Significant differences were found between males and females in the fragmocone, external cone and widths of the cuttlebone in Sepia officinalis caught in the small-scale trap fishery off Gran Canaria Island (Spain). It is suggested that: (a) differences may depend on morphological adaptations of females for egg laying; (b) cuttlebones represent over 50% of the total cuttlefish caught (which is unrecorded in the fishery); and (c) the relationships between several morphometric measures of the cuttlebone and the mantle length and wet weight may allow more accurate biomass estimations of this species in the fishery.

Many avian species are considered sexually monomorphic. In monomorphic bird species, especially in young birds, sex is difficult to identify based on an analysis of their external morphology. For nestlings, sex identification is usually impossible by morphological examination. Sex identification in avian species is one of the key points of avian breeding and evolutionary studies. Through the knowledge of sex identification genes, poultry breeding programmes can be applied more successfully. Vent sexing, laparoscopy, steroid sexing and karyotyping are methods for sex identification used in monomorphic birds. However these methods are unreliable, time-consuming, and expensive while some of them could be painful and even lifethreatening for birds. The sex of an individual is established from the genes located on sex chromosomes. Female birds carry one copy of both Z and W, and male birds carry two copies of Z avian sex chromosomes. However, there are many DNA techniques, the most reliable one is amplifying sex specific CHD1 gene by P2 – P8 primer pairs.