Capture of Prey, Feeding, and Functional Anatomy of the Jaws in Velvet Worms (Onychophora)

Abstract

Onychophorans are carnivorous, terrestrial invertebrates that occur in tropical and temperate forests of the Southern Hemisphere and around the Equator. Together with tardigrades, onychophorans are regarded as one of the closest relatives of arthropods. One of the most peculiar features of onychophorans is their hunting and feeding behavior. These animals secrete a sticky slime, which is ejected via a pair of slime-papillae, to entangle the prey. After the prey has been immobilized, its cuticle is punctured using a pair of jaws located within the mouth. These jaws constitute internalized appendages of the second body segment and are innervated by the deutocerebrum; thus, they are homologous to the chelicerae of chelicerates, and to the (first) antennae of myriapods, crustaceans, and insects. The jaws are also serial homologs of the paired claws associated with each walking limb of the trunk. The structure of the jaws is similar in representatives of the two major onychophoran subgroups, the Peripatidae and Peripatopsidae. Each jaw is characterized by an outer and an inner blade; while the outer blade consists only of a large principal tooth and up to three accessory teeth, the inner blade bears numerous additional denticles. These denticles are separated from the remaining part of the inner jaw by a diastema and a soft membrane only in peripatids. The onychophoran jaws are associated with large apodemes and specialized muscles that enable their movement. In contrast to the mandibles of arthropods, the onychophoran jaws are moved along, rather than perpendicular to, the main axis of the body. Our elemental analysis reveals an increased incorporation of calcium at the tip of each blade, which might provide rigidity, whereas there is no evidence for incorporation of metal or prominent mineralization. Stability of the jaw might be further facilitated by the cone-in-cone organization of its cuticle, as each blade consists of several stacked, cuticular elements. In this work, we summarize current knowledge on the jaws of onychophorans, which are a characteristic feature of these animals.

Mechanoresponsive lipid-protein nanoglobules facilitate reversible fibre formation in velvet worm slime

“…spiders, mussels) have emerged as important role models for inspiring sustainable production of advanced polymeric materials 1–4 . Velvet worms (Onychophora) are terrestrial invertebrates inhabiting humid microhabitats of tropical and temperate forests in the southern hemisphere 5 , which deploy a fibre-forming projectile slime for defence and entangling prey 6–8 . The adhesive slime, which is stored as a fluid within slime gland reservoirs, is ejected through papillae—small nozzles on either side of the head—leading to the rapid self-assembly into sticky entangling threads outside the body, which dry and harden into stiff polymeric fibres (Fig.…”

Der „Sekundenkleber“ der Stummelfüßer

“…Die Stummelfüßer bilden eine eigenständige, stammesgeschichtlich sehr alte Gruppe von weichhäutigen, wirbellosen Tieren, die hauptsächlich in den Wäldern der südlichen Hemisphäre unserer Erde vorkommen (Abbildung ). Dort leben sie in feuchten Lebensräumen, verborgen in verrotteten Baumstämmen oder in der Spreuschicht . Derzeit gibt es knapp über 200 beschriebene Arten, aber vor allem in Brasilien werden viele noch unbekannte Arten vermutet.…”

“…Sobald die Beute fixiert ist, reißt der Räuber die Körperhülle mit seinen kräftigen Kiefern auf und injiziert einen Cocktail aus Enzymen, welche das Innere der Beute verdauen. Der Stummelfüßer saugt dann die flüssige Nahrung aus, ähnlich wie es bei den Spinnen zu beobachten ist . Die großen Mengen an versprühtem Beutefangsekret sind für die Tiere sehr wertvoll.…”

“…c) Schleimfäden fixieren die Beute (in diesem Fall ein Heimchen) am Untergrund. Bild a aus , © 2019 The Society for Integrative and Comparative Biology.…”

Evaluation of contrasting techniques for X‐ray imaging of velvet worms (Onychophora)

“…In particular, onychophorans are pivotal for understanding intricate evolutionary processes underlying the successful radiation of arthropods, such as arthropodisation (evolution of jointed limbs), arthrodisation (evolution of body sclerotisation), tagmatisation (fusion of body segments into functional units) and establishment of a specialised ganglionated nervous system (Martin et al ., ). Even though onychophorans have never been investigated comprehensively by CT techniques, recent studies suggested that this method is promising for studying their anatomy and may eventually help to shed light on evolutionary questions that remain unanswered (Mayer et al ., ; Müller et al ., ).…”