Notothfix halsei gen. n., sp n., representative of a new family of freshwater cladocerans (Branchiopoda, Anomopoda) from SW Australia, with a discussion of ancestral traits and a preliminary molecular phylogeny of the order

Abstract

The parthenogenetic female of a new anomopod crustacean, Notothrix halsei gen. n. et sp. n., is described from Lake Angove and found in five other sites in SW Australia. Although macrotrichid-like at first glance, a detailed morphological study including thoracic appendages revealed a set of primitive characters and similarities with primitive families, in particular with the Eurycercidae and Acantholeberidae. Ancestral traits of Notothrix gen. n. comprise: (i) a single large head pore; (ii) second maxilla; (iii) incomplete dorsal merger of valves; (iv) second antenna with a three- and a four-segmented branch; (v) six trunk limbs; (vi) two setae on a sixth endite in the first limb, vs. complete row of posterior setae on the second limb; (vii) large number of setae on exopodites III-V; (viii) well-developed gnathobase V; and (ix) massive postabdomen with wide, telson-like terminus between end-claws that show complex spinulation but no basal spine. Analysis of the complete 18S (SSU) rRNA gene sequence including taxa from all but four anomopod families and using Ctenopoda as an outgroup, confirms our separation of the new taxon, the Nototrichidae fam. n. Although different alignments resulted in different trees, the analyses confirm an isolated position of Notothrix, which has the shortest SSU rRNA gene length known for anomopods. However, the phylogenies derived from a comparison of 18S rRNA gene sequences between families of the order Anomopoda, does not resolve the descent of the various family groups.