Role of musculature during defecation in a particle‐feeding arachnid, Archegozetes longisetosus (Acari, Oribatida)

Abstract

Most extant Chelicerata are characterized by external digestion and the ingestion of fluid food. Exceptions include the marine taxa, most Opiliones, and the mite groups Opilioacarida (Parasitiformes) and Sarcoptiformes (Acariformes), which ingest particulate food. This leads to different physiological and morphological adaptations for food processing, including the production and extrusion of solid fecal pellets, which are rather large in sarcoptiform mites. Few studies have investigated the defecation of such large fecal pellets, and available information is contradictory. We use a combination of non invasive microscopical techniques and in vivo examination to investigate the complex functional morphology of the anal region of the oribatid mite Archegozetes longisetosus Aoki. The opening of the anus is at least initiated by indirect muscular action via an increase of hemolymph pressure, through the action of dorsoventral muscles (dvm). Extrusion of the fecal pellet is accomplished by the prerectal muscle collar, with full opening of the anus and rotation and bowing of the plates probably resulting from pressure of the pellet. The sequential nature of these actions was demonstrated by many observations in which the anus opened only partially; these were concomitant with dmv contraction but pellets were not being extruded. All muscles directly connected to the anal and adanal regions assist in keeping the anus closed; they are antagonists to hydrostatic forces that are necessary for normal activity. Based on the literature, no obvious similarities were noted with defecation musculature in other particle-feeding chelicerates, but most muscles can be homologized with those of more specialized oribatid mites. The function of the outer anal muscles has been modified in both Euphthiracaridae and Brachypylina to assist in providing general hemolymph pressure.

Mechanics of the ptychoid defense mechanism in Ptyctima (Acari, Oribatida): One problem, two solutions

“…Non-ptychoid mites often achieve pressure build-up by direct muscular dorsoventral compression of the hysterosoma, such as by contraction of "dorsoventral muscles" of Archegozetes longisetosus (Aoki, 1965) (dvm in Heethoff and Norton, 2009b; cf. Fig.…”

“…Like Acari in general, both groups lack most antagonistic musculature (except e.g. in the claws and chelicerae; Heethoff and Koerner, 2007;Heethoff and Norton, 2009b), such that movements of appendages, e.g. the straightening of a flexed leg segment, require a hydraulic system.…”

The 20th anniversary of a model mite: A review of current knowledge about Archegozetes longisetosus (Acari, Oribatida)

“…The plesiomorphic feeding mode of chelicerates, however, is presumably particle feeding, as can be found in the extant marine chelicerate classes Xiphosura and Pycnogonida. Within terrestrial Arachnida, particle feeding is restricted to some Opiliones (Acosta and Machado, 2007) and several groups of Acari (Heethoff and Norton, 2009a), including oribatid mites. Archegozetes longisetosus is one of the bestknown arachnids regarding food processing, from the standpoint of both structure and function.…”

“…Heethoff and Norton (2009b) established a biomechanical model of the chelicera, which was subsequently used to study trophic positions of other oribatid mites (Perdomo et al, 2012). Alberti et al (2003) provided a detailed study on the fine structure of the digestive system and fat body of A. longisetosus, and Heethoff and Norton (2009a) analyzed the functional morphological basis of defecation.…”

Attack and defense in a gamasid-oribatid mite predator-prey experiment – sclerotization outperforms chemical repellency

“…Most of the species are particlefeeding saprophages and mycophages, inhabiting diverse microhabitats (Norton, 2007;Heethoff and Norton, 2009;Wehner et al, 2016). The high number of individuals (up to several hundred thousand per square meter) and ubiquitous distribution render oribatid mites a potential resource for predators in terrestrial food webs (e.g., Hunt and Wall, 2002;Schneider and Maraun, 2009).…”