Hermit crabs are anomuran decapod crustaceans that have adapted to occupation of empty snail shells (and a few other types of cavities). Lack of calcification of the abdominal exoskeleton both allows and dictates the occupation of shelter not produced by the crabs themselves. Many animals utilize exogenous shelters, but almost all 800 species of hermit crabs are mobile while sheltered. The combination of mobility and protection afforded by this life style must contribute to the large numbers of these crustaceans found in virtually all marine environments, as well as on tropi­ cal terrestrial shores. The strong association between these crabs and their adopted shelters has greatly influenced almost all aspects of their biology. In most species, meta­ morphosis from larva to adult involves the assumption of morphological asymmetries associated with inhabitation of gastropod shells as well as behavioral changes as the free-swimming glaucothoe becomes a benthic, shell-seeking crab (3). Not surprisingly, most biological studies on hermit crabs have focused on the crab-shell association. Behavioral investigations on shell selection and shell exchange are obviously shelter-related, while the visual display systems utilized by these crabs (32, 46) are indirectly asso­ ciated with distribution of the shell resource. Most ecological studies have focused completely on the crab-shell interaction, and relatively little work has been done on the crabs as an element of marine ecosystems. Accord­ ingly, this paper only briefly reviews aspects of the crabs' behavioral ecology other than the crab-shell association and its influence on both individual behavior and population-related processes. While individual hermit crabs have been found in a variety of objects and some specialize in the use of scaphopod shells (some Py/opagurus spp.) (33) or even bamboo tubes

The Behavioral Ecology of Hermit Crabs

The ‘Large Branchiopod’ fauna of Europe consists of 72 species and sub-species: 50 anostracans, 8 notostracans, 12 spinicaudatans, and 2 laevicaudatans Their geographical distribution is mapped, and remarks on ecological requirements of species are given

The geographic distribution of the European Branchiopods (Anostraca, Notostraca, Spinicaudata, Laevicaudata)

Morphology, dynamics, ecology and fauna of Arctotheca populifolia and Gazania rigens nabkha dunes

Females from female-biased populations of the notostracan Triops newberryi produce viable eggs when reared in isolation. Clutches produced under such conditions exhibit sex-ratio polymorphism. One category of females (monogenics) produces only female offspring; the second category (amphigenics) produces clutches with a sex ratio of 3 females: 1 male. The relative proportions of the two categories of females varies significantly between populations and is correlated with population sex ratio. This correlation, and the pattern of offspring distribution in amphigenics, suggests that sex is determined by an autosomal Mendelian gene locus for which the male-determining allele is recessive. Limited pedigree analysis of lineages under selfing support the genetic model.

Sex ratio variation in female-biased populations of Notostracans

Electrophoretic analysis of 31 populations, ranging from California to Kansas, indicates that the North American tadpole shrimp Triops longicaudatus (LeConte) is actually a mixture of at least two reproductively isolated species. In the central United States, the predominant species is T. longicaudatus, which is found typically in ephemeral prairie pools. In the southwestern United States, the predominant species is Triops newberryi (Packard), which characteristically inhabits large playa pools. The two species coexist occasionally and in sympatric situations they are reproductively isolated from each other. The two species are genetically distinct at a level greater than is typical of conspecific populations. These genetic differences are correlated with subtle morphological differences and profound differences in reproductive biology. Both species represent complexes of bisexual and unisexual populations. Bisexual populations of T. longicaudatus are usually composed of males and females in approximately equal frequencies; bisexual populations of T. newberryi are composed of males in low frequencies and self-compatible hermaphrodites. Unisexual populations of both species apparently consist entirely of self-compatible hermaphrodites.

http://home.sandiego.edu/~simo/Papers/Sassaman%201997%20reproductive%20isolation%20and%20genetic%20differentiation.pdf

Reproductive isolation and genetic differentiation in North American species of Triops (Crustacea: Branchiopoda: Notostraca)

SUMMARY A large number of an unidentified species of Encyrtoscelio Dodd was collected on coastal sandy dunes in Somalia, mainly in the retrodunal zone. This genus includes only a few species of which very little is known from a bionomic point of view. The daily rhythm has two peak periods of activity, the highest at sunset and the other, smaller, at dawn. Females and wingless specimens are more predominant than males and winged ones. It is suggested that the host of this Encyrtoscelio sp. could be the Heteroptera Cydnidae Aethus perithrix (Mc.) and it is concluded that the habitat of this genus is provided by sandy places.

F Zaffagnini

Papers

The distribution and reproduction of triops cancriformis (bosc) in europe (crustacea, notostraca)