Abstract
Small to very small bones (ossicles) in one species each of the families Cyclopteridae and Liparidae (Cottiformes) of the Baltic Sea are described and for the first time illustrated with SEM images. These ossicles, mostly of dermal origin, include dermal platelets, scutes, tubercles, prickles and sensory line segments. This work was undertaken to reveal characteristics of the morphology, sculpture and ultrasculpture of these small ossicles that could be useful as additional features in taxonomy and systematics, in a manner similar to their use in fossil material. The scutes and tubercles of the cyclopterid Cyclopterus lumpus Linnaeus are built of small denticles, each having its own cavity viscerally. The thumbtack prickles of the liparid Liparis liparis (Linnaeus) have a tiny spinule on a porous basal plate; the small size of the prickles seems to be related to their occurrence in the exceptionally thin skin, to an adaptation for minimizing weight and/or metabolic cost and possibly to their evolution from isolated ctenii no longer attached to the scale plates of ctenoid scales. Nodular ultrasculpture was found on the tubercle denticles of C. lumpus, resembling some kinds of ultrasculpture seen in Palaeozoic vertebrates. Samples from the posterior part of the head of C. lumpus and the anterior part of the trunk of L. liparis each contained an ossified sensory line segment with distinct characteristics, as also reported in other cottoids.
Highlights
An Estonian Science Foundation project to investigate the fine structure of the small ossicles of recent fishes of the Baltic Sea is based on knowledge from palaeontology that the morphology, surface sculpture and ultrasculpture of microscopic dermal elements are often characteristic of particular fish taxa and can be used in taxonomy and systematics for identification and characterization of taxa
The morphology, variability, ultrasculpture and inferred growth of small dermal and other ossicles of Cyclopterus lumpus and Liparis liparis from the Baltic Sea can be compared with those seen in three genera and species (Triglopsis quadricornis – fourhorn sculpin, Myoxocephalus scorpius – shorthorn sculpin, Taurulus bubalis – longspined bullhead) of the related cottoid family Cottidae as described by Märss et al (2010)
The morphology of dermal ossicles varies among the examined cottoids of the Baltic Sea
Summary
An Estonian Science Foundation project to investigate the fine structure of the small ossicles of recent fishes of the Baltic Sea is based on knowledge from palaeontology that the morphology, surface sculpture and ultrasculpture of microscopic dermal elements are often characteristic of particular fish taxa and can be used in taxonomy and systematics for identification and characterization of taxa. They can be useful for phylogenetic analyses, for elucidating faunal migration routes and for biostratigraphy. The present contribution examines, illustrates and describes the tiny dermal ossicles and bony units in the representatives of the related families Cyclopteridae and Liparidae
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