Caridina biyiga sp. nov., a new freshwater shrimp (Crustacea: Decapoda: Atyidae) from Leichhardt Springs, Kakadu National Park, Australia, based on morphological and molecular data, with a preliminary illustrated key to Northern Territory Caridina

Abstract

Caridina biyiga sp. nov. is described from Leichhardt Springs, Kakadu National Park, Northern Territory, Australia, based on morphological and molecular data. The new species is highly distinctive among its congeners in having the dactylus of pereiopod 5 similar to the dactyli of pereiopods 3–4 and lacking the comb-like row of spiniform setae typical of the genus. The branchial formula is also distinctive for the genus in lacking an arthrobranch at the base of pereiopod 1 and in having a vestigial epipod on maxilliped 1. Despite the distinctive morphology of the new species, the molecular data did not provide strong support for the recognition of a new genus. Phylogenetic analyses of Australian Caridina using the mitochondrial 16S rDNA gene fragment placed the new species in a well-supported clade containing at least one typical species of Caridina. Within this clade, referred to as the ‘thermophila’ group, Kimura 2-parameter (K2P) genetic distances of 16S rDNA between the new species and sister taxa ranged from 5.1–6.0%. Analyses using the mitochondrial 3’ COI gene fragment from species of the ‘thermophila’ group yielded K2P genetic distances between the new species and its sister taxa ranging from 10.4–15.1%. A preliminary illustrated key to Northern Territory Caridina is provided. The conservation significance of Leichhardt Springs and its aquatic fauna are also briefly discussed.

Three New Species of the Freshwater Shrimp Genus Caridina from Australia

“…Contigs of forward and reverse strands were assembled using Geneious Prime (v. 2019.2.1) and corrected by eye. In addition, published sequences, notably twelve sequences of the three new species published by von Page et al [7], Cook et al [12], Short et al [4] and de Mazancourt et al [13], have been included in the analysis (Table 1). Sequences were aligned with MAFFT [14].…”

“…Colouration: Variable. Some specimens reddish with a pale median dorsal line extending from the rostrum to the sixth pleomere, some specimens mottled with reddish and creamy chromatophores, smaller specimens mostly transparent [4,25].…”

“…A significant number of species of the largest genus within the Atyidae, Caridina H. Milne Edwards, 1837 are known from Australia but are still awaiting formal species descriptions [2]. Some new species were recently described from the northern part of Australia like Caridina malanda Choy, Page, de Mazancourt and Mos, 2019, a species belonging to the Caridina zebra species complex [3], Caridina biyiga Short, Page and Humphrey, 2019, a member of the C. thermophila species group [4] or Caridina pagei Christodoulou and De Grave, 2023, a morphological cryptic species related to Caridina sobrina Riek, 1953 [5]. Christodoulou and De Grave [5] also provided an overview on the species of genus Caridina from Australia.…”

“…Christodoulou and De Grave [5] also provided an overview on the species of genus Caridina from Australia. Short et al summarized the information on Caridina originating from the Northern Territory and gave a morphological key for their identification [4]. Page et al [6] already suggested the existence of species complexes of problematic, cryptic Australian species within the genus Caridina.…”

“…They found several genetically distinct and putatively new species of the genus Caridina. This material was subsequently included in a paper on the molecular and conservation biogeography of Caridina shrimps from northwestern Australia [7] and, with additional samples, to discuss the relationship within shrimp of the genus Caridina from the Northern Territory [4].…”