Department of Anatomy and Cell Biology, Faculty of Medicine, University of Cantabria, Santander, Spain.
Department of Chemical, Biological, Pharmaceutical and Environmental Sciences, University of Messina, Messina, Italy.
J Morphol. 2023 May;284(5):e21584. doi: 10.1002/jmor.21584.
This work reports on the structural characteristics of the respiratory gas bladder of the osteoglossiform fish Heterotis niloticus. The bladder-vertebrae relationships are also analyzed. A slit-shaped orifice in the mediodorsal pharyngeal wall is surrounded by a muscle sphincter and serves as a glottis-like opening to the gas bladder. The dorsolateral internal surface of the gas bladder is lined by a parenchyma of highly vascularized trabeculae and septa displaying an alveolar-like structure. The trabeculae contain, in addition to vessels, numerous eosinophils probably involved in immune responses. The air spaces are endowed with a thin exchange barrier indicating a good potential for respiratory gas exchange. The ventral wall of the gas bladder is a well-vascularized membrane that exhibits an exchange barrier in the luminal face and an inner structure dominated by the presence of a layer of richly innervated smooth muscle. This is suggestive of an autonomous adjustability of the gas bladder ventral wall. The trunk vertebrae show large transverse processes (parapophyses) and numerous surface openings that lead into intravertebral spaces that become invaded by the bladder parenchyma. Curiously, the caudal vertebrae show a regular teleost morphology with neural and hemal arches, but have similar surface openings and intravertebral pneumatic spaces. The African Arowana hence rivals the freshwater butterfly fish Pantodon in its exceptional role of displaying postcranial skeletal pneumaticity outside of Archosauria. The possible significance of these findings is discussed.
本文报道了骨舌鱼目鱼类非洲龙鱼的呼吸气囊的结构特征，并分析了气囊与脊椎的关系。在咽腔背侧正中壁有一裂缝状的孔，周围有肌肉括约肌围绕，类似于气囊的气门。气囊的背外侧内表面衬有一层富含血管的小梁和隔，呈肺泡样结构。小梁除了血管外，还含有许多嗜酸性粒细胞，可能参与免疫反应。气腔具有薄的交换屏障，表明具有良好的呼吸气体交换潜力。气囊的腹侧壁是一层富含血管的膜，在腔面具有交换屏障，内层结构主要由富含神经支配的平滑肌层组成。这表明气囊腹侧壁具有自主调节能力。躯干椎具有大的横突（副突）和许多表面开口，这些开口通向椎体内腔，被气囊实质侵入。奇怪的是，尾椎具有典型的硬骨鱼形态，具有神经弓和脉弓，但具有相似的表面开口和椎体内的气腔。非洲龙鱼因此与淡水蝴蝶鱼 Pantodon 一样，在非恐龙类动物中具有独特的后骨骼充气特性。这些发现的可能意义将在文中进行讨论。
