Ontogeny of the skull of the Australian lungfish Neoceratodus forsteri (Osteichthyes: Dipnoi)

Abstract

Development of the sensory lines, dermal skull bones, neurocranium, quadrate, mandible and hyoid apparatus of the Holocene Australian lung®sh Neoceratodus forsteri is described, beginning at stage 40, before the formation of any skeletal elements, until skull development is complete in the sub-adult ®sh. The sequence of the initial development of skeletal structures of the head and shoulder girdle re¯ects the need to feed and to acquire ef®cient gill respiration. The appearance of the neurocranium and dermal bones of the skull follows the formation of teeth, jaw bones and the cartilaginous quadrate, and the opercular bones, the skeletal elements directly associated with these functions. Dermal skull elements are closely related to the distribution of the sensory line system of the head. Each bone of the normal developing skull roof arises from a single centre of ossi®cation, forming in a collagenous template secreted by mesenchymal cells. The numbers and arrangement of the skull bones found in the adult N. forsteri is the same as the pattern of bones laid down in the hatchling and juvenile, and the structures develop in an ordered and functional sequence.

Skin structure in the snout of the Australian lungfish, Neoceratodus forsteri (Osteichthyes: Dipnoi)

“…in southeast Queensland according to the methods described in Kemp (1981Kemp ( , 1999. Stages follow Kemp (1982Kemp ( , 1999. The hatchlings and juveniles ranged from stage 45 to stage 60 ( Table 1).…”

“…Hatchling and juvenile lungfish were reared from eggs collected in the Brisbane River at Lowood http://dx.doi.org/10.1016/j.tice.2014.07.004 0040-8166/© 2014 Elsevier Ltd. All rights reserved. in southeast Queensland according to the methods described in Kemp (1981Kemp ( , 1999. Stages follow Kemp (1982Kemp ( , 1999.…”

“…Blocks of subadult and adult tissue for histology were washed and dehydrated in a graded series of ethanols, and then embedded in Technovit resin (Kemp, 1999) or in Epon Araldite resin, sectioned at 2 m and stained with Toluidine blue in buffer. Heads of hatchling and juvenile lungfish, fixed in neutral buffered formalin, rinsed in water and dehydrated in ethanol, were embedded whole in Technovit resin, then sectioned and stained with 1% Toluidine blue in phosphate buffered saline.…”

“…4B). In juveniles and adults, mechanoreceptors are confined to deep and wide sensory canals, running in a defined pattern over the head (Pehrson, 1949;Kemp, 1999), except on the tip of the snout, where the mechanoreceptors may still be superficial. The canals are huge, at least 200 m in diameter and often larger.…”

“…1B). On the snout they are single, and on the dorsal, lateral and ventral surfaces of the head they are arranged in pit lines (Kemp, 1999). Rows of electroreceptors run above and below the lateral line of the trunk (Kemp, 2012b).…”