Nanoscale ultrastructures increase the visual conspicuousness of signalling traits in obligate cleaner shrimps.

Signal theory predicts organisms should evolve signals that are conspicuous to intended receivers in natural signalling environments. Cleaner shrimps remove ectoparasites from reef fish clients and many signal their intent to clean by whipping long, white antennae. As white is a reliably conspicuous colour in aquatic environments, we hypothesized that selection has acted to increase broad-spectrum antennal reflectance in cleaners. Using scanning electron microscopy, optical models and reflectance measurements, we found that the antennae in three obligate cleaner species from two families (Palaemonidae and Lysmatidae) had thick (∼6 µm) chitinous layers or densely packed high refractive index spheres (300-400 nm diameter), which models show increase reflectance (400-700 nm). Two facultative and non-cleaning species had no visible antennae ultrastructure beyond the chitinous exoskeleton. Antennae reflectance was significantly higher in obligate cleaners than in facultative and non-cleaning species. Our results suggest that some obligate cleaners may have evolved ultrastructures that increase the conspicuousness of their antennae as signals.

Male reproductive system of the freshwater prawn Macrobrachium brasiliense (Decapoda: Palaemonidae): Notes on spermatophore formation and sperm count.

Studies on the morphology of the reproductive system are essential for understanding the reproduction processes of species or even within genera or families. The present study aimed to describe the functional morphology of the male reproductive system, spermatophore formation, and sperm count of Macrobrachium brasiliense. The anatomy of the reproductive system consists of a pair of testes from which the vasa deferentia (VD) starts, extending to the fifth pair of pereopods. The VD is divided into three regions: proximal (PVD), middle (MVD), and distal (DVD). In the PVD, there is a prominent fold, the typhlosole, formed by columnar cells. The typhlosole disappears in the MVD, being incorporated into one of the faces of the VD wall, identified by its simple columnar epithelium while the remainder of the vessel wall is formed by squamous or simple cubic epithelium. Columnar cells produce type-II and III secretion. The epithelium in the DVD is made up only of cubic cells. Low sperm concentration was observed when compared to other species of the genus Macrobrachium. In conclusion, the typhlosole and columnar epithelium are responsible for the asymmetric spermatophore, which seems the pattern of Macrobrachium that is probably shared with other caridean shrimps.

Comparison of morphology and genetic diversity between broodstock and hybrid offspring of oriental river prawn, Macrobrachium nipponense based on morphological analysis and SNP markers.

Hybridization is an effective method for the genetic improvement of farmed species. In this study, three broodstock populations (Changjiang, CJ, Dongting, DT, and Dianshan, DS) of oriental river prawn, Macrobrachium nipponense were used, and DS was used as the female broodstock. Through three-line hybridization, two hybrid populations were finally obtained. The F3 generation of the broodstock population and the F1 generation of the hybrid population were cultured indoors for 3 months. Through morphological analysis (cluster analysis, discriminant analysis and path analysis) it was found that the hybrid population and the broodstock had some differences, but not enough to reach the subspecies level, and the dominant traits exhibited differentiation and reorganization. This study identified SNP genetic markers, carried out systematic evolution analysis and genetic diversity analysis and found that the nucleotide diversity π and heterozygosity Het of the hybrid population were higher than those of the broodstock. Among broodstocks, the differentiation index (Fst ) of SCD and SDC was smallest (0.055). This research provides some valuable reference for genetic breeding.

New data on Beurlenia araripensis Martins-Neto & Mezzalira, 1991, a lacustrine shrimp from Crato Formation, and its morphological variations based on the shape and the number of rostral spines.

Fossil freshwater carideans are very rare worldwide. Here, we present new taxonomic remarks about Beurlenia araripensis from the Early Cretaceous laminated limestones of the Crato Formation, Araripe Basin, northeastern Brazil. We analyzed five fossil samples, testing the morphological variations such as, rostrum with 5 to 14 supra-rostral spines and 2 to 3 sub-rostral spines, which appears as serrate for Caridea. This variation demonstrates a morphologic plasticity also seen in extant species of the group, such as those of the genera Macrobrachium and Palaemon.

Myology of juvenile freshwater prawn Macrobrachium amazonicum (Decapoda, Caridea): Morphology and swimming implication.

Little is known about the functional morphology of locomotion in prawns, and even fewer studies have succeeded in relating a specific muscular group to the movement of the body. The present study aimed to describe the morphology of the thoracoabdominal muscle system and its implications for swimming in juveniles of Macrobrachium amazonicum. Ten muscles were observed in the abdominal muscular system in juveniles of M. amazonicum. The complex arrangement of the anterior oblique muscle in association with the central muscles occupies most of the abdominal space. This muscular compound could promote a flexion movement of the abdomen for body propulsion as well as the tail movement during swimming. Morphofunctional continuity between thoracic and abdominal muscles could aid in locomotion and support the abdominal movement. Moreover, collagen plays a valuable role in connecting deep muscles not inserted in the carapace. Collagenous fascia could transmit the tension during the contraction of deep muscles for coordinated movement.

Morphology of the male reproductive system of freshwater prawn Macrobrachium carcinus (Decapoda, Caridea): Functional and comparative aspects.

Testes and vasa deferentia are parts of the male reproductive system of decapod crustaceans. Both organs show morphological differences among decapod species in terms of anatomical and histological patterns reflecting the diversity of this group. Describing these features may assist in systematics, phylogenetics, and studies of reproductive behavior, especially for species of commercial interest, such as Macrobrachium carcinus, a native American species that, unusually for this genus, has no precopulation courting behavior. This study aims to describe the reproductive morphology and spermatogenesis of the male freshwater prawn M. carcinus. The male reproductive system of this species consisted of lobed testes connected to the vasa deferentia. The testis of M. carcinus was divided into several lobules. Each lobule was formed by a cluster of germ cells surrounded by connective tissue and nurse cells. This microscopic anatomy and histology of the testicular histoarchitecture has been described for many species of Decapoda and may represent a derived design of the testes. Unlike that in other decapod species, spermatogenesis proceeds in short transitory phases that produce spermatozoa at high concentrations and frequencies, corroborating the uncommon male reproductive behavior of this species. In the spermatic pathway, the lobules develop and fuse before releasing spermatozoa from the testes; however, this process has not been observed in decapods, yet. The neutral compounds secreted by the vas deferens are important for sperm nutrition as females secrete a substance for spermatophore adhesion during reproduction. This study presents different features and dynamics of the spermatogenic process in the male reproductive system of M. carcinus that have not yet been presented in the literature for decapods.

The first amber caridean shrimp from Mexico reveals the ancient adaptation of the Palaemon to the mangrove estuary environment.

The aquatic and semiaquatic invertebrates in fossiliferous amber have been reported, including taxa in a wide range of the subphylum Crustacea of Arthropoda. However, no caridean shrimp has been discovered so far in the world. The shrimp Palaemon aestuarius sp. nov. (Palaemonidae) preserved in amber from Chiapas, Mexico during Early Miocene (ca. 22.8 Ma) represents the first and the oldest amber caridean species. This finding suggests that the genus Palaemon has occupied Mexico at least since Early Miocene. In addition, the coexistence of the shrimp, a beetle larva, and a piece of residual leaf in the same amber supports the previous explanations for the Mexican amber depositional environment, in the tide-influenced mangrove estuary region.

Chemically induced plasticity in early life history of Palaemon argentinus: are chemical alarm cues conserved within palaemonid shrimps?

Most aquatic animals use infochemicals from both conspecifics and heterospecifics to assess local predation risks and enhance predator detection. Released substances from injured conspecifics and other species (chemical alarm cues) are reliable cues to indicate an imminent danger in a specific habitat and often mediate the development of inducible defenses. Amphibian and fish embryos have been shown to acquire this information while at the embryonic stage of development, in relation to the developing nervous system and sensory development. With the exception of Daphnia, there is no information on chemically mediated responses to alarm cues in embryos of any crustacean groups. Therefore, we tested whether embryo exposure to chemical cues simulating predation on conspecifics or heterospecifics (closely related, non-coexisting species), or a mixture of both, alters embryonic developmental time, size and morphology of the first larval instar in Palaemon argentinus (Crustacea: Decapoda). Embryonic exposure to chemical alarm cues from conspecifics shortened the embryonic developmental time and elicited larger larvae with a longer rostrum. Rostrum length of the first larval instar changed independently of their size, thus elongated rostra can be considered a defensive feature. Embryonic developmental time was not altered by chemical alarm cues from either heterospecifics or the mixed cues treatment; however, exposure to these cues resulted in larger larvae compared with the control group. Chemically induced morphological plasticity in larvae in response to alarm cues from con- and heterospecifics suggests that such cues are conserved in palaemonids shrimps, providing embryos with an innate recognition of heterospecific alarm cues as predicted by the phylogenetic relatedness hypothesis.

The hematopoietic organ of Macrobrachium rosenbergii: Structure, organization and immune status.

The hematopoietic organ (HO) of the giant freshwater prawn Macrobrachium rosenbergii is a discrete, whitish mass located in the epigastric region of the cephalothorax, posterior to the brain. It is composed of hematopoietic cells arranged in a thick layer of numerous lobules that surround a central hemal sinus from which they are separated by a thin sheath. At the center of the sinus is the muscular cor frontale. The lobules extend radially outward from the sinus in three developmental zones. Basal Zone 1 nearest the sinus contains large hematopoietic stem cells with euchromatic nuclei that stain positive for proliferation cell nuclear antigen (PCNA). Zone 2 contains smaller, actively dividing cells as indicated by positive 5-bromo-20-deoxyuridine (BrdU) staining. Distal Zone 3 contains small, loosely packed cells with heterochromatic nuclei, many cytoplasmic granules and vesicles indicating that they will eventually differentiate into hemocytes and enter circulation. Three main arteries, namely the ophthalmic and the 2 branches of the antennary, connect the heart to the HO. Use of India ink and 0.1 µm fluorescent micro-beads injected into the heart revealed that the cor frontale could immediately remove foreign particles from hemolymph by filtration. Fluorescent beads were also detected in the hematopoietic tissue at 30 min after injection, indicating that it could be penetrated by foreign particles. However, the fluorescent signal completely disappeared from the whole HO after 4 h, indicating its role in removal of foreign particles. In conclusion, the present study demonstrated for the first time the detailed histological structures of the HO of M. rosenbergii and its relationship to hematopoiesis and removal of foreign particles from hemolymph.

The androgenic gland in male morphotypes of the Amazon River prawn Macrobrachium amazonicum (Heller, 1862).

Sexual differentiation and primary and secondary sexual characteristics in male crustaceans are modulated by hormones produced in the androgenic gland (AG). The AG is also responsible for the determination of morphotypes in caridean shrimps, such as Macrobrachium amazonicum that shows four morphotypes: translucent claw (TC), cinnamon claw (CC), green claw 1 (GC1) and green claw 2 (GC2). Here, we verified the anatomical, histological and ultrastructural characteristics of the AG in different morphotypes of this species with both amphidromous and hololimnetic life cycles. In submissive morphotypes (TC and CC), the AGs are reduced and concentrated in the terminal expansion of the distal portion of vasa deferentia (DVD), the ejaculatory ducts (ED). In dominant morphotypes (GC1 and GC2) these glands lie along the DVD and ED. Two morphological stages (I and II) were recorded for AG cells. In submissive morphotypes stage I cells predominated in the AGs, while in dominant morphotypes stage II cells were more common. AG cells in both stages were positive for proteins, confirming the protein nature of the secreted hormone. Stage I cells have abundant rough endoplasmic reticulum (RER) with numerous parallel cisternae, whereas in stage II cells, the cisternae of RER are highly dilated. Stage II cells do not produce secretory granules, but they undergo hypertrophy and the hormone release to hemolymph probably occurs by holocrine secretion. The AGs in TC, GC1 and GC2 morphotypes increase as the animals grow and are larger in GC1 males. On the other hand, AGs decrease in the CC morphotype as the animal grows. These differences are related to the type of reproductive strategy adopted by each morphotype. In M. amazonicum, the AGs show the same morphological, histochemical and ultrastructural patterns between the different life history populations.

Growth, antioxidant capacity, intestinal morphology, and metabolomic responses of juvenile Oriental river prawn (Macrobrachium nipponense) to chronic lead exposure.

Understanding the mechanisms of metal toxicity to organisms farmed for food may suggest mitigation strategies. We determined the 24-, 48-, 72-, and 96-h median lethal concentrations of lead in juvenile oriental river prawn (Macrobrachium nipponense). The prawns were then exposed to sub-lethal concentrations (13.13 and 26.26 µg/L) of lead for 60 days and growth, antioxidant enzyme activity, intestinal morphology, and metabolite profiles were assessed. Prawns exposed to 26.26 µg/L but not to 13.13 µg/L lead exhibited lower weight gain than controls. The lead burden in muscle was 0.067 and 0.25 µg/g of dry weight exposed to 13.13 and 26.26 µg/L, respectively. Levels of glutamic oxaloacetic transaminase and glutamic-pyruvic transaminase were not altered following exposure. Exposure increased malondialdehyde activity in the hepatopancreas and decreased superoxide dismutase and glutathione peroxidase activities. Catalase activity first increased and then decreased as lead concentrations increased. Some intestinal epithelial cells disassociated from the basement membrane in prawns exposed to 13.13 µg/L lead. Intestinal epithelial cells in prawns exposed to 26.26 µg/L lead separated completely from the basement membrane. Gas chromatography-mass spectrometry metabolomics assays showed the 13.13-µg/L exposure did not elicit significant metabolic alterations. Exposure to 26.26 µg/L lead differentially up-regulated 58 metabolites and down-regulated 21 metabolites. The metabolites identified were involved in galactose, purine, glutathione, and carbon metabolism, biosynthesis of amino acids and steroids, and neuroactive ligand-receptor interaction. These data indicate that chronic lead exposure can adversely affect growth, increase accumulation in muscle, impair intestinal morphology, and induce oxidant stress or neurotoxicity-related effects in M. nipponense.

Isolation and characterization of three skeletal troponin genes and association with growth-related traits in Exopalaemon carinicauda.

Growth is among the most important traits for animal breeding. Muscle growth is controlled by different cellular and molecular pathways and environments, and it also relies heavily on high-quality muscle contractions. The troponin complex, composed of troponin T (TnT), troponin C (TnC) and troponin I (TnI), plays a vital role in the regulation of muscle contraction. In this study, the cDNA of EcTnT, EcTnC and EcTnI of the ridgetail white prawn Exopalaemon carinicauda were cloned and characterized. The full length cDNA of EcTnT, EcTnC and EcTnI were 1 373 bp, 692 bp, and 1 475 bp, encoding a protein of 385, 150 and 193 amino acid residues, respectively. The expression of all genes was predominantly detected in abdominal muscle, while extremely lesser expressed in gill and hepatopancreas. Higher expression level of EcTnI was observed in heavier shrimp of the same age during different developmental stages, excepted for 120 days. Eleven single nucleotide polymorphisms (SNPs) were revealed in the three skeletal troponin genes, and only c.TnI66 A>G from EcTnI was significantly associated with both body weight and body length (P < 0.05). In summary, the result of this study suggested that EcTnI is growth-related gene of the troponin complex gene and the presence of SNP suggests that it could be a candidate gene for shrimp genetic improvement research.

Seasonal variations of contamination and exoskeletal malformations in the white shrimps Palaemon longirostris in the Gironde estuary, France.

Since the end of the 1980s, white shrimps (Palaemon longirostris) from the Gironde estuary have exhibited exoskeletal malformations, mainly involving cephalothorax, rostrum, scaphocerites and uropods. An 8-month study was carried out in 2015. Each month, 200 individuals were sampled and examined for exoskeletal malformations. Temporal variations in malformation frequency were noted, particularly during the breeding period, along with decreases in the size of non-deformed shrimps related to the appearance of juveniles in breeding sites, and high mortality among deformed shrimps. A significant increase in proportions of deformed shrimp was observed, relating particularly to the size (and therefore the age) of individuals. No significant difference was found between shrimp proportions with different numbers of malformations (one to four) for a fixed size class, nor was there any variation in proportions within different size classes for a fixed number of malformations. This would appear to indicate that the number of malformations is acquired and new malformations do not seem to appear during the life cycle, except for the smallest (youngest) shrimps. The malformation spectrum showed no significant differences between the biggest and smallest individuals for the different malformation associations, except for those involving cephalothorax, rostrum and uropods. This would suggest that some malformation associations lead to a higher mortality rate in shrimps subjected to them, due to greater impairment of feeding and/or swimming behaviour. Multiple component analysis of the different types of malformation showed correlations between exoskeletal pieces (rostrum and cephalothorax) and appendixes (scaphocerites and uropods). Regarding metal contamination in shrimp, no significant difference was highlighted between deformed and non-deformed shrimps. Organic pollutants were not measured in tissues. Certain herbicides such as metolachlore and chlortoluron were detected at high concentrations in the Gironde estuary during the breeding period corresponding to the higher occurrence of exoskeletal malformations.

Parallel Saltational Evolution of Ultrafast Movements in Snapping Shrimp Claws.

How do stunning functional innovations evolve from unspecialized progenitors? This puzzle is particularly acute for ultrafast movements of appendages in arthropods as diverse as shrimps [1], stomatopods [2], insects [3-6], and spiders [7]. For example, the spectacular snapping claws of alpheid shrimps close so fast (∼0.5 ms) that jetted water creates a cavitation bubble and an immensely powerful snap upon bubble collapse [1]. Such extreme movements depend on (1) an energy-storage mechanism (e.g., some kind of spring) and (2) a latching mechanism to release stored energy quickly [8]. Clearly, rapid claw closure must have evolved before the ability to snap, but its evolutionary origins are unknown. Unearthing the functional mechanics of transitional stages is therefore essential to understand how such radical novel abilities arise [9-11]. We reconstructed the evolutionary history of shrimp claw form and function by sampling 114 species from 19 families, including two unrelated families within which snapping evolved independently (Alpheidae and Palaemonidae) [12, 13]. Our comparative analyses, using micro-computed tomography (microCT) and confocal imaging, high-speed video, and kinematic experiments with select 3D-printed scale models, revealed a previously unrecognized "slip joint" in non-snapping shrimp claws. This slip joint facilitated the parallel evolution of a novel energy-storage and cocking mechanism-a torque-reversal joint-an apparent precondition for snapping. Remarkably, these key functional transitions between ancestral (simple pinching) and derived (snapping) claws were achieved by minute differences in joint structure. Therefore, subtle changes in form appear to have facilitated wholly novel functional change in a saltational manner. VIDEO ABSTRACT.

Histomorphologic characterization of the hepatopancreas of freshwater prawn Macrobrachium rosenbergii (De Man, 1879) / Caracterização histomorfológica do hepatopâncreas do camarão-de-água-doce Macrobrachium rosenbergii (De Man, 1879)

This study aimed to describe the Macrobrachium rosenbergii hepatopancreas histomorphology. The hepatopancreas is constituted by a set of blind end tubules, divided into proximal, middle, and distal regions, with the epithelium formed by E, F, B, R, and M cells differently of other species. Measurements of the length and width of the tubules were 419.64+69.09µm and 117.42+16.99µm, respectively. The percentage of each cell type per region was: proximal region (40%B, 20%F, 6.7%M, 33.3%R), middle region (45.4%B, 18.2%F, 9.1%M, and 27.3%R) and distal region (36.4%E, 27.2%B, 18.2%F, 9.1%M, 9.1%R). Cell B that stores glycogen and lipids, is the most commonly found cell in proximal and middle regions. In the distal region, the E, responsible for the mitosis, is the most prominent. M, responsible by nutrient storage, is numerically constant among the portions differently in the Macrobrachium amazonicum. The study for the first time also suggests that in addition to digestive enzymes, the F cell produces protective mucus. The present study generated for the first time a morphometric profile of M. rosenbergii hepatopancreas, demonstrating differences from other species, and can be an important tool for new studies in nutrition, reproduction, and production with the species.(AU)

O objetivo do presente estudo foi descrever a histomorfologia do hepatopâncreas do camarão-de-água-doce Macrobrachium rosenbergii. Observou-se que ele é constituído por um conjunto de túbulos de fundo cego, sendo cada túbulo dividido em regiões proximal, média e distal, com o epitélio formado por cinco tipos de células (E, F, B, R, M), diferentemente de outras espécies. As medidas de comprimento e largura dos túbulos foram de 419,64+69,09µm e 117,42+16,99µm, respectivamente. A porcentagem de cada tipo celular por região foi: região proximal (40%B, 20%F, 6,7%M, 33,3%R), região média (45,4%B, 18,2%F, 9,1%M e 27,3%R) e região distal (36,4%E, 27,2%B, 18,2%F, 9,1%M, 9,1%R). Assim, a B, que armazena glicogênio e lipídeos, é a célula mais encontrada nas regiões proximal e média. Na região distal, a célula E, responsável pela mitose, é a mais encontrada. A célula M, responsável pelo acúmulo de nutrientes, tem um número constante de células nas porções do túbulo, diferentemente do Macrobrachium amazonicum. O estudo também sugere, pela primeira vez, que a célula F produz, além de enzimas digestivas, um muco protetor para o túbulo hepatopancreático. O presente estudo foi o primeiro a gerar um perfil morfométrico do hepatopâncreas do M. rosenbergii e demonstrou diferenças em relação a outras espécies, bem como serviu de importante ferramenta para novos estudos que abranjam a produção, a nutrição e a reprodução para a espécie.(AU)

Antennular Morphology and Contribution of Aesthetascs in the Detection of Food-related Compounds in the Shrimp Palaemon adspersus Rathke, 1837 (Decapoda: Palaemonidae).

Shrimp are an essential ecological component of marine ecosystems, and have commercial importance for human consumption and aquaculture. Like other decapod crustaceans, shrimp rely on chemical senses to detect and localize food resources by means of chemosensilla that are located mainly on the cephalothoracic appendages. Using the shrimp Palaemon adspersus, a model organism with omnivorous feeding behavior, we aimed to provide comparative information on the role of aesthetascs, antennular sensilla, and flicking behavior in food detection. To this end, we examined i) the morphology of antennular sensilla by field emission scanning electron microscopy, ii) the shrimp's sensitivity to a number of food-related compounds (amino acids and sugars) by means of whole-animal bioassays, and iii) the contribution of the aesthetasc sensilla to food detection. Our results showed that, aside from the aesthetascs, only three other main morphotypes of setae with chemoreceptive features were present in the antennules, thus accounting for relatively simple sensillar equipment. Nevertheless, we found broad-spectrum sensitivity of the shrimp to a number of amino acids (i.e., isoleucine, leucine, methionine, phenylalanine, glycine, tryptophan, cysteine, and tyrosine) and carbohydrates (trehalose, maltose, cellobiose, and fructose) that was consistent with the omnivorous or scavenging habits of the animal. Although aesthetasc ablation attenuated flicking behavior in a chemical stimulus-independent manner, success in detection and short-range localization of food did not rely on the presence of aesthetasc sensilla. This finding confirms the existence of a non-aesthetasc alternative pathway for feeding, with functional redundancy in simple generalist feeder models such as shrimp.

Partial redescription of pontoniine shrimps Cuapetes nilandensis (Borradaile, 1915) and Cuapetes seychellensis (Borradaile, 1915) (Decapoda: Palaemonidae: Pontoniinae) with remarks on taxonomic status of Cuapetes Clark, 1919 and Kemponia Bruce, 2004.

Pontoniine shrimps Cuapetes nilandensis (Borradaile, 1915) (the type species of the genus) and Cuapetes seychellensis (Borradaile, 1915) are re-described showing clear morphological difference from representatives of the genus Kemponia Bruce, 2004. Several specific morphological features show the validity of both pontoniine genera.

A new species of symbiotic palaemonid shrimp of the genus Pseudocoutierea Holthuis, 1951 (Decapoda: Caridea: Palaemonidae) from the eastern Gulf of Mexico, with an updated key for the identification of species of the genus.

A new species of symbiotic palaemonid shrimp of the genus Pseudocoutierea Holthuis, 1951, is described based on a specimen collected in the eastern Gulf of Mexico, off the southwest coast of Florida. Pseudocoutierea stephanieae sp. nov., is the seventh known in this genus, and morphologically most similar to P. antillensis Chace, 1972, and P. conchae Criales, 1981, from the western Atlantic, and P. elegans Holthuis, 1952, from the eastern Pacific, all sharing an expanded rostral base or eaves that terminate supra-distally in an acute tooth. This new species can be separated by: the presence of an epigastric knob or tubercle on the anterior mid-dorsal third of the carapace, which is absent in all other congeneric species; the shape of the pterygostomial sinus, which is shallow in this new species, whereas it is deep and well defined in all other congeneric species. An updated dichotomous key to species of Pseudocoutierea is presented.

Lysmata leptodactylus, a new species of lysmatid shrimp (Crustacea: Decapoda: Caridea) from China.

A new species of lysmatid shrimp, Lysmata leptodactylus n. sp., is described and illustrated based on specimens collected from the subtidal zone in Guangdong province, South China Sea. The new species bears distinctly unequal second pereiopods and uniquely elongated gracile dactyli of the ambulatory pereiopods. These characters, combined with the rostral formula, and stylocerite proportion, immediately distinguish Lysmata leptodactylus n. sp. from all known species of lysmatid shrimp.

The 'scorpion shrimp', a new species of the genus Metapontonia (Crustacea: Decapoda: Palaemonidae) from Taiwan, with new generic record from Papua New Guinea.

A new species of shrimp Metapontonia scorpio symbiotic with scleractinian coral Diploastrea heliopora is described from Taiwan. The species belongs to the smallest symbiotic shrimps of the family Palaemonidae. It is remarkable by a unique ability to turn its last two pleonites with tail fan dorsally over the 4th and preceding pleonal segments, thus resembling scorpions. For such movement, the respective opposing dorsal margins of the 4th-6th segments are deeply concave. The new species is characterized by a short dorsally directed rostrum, incomplete orbit, semicircular scaphocerite, and medially concave basal antennular segment. The only species of the genus, M. fungiacola, is compared with the new species based on morphology and DNA. Metapontonia fungiacola is for the first time reported from Taiwan and Papua New Guinea. The morphological and colour variability of the species is discussed. The scleractinian corals Platygyra lamellina (Merulinidae), Lobophyllia hemprichii, cf. Micromusa sp., Symphyllia cf. radians (Lobophylliidae), and Galaxea sp. (Oculinidae), are new host records for the species.