The Anostraca (crustacea : Branchiopoda) of southern Africa.
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Date
1994
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Abstract
The Anostraca are a group of crustaceans belonging to the class Branchiopoda. They
are predominantly restricted to temporary, inland waterbodies, which in southern Africa,
include rockpools, animal wallows, and large "pans". The anostracan fauna of southern Africa
was last examined in detail in 1929 by Barnard, and recent collecting in a number of areas
indicated the need to update earlier work. A total of four genera, each belonging to a separate
family, and forty-six species, some of which had not previously been described, are presented
in this thesis.
The monogeneric family Streptocephalidae is well represented in Africa, and the fauna
of Africa south and north of the Zambezi and Kunene Rivers, as well as Madagascar is
reviewed. The Streptocephalus species are characterised by having an S-shaped antennal
process, terminating in a cheliform "hand" region. The species were divided into ten groups
based on similarities in antennal process morphology. The descriptions of five new species
have been published, and an update on distribution and specimen data for a number of species
are presented. An additional, as yet unpublished new species from Zimbabwe is presented.
The genus Artemia, although well researched in other parts of the world, has been
largely ignored in southern Africa. Bisexual populations occur along the Cape coast, and a set
of specimens from Namibia, which includes only females, may indicate that A.
parthenogenetica is also present on the subcontinent. The frontal knob morphology of the
Cape specimens is similar to that of A. tunisiana from northern Africa and the Mediterranean.
The family Branchipodidae is characterised by the fusion of the basal joints of the male
antennae to form a so-called "clypeus". This family is represented in southern Africa by a
diverse fauna of the genus Branchipodopsis. Eleven previously described species, as well as
five new species are presented. An attempt was made to divide the sixteen species into
species groups, as was done for the streptocephalids, but this proved difficult. The
taxonomically useful characters in this genus are largely restricted to the basal processes. An
additional character, the presence of expansions of the posterior thoracic segments in the
females of some species could be useful. Much intraspecific variation in clypeus morphology
was evident, particularly in two of the widespread species. Branchipodopsis species
commonly occur in small pools which fill a number of times during the wet season and this has probably led to the development of localised adaptations, and intraspecific variation, or
even species endemic to very restricted areas.
Three sets of specimens which belong to the family Branchipodidae, but to no known
genus, were recently collected from north-eastern Natal, the eastern Cape and the Namib
desert in Namibia. These specimens share a single, large process positioned medianly on the
fused basal joints, as opposed to a pair of processes in this position. However, the
morphology of the penes, and the position and form of other antennal processes could
indicate that the specimens are not congeneric. Unfortunately, more material is necessary
before the descriptions of two of these possible new genera can be published.
Three species of the genus Branchinella, of the family Thamnocephalidae, occur in
southern Africa. These species have a well developed frontal process, and fully retractible
penes. Bran chin ella spinosa was recorded from the Makgadikgadi Pan in northern Botswana,
and was probably introduced to this area from north Africa, or Europe, where it has a wide
distribution. The other two southern African species have been collected from few localities,
and in small numbers, and this may be connected to cyst hatching processes.
The southern African anostracan fauna exhibits distinct distribution patterns and these .
appear to be influenced by climate, with rainfall having the dominant influence in the western
half of the subcontinent, and temperature influencing distribution in the eastern half. The high
altitude Escarpment forms a barrier to the movement of species between the coastal margin
and the central plateau region. The formation of the Escarpment could have resulted in
vicariance speciation in some anostracans, but in most cases, allopatric speciation appears
to have occurred. The type of habitat also influences species distribution in a number of ways.
The great anostracan species richness in southern Africa is probably related to the climatic
heterogeneity of the subcontinent, as well as the possible origin of two genera in
Gondwanaland, and the absence of a Pleistocene glaciation in Africa. Large parts of southern
Africa have not been sampled, and the exact status and distribution of many species is
uncertain.
Description
Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1994.
Keywords
Anostraca--Africa, Southern., Anostraca--Classification., Theses--Zoology.