Sequence data for the complete 18S rDNA gene were used to address unresolved phylogenetic issues concerning branchiopod evolution. Representative taxa include all 8 extant orders of branchiopods, additional crustaceans from the Malacostraca, and 3 alternative outgroups (Myriapoda, Chelicerata, and Insecta). The results of both maximum parsimony and neighbor-joining phylogenetic analyses are congruent and indicate that branchiopods are a monophyletic class of crustaceans, and that the Anostraca are monophyletic and the sister group to all other branchiopods. The phylogenetic position of the Laevicaudata cannot be resolved, but analyses suggest a notostracan clade that is the sister group to the Diplostraca (=Conchostraca and Cladocera). Within the Diplostraca, the Conchostraca and Spinicaudata are paraphyletic as currently recognized, because the spinicaudatan clam shrimp Cyclestheria hislopi is the sister taxon to a clade (Gymnomera) comprising the cladoceran orders Anomopoda, Ctenopoda, Haplopoda, and Onychopoda. We therefore propose that the taxonomic heading “Cladocera” include a new taxon, Cyclesthera, equal in rank to the Gymnomera. Cladoceran monophyly, as described above, is further substantiated by the shared presence of expansion segments in the 18S rDNA genes of anomopods, ctenopods, haplopods, and onychopods, as well as that of C. hislopi. A phylogenetic view of the Cladocera that includes the above taxa corroborates views based on morphological comparisons that the cladoceran lineage arose from a cyclestherid-like ancestor.

The inheritance of a blue body color phenotype found in Cherax destructor (the yabby) was investigated in a series of experimental crosses including both F₂ and backcrosses. The blue phenotype, which can be easily distinguished from the normal color phenotype in newly released juvenile yabbies, was found to be inherited as an autosomal recessive trait. Color phenotype was independent of age for juveniles maintained over a 12-week period, and no association was found between color and sex. The potential for the use of this blue trait as a genetic marker in growth comparisons of yabby strains is discussed.

A full description of the subadult male holotype of the diastylid Ektonodiastylis robusta, new genus, new species, is presented, as well as of the adult male and adult female of E. nimia. Ektonodiastylis nimia is transferred from Brachydiastylis to Ektonodiastylis. The family definition of Diastylidae is expanded. The implications of this expansion on the systematics of the Cumacea in general, and Diastylidae and Gynodiastylidae in particular, are discussed.

A molt staging technique is described for use in the southern rock lobster Jasus edwardsii and estimates are presented for the length of molt stage and of molt cycle in juvenile lobsters.

The molt cycle can be divided into 13 stages or substages, of which 10 are relatively easy to distinguish using a combination of cephalothorax rigidity, pleopod epidermis retraction, and setal formation. The stages are similar to those described for other lobsters and crustaceans with interspecific differences, including the length of D0 (apolysis) and the timing of barbule appearance. The application of this technique to field studies is discussed.

We compared aggressive behavior among four crayfish species by measuring the number and duration of agonistic acts occurring in fighting bouts between intraspecific pairs of animals. Our study included 3 congeneric species from the family Cambaridae (Orconectes rusticus, Orconectes propinquus, and Orconectes immunis) and 1 from the family Astacidae (Pacifastacus leniusculus). Based on our measurements, crayfishes differed in their level of aggressiveness and differed in the extent to which they used particular agonistic behaviors. Contrary to previous reports, O. rusticus did not appear to be especially aggressive. Of the species in our sample, O. rusticus was clearly more aggressive than only 1 species, O. immunis. Orconectes propinquus was likewise significantly more aggressive than O. immunis. Pacifastacus leniusculus (Astacidae) appeared to be the most aggressive, differing from the other 3 species in the amount of time spent fighting and in individual behaviors, especially those associated with use of antennae. Understanding species-specific differences in aggressiveness may yield insights into species replacements in natural crayfish populations, and may contribute to the value of these animals as models for investigating the neural basis of aggression.

The osmoregulatory responses and survival of 3 species of landhoppers (Austrotroides maritimus, Keratroides rex, and Tasmanorchestia annulata) confined to the coastal zone of western Tasmania and 2 species from inland forests (Mysticotalitrus tasmaniae and M. cryptus) are described over a range of external concentrations, from tap water to full strength sea water (approximately 1,000 mOsm·kg⁻¹). Austrotroides maritimus and K. rex showed a hyper-iso-osmotic osmoregulatory pattern (maintaining the hemolymph between 362–1,080 mOsm·kg⁻¹ and 412–1,045 mOsm·kg⁻¹, respectively, over a concentration range of 40–1,045 mOsm·kg⁻¹), whereas T. annulata showed a trend toward a hyper-hypo-osmoregulatory pattern (maintaining the hemolymph between 423–948 mOsm·kg⁻¹ over the same concentration range). Mysticotalitrus tasmaniae and M. cryptus, the inland species, also showed a hyper-iso-osmotic regulatory pattern. Among the coastal species, there were significant interspecies differences in hemolymph osmotic concentration at dilute external concentrations and at the most concentrated external concentration examined. Tasmanorchestia annulata showed 100% survival over the full range of salinities examined, A. maritimus showed increased mortality on more dilute media, and K. rex showed increased mortality on more concentrated media. Silver-staining studies did not reveal evidence for the existence of extrabranchial sites of ion exchange in the 3 species. The data support the hypothesis that, of these coastal landhoppers, A. maritimus, at least, is physiologically limited to the coastal habitat by a dependence on the supply of ions from sea spray.

Five zoeal stages and the first juvenile stage of the crangonid shrimp Philocheras monacanthus are described and illustrated from laboratory-reared specimens. Development to the first juvenile stage took 15 days at 18°C and 36‰ salinity. Larval morphology is compared with that of other described species of Philocheras, and a provisional key is provided.

The reproductive biology of the Taiwanese fresh-water crab Candidiopotamon rathbunae (de Man) was investigated. The maturity, gonad development, mating behavior, breeding season, timing of release of young crabs, fecundity, and behavior of ovigerous females were studied. Mature males have sperm available for mating throughout the year. The deposition of yolk in females takes place mostly from April to June, with most of the eggs reaching maturity at the end of June. The main breeding season is from late June to October, although mating can occur all year round. In C. rathbunae, discernible courtship behavior is absent and a forced copulation strategy is practiced by males. Ovigerous females leave streams to live on the forest floor several meters away from the stream and are difficult to locate along the banks of streams. Ovigerous females return to the stream a few hours before hatching of the eggs. Most young crabs are released after mid-September, which is the end of the rainy season. This is believed to be a strategy to avoid destructive flash floods which are common from mid-May to early September. The number of eggs carried by each ovigerous female ranges 9–117, fecundity being highest for females of about 30-mm carapace width.

Descriptions of the zoeal and decapodid stages of the ghost shrimp Callichirus islagrande were based on laboratory cultures from a population inhabiting the coast of Louisiana. Whereas morphological studies were based upon animals from mass cultures, 40–120 larvae from each of 8 parental females were reared individually to obtain stage-duration data. Larvae passed through 4 or 5 zoeal stages before molting to the decapodid stage. The proportion of individuals that molted to a fifth zoeal stage varied widely (9–89%) between clutches of different parental females. The first juvenile stage was usually reached 16–20 days after hatching, and durations of larval stages were similar in larvae from different females. Morphological comparisons with congeneric species revealed larvae of C. islagrande to be more similar to larvae of C. garthi, a species from the coast of Chile, than to larvae of a Gulf of Mexico population of Callichirus major.

Population-genetic and morphometric investigations were undertaken in 28 populations of the palaemonid prawn Macrobrachium nipponense with different-sized eggs which occur in different habitats from estuaries to inland waters of the Japanese islands, in order to elucidate the process of their differentiation. In estuarine populations with small eggs, allele frequencies in the Pgm locus changed with a cline along the Pacific coast. This appears to have resulted from infrequent unidirectional gene flow by sea current-mediated larval dispersal. Estuarine populations along the coast of the Sea of Japan, on the other hand, were genetically homogeneous, suggesting more frequent gene flow in them. Populations with medium and large eggs, which are observed in brackish- or fresh-water limnetic systems of sea-relict lake origin on both sides of the Japanese islands, are considered to have differentiated from estuarine populations after the Holocene marine transgression. Some lacustrine populations were significantly different in their genetic content and morphometric traits, implying their independent derivation.

Observations of Chaceon affinis, from the French deep submersible Nautile, were made at the Menez Gwen hydrothermal vent site (Mid-Atlantic Ridge, 37°50′N) in June 1994. This was the first time that specimens of this species were seen in the inner periphery of an active vent field. Almost all specimens were observed very near mytilid mussel beds, and on one occasion a crab was seen eating the remains of one of these vent mussels. In addition, baited fish traps were deployed in the close vicinity of the active vent field for periods of 24 h. The yield of these catches was much higher than the one obtained at a similar depth in a place without any influence of an active vent field. It is suggested that the population of C. affinis living in the vicinity of this vent field can profit from the amount of biomass available inside it.

The juvenilis complex of the crayfish genus Orconectes has been problematic for over 100 years. Morphological variation across the range of the complex was examined to determine species boundaries and geographic distribution. Multivariate and univariate analyses of characters support the recognition of O. juvenilis and warrant the descriptions of two new species, O. ronaldi and O. cristavarius. The shape of the form I male pleopod, the shape of the rostrum, and the length of the areola are the most useful characters for diagnosing species within the O. juvenilis complex. A key to members of the O. juvenilis complex is provided.

We used nucleotide sequence data from the ribosomal RNA (rRNA) gene cluster to determine the affinities of rhizocephalans reported to be Sacculina carcini which parasitize different portunid hosts: the green crab Carcinus maenas from Sweden; C. maenas from England; Liocarcinus marmoreus from Ireland; and Liocarcinus holsatus from Wales. There were no differences in nucleotide sequence data from the 3′ region of the small subunit (SSU) (160 bp) and internal transcribed spacer 1 (ITS1) (274 bp) rRNA of these parasites. The same region was sequenced from Sacculina granifera from Queensland, Australia, parasitic on Portunus pelagicus; Sacculina oblonga from Kyushu, Japan, parasitic on Cyclograpsus intermedius; and an undescribed rhizocephalan from Victoria, Australia, parasitic on Nectocarcinus integrifrons. The consensus nucleotide sequence of S. carcini from the ITS1 rRNA differed from S. granifera by 52% (146/282 sites), from S. oblonga by 56% (162/289 sites) and from the rhizocephalan from N. integrifrons by 33% (94/284 sites). The consensus nucleotide sequence of the 3′ region SSU rRNA of S. carcini and the rhizocephalan from N. integrifrons, which included the V9 domain, differed from S. granifera and from S. oblonga by 6% (9/160 bp). The high divergence rate of ITS1 rRNA sequence between species of Sacculina makes it a valuable diagnostic tool for parasites in this genus. On that basis, the nucleotide sequence data suggest that S. carcini infests at least two genera of crabs from a broad geographic distribution. This may limit the use of this parasite for biological control of introduced populations of green crabs.

The genus Macrobrachium, or river shrimps, is represented in the United States by 6 species: M. acanthurus, M. carcinus, M. faustinum, M. heterochirus, M. ohione, and M. olfersii. River shrimps are the largest fresh-water crustaceans in North America, and specimens of the largest species, M. carcinus, can be the size of lobsters. Most of these species are distributed among the southern states of the Gulf Coastal Plain, Mexico, and the Caribbean Islands. Macrobrachium ohione is known also from the Red River drainage in Arkansas and Oklahoma, and the Mississippi River-Ohio River drainage in Illinois, Indiana, and Ohio. Because of their complex amphidromous life cycle, populations of Macrobrachium are vulnerable to anthropogenic disturbances such as construction of impoundments, water pollution, commercial fishing, and introductions of exotic species. Preliminary data from Mississippi and Texas support the notion that populations of river shrimps are restricted by impoundments, and populations, in general, are in decline. A review of the species and a revised key are presented.

At least 7 distinct eye types have evolved in the Stomatopoda. This reflects adaptations to the wide range of habitats and depths in which stomatopods occur. However, there are some species for which eye design does not correlate with environmental factors. The distribution of certain eye types in taxonomically unrelated groups suggests that their occurrences result from convergent evolution. The current classification of stomatopods into five superfamilies is not supported by eye design. Polyphyly in the Gonodactyloidea is proposed. Eye structure cannot be used as a taxonomic character to superfamily or family level in stomatopods, but is helpful in the diagnosis of genera and species. A few genera and species can be distinguished from their eye design alone.

Macrobrachium vicconi, new species, from a rain forest of southeastern Mexico is described. It is similar to Macrobrachium quelchi and Macrobrachium atabapense in total length, partially abbreviated larval development, and cornea not reduced. Macrobrachium vicconi differs from those species in the size-ratio of the articles of the legs, the spinous ornamentation, and the length of the second pereiopods. Macrobrachium vicconi is more closely related to the inland South American complex of Macrobrachium in bearing few large eggs, than to other epigean species described in the genus from the Americas. The new species is the first epigean species of Macrobrachium with partially abbreviated larval development described from North America, Central America, and the Caribbean.

The complexity of the fifth limb of myodocopine Ostracoda has led to many interpretations of its homologies. The presence of muscles interpreted to mark the axis of the endopod of Isocypridina quatuorsetae supports the interpretations by H. J. Hansen and by G. Boxshall contending that the fifth limb of the Cypridinidae bears an unsegmented exopod.