Morphological symmetry abnormalities in cheliped appendages of alpheid shrimps are extremely rare and poorly recorded in the literature. A symmetric minor cheliped were, for example, observed in queen females belonging to Synalpheus eusocial species. Symmetric major chelipeds were now described in Synalpheus fritzmuelleri individuals living in shallow Brazilian waters. These individuals were found in symbiotic association with the bryozoan Schizoporella sp. (biogenic substrate) adhering to the pilings of Ubatuba Bay docks, São Paulo State. Only one of 20 sampled S. fritzmuelleri individuals presented anomalous symmetric chelipeds. Based on carapace length, size, and morphological features, the analyzed specimens seemed to be juvenile; thus, the hypothesis of anomalous condition can be directly linked to genetic inhibition of the mechanism accounting for major cheliped development in this ontogeny phase. Studies like the present one often provide remarkable information on animal morphology and can be used as reference in evolutionary assessments to be conducted in the future.

We report for the first time the association of some caridean shrimps with the octocoral Carijoa riisei (Cnidaria: Clavulariidae) and the sponge Dragmacidon reticulatum (Porifera: Axinellidae), in estuaries from north-eastern Brazil. The alpheid shrimp Synalpheus apioceros, Synalpheus fritzmuelleri, Alpheus formosus, Alpheus carlae and the palaemonid Cuapetes americanus are reported in association with Carijoa riisei. The latter two species, plus the alpheid Alpheus buckupi, are recorded in association with D. reticulatum.

Eight species of alpheid shrimps are reported for the first time from the coral reef systems off Mexico's northern Yucatan Peninsula (Alacranes, Madagascar and Serpiente Reefs). These species are: Alpheus immaculatus; Alpheus paraformosus; Alpheus punctatus; Parabetaeus hummelincki; Salmoneus depressus; Synalpheus chacei; Synalpheus dominicensis; and Synalpheus elizabethae. The geographical ranges of these species are extended into the southern Gulf of Mexico; most of them are recorded from Mexican territorial waters for the first time. Brief notes on their ecology and taxonomy are provided. Six species are illustrated by colour photographs.

The alpheid shrimp Prionalpheus gomezi, previously only known from the incomplete type specimen from Cuba, is reported from Guadeloupe, Belize and Honduras. The previously unknown cheliped is illustrated, as is the diagnostic colour pattern.

The Atlantic species of the alpheid shrimp genus Parabetaeus, P. hummelincki, is reported for the first time from São Tomé in the Gulf of Guinea, and Cozumel off Mexico's Yucatan Peninsula. These records extend the distribution range of P. hummelincki into the tropical eastern Atlantic and western Caribbean Sea, making this species amphi-Atlantic and the genus Parabetaeus fully pantropical.

The symbiotic alpheid shrimp Aretopsis amabilis De Man, 1910 (Decapoda: Caridea: Alpheidae) is reported from Vietnam for the first time. A male–female pair of mature individuals of this species was found inside a large strombid shell occupied by a hermit crab Dardanus cf. lagopodes (Forskål, 1775) (Diogenidae). The live coloration of the shrimps and their host, as well as its known associations and information on the species distribution are given.

Several Synalpheus species have been reported as hosts of bopyrid parasites; however, the impact of infestation on egg production is still unknown. Therefore, the present work studied reproductive aspects and the effect of parasitism on fecundity of the alpheid shrimp Synalpheus yano from Bocas del Toro, Caribbean coast of Panama. Un-infested females (N = 84) ranging from 3.7 to 9.6 mm carapace length, produced between 5 and 246 eggs (average: 98±64.6), and egg number increased significantly with female size. The eggs were relatively large (0.6–1.3 mm in diameter), but within the range of other Synalpheus species, and egg size did not differ significantly between un-infested and infested females. Despite these large eggs, the morphological characteristics of hatching larvae indicate a planktotrophic development. During the incubation period, the egg volume increased from 0.100 to 0.218 mm3, representing an overall increase of 118%. A total of 18 females (16% of all ovigerous individuals) were infested, and the occurrence of parasitic infestation was more pronounced in larger females. Infested females ranging from 4.6 to 9.4 mm carapace length, produced between 22 and 166 eggs (average: 81±44.4). Egg-bearing females infested by parasitic bopyrids carried on average 41% fewer eggs than similar-sized females without parasites. The co-occurrence of parasites and developing eggs, however, indicates that the bopyrid parasite does not necessarily castrate its host. Therefore, we encourage more comparative intraspecific studies on egg production in infested and un-infested females to assess the impact of infestation on fecundity in caridean shrimp.