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Polkamenes pycnodontae (Bruce, 1978), Tympanicheles ornatus (Holthuis, 1952), B) Anchistus australis, D) A. demani, F, H) A. miersi, in de Gier et Fransen. 2023. photographs by C.H.J.M Fransen |
Abstract
Most marine shrimp species of the family Palaemonidae are characterized by symbiotic associations with hosts that belong to a wide range of invertebrate phyla. One clade of related endosymbiotic species has evolved to live inside the branchial chambers of ascidians and the mantle cavities of bivalve molluscs. The phylogeny of this clade (comprising 15 bivalve-associated species in the genera Anchistus, Neoanchistus, and Paranchistus, and three species of ascidian-associated species in the genus Dasella) is the topic of the present study, which is based on both morphological and molecular data. A concatenated phylogeny reconstruction was built by using the markers coi and 16S. With the help of a total evidence approach (with a scored morphological datamatrix), species could be added for which no molecular data were available. An ancestral character state analysis was performed to detect host switches. In contrast to another endosymbiotic clade, the ancestral host state was found to be slightly in favour of bivalves. The phylogenetic relevance of morphological features is discussed with a focus on a tympanal organ located in the major chelipeds of some bivalve-associated shrimp species. This little-known anatomical structure is illustrated by sem and µCT scans. Its possible function is discussed. In the phylogeny reconstructions, both Anchistus and Paranchistus were found to be polyphyletic. They were reclassified to obtain a more natural classification: Anchistus custoides and Anchistus custos were transferred to the resurrected genus Ensiger. Paranchistus liui, P. nobilii, P. pycnodontae, and P. spondylis were transferred to Polkamenes gen. nov. Anchistus pectinis and P. ornatus were transferred to Tympanicheles gen. nov. Per genus, a key to the species is provided.
Keywords: commensal shrimp, host switching, symbiosis, taxonomic revision, total evidence
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| A) Anchistus australis Bruce, 1977, RMNH.CRUS.D.58048, stn ber.28, in Tridacna squamosa Lamarck, 1819; B) A. australis, RMNH.CRUS.D.53540, stn ter.12, in T. squamosa; C) Anchistus demani Kemp, 1922, RMNH.CRUS.D.42792, stn sey.792, in Tridacna maxima (Röding, 1798); D) A. demani, RMNH.CRUS.D.58049, stn thu.07, in T. maxima; E) Anchistus gravieri Kemp, 1922, RMNH.CRUS.D.58052, stn FR15, in Hippopus hippopus (L., 1758); F) Anchistus miersi (De Man, 1888), RMNH.CRUS.D.42970, stn sey.720, in T. squamosa: G) A. miersi, RMNH.CRUS.D.46473, sw Sulawesi, in T. squamosa; H) A. miersi, RMNH.CRUS.D.53568, stn ter.19, in T. squamosa. photographs by C.H.J.M Fransen |
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| Polkamenes pycnodontae (Bruce, 1978) RMNH.CRUS.D.48261, from Hyotissa hyotis (L., 1758) |
Genus Polkamenes gen. nov.
Etymology. ‘Polkamenes’: named after the characteristic blue-, red-, and orange-dotted pattern seen on the species’ carapace, abdomen, and appendages ‘Polka dots’ (English, in combination with the common palaemonid suffix ‘-menes’; see e.g., Ancylomenes Okuno & Bruce, 2010, Laomenes Clark, 1919, Periclimenes). Gender: masculine.
recognize four species: Polkamenes liui (Li, Bruce & Manning, 2004); Polkamenes nobilii (Holthuis, 1952); Polkamenes pycnodontae (Bruce, 1978); and Polkamenes spondylis (Suzuki, 1971).
Distribution. Shiraiso, Manazura-Machi, Kanagawa Prefecture, Japan, (cf. Suzuki, 1971, Hayashi, 2005, 2006); South China Sea (Li et al., 2004).
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| Tympanicheles ornatus (Holthuis, 1952), RMNH.CRUS.D.42794, from Atrina vexillum (Born, 1778) |
Genus Tympanicheles gen. nov.
Etymology. ‘Tympanicheles’: named after the ‘drum-like’ veil on the species’ major chela. Built from ‘Tympani-’, a suffix for drum in Latin (‘Tympanum’), and ‘-cheles’ for claws in Latin. Gender: masculine.
recognize two species: Tympanicheles ornatus (Holthuis, 1952), and Tympanicheles pectinis (Kemp, 1925).
Werner de Gier and Charles H.J.M. Fransen. 2023. Polka-dotted Treasures: Revising A Clade of Ascidian- and Bivalve-associated Shrimps (Caridea: Palaemonidae). Contributions to Zoology. 92(3); 179-282. DOI: doi.org/10.1163/18759866-bja10042
