Abstract
On basis of a SEM study the homology between the neck/dorsal organ of the Conchostraca and the head pores of the cladoceran family Chydoridae is established. Species of Lynceus (Conchostraca) and Eurycercus (Chydorinae) show a characteristical similar arrangement of four elevated areas within a circular/oval organ. Presence of two lateral pores may be an apomorphy for the Chydoridae lost in the Chydorinae and in some other genera. Some species of the Chydoridae (Rhynchotalona falcta and Tretocephala ambigua) display what can be interpreted as intermediate stages between the circular/oval organs in Eurycerus and more aberrant neck organ structures in the remaining Chydoridae. A characteristic neck organ morphology — two widely separated median pores with two smaller pores in between and without lateral pores — is considered as a synapomopphy for the Chydorinae. In contrast, no component of the neck organ morphology could be given synapomorphic status for all the species of the Aloninae. A number of potential apomorphies, related to the neck organ, seem to place subgroups of the Aloninae closer to the Chydorinae than to the rest of the subfamily. These apomorphies include, among others, ‘elongation of the neck organr’ after Eurycercus has been branched off and subdivision of the neck organ into discrete pores after Rhynchotalona and Tretocephala has been branched off. If this interpretation is correct it will leave the Aloninae paraphyletic with respect to the Chydorinae.
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Olesen, J. External morphology and phylogenetic significance of the dorsal/neck organ in the Conchostraca and the head pores of the cladoceran family Chydoridae (Crustacea, Branchiopoda). Hydrobiologia 330, 213–226 (1996). https://doi.org/10.1007/BF00024209
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DOI: https://doi.org/10.1007/BF00024209