Holopedium amazonicum Stingelin 1904
Creators: name: Rowe, Chad L.
name: Adamowicz, Sarah J.
name: Hebert, Paul D. N.
Publisher: name: Zenodo
Year: 2007
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Branchiopoda
Diplostraca
Holopediidae
Holopedium
Holopedium amazonicum

description: Holopedium amazonicum Stingelin, 1904
Historical literature descriptions. Holopedium amazonicum is restricted to the Amazon River basin. Individuals from North America previously identified as this species are either H. atlanticum or H. acidophilum.
Stingelin (1904 a): 54–64, Table 1, Figs. 1–2
Stingelin (1904 b): 577–578, Table 20, Figs. 1–2
Thomasson (1955): No figures (paper incorrectly identifies specimens as H. gibberum)
Korovchinsky (1992): 77–78, Figs. 378–381
Paggi (1995): 912, 930–931. Figs. 14–15
Korovchinsky (2004): 345–348, Fig. 141
Etymology. amazonicum refers to the distribution of this species in waterbodies throughout the Amazon River basin.
Type locality. Rio Aramá Grande on Marajó Island at the mouth the Amazon River in Brazil (Stingelin 1904 a; approx. 1.02° S, 49.24° W).
Type specimens. Stingelin’s (1904 a) type material is housed in the Naturmuseum Olten (Kirchgasse 10, CH –4600 Olten, Switzerland; Dr. D. Vallen, curator). The material consists of two mounts, with some adult females and many juveniles from “Amazonas, 1900”. One of the females is designated as the lectotype, and the others as paralectotypes.
Voucher specimens. Twenty ovigerous females from Lago Coari, Amazonas, Brazil (collected by P. Mera, INPA, Manaus, Amazonas, on May 24, 1996; 4.08° S, 63.14° W) were deposited in the CMN under accession number CMNC 2007-0740 and an additional 30 ovigerous females from this collection were deposited at INPA, Manaus, Amazonas.
Material examined. Other habitats with H. amazonicum are listed in Appendix A.
Morphological description. FEMALE. Representative photomicrographs are shown in Fig. 8. In this study, due to specimens’ preservation in formalin, jelly coat sculpturing was not discernable.
Females are small, with adult carapace lengths ranging from 0.39–1.27 mm (mean 0.74 mm), while carapace heights range from 0.32–1.17 mm (mean 0.71 mm). The H/L ratios range from 0.66–1.64 (mean 0.99). The ventral carapace margin has many, tightly-spaced spinules posteriorly, but is smooth anteriorly.
Anal spine number ranges from 5–12 (mean 8.37). Holopedium amazonicum lacks a basal spine on each postabdominal claw. Each claw ordinarily has a row of denticles running laterally from the base of the claw to its midpoint, although individuals were observed lacking claw denticulation.
MALE. Two males were discovered by CLR in a collection from Lago Coari, Amazonas, Brazil (4.08º S, 63.14º W), which constitutes their first report from South America. The jelly coat was present, but due to its preservation in formalin, sculpturing was not discernable. The specimens were small, with a mean length and height of 0.36 mm and 0.21 mm, respectively. The ventral carapace margin has many, tightly-spaced spinules posteriorly, but is smooth anteriorly.
Differential diagnosis. Holopedium amazonicum is morphologically indistinguishable from H. atlanticum, but these species have allopatric distributions (Fig. 4 c,e). H. amazonicum is distinguished from H. acidophilum by its smaller size and smaller number of anal spines. It differs from members of the H. gibberum complex by its absence of a basal spine on either postabdominal claw. COI mtDNA sequence divergence between H. amazonicum and H. atlanticum averages 12.3%, while the divergence between H. amazonicum and H. acidophilum averages 8.7%. Levels of genetic variation within this species remain poorly known, but, based on patterns in the other Holopedium species, individuals showing less than 4% divergence from a representative COI mtDNA sequence (GenBank AF 245351) are likely to belong to H. amazonicum.
Distribution. H. amazonicum appears restricted to the Amazon River basin (see also Rowe 2000), from which it was described (Stingelin 1904 a) (Fig. 4 e). It has been reported from several ria lakes throughout the Amazon River basin, typically associated with highly humic-stained “blackwater”. Records indicate that H. amazonicum is present throughout the year, with highest densities during the semi-annual rising and lowering of the water level (E.R. Hardy, INPA, Manaus, Amazônia, unpubl. data). It has occasionally been collected in low densities from whitewater ria lakes, but it has likely been washed into these habitats from blackwater habitats during periodic flooding.
Breeding system. Members of this species were not included in allozyme analyses, and so the breeding system cannot be diagnosed in this fashion. However, males of H. amazonicum were detected by CLR in a collection made by Pedro Mera (INPA, Manaus, Amazônia) from Lago Coari, Brazil (4.077° S, 63.140° W; May 24, 1996), suggesting that cyclic parthenogenesis may be the mode of reproduction.
description: Published as part of Rowe, Chad L., Adamowicz, Sarah J. & Hebert, Paul D. N., 2007, Three new cryptic species of the freshwater zooplankton genus Holopedium (Crustacea: Branchiopoda: Ctenopoda), revealed by genetic methods, pp. 1-49 in Zootaxa 1656 on pages 30-32, DOI: 10.5281/zenodo.179852