Three of portunid crabs – Thalamita chaptalii (Audouin, 1826), Thalamita picta Stimpson, 1858, and Thalamitoides quadridens A. Milne-Edwards, 1869 – are recorded for the first time from Maldivian waters during the current study. The important diagnostic features of these species are presented and an identification key for all Thalamita , Trierarchus and Thalamitoides currently reported from the Maldives is provided. The taxonomy of Thalamita admete Herbst, 1803, and Thranita exetastica Alcock, 1899, both also reported by Borradaile (1902) from the Maldives is discussed.

Larvae of the mangrove fiddler crab Austruca albimana (Kossmann, 1877), hatched from an ovigerous female collected from the mangroves of Sumariat, Jazan Province, Saudi Arabia in the southern Red Sea, were reared in the laboratory. Four zoeal and a megalopal stages were recorded, and their morphological features are described herein for the first time. The setations of the cephalothoracic appendages of the zoeas of A. albimana and their congeners exhibit several variations that help differentiate larvae of this genus easily from other meroplankton. However, a character of phylogenetic significance -minute spines on the forks of the telson of pleon -is common to larvae of this genus. These minute spines were studied with the aid of scanning electron microscope images. There were five common morphological features between A. albimana and other fiddler crab megalope, including Minuca burgersi, Leptuca uruguayensis and Leptuca thayeri. These features were a deflexed front, rounded to obtuse frontal margin, seven-segmented antennal flagellum, unsegmented endopod of maxilla and three cincinnuli on the endopods of pleopods. Two zoeal morphological features described in this study and other studies (i.e., the absence of lateral spines on carapace [vs. their presence in species of Uca, Afruca and Ocypode in the Ocypodinae] and the presence of a maximum of four pairs of inner setae on the telson of pleon [vs. presence of more than four pairs of setae in species of Uca, Afruca and Ocypode]) support the taxonomic amendment of transferring Uca spp. and Afruca spp. crabs from Gelasiminae to Ocypodinae.

Nine species of fiddler crabs (Crustacea: Ocypodidae: Gelasiminae) are known from the Arabian Sea and adjacent waters (Red Sea, Gulf of Aden, Gulf of Oman and Arabian/Persian Gulf): five species of Austruca, one Cranuca, two Gelasimus and one Tubuca. COI sequence data match morphological species boundaries and shows high connectivity within each. The fauna is highly endemic, with three species of Austruca (A. albimana, A. iranica and A. sindensis) confined to this region, and four others restricted to the Indian Ocean. restricted to the Indian Ocean. Austruca albimana and A. iranica speciated locally and now have narrowly overlapping ranges in Oman. Our results confirm the westernmost distributions of Austruca annulipes and Tubuca alcocki are Pakistan and the Red Sea, respectively. A key for the nine species is also provided to help identification.

Ovigerous females of 10 species of xanthid crabs (Xanthidae MacLeay, 1838), from five subfamilies, namely, Pseudoliomera speciosa (Dana, 1852) (Actaeinae), Chlorodiella cytherea (Dana, 1852), Chl. laevissima (Dana, 1852), Chl. nigra (Forskål, 1775), Cyclodius granulosus (De Man, 1888) (Chlorodiellinae), Danielea noelensis (Ward, 1942) (Euxanthinae), Liomera rugata (H. Milne Edwards, 1834), Lio. tristis (Dana, 1852) (Liomerinae), Lachnopodus subacutus (Stimpson, 1858) and Leptodius sanguineus (H. Milne Edwards, 1834) (Xanthinae), were collected from the Gulf of Aqaba, and the zoea I obtained from them have been described herein. Six species, viz. Chl. cytherea, Chl. laevissima, Cyc. granulosus, Lio. rugata, Lio. tristis and Lep. sanguineus, are described for the first time, and Lac. subacutus and D. noelensis are re-described. Spinulations of dorsal and rostral spines of cephalothorax, length of rostral spine of cephalothorax to protopod of antenna, setations of antennule, ratio of antennal exopod to protopod and setations of exopod of antenna are important characters that distinguish xanthid larvae from their congeners and other closely related species at subfamilial levels.

A new species of Schizophrys collected from the coral reef of Biadah, Jeddah, Saudi Arabia is described herein with its first zoeal morphological features. Each rostral extension of this species has one accessory spine on the outer and inner margin, a character unique to this species. Several other combinations of characters distinguishing this species from its congenerics are provided. A set of characters demarcate the first zoea of this species from its congenerics: the presence of seven setae on the coxae of maxillule, one seta on the proximal segment of the endopod of maxilliped II and two lateral spines on each of the forks of the telson. Other morphological differences of the larvae of this species with the other majid larvae are also discussed herein.

Ovigerous females of Cymo melanodactylus, C. andreossyi and C. quadrilobatus were collected from a coral reef, Jeddah (Biadah, Obhur) and Thuwal, Saudi Arabia and reared in the laboratory. The morphological features of the zoea I of C. andreossyi, and zoeae I and II of C. quadrilobatus, as well as the complete larval stages of C. melanodactylus, have been described for the first time. Some characters distinguish these species: cephalothorax size; ratio of the length of antennal protopod and exopod; setations of the endopod of second maxilliped and the presence of a small tooth on the basal endite of the maxillule in the zoea I of C. melanodactylus and C. andreossyi. Morphological features of cephalothorax spines, setations of the endopod of antenna, first and second maxillipeds and the inner spines of telson change as the larval stages of C. melanodactylus progress. The morphological features of the zoeal and megalopal stages of the above-mentioned crabs were compared with those of the larvae of some conspecifics and other xanthid larvae described from the Red Sea. The megalopa of C. melanodactylus can easily be differentiated from those of Chlorodiella nigra and Leptodius exaratus by the setations of the exopod and endopod of antennule, antenna, maxillule and first to third maxillipeds.

Larvae of Leptodius exaratus from an ovigerous female collected from the intertidal region of North Obhur, Jeddah, Saudi Arabia, were reared in the laboratory up to megalopa stage, and all the larval stages are described and illustrated. Mostly, former descriptions of this species were inconsistent, made about two decades before, and some were incomplete. Therefore, all the zoeal and megalopa stages of L. exaratus are redescribed and illustrated. The morphological features of the larvae of the present study were compared with those of the same species and L. affinis described from worldwide. The male gonopds of L. exaratus collected from the study sites are described and compared with those of the male gonopds of L. exaratus sensu lato described from elsewhere using SEM micrographs.

The complete larval development of the oziid crab Epixanthus frontalis (H. Milne Edwards, 1834) hatched from ovigerous specimens collected from Saso Island, southern Red Sea, was obtained under laboratory conditions. Four zoeae, one additional zoea and a megalopa were obtained and these are described and illustrated in detail for the first time. Larvae of this species can be differentiated from those of other oziid species based on a combination of characters such as the number of aesthetascs and setae of the antennule, and the coxal and basial setal numbers and patterns of the maxilla and maxillule.

A 2-year spatio-temporal survey of intertidal brachyuran crabs involving five sites was conducted in the Maavah reef system, Laamu Atoll, Maldives, from April 2001 to March 2003. In December 2004, the sites were hit by the catastrophic Sumatran tsunami. An 8-month-long study was carried in the same five sites after the tsunami, and the data obtained were compared with the pre-impact baseline data. A sand dune formed at the north-eastern side of the island as a result of the tsunami was also included in the post-tsunami study (site 6). Nine brachyuran crab species not recorded during pre-tsunami sampling in the five study sites were collected after the event. Of these, six species were recorded in site 6 during January 2005, and they started to appear in the other sites in the following months. Nine species of crabs collected during the pre-tsunami periods from four sites were not represented in the post-tsunami collections. Abundance, evenness and diversity of the post-tsunami brachyuran communities of sites 1 and 2 exhibited downward trends, and the evenness and diversity of the post-tsunami communities of site 4 exhibited upward trends when compared with pre-tsunami patterns. Multivariate analyses revealed that the tsunami had changed the post-tsunami brachyuran communities of sites 1–4. However, tests revealed that in site 4, the pre-tsunami brachyuran assemblage 1 (2001–2002) differed from pre-tsunami assemblage 2 (2002–2003) and post-tsunami assemblages. The roles of tsunami-transported species and site-specific dominant species in contributing to faunal dissimilarities between the pre- and post-tsunami brachyuran assemblages were found to be patchy. Further studies would reveal whether the population of any newly added species increases or decreases in the long term.

Atoll Research Bulletin, no. 588. Spatio-Temporal Distribution of Assemblages of Brachyuran Crabs at Laamu Atoll, Maldives.