The ultimate legs of Chilopoda (Myriapoda): a review on their morphological disparity and functional variability

Abstract

The arthropodium is the key innovation of arthropods. Its various modifications are the outcome of multiple evolutionary transformations, and the foundation of nearly endless functional possibilities. In contrast to hexapods, crustaceans, and even chelicerates, the spectrum of evolutionary transformations of myriapod arthropodia is insufficiently documented and rarely scrutinized. Among Myriapoda, Chilopoda (centipedes) are characterized by their venomous forcipules—evolutionarily transformed walking legs of the first trunk segment. In addition, the posterior end of the centipedes’ body, in particular the ultimate legs, exhibits a remarkable morphological heterogeneity. Not participating in locomotion, they hold a vast functional diversity. In many centipede species, elongation and annulation in combination with an augmentation of sensory structures indicates a functional shift towards a sensory appendage. In other species, thickening, widening and reinforcement with a multitude of cuticular protuberances and glandular systems suggests a role in both attack and defense. Moreover, sexual dimorphic characteristics indicate that centipede ultimate legs play a pivotal role in intraspecific communication, mate finding and courtship behavior. We address ambiguous identifications and designations of podomeres in order to point out controversial aspects of homology and homonymy. We provide a broad summary of descriptions, illustrations, ideas and observations published in past 160 years, and propose that studying centipede ultimate legs is not only essential in itself for filling gaps of knowledge in descriptive morphology, but also provides an opportunity to explore diverse pathways of leg transformations within Myriapoda.

Millipede genomes reveal unique adaptations during myriapod evolution

“…Myriapods were among the first arthropods to invade the land from the sea, during an independent terrestrialisation from early arachnids and insects, which occurred during the Silurian period approximately 400 million years ago [7]. Today, the Myriapoda consists of approximately 16,000 species, all of which are terrestrial [8]. Currently, just 2 myriapod genomes are available: the centipede Strigamia maritima [9] and a draft genome of the millipede Trigoniulus corallinus [10].…”

New avatars for Myriapods: Complete 3D morphology of type specimens transcends conventional species description (Myriapoda, Chilopoda)

“…Information on the biology and reproduction of Lithobiomorpha is scarce, although sexual dimorphism has been documented in a number of species of the class Chilopoda and the modifications of the ultimate legs were recently reviewed [ 14 ]. Kenning et al further summarised the reports on the possible role of these appendages in preying, mating, and defensive strategies and as sensory organs [ 14 ].…”

“…These sensilla are generally assumed to have a mechano- and chemoreceptive function (and are named as such), a role very plausibly also played by the prefemoral ones. This comes as no surprise as several cuticular sensory microstructures of the ultimate legs have hitherto been homologised to those of the antenna ([ 14 ] and references therein).…”

Millipede genomes reveal unique adaptation of genes and microRNAs during myriapod evolution

“…Myriapods were among the first arthropods to invade the land from the sea, during an independent terrestrialisation from early arachnids and insects, which occurred during the Silurian period ~400 million years ago (Minelli 2015). Today, the Myriapoda consists of ~I6,000 species, all of which are terrestrial (Kenning et al 2017). Currently, just two myriapod genomes are available: the centipede Strigamia maritima (Chipman et al 2014), and a draft genome of the millipede Trigoniulus corallinus (Kenny et al 2015).…”