Exoskeleton anchoring to tendon cells and muscles in molting isopod crustaceans

Abstract

Specialized mechanical connection between exoskeleton and underlying muscles in arthropods is a complex network of interconnected matrix constituents, junctions and associated cytoskeletal elements, which provides prominent mechanical attachment of the epidermis to the cuticle and transmits muscle tensions to the exoskeleton. This linkage involves anchoring of the complex extracellular matrix composing the cuticle to the apical membrane of tendon cells and linking of tendon cells to muscles basally. The ultrastructural arhitecture of these attachment complexes during molting is an important issue in relation to integument integrity maintenance in the course of cuticle replacement and in relation to movement ability. The aim of this work was to determine the ultrastructural organization of exoskeleton – muscles attachment complexes in the molting terrestrial isopod crustaceans, in the stage when integumental epithelium is covered by both, the newly forming cuticle and the old detached cuticle. We show that the old exoskeleton is extensively mechanically connected to the underlying epithelium in the regions of muscle attachment sites by massive arrays of fibers in adult premolt Ligia italica and in prehatching embryos and premolt marsupial mancas of Porcellio scaber. Fibers expand from the tendon cells, traverse the new cuticle and ecdysal space and protrude into the distal layers of the detached cuticle. They likely serve as final anchoring sites before exuviation and may be involved in animal movements in this stage. Tendon cells in the prehatching embryo and in marsupial mancas display a substantial apicobasally oriented transcellular arrays of microtubules, evidently engaged in myotendinous junctions and in apical anchoring of the cuticular matrix. The structural framework of musculoskeletal linkage is basically established in described intramarsupial developmental stages, suggesting its involvement in animal motility within the marsupium.

The harvestman tarsus and tarsal flexor system with notes on appendicular sensory structures in laniatores

“…This process of maintaining muscle attachments during new cuticle formation was recently described for crustaceans (Yamada and Keyser, 2009;Znidar sič et al, 2012) and was similarly observed for insects (Lai-Fook, 1967). In this case, during the premolt stage, the new cuticular matrix would be deposited around the tonofibrillae such that the tonofibrillae extend from the pulley cell through the newly forming cuticle and ecdysal space and remain attached to the old cuticle.…”

Comparative ultrastructure of cells and cuticle in the anterior chamber and papillate region of Porcellio scaber (Crustacea, Isopoda) hindgut

“…Accordingly, the ratio of epicuticle thickness to procuticle thickness is considerably higher in hindgut cuticle than in exoskeletal cuticle of P.scaber . The hindgut cuticle is connected to individual epithelial cells by cuticle–epithelium attachments, which ultrastructurally resemble connections between the exoskeletal cuticle and specialised epidermal cells (tendon cells) in arthropods (Buchholz and Buchholz 1989, Mellon 1992, Lai-Fook and Beaton 1998, Bitsch and Bitsch 2002, Žnidaršič et al 2012).…”

Push or Pull? The light‐weight architecture of the Daphnia pulex carapace is adapted to withstand tension, not compression

“…These are analogous to the anchoring fibers in arthropods that reach through the epidermis and into the procuticle to attach muscle (Bitsch and Bitsch, ). Znidaršič et al ()showed for isopods, that these fibers even reach through the new procuticle and anchor in the old procuticle just before molting. In Daphnia , such attachment fibers to the exoskeleton were described for muscles by Schulz and Kennedy (Schultz and Kennedy, ) and in association with pillars by Halcrow (Halcrow, ).…”