Morphology and ultrastructure of the esophagus during the ontogeny of the spider crab Maja brachydactyla (Decapoda, Brachyura, Majidae)

Abstract

The esophagus of the eucrustaceans is known as a short tube that connects the mouth with the stomach but has generally received little attention by the carcinologists, especially during the larval stages. By this reason, the present study is focused on the morphology and ultrastructure of the esophagus in the brachyuran Maja brachydactyla during the larval development and adult stage. The esophagus shows internally four longitudinal folds. The simple columnar epithelium is covered by a thick cuticle. The epithelial cells of the adults are intensively interdigitated and show abundant apical mitochondria and bundles of filamentous structures. The cuticle surface has microspines and mutually exclusive pores. Three muscle layers surrounded by the connective tissue are reported: circular muscles forming a broad continuous band, longitudinal muscle bundles adjacent to the circular muscles, and dilator muscles crossing the connective tissue vertically toward the epithelium. The connective tissue has rosette glands. The esophagus of the larvae have epithelial cells with big vesicles but poorly developed interdigitations and filamentous structures, the cuticle is formed by a procuticle without differentiated exocuticle and endocuticle, the connective layer is thin and the rosette glands are absent. The observed features can be explained by his role in the swallowing of the food.

Micro-computed tomography and histology to explore internal morphology in decapod larvae

“…The oesophagus is a short tube whose function is to swallow the food (for an extensive study, see Castejón et al . 32 ). In the megalopa stage, the stomach develops a gastric mill as reported in numerous species of true crabs (Brachyura) 33 – 36 and other decapods 37 , 38 : it mills the food before it enters the midgut gland 29 – 31 .…”

Description of the larval and adult hindgut tract of the common spider crab Maja brachydactyla Balss, 1922 (Brachyura, Decapoda, Malacostraca)

“…Similar glands appear in the hindgut of other adult decapods (Barker and Gibson 1977;Barker and Gibson 1978;To et al 2004), as well associated to other body structures, e.g. shrimp gills (Doughtie and Rao 1982) and mouthparts (Alexander 1989), crab oesophagus (Castejón et al 2018c), ghost shrimp pereiopods (Dworschak 1998), and clawed lobster pleopods (Talbot et al 1991). Despite being distributed widespread within the decapods, to our knowledge the presence of those glands in non-crustacean arthropods is non-described.…”

“…Several digestive organs of M. brachydactyla during larval and adult stages have been described in previous studies, e.g. the general digestive tract anatomy (Castejón et al 2018a), oesophagus (Castejón et al 2018c), stomach (Castejón et al 2015;Castejón et al 2019c), and midgut gland or hepatopancreas (Castejón et al 2019a).…”

Structure of the stomach cuticle in adult and larvae of the spider crab Maja brachydactyla (Brachyura, Decapoda)

“…Similar properties were observed in the arthrodial membrane of different arthropod species (Dillaman et al, ; Hepburn & Chandler, ; Williams et al, ), which suggests that the cuticle of the cardiac sac might has similar properties of the cuticle of the arthrodial membrane and would provide the elasticity required to expand the cardiac sacs when a large amount of food is ingested. The morphology of the cardiac sacs cuticle resembles to the morphology of the esophagus cuticle of M. brachydactyla (the esophagus has a thickened epicuticle), which is also a structure that requires high flexibility because has to allow the peristaltic movements required to swallow the food (Castejón, Rotllant, Ribes, Durfort, & Guerao, ).…”