Macroscopic and microscopic morphology of the trachea and lungs of giant anteater (Myrmecophaga tridactyla)

Abstract

Giant anteater (Myrmecophaga tridactyla) is a wild mammal distributed in Central and South America; nowadays, it is classified as an endangered species. Research about the macroscopic and histomorphological aspects of its respiratory tract is scarce, and, sometimes, it limits the treatment provided to sick animals and impairs species preservation. Thus, the present study aims to describe the macroscopic and microscopic morphology of its lower respiratory tract, including trachea and lungs. To do so, 12 adult giant anteaters from “Centro de Triagem de Animais Silvestres de Goiânia” (CETAS-GO), Goiás State, Brazil, were used in the research after natural death or euthanasia. Three of these animals were used for macroscopic assessments; they were fixed in 10% buffered formalin and dissected. Trachea and lung tissue samples were collected from nine animals right after death and fixed in 10% buffered formalin for histomorphological analysis; they were processed, embedded in paraffin, and inked with hematoxylin-eosin (HE), periodic acid-Schiff (PAS), and Masson’s trichrome. The macroscopic analysis showed that the trachea in this species is proportionally short and presents from 19 to 27 tracheal cartilages. The right lung presents four lobes and the left one, two. The microscopic analysis evidenced respiratory epithelium of the ciliated cylindrical pseudostratified type, without evident goblet cells in the mucosa layer of the trachea and bronchi. The pulmonary visceral pleura is thick, similar to other large domestic mammals - complete septa extend from the pulmonary visceral pleura. In conclusion, the macroscopy and histomorphology of giant anteater’s lower respiratory tract, represented by trachea and lungs, are similar to that of other domestic and wild mammals. Pulmonary histomorphology is mainly similar to that of pigs and ruminants: it has thick visceral pleura that emits complete septa of conjunctive tissue, which enable lobular parenchymal architecture.

Morphology and computed tomography of the larynx in the white‐eared opossum (Didelphis albiventris)

“…The larynx in the white‐eared opossum is formed by four distinc cartilages (epiglottis, and thyroid, cricoid and arytenoids cartilages), similar to those observed in other wild mammals such as crab‐eating fox (Souza Junior et al., 2016), nine‐banded armadillo (Fonseca et al., 2017), paca (Ruaro et al., 2021) and giant anteater (Oliveira et al., 2023). However, cuneiform and corniculate cartilages cited in the agouti (Silva et al., 2014) were not observed in the white‐eared opossum.…”

“…The cricoid cartilage in the white‐eared opossum appears as a complete ring laterally extended, divided into a dorsal plate called lamina and a narrower ventral part called arch of the cricoid cartilage. The same gross anatomy has been described for crab‐eating fox (Souza Junior et al., 2016), nine‐banded armadillo (Fonseca et al., 2017) and giant anteater (Oliveira et al., 2023). The thyroid and cricoid cartilages were fused ventromedially and this anatomical feature has been previously reported in marsupials such as koala (Frey et al., 2018).…”

“…The muscular process projects laterally and it serves as an attachment of laryngeal muscles. Thyroid, cricoid, and arytenoid cartilages are formed by hyaline cartilage, with typical arrangement consisting of chondrocytes and extracellular matrix surrounded by perichondrium, as reported in coatis (Oliveira et al., 2012), capybaras (Moreto et al., 2017), nine‐banded armadillo (Fonseca et al., 2017), and giant anteater (Oliveira et al., 2023). The hyaline cartilage provides the necessary rigidity for muscle fixation that promotes movement between these cartilages (Ruaro et al., 2021).…”

“…The same topography was related to the crab‐eating fox (Souza Junior et al., 2016). On the other hand, the larynx is located a position at the level of the sixth (C6) and seventh (C7) cervical vertebrae in the giant anteater (Oliveira et al., 2023). The knowledge of the larynx topography is important because for the knowledge of the anatomical characteristics of the species and for clinical and surgical procedures, such as endotracheal intubation.…”

Macroscopic and histological aspects of the pharynx and larynx of the giant anteater (Myrmecophaga tridactylaLinnaeus, 1758)

“…With regard to giant anteaters, the gross morphology of the upper respiratory system was first investigated in 19th century by Owen (1854). Recent studies approached aspects of the anatomy of the lower respiratory system (Giraldi et al, 2017; Oliveira et al, 2020), as well as of the upper respiratoy system of this species (Borges et al, 2017; Farha et al, 2021; Naples, 1999). However, this is the first study to date that describes a more detailed anatomy of the pharynx and larynx of M. tridactyla , including the histological aspects of these organs.…”