Phylogenetic trends in the abundance and distribution of pit organs of elasmobranchs

Abstract

 Abstract Peach, M.B and Rouse, G.W. 2004. Phylogenetic trends in the abundance and distribution of pit organs of elasmobranchs. -Acta Zoologica (Stockholm) 85 : 233-244Pit organs (free neuromasts of the mechanosensory lateral line system) are distributed over the skin of elasmobranchs. To investigate phylogenetic trends in the distribution and abundance of pit organs, 12 relevant morphological characters were added to an existing matrix of morphological data (plus two additional end terminals), which was then re-analysed using cladistic parsimony methods (  * 4.0b10). Character transformations were traced onto the most parsimonious phylogenetic trees. The results suggest the following interpretations. First, the distinctive overlapping denticles covering the pit organs in many sharks are a derived feature; plesiomorphic elasmobranchs have pit organs in open slits, with widely spaced accessory denticles. Second, the number of pit organs on the ventral surface of rays has been reduced during evolution, and third, spiracular pit organs have changed position or have been lost on several occasions in elasmobranch evolution. The concentrated-changes test in  (version 4.05) was used to investigate the association between a pelagic lifestyle and loss of spiracular pit organs (the only character transformation that occurred more than once within pelagic taxa). Depending on the choice of tree, the association was either nonsignificant at P = 0.06 or significant at P < 0.05. Future studies, using species within more restricted elasmobranch clades, are needed to resolve this issue.

Denticle-embedded ampullary organs in a Cretaceous shark provide unique insight into the evolution of elasmobranch electroreceptors

“…However, no partial or complete fusion is observed between these denticles (Budker 1938;Reif 1985;Peach and Marshall 2009). These denticle-covered pit organs are a derived feature found mainly in galeomorph sharks, including all lamniforms except Mitsukurina (Reif 1985;Peach and Rouse 2004). It is now known that ampullary organs arise from lateral line placodes in the cartilaginous fish clade (Gillis et al 2012;Baker et al 2013).…”

Molecular and Chromosomal Markers for Evolutionary Considerations in Torpediniformes (Chondrichthyes, Batoidea)

“…A large number of different interpretations exists in scienti�c literature based on morphological characters [3][4][5][6][7][8][9][10][11], on molecular studies [12][13][14], and on conventional cytogenetics [14,15]. Many scientists consider that batoids are monophyletic, even if the time of their divergence from the other elasmobranch �sh remains controversial.…”

Sensory Systems in Sawfishes. 2. The Lateral Line

“…This condition is identified as plesiomorphic, contrasting the apomorphic conditions of having either overlapping denticles that cover the sensory structures in galean sharks or no accessory denticles as in 'recent batoids' (e.g. mylobatiformes) [Peach and Rouse, 2004]. Both the mylobatiforms and lamnids have independently lost their spiracular pit organs, which may be due to their pelagic lifestyle [Peach and Rouse, 2004].…”

“…mylobatiformes) [Peach and Rouse, 2004]. Both the mylobatiforms and lamnids have independently lost their spiracular pit organs, which may be due to their pelagic lifestyle [Peach and Rouse, 2004]. Whether the absence of spiracular pit organs in A. cuspidata is related to a pelagic lifestyle is unclear; a comparison with other pristids is needed first.…”

“…This group of sensory receptors appears to be present only in sharks and rhinobatid rays [Peach, 2003]. Its absence in all other batoids is regarded as an apomorphic condition, and in mylobatid rays, the reduction of ventral pit organs may be related to the reduction of accessory denticles, and therefore the loss of protection against abrasion [Peach and Rouse, 2004].…”