ABSTRACT

Th e transition of water living organisms to terrestrial life is a huge great step which demands drastic adaptations during evolution. Nevertheless, several taxonomic groups have successfully conquered an environment which was attractive as prey source and as shelter against water living predators. Preliminaries for an existence on land are: 1. suited extremities to move in a medium which has a far lower compactness than water where buoyancy allows swimming; 2. prevention of desiccation which concerns especially the external skin and the water respiration organs; 3. gills must be compensated by air breathing organs which had to be situated internally in the land living organisms; 4. alteration or reduction of sense organs which operate in water; e.g. eyes must be adapted to see in air where light rays pass a medium with another refraction patterns than water; sounds spread out in water four times faster than in air; lateral lines with current sense organs can only operate in water, not in air; 5. developmental stages, larvae and young are very sensitive against desiccation which requires special protection mechanisms. Whereas Boleophthalmus spp. and Periophthalmus chrysospilus possess joint ventral fi ns, the suckers of other Periophthalmus and Periophthalmodon spp. present a trend of reduction (Fig. 3.2.1). This reduction is not a pattern of better adaptation to the way of living on land but may be rather dependant to the respective habitats. P. chrysospilus climbs on trees (Fig. 3.2.3: 10) where a sucker can be advantageous whereas these organs do not function on mud bottoms. Boleophthalmus spp. (Fig. 3.2.3: 9) are active during low water on the soft sediment but vanish by running aground when the water rises (Harms, 1929). Th eir skin is adapted to the boring way of life by an epidermis with vesicular cells and a thick cuticula which will be described below (Fig. 3.2.7). Movements of the amphibious Periophthalmus and Periophthalmodon spp. on land are performed either by sliding with help of the pectoral fi ns or by leaps with the help of the tail, e.g. on fl ight, during courtship or when chasing competitors. They are not able to move as similar as the land vertebrates because the ventral fi ns are situated directly behind the pectoral fins and the pelvis is connected with the shoulder girdle; these morphological patterns exclude quadruped walking. Th erefore, it is without importance whether the ventral fi ns are combined or secondarily separated because both patterns are found in this group. When walking, the prolonged pectoral fi ns are simultaneously swung forward, raised, moved backward and set down on the ventral fi ns (Harris, 1960; Magnus, 1978).