Denton Belk

Checklist of the Anostraca

In this checklist, we number the named anostracan fauna of the world at 258 species and seven subspecies oraganized in 21 genera. The list contains all species described through 31 December 1993, and those new species names made available in previous pages of this volume. The most species rich genus isStreptocephalus with 58 described species level taxa.Chirocephalus with 43,Brachinecta 35, andBranchinella 33 occupy the next three places. With the exception ofBranchipodopsis andEubranchipus each having 16 species, all the other genera include less than 10 species each. The need for zoogeographic study of these animals is demonstrated by the fact that almost 25% of the named taxa are known only from their type localities.

Identification of species in the conchostracan genus Eulimnadia by egg shell morphology

ABSTRACT Clam shrimps in the genus Eulimnadia (Branchiopoda: Spinicaudata) cover their eggs with tertiary envelopes that on close examination exhibit species-specific morphologies. Most of the other characters used by previous students of this group are misleadingly variable. I review the 12 species described from North America. Egg morphology suggests that only 5 of these are valid. To these 5, I add 2 new species clearly recognizable by egg morphology.

Large branchiopod assemblages common to Mexico and the United States

We present observations on the frequency of large branchiopod associations found in north-central Mexico, and in Arizona, USA. Of a total of 25 species involved in these assemblages, 12 were common in both areas. Fifty-eight (43.3%) of the ponds in Mexico, and seventy-eight (47%) of those in Arizona had two or more species present. The combinations of species which occurred with highest frequency were Streptocephalus mackini with Thamnocephalus platyurus for Arizona, and T. platyurus, Triops sp., and Leptestheria compleximanus for Mexico. In Mexico, and Arizona, as in many parts of the world, multispecies assemblages of large branchiopods are a common phenomenon. Therefore, the ’common rule‘ of’one-phyllopod-per-habitat‘ advanced by Weise (1964) is inconsistent with field observations. Furthermore, since cases of co-occurrence of two or more congeneric species of Anostraca and Notostraca are not uncommon, generalizations about congeners not coexisting remain applicable only for the Spinicaudata and Laevicaudata. On the basis of the literature, and of observations in the field and in the laboratory, we list potential factors contributing to the co-occurrence of several species within a pond.

Review of the clam shrimp family Lynceidae Stebbing, 1902 (Branchiopoda: Conchostraca), in the Americas

ABSTRACT The North, South, and Central American species of the Lynceidae Stebbing are reviewed. Morphological characters that distinguish the family, including several not previously known or not recognized as being of familial importance, are illustrated and discussed. Of the three known genera in the family, only two, Lynceus Muller and Paralimnetis Gurney, are known from North, Central, and South America; the genus Lynceiopsis Daday, known only from Africa, is described and discussed for comparative purposes. Taxonomic characters that can be reliably used to identify American species are primarily those of the male first thoracopods (claspers) and head region (rostrum). All American species are redescribed, with two exceptions. The validity of two species, Lynceus tropicus and L. rotundirostris. is questioned on the basis of the poor condition of type material and inadequate original descriptions. One new species of Paralimnetis Gurney is described from Texas. A key to the American species is included.

A contribution to the systematics of the Streptocephalidae (Branchiopoda: Anostraca)

While developing a data base for phylogenetic analysis of the New World streptocephalids we compared them with species from Africa, Europe, and India. In doing this, we found that the morphology of the peduncle of the distal antennal outgrowth and the biramous ovaries developed in seven North American species can contribute to the systematics of the genus. Thus, our investigation consisted of (1) a review of the external morphology of the antenna, (2) biometry of selected parts of the antenna to obtain informative ratios, (3) a review of the presence or absence of genital linguiform outgrowths, extension of the non-retractile parts of the penes, and general morphology of the cercopods, (4) a study of the location of the ovaries, and extension of the brood-pouch. On the basis of the results we classify Streptocephalus into nine species groups. Five subgroups are identified within two of the species groups. Several implications of the present approach are discussed.

Additional Observations on Variations in Egg Size Among Populations of Streptocephalus-Seali (Anostraca)

ABSTRACT We evaluated the interrelationships between egg size, maternal length, and habitat type for the fairy shrimp Streptocephalus seali from a variety of localities. Our analyses demonstrated a correlation between female length and egg size for samples from California, Florida, and Montana, and for pooled data using all samples. However, there was no such correlation for the sample from Louisiana. The regression between egg size and female length for meltpool populations that generally produce larger eggs is significantly different from the regression for the rainpool populations that typically form smaller eggs. Belk (1977) first observed this difference in egg size between meltpool and rainpool populations in a comparison of S. seali from Arizona and Louisiana. We confirmed this difference and extended it to include samples from Alabama, California, Florida, Montana, North Carolina, and Chiapas, Mexico. Other factors demonstrated to significantly affect egg size are habitat latitude, habitat altitude, and the interactive effects of the independent variables evaluated. We concluded that egg-size variations between populations of S. seali inhabiting rainpools and meltpools reveal evolutionary responses to differing ecological situations.

On potentials and relevance of the use of copulatory structures in anostracan taxonomy

This paper reviews and extends the knowledge of anostracan penile morphology and its taxonomic significance. Since Linder‘s pioneering classification(based partly on male genital characters), the morphology of both basal and distal penile parts has been applied repeatedly to reorganize or establish higher anostracan taxa, or to extend their diagnoses. In general, the configuration of both basal and distal penile structures follows a constant pattern in well-defined genera. Size and shape of processes and spinulation on the basal (in Linderiella and Chirocephalidae) and the distal parts (in Parartemia), however, may show inter-specific differences. Variability in penile structures in the current genus Brachinella indicates the need for a taxonomic revision of this genus. Similar intra-generic penis morphology may contribute to hybridizability of congeners and validate Dubois‘genus concept for use in anostracans.

Diagnosis and phylogeny of the new world streptocephalidae (Branchiopoda: Anostraca)

We present an updated diagnosis of 13 Streptocephalus species of North America. Three new species are included. A key to the species is provided.

Antennal Appendages and Reproductive Success in the Anostraca

ABSTRACT I present evidence that antennal appendages contribute to male reproductive success in Eubranchipus serratus Forbes. Males will mate or clasp females in an attempt to mate repeatedly. However, receptive females typically reject a number of mating attempts before finally accepting a mate. Males with their antennal appendages removed succeeded in inseminating only 13 females out of 250 mating attempts while intact males were successful in 53 of 253 tries (x2 = 27.4, df = 1, P < 0.005). During unsuccessful mating attempts, receptive females were able to reject courting males by freeing themselves from the clasping males in less than 6 s in over 60% of cases regardless of whether the males had antennal appendages or not. The data suggest a mate recognition function for the antennal appendages.

Uncovering the Laurasian roots of Eubranchipus

The species of the anostracan genusEubranchipus Verrill, 1870 can be recognized as belonging to the same taxon and unambiguously distinguished from all other taxa in the family Chirocephalidae Daday, 1910 by the common morphology of their eversible penes. These reproductive structures are short, fat, and cylindrical with a single long, thin spine on the lateral margin at the tip of each penis. This ends the erroneous perception ofEubranchipus as a New World genus and recognizes it as an old taxon with members distributed accross the modern continents that once comprised Laurasia.