite the distinctive morphology and ecological importance of these appendages, their anatomy remains underexplored. To rectify this, we examined the pedipalps of the Australian black rock scorpion, Urodacus manicatus , using a multifaceted approach consisting of microcomputed tomography, scanning electron microscopy, energy dispersive X-ray spectroscopy, and live pinch force measurements. In doing so, we document the following aspects of the pedipalps: (1) the musculature in three dimensions; (2) the cuticular microstructure, focusing on the chelae (tibial and tarsal podomeres); (3) the elemental construction of the chelae teeth; and (4) the chelae pinch force. We recognise 25 muscle groups in U. manicatus pedipalps, substantially more than previously documented in scorpions. The cuticular microstructure – endo-, meso-, and exocuticle – of U. manicatus pedipalps is shown to be similar to other scorpions and that mesocuticle reinforces the chelae for predation and burrowing. Elemental mapping of the chelae teeth highlights enrichment in calcium, chlorine, nickel, phosphorus, potassium, sodium, vanadium, and zinc, with a marked lack of carbon. These elements reinforce the teeth, increasing robustness to better enable prey capture and incapacitation. Finally, the pinch force data demonstrate that U. manicatus can exert high pinch forces (4.1 N), further highlighting the application of chelae in subduing prey, as opposed to holding prey for envenomation. We demonstrate that U. manicatus has an array of adaptions for functioning as a sit-and-wait predator that primarily uses highly reinforced chelae to process prey. We examine the pedipalps of the Australian black rock scorpion using microcomputed tomography, scanning electron microscopy, energy dispersive X-ray spectroscopy, and live pinch force measurements. We recognise 25 muscle groups within the pedipalp and, through documentation of the cuticular microstructure and composition, as well as pinch force values, demonstrate the robust and powerful nature of these appendages that is congruent with the style of prey capture and processing of this sit-and-wait predator. Photograph by R. Bicknell. [ABSTRACT FROM AUTHOR]

The southern Australian nuculid Nucula pusilla is < 3 mm in shell length, making it one of the smallest known protobranchs and one of the smallest bivalves. It lives in clean, well-aerated, coarse, offshore marine sands in the southern half of the Australian continent. The bivalve lies in the sand with the pointed anterior end of the shell directed upwards at an angle of ~45° to the sediment surface and inhales water into the mantle cavity from this direction. The more rounded posterior shell margin sits within the sediment. The posterior exhalant current, created by the posterior, largely respiratory ctenidia assist in the removal, along with ciliary currents on the mantle surface and visceral mass, of unwanted particles. Nucula pusilla possesses a pair of large, closed statocysts with numerous statoconia, situated above the pedal ganglia and these are likely to be responsible for the bivalve's orientation. There is also a minute Stempel's organ located on the outer face of the anterior adductor muscle. Feeding is largely by means of palp proboscides that collect subsurface material and transport it along anterior ciliated grooves where it reaches and is sorted by the labial palps where some particles are accepted and others are rejected. The intestine is coiled complexly in the visceral mass but the style sac is much simplifi ed in comparison with N. sulcata. The mantle margin of Nucula pusilla is simplifi ed, with the periostracal groove, in contrast to N. sulcata, extending almost to the pallial line. Other features of N. pusilla anatomy are described and although this species is clearly closely similar in morphological terms to other widely accepted 'primitive' nuculids, it appears that miniaturisation has resulted in some anatomical simplifi cation. As with all species, form and function result ultimately from ancestry and the evolutionary path arising from natural selection. Aspects of the morphology of N. pusilla, such as the mantle margin, the simply structured style sac, the uniquely protobranch Stempel's organ, and the mantle cavity brooding of lecithotrophic larvae, are indicative of a 'primitive', perhaps ancestral, nuculid condition. Other aspects of the overall body plan, such as the loss of the anterior pedal retractor muscles, suggest simplifi cation resulting from miniaturisation. It is suggested that through paedomorphosis, miniaturisation of a nuculid ancestor could be the means by which the 'higher' lamellibranch bivalves have so successfully adopted a ctenidial and suspension feeding lifestyle and been released from the constraints that deposit feeding imposes. These bivalves have subsequently diverged into a complex array of species inhabiting virtually every aquatic habitat on Earth. [ABSTRACT FROM AUTHOR]