Hyaline-cell cartilage (chondroid) in the heads of teleosts

Abstract

The structure and distribution of hyaline-cell cartilage (chondroid) (HCC) in the heads of teleosts has been studied in 48 species from 16 families. The tissue is pale-staining and has closely-packed, hyaline cells that are separated by a small quantity of matrix. The matrix has only a mild affinity for alcian blue and the cells are not shrunken within lacunae. Two subtypes of the tissue are here described--fibrohyaline-cell cartilage (chondroid) where collagen fibres are prominent in the matrix, and lipohyaline-cell cartilage where fat and hyaline cells are intermingled. An elastic hyaline-cell cartilage has been described previously. Associations of HCC with dense fibrous connective tissue, mucochondroid, hyaline cartilage and bone are described. Lists are provided of membrane and cartilages bones to which the tissue is attached and of species in which it is common. Suitable 'type examples' for reference and for further study include the cartilage in the rostral folds of the red-tailed black shark, Labeo bicolor and the flying fox, Epalzeorhynchus kalopterus. HCC occurs in lips and rostral folds, in pre-palatine and submaxillary menisci, in ligaments, at the anterior end of the basihyal, in the pectoral girdle, in adhesive discs, in gill arches, beneath the basioccipital chewing pad, in barbels, next to the facial nerve, around the olfactory region and in the core of the nasal skin flaps. It is a particularly important tissue in cyprinids and related fish, and enormous masses of it are present in the black shark, Morulius chrysophekadion and the Hong Kong pleco, Pseudogastromyzon myersi. It acts as a damper against the contractions of the heart or the pressure of occluding pharyngeal teeth, and it provides the mouth region of bottom-dwelling, algal eaters with flexible support. In relation to Schaffer's classification of supporting tissues, I confirm a distinction between HCC and Zellknorpel.