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Abstract

The hypothesis that size of tentacle clubs – the organs by which decabrachian cephalopods catch prey – has some effects on the quantity of food caught and ingested was tested in four somatically distinct groups of cuttlefish, namely males and females of both Sepia elegans and Sepia orbignyana. To this purpose the relationship between individual body condition, which is the result of diet over time, and relative club length was examined. A statistically significant positive correlation was found between relative body condition factor, Kn=W/aMLb (where W is the individual cuttlefish body mass, ML is the individual mantle length, and a and b are the parameters of the body mass–mantle length regression) and relative tentacle club condition factor, Tn=CL/cMLd (where CL is the observed value of club length, ML is the individual mantle length, and c and d are the parameters of the club length–mantle length regression). On average, a 10% departure of club length from its expected value causes a slight, proportionally direct departure of body mass from its expected value in the range of 1.6–2.0%, according to sex and species. The demonstration of such a correlation in four distinct cuttlefish groups corroborates the existence of an actual cause–effect relationship between relative tentacle club length and condition. Accordingly, it may be supposed that the character ‘club length’ is affected by natural selection.