Types, Distribution and Rhythmical Behaviour of the Chromatophores of Juvenile Carcinus maenas (L.)

Abstract

Colour change in Brachyura is effected by chromatophores located within the hypodermis. Abramowitz (1935) found that Portunus anceps, the white crab, possesses three types of monochromatic chromatophore containing white, black and yellow pigment respectively, whilst P. ordwayi, the red crab, possesses three similar pigments and an additional red pigment. In this respect Uca pugilator (Carlson 1936) and Eriocheir japonicus (Matsumoto 1954) resemble Portunus ordwayi. Enami (1951) working on crabs of the genus Sesarma, described monochromatic black, white, red and vermilion chromatophores. All these workers concluded that the chromatophores are scattered throughout the hypodermis and do not form striking colour patterns. In 1937, Abramowitz described a 24-hour rhythm of colour change in the fiddler crab Uca, the animal having a dark day phase caused by the dispersion of the darker pigments, and a light night phase, the pigments being concentrated. Brown & Webb (1948) described how this rhythm persisted for as long as 30 days in continuous darkness, and was independent of temperature within the range 6-26? C. Brown, Fingerman, Sandeen & Webb (1953) in a further investigation of this 24-hour rhythm in U. pugnax, described a persistent tidal rhythm of melanophore expansion which was superimposed upon the diurnal rhythm leading to a third - a semi-lunar rhythm. Here the phase of melanophore dispersion bore a definite relationship to the time of low water in the area in which the crabs were collected. Fingerman (1955, 1956), described persistent daily and tidal rhythms of colour change in the blue crab, Callinectes sapidus, and in two other species of Uca, U. pugilator and U. speciosa. In all these cases, the crabs darkened by day and paled at night, with a supplementary dispersion of dark pigment at or near the time of low water. This investigation was performed to describe the types and distribution of chromatophores in Carcinus maenas, and to find out whether Carcinus, an animal which is known to have persistent daily and tidal rhythms of locomotory activity (Naylor 1958), has similar rhythms of colour change.