As far as is known, this paper gives the first description of a two‐headed shark embryo belonging to an oviparous species, Galeus atlanticus (Carcharhiniformes: Scyliorhinidae). The specimen was ...detected among 797 embryos intended for cardiovascular studies, which represents a defect incidence of 0·13%. Each head had a mouth, two eyes, a brain, a notochord and five gill openings on each side. The two heads fused behind the gills. On the single body, there were four anticipated dorsal fins, two anterior, right and left and two posterior, right and left. Ventrally, the specimen possessed two pairs of pectoral fins, a pair of pelvic fins and one anal fin. Two adjacent notochords, two neural tubes and two dorsal aortas ran along the body, which bent 180° at its posterior portion. There were two hearts, two oesophaguses, two stomachs, two livers, but a single intestine with a spiral valve. Previous reports of conjoined twins in sharks are scarce and only refer to oviparous and ovoviviparous species. Seven dicephalous sharks reported so far were similar to the specimen described here, namely, with two totally separated heads on one body. Instead, only one case of diprosopus shark has been reported; it had a single body and a single head with partial duplication of the face. Two further cases described in the literature as dicephalous or simply as abnormal sharks should be better regarded as diprosopus, while another three cases, also considered dicephalous, showed a mixture of characteristics of diprosopia and dicephalia.
Summary
The concept that anatomical variations in the coronary artery tree might be influenced by genes is relatively old. However, empirical evidence on the effect of genotype on the coronary ...morphology is still scarce. In the Syrian hamster, there is a septal coronary artery which arises from the left or from the right coronary artery and supplies most of the interventricular septum. The aim was to decide whether the anatomical origin of the septal artery is subject to inheritance factors. Overall, 483 internal casts of the heart and coronary arteries were examined. All the hamsters included in this study had normal coronary arteries. The results of 74 crosses were compared statistically to seek for any significant difference between the phenotypes of the offspring and the phenotypes of the parents. The left septal artery was over‐represented in the offspring of crosses between parents having both a left septal artery (p < .01), while the right septal artery was over‐represented in the offspring of crosses between parents, one with a right and the other with a left septal artery (p < .001), and, more markedly, in the offspring of crosses between parents both with a right septal artery (p < .001). These results are the first to reveal that the coronary artery pattern is influenced by genetic factors, at least in its proximal portion with regard to the aorta.
As far as is known, this paper gives the first description of a two‐headed shark embryo belonging to an oviparous species,
Galeus atlanticus
(Carcharhiniformes: Scyliorhinidae). The specimen was ...detected among 797 embryos intended for cardiovascular studies, which represents a defect incidence of 0·13%. Each head had a mouth, two eyes, a brain, a notochord and five gill openings on each side. The two heads fused behind the gills. On the single body, there were four anticipated dorsal fins, two anterior, right and left and two posterior, right and left. Ventrally, the specimen possessed two pairs of pectoral fins, a pair of pelvic fins and one anal fin. Two adjacent notochords, two neural tubes and two dorsal aortas ran along the body, which bent 180° at its posterior portion. There were two hearts, two oesophaguses, two stomachs, two livers, but a single intestine with a spiral valve. Previous reports of conjoined twins in sharks are scarce and only refer to oviparous and ovoviviparous species. Seven dicephalous sharks reported so far were similar to the specimen described here, namely, with two totally separated heads on one body. Instead, only one case of diprosopus shark has been reported; it had a single body and a single head with partial duplication of the face. Two further cases described in the literature as dicephalous or simply as abnormal sharks should be better regarded as diprosopus, while another three cases, also considered dicephalous, showed a mixture of characteristics of diprosopia and dicephalia.
•The cardiac outflow tract of the arowana consists of bulbus and conus arteriosus.•The structure of these components shows primitive traits within teleosts.•The bulbus has two prominent luminal ...ridges to which the conal valves are anchored.•This anatomical bulbar structure has not been described so far in any fish species.•Pigment cells, presumably of neural crest origin, occur in the bulbar subepicardium.
The cardiac outflow tract of chondrichthyans and actinopterygians is composed of a myocardial conus arteriosus and a non-myocardial bulbus arteriosus. In teleosts, the conus has been subjected to a reduction in size over the evolution in conjunction with the further development of the bulbus. Most studies on the outflow tract of the teleost heart refer to species of modern groups and are mainly devoted to the bulbus. Knowledge on the outflow tract of species belonging to early teleost groups is scarce. The aim here was to characterise the structure of the cardiac outflow tract of the silver arowana, a representative of the ancient teleost clade of the Osteoglossomorpha. The material consisted of hearts from six juvenile animals. The cardiac outflow tract of the silver arowana is composed of a conus, which supports two conal valves, and a bulbus. Both components are lined externally by the epicardium and internally by the endocardium. The conus is immunoreactive to antibodies against myosin heavy chains and is composed of compact myocardium, thus contrasting with the ventricle, which has exclusively trabeculated myocardium. The bulbus is immunoreactive to antibodies against smooth muscle α-actin and mainly consists of elastic fibres and smooth muscle cells, both arranged in three layers, outer, middle and inner. The most remarkable feature of the bulbus is the presence of two prominent longitudinal ridges, dorsal and ventral, at the luminal side, which serve to anchor the commissures of the conal valves. This arrangement has not been described so far in any fish species. Pigment cells, presumably of neural crest origin, are present in the subepicardium of the bulbus and anterior part of the ventricle.
