title: Morphological analysis of the hagfish heart. II. The venous pole and the pericardium.
abstract: The morphological characteristics of the venous pole and pericardium of the heart were examined in three hagfish species, Myxine glutinosa, Eptatretus stoutii, and Eptatretus cirrhatus. In these species, the atrioventricular (AV) canal is long, funnel-shaped and contains small amounts of myocardium. The AV valve is formed by two pocket-like leaflets that lack a papillary system. The atrial wall is formed by interconnected muscle trabeculae and a well-defined collagenous system. The sinus venosus (SV) shows a collagenous wall and is connected to the left side of the atrium. An abrupt collagen-muscle boundary marks the SV-atrium transition. It is hypothesized that the SV is not homologous to that of other vertebrates which could have important implications for understanding heart evolution. In M. glutinosa and E. stoutii, the pericardium is a closed bag that hangs from the tissues dorsal to the heart and encloses both the heart and the ventral aorta. In contrast, the pericardium is continuous with the loose periaortic tissue in E. cirrhatus. In all three species, the pericardium ends at the level of the SV excluding most of the atrium from the pericardial cavity. In M. glutinosa and E. stoutii, connective bridges extend between the base of the aorta and the ventricular wall. In E. cirrhatus, the connections between the periaortic tissue and the ventricle may carry blood vessels that reach the ventricular base. A further difference specific to E. cirrhatus is that the adipose tissue associated with the pericardium contains thyroid follicles. J. Morphol. 277:853-865, 2016. © 2016 Wiley Periodicals, Inc.
authors.affiliation: Department of Anatomy and Cell Biology, Faculty of Medicine, University of Cantabria, 39011-, Santander, Spain.
authors.forename: José M
authors.initials: JM
authors.lastname: Icardo
authors.affiliation: Department of Anatomy and Cell Biology, Faculty of Medicine, University of Cantabria, 39011-, Santander, Spain.
authors.forename: Elvira
authors.initials: E
authors.lastname: Colvee
authors.affiliation: Department of Integrative Biology, University of Guelph, Ontario, N1G-2W1, Canada.
authors.forename: Sarah
authors.initials: S
authors.lastname: Schorno
authors.affiliation: Department of Biomedical and Dental Sciences and Morphofunctional Imaging, University of Messina, I-98166, Messina, Italy.
authors.forename: Eugenia R
authors.initials: ER
authors.lastname: Lauriano
authors.affiliation: Department of Integrative Biology, University of Guelph, Ontario, N1G-2W1, Canada.
authors.forename: Douglas S
authors.initials: DS
authors.lastname: Fudge
authors.affiliation: School of Biological Sciences, University of Canterbury, Christchurch, 8140, New Zealand.
authors.forename: Chris N
authors.initials: CN
authors.lastname: Glover
authors.affiliation: Department of Biomedical and Dental Sciences and Morphofunctional Imaging, University of Messina, I-98166, Messina, Italy.
authors.forename: Giacomo
authors.initials: G
authors.lastname: Zaccone
mesh_terms: D000818:Animals; D001011:Aorta / Q000033:anatomy & histology; D006196:Hagfishes / Q000033:anatomy & histology*; D006325:Heart Atria / Q000033:anatomy & histology; D006352:Heart Ventricles / Q000033:anatomy & histology; D010496:Pericardium / Q000033:anatomy & histology*; D014680:Veins / Q000033:anatomy & histology
keywords: Eptatretus cirrhatus; Eptatretus stoutii; Myxine glutinosa; atrioventricular canal; atrium; sinus venosus; thyroid follicles