The Shape of the Skeletal Elements in the Head of a Generalized Haplochromis Species: H. Elegans Trewavas 1933 (Pisces, Cichlidae)

Abstract

The present paper is the first publication in a series dealing with current investigations on the comparative functional morphology of various Haplochromis species. The paper deals mainly with the shape-description of the primary skeletal elements in the head of H. elegans, a generalized insectivorous Haplochromis from the East-African Lakes George and Edward. A primary skeletal element is defined as the largest skeletal unit whose shape is taken to be unchangeable over the period of observation and within the limits of observational techniques. The shape-description concentrates on the topological definition of features relevant to comparative functional morphology of Haplochromis species (e.g. crests, processes, articulation facets). To avoid ambiguity, the essential topological and directional terms are used in a restricted sense, defined in the section on morphological terms. A so-called reference is defined for each element. Positions and directions in the shape-description of an element always refer to its relative reference grid. In this way the shape-description of an element becomes independent of its positions in the head. An element-bound reference grid is necessary for the quantitative comparison of corresponding elements from different specimens. The aim of the present paper is to provide a set of nomenclatorial tools to be used for tracing, describing and measuring functional relevant shape-differences in the skeletal elements of Haplochromis species. It is hoped that the two examples in the section on trophically correlated shape-differences will demonstrate the applicability of this idea. One example deals with the characteristic shape of pharyngobranchial 3,4 in intrapharyngeal mollusc-crushers, the other example concerns the typical shape of the palatine region in paedophagous Haplochromis species.