Male Gonopores Research Articles

A new species of Orobdella (Hirudinida, Arhynchobdellida, Orobdellidae) from Taipei, Taiwan

A new quadrannulate species of Orobdella, Orobdella ketagalan sp. n., from Taipei, Taiwan, is described. This is the first record of Orobdella and the family Orobdellidae from Taiwan. This new species possesses small, paired sperm duct bulbs in the male reproductive system. In addition to these bulbs, the following combination of characters distinguishes this new species from other quadrannulate species: somite IV uniannulate, male gonopore at XI b6, female gonopore at XIII a1, 1/2 + 4 + 1/2 between gonopores, simple tubular gastroporal duct, lacking epididymides, and undeveloped atrial cornua. Phylogenetic analyses using nuclear 18S rDNA and histone H3 as well as mitochondrial COI, 12S rDNA, tRNAVal, and 16S rDNA markers showed that Orobdella ketagalan is related to the two Ryukyu Archipelago species Orobdella dolichopharynx Nakano, 2011 and Orobdella shimadae Nakano, 2011.

Piscicola siddalli n. sp., a Leech Species from the United Kingdom (Clitellata: Hirudinida: Piscicolidae)

A new species of fish leech from England, Piscicola siddalli n. sp. (Piscicolidae), was collected in 2006 on stones and on grayling (Thymmallus thymmallus L.) in the River Ure, North Yorkshire, Great Britain. The leech is 4(12) annulate; gonopores are separated by four annuli. The male gonopore is much larger than the female gonopore. Seminal receptacle consists of a round aperture, located at a distance of 3 annuli behind the female gonopore. Copulatory area on the clitellum is in the form of a circle. Vector tissue has the form of a circular plate, below the oviduct opening.

A new sexannulate species of Orobdella (Hirudinida, Arhynchobdellida, Orobdellidae) from Yakushima Island, Japan

A new sexannulate species of the genus Orobdella Oka, 1895, Orobdella mononoke sp. n., is described on the basis of five specimens collected from Yakushima Island, Japan. Orobdella mononoke sp. n. differs from other sexannulate Orobdella species in its possessing the following combination of characters: dorsal surface bicolor in life, I–XIII, XXVII and caudal sucker grayish purple, XIV–XXVI amber, male gonopore at XI c11/c12, female gonopore at XIII b2, 8 + 1/2 between gonopores, tubular but bulbous at junction with crop gastroporal duct, epididymides in XV–XIX, and atrial cornua ovate. Phylogenetic analyses using nuclear 18S rDNA and histone H3, and mitochondrial COI, tRNACys, tRNAMet, 12S rDNA, tRNAVal and 16S rDNA markers show that Orobdella mononoke sp. n. is closely related to Orobdella esulcata Nakano, 2010 from Kyushu, Japan, and two species, Orobdella dolichopharynx Nakano, 2011 and Orobdella shimadae Nakano, 2011, from the Ryukyu Archipelago, Japan.

A new species of Orobdella (Hirudinida, Arhynchobdellida, Gastrostomobdellidae) and redescription of O. kawakatsuorum from Hokkaido, Japan with the phylogenetic position of the new species

A new quadrannulate Orobdella Oka, 1895 species, Orobdella koikei sp. n., is described on the basis of six specimens collected from Hokkaido, Japan. In addition, an emended description of quadrannulate Orobdella kawakatsuorum Richardson, 1975 is also provided. Orobdella koikei differs from other quadrannulate species of Orobdella in possessing the following combination of characters: color dorsally brown, IV uniannulate, male gonopore at XI b6, gastropore and female gonopore at XIII a1, 1/2 + 4 + 1/2 between gonopores, XXV triannulate, tubular but bulbous at junctions with gastropore and crop gastroporal duct, epididymides in XVII to XIX, and atrial cornua ovate. The phylogenetic position of the newly described species is estimated using mitochondrial COI, tRNACys, tRNAMet, 12S rDNA, tRNAVal and 16S rDNA markers. Orobdella koikei is a sister taxon of Orobdella kakawatsuorum according to the molecular phylogenetic analyses.

Protandric simultaneous hermaphroditism in Parhippolyte misticia (Clark, 1989) (Caridea: Hippolytidae): implications for the evolution of mixed sexual systems in shrimp

The sexual system of the shrimp Parhippolyte misticia (Clark, 1989), inhabiting the rocky subtidal at Okinawa, Japan and Kimbe Bay, Papua New Guinea, was examined. Dissections suggested that the population consisted of male phase (MP) and functional simultaneous euhermaphrodite (EH) individuals. MPs have cincinulli and appendices masculinae on the first and second pair of pleopods, respectively, gonopores located at the coxae of the third pair of walking legs, and ovotestes with a well-developed male portion containing sperm, but an undeveloped female portion. EHs lacked appendices masculinae and cincinulli. However, they have male gonopores and ovotestes with well-developed ovaries containing mature oocytes and testes with sperm. When EHs were maintained in pairs, both shrimp molted and spawned eggs which attached below the pleon and developed as embryos, demonstrating that EHs can reproduce as males and inseminate other EHs acting as females. These results demonstrate that P. misticia is a protandric simultaneous hermaphrodite, as reported before for other shrimp of the genera Lysmata and Exhippolysmata. Also, these results suggest that protandric simultaneous hermaphroditism might have evolved more than once independently in shrimp from the diverse and species-rich Infraorder Caridea. Future research aimed at disentangling the phylogenetic relationship of Parhippolyte, Lysmata, Exhippolysmata and other closely related genera (Calliasmata, Lysmatella, Barbouria) and describing the sociobiology of additional representatives from the genera above is needed to understand the evolutionary history of sexual systems in caridean shrimp.

Effects of androgenic gland ablation on growth and reproductive parameters of Cherax quadricarinatus males (Parastacidae, Decapoda)

This work investigates the effects of androgenic gland (AG) ablation on the structure of the reproductive system, development of secondary sexual characters and somatic growth in Cherax quadricarinatus males. The AG ablation, which was performed at an early developmental stage (initial weight: 1.85 ± 0.03 g), had no effect on the somatic growth parameters (specific growth rate and growth increment), but it prevented the re-formation of male gonopores and appendices masculinae. However, the red patch differentiation and chelae size were similar to those in control males. All the ablated animals developed a male reproductive system. Testis structure was macroscopically and histologically normal. The distal portion of the vas deferens (DVD) was enlarged in some animals, with histological alterations of the epithelium and the structure of the spermatophore. Results suggest that the higher growth in males than in females may be due to an indirect effect of the AG on energy investment in reproduction rather than to a direct effect of an androgen. This is the first report of a potential action of the AG on the secretory activity of the distal VD and the structural organization of the spermatophore. Although the AG may play a role in the development of male copulatory organs, its association with the red patch development deserves further research. The results obtained in the present study support and complement those from intersexes of the same species.

Holotype redescription of Mimobdella japonica (Hirudinida, Arhynchobdellida, Erpobdelliformes) and taxonomic status of the genus Mimobdella

Mimobdella japonica Blanchard, 1897, the type species of the genus Mimobdella Blanchard, 1897, is redescribed based on the holotype. This species is characterized by the following characteristics: mid-body somites novem-annulate, two post-anal annuli, male gonopore in XI/XII, female gonopore in XII/XIII, 9 annuli (one full somite) between gonopores, strepsilaematous pharynx and three myognaths with stylets, possessing post-crop caeca in pairs, ovisacs reaching to XXI a2. The genus Mimobdella is placed under the family Salifidae, not Gastrostomobdellidae or Erpobdellidae, according to its possessing three myognaths bearing pharyngeal stylets.

The position of the Hymenosomatidae MacLeay, 1838, within the Brachyura (Crustacea, Decapoda)

The Hymenosomatidae is unique among the Brachyura on the basis of spermatozoal ultrastructure and morphological characters of the adults and larvae. The location of the hymenosomatid male gonopore, always a controversial question, is here shown to be sternal, not coxo-sternal. This disposition, analogous to the arrangement of Thoracotremata, contradicts all morphological characters that indicate a heterotreme affiliation, close to the Majoidea and Dorippoidea. Molecular data also support such an assignment. The multiple hymenosomatid plesiomorphies are reviewed. The exceptional male reproductive system, a new scheme for the Eubrachyura, is assumed, at least in part, to be the result of a strong carcinisation in an ancient, deeply rooted group, at present the most ecologically diverse in Brachyura. The presence of the Hymenosomatidae on the former Gondwanan landmasses and its worldwide pattern of distribution are consistent with the hypothesis of a Gondwanan origin of the family.

Development of secondary sexual characters in the seabob shrimp Xiphopenaeus kroyeri (Heller 1862) (Crustacea, Decapoda, Penaeidae): a scanning electron microscope study

The development of secondary sexual characters, the petasma, and thelycum growth were studied in Xiphopenaeus kroyeri. In adult females, the thelycum is a single plate and its anterolateral portion is characterized by a reduced hood. The aperture resembles a transverse ridge. In immature stages, the ridge has a space between the plates, which becomes narrower as it reaches the end of development. The female gonopore is ‘comma’ shaped. In adult males, the endopods of the petasma are linked at the dorsomedial margin by a large quantity of cincinnuli. In juveniles, cincinnuli gradually increase in number until they join both endopods. At the end of development the petasma is T-shaped. The male gonopore is C-shaped. The relative growth of the petasma total length versus juvenile body length showed a highly positive allometry, whereas in adults the growth was isometric. For the relationship carapace length versus thelycum width, the juvenile phase of females is characterized by an isometry and the adult phase by a negative allometry.

Sperm capacitation of the shrimp Litopenaeus vannamei

Litopenaeus vannamei is one of the most important species of farmed shrimp. The females have an ‘open’ thelycum. Mating is accomplished by attaching the male spermatophore onto the surface of the thelycum 4–6 h before spawning. During this period, sperm may have to undergo morphological changes associated with a capacitation process that has been described for other shrimp species. The objective of this research was to extend research on sperm capacitation in L. vannamei by ultrastructural and biochemical means. The sperm of L. vannamei were divided into those freshly prepared from the spermatophore (S-sperm), extracted from the male gonopores, and those extracted from the female thelycum (T-sperm). Under transmission electron microscopy, ultrastructural differences were detected between the S- and the T-sperm in the nuclear material, the filamentous meshwork and the cytoplasmic particles. Under scanning electron microscopy, the difference was observed in the cap and spike regions. Immunofluorescence using confocal microscopy to detect tyrosine phosphorylated proteins revealed different distribution patterns between S- and T-sperm. The location of phosphorylation activity changed from the spike in S-sperm, to the filamentous meshwork in the T-sperm. These morphological and biochemical changes confirm that capacitation of L. vannamei sperm takes place following mating.

A new genus and species of the family Lethaxonidae (Acari, Parasitengona, Hydrachnidia) from the island of Coiba (Panama)

Transitia carlosi n. gen. n. sp. of the family Lethaxonidae is described from the interstitial environment of a small stream in Central America. Following a morphological revision of the adult variation in the family, Transitia n. gen. is proposed, characterized by a posteriorly tapering body shape, three pairs of acetabula arranged linearly, median position of male gonopore in relation to first pair of genital acetabula and slight sexual dimorphism of male legs.

A cladistic revision of Tortopus Needham & Murphy with description of the new genus Tortopsis (Ephemeroptera: Polymitarcyidae)

The 12 species previously placed in Tortopus together with 3 species newly described here, are revised and included in a phylogenetic analysis. Based on synapomorphic characters on the nymphs and adults of both sexes, Tortopus is restricted to T. igaranus Needham & Murphy, T. circumfluus Ulmer, T. harrisi Traver, T. zottai (Navás), T. bellus Lugo-Ortiz & McCafferty, and T. arenales sp. nov., and the genus is defined by: female parastyli receptors with long furrows anterior to sockets; penes entirely flattened; male ninth abdominal sternum almost separated in two portions by a median notch; mesosternum with furcasternal protuberances contiguous only on basal corner; and nymphs with two subapical tubercles on mandibular tusks. Tortopsis is newly described for T. bruchianus (Navás), T. limoncocha sp. nov., T. obscuripennis (Domínguez), T. parishi (Banks), T. primus (McDunnough), T. puella (Pictet), T. sarae (Domínguez), T. spatula sp. nov., and T. unguiculatus (Ulmer). Tortopsis is characterized by: R sector of female fore wing without additional veins between R 2 and IR; female parastyli receptors C or V-shaped, with sockets opening towards median line; male gonopore associated with a claw-like structure; penes separated from the base; parastyli more than 5 times length of pedestals; parastyli curved in lateral view; nymphs with a single subapical tubercle on mandibular tusks. The study of available type material permitted inclusion of comparative diagnoses, with figures and redescriptions as needed. The male imago of the type species of Tortopus (T. igaranus Needham & Murphy) is described for the first time, as are the female adults of Tortopus bellus Lugo-Ortiz & McCafferty and T. harrisi Traver. Three new Neotropical species based on male and female adults are described: Tortopus arenales and Tortopsis limoncocha from Ecuador, and Tortopsis spatula from Colombia. Keys to separate the adults and nymphs of the genera of Polymitarcyidae, and for male and female adults of all the species of Tortopus and Tortopsis are presented, as well as line drawings, pictures and SEM photographs of important structures.

Description of the male reproductive system of Paguristes eremita (Anomura, Diogenidae) and its placement in a phylogeny of diogenid species based on spermatozoal and spermatophore ultrastructure

The male gonopores, male reproductive apparatus, spermatophore and spermatozoa of the Mediterranean hermit crab Paguristes eremita are described, using interference phase microscopy, scanning electron microscopy and transmission electron microscopy. A correlation is made between the gonopore morphology and the different kinds of setae accompanying them, and the reproductive biology of these crabs. Each testes merges into a tubular duct made up of four zones: (1) the collecting tubule with free spermatozoa; (2) the proximal zone, where the ampulla of the spermatophores starts to be formed; (3) the medial zone, where the ampulla is completed, the stalk lengthens and the pedestal is formed; (4) the distal zone, where the mature spermatophores are stored. The sizes of the different parts of the spermatophore and of the sperm are given and their exterior morphology and ultrastructure described and compared to congeners. The morphology of the gonopore, male reproductive system, spermatophore and spermatozoa of P. eremita are species-specific, clearly distinguishing the species from the other members of the family. The available spermatozoal and spermatophore data is used to place P. eremita within a sperm phylogeny of the hermit crab family Diogenidae.

Anatomical and histological studies on the male reproductive system of the red swamp crayfish Procambarus clarkii.

he male reproductive system of Procambarus clarkii consists of two milky white testes; each one consists of anterior and posterior portions. The two testes are separated anteriorly and united posteriorly. A collecting duct arises from each testis. These ducts meet together at the middle point between the anterior and posterior testes, from this point; a long coiled, thread-like vas deferens extends. It is tubular and white in colour. The right one is longer, thicker and coiled, while the left one is shorter transparent and not coiled. Both the left and right vasa deferentia extend posteriorely to open with the male gonopore on the last thoracic appendages. Histologically, the testis consists of acini in which stages of spermatogenesis occur. Spermatides pass to the collecting tubules, where they become mature sperm and packed in a spermatophore in the vas deferens. The wall of the collecting tubules consists of simple cuboidal cells. The vas deferens is divided into two regions; the glandular and ejaculatory regions. The first is lined with secretory columnar epithelium, while the second has a muscular wall of longitudinal and circular muscles and lined with single layer of ciliated columnar epithelium.

Aphanodactylidae, a new family of thoracotreme crabs (Crustacea: Brachyura) symbiotic with polychaete worms

The pea crabs of the family Pinnotheridae De Haan, 1833, have traditionally been recognised on the basis of their simplified external morphology, modified third maxillipeds, and general habit of living in association with invertebrate hosts, usually bivalve molluscs. Recent morphological and molecular studies of Pinnotheridae show that it is not a natural group as traditionally conceived. The subfamily Asthenognathinae Stimpson, 1858, actually belongs in the Varunidae H. Milne Edwards, 1853, and the subfamily Tritodynamiinae Števčić, 2005, is part of the Macrophthalmidae Dana, 1851. However, several ‘pinnotherid’ genera that are superficially similar to asthenognathines and allied to Aphanodactylus Tesch, 1918, appear to form a discrete group, but lack the chief synapomorphy of Pinnotheridae, namely, the highly modified maxilliped 3. Moreover, Aphanodactylus and allies do not share synapomorphies with of any presently recognised thoracotreme family. A new family, Aphanodactylidae, is therefore established for Aphanodactylus, Gandoa Kammerer, 2006, Uruma Naruse, Fujita & Ng, 2009, and a new genus and species described herein, Gustavus mecognathus. Aphanodactylids (where known) are symbiotic with terebellid polychaete worms and share short, stout, ambulatory legs with one or more spines lining the flexor margins of the ischiomeri of at least some of the ambulatory legs; a row of distal flexor spines on the ambulatory propodi opposing a claw-like dactylus; very short ambulatory dactyli that are less than half the respective propodus length; and marked sexual dimorphism in which the female is distinctly wider than the male. The phylogenetic position of Aphanodactylidae remains to be determined but the morphology of the third maxillipeds and the position of the male gonopore suggests that it may belong in the Pinnotheroidea, to which it is tentatively assigned. Each genus of the Aphanodactylidae is diagnosed and illustrated, and a key to the genera provided.

Serotonergic and SCPb-like innervation of the atrial complex in Gyratrix hermaphroditus (Platyhelminthes, Kalyptorhynchia) revealed with CLSM

The platyhelminth reproductive system is a complex series of canals, glands, and sclerotic components that figure prominently in our understanding of reproductive physiology, taxonomy, and evolution of the Platyhelminthes. Yet, there is limited information on its innervation, especially for free-living species of Rhabdocoela, the most speciose and ecologically diverse assemblage. Here, innervation of the reproductive system in the common marine kalyptorhynch, Gyratrix hermaphroditus, is studied using confocal laser scanning microscopy (CLSM), fluorescent phalloidin, and antibodies to serotonin (5HT) and small cardioactive peptide b (SCPb). Results show that portions of the female atrial system (uterus, female gonopore) are innervated by peptidergic (SCPb) neurons that may function to control muscles involved in egg movement. In contrast, portions of the male atrial system (male atrium, male gonopore) are innervated by both peptidergic and serotonergic neurons. These neurons form a complex series of hoops around the musculature of the male atrium that houses prostate stylet type II. It is hypothesized that 5HT is the primary myoexcitatory neurotransmitter, and that it acts either synergistically with SCPb to trigger muscle contractions of the male atrium and protract the copulatory stylet, or that SCPb plays an inhibitory role during contraction of the male atrium. A comparison of the distribution of peptidergic and serotonergic neurons in G. hermaphroditus with other free-living species and parasitic rhabdocoels (Neodermata) reveals similarities in innervation of comparable (though probably not homologous) reproductive organs. These results suggest that the atrial systems of phylogenetically diverse species may share a common neuronal physiology despite their structural differences and potential independent evolutionary origins within the Platyhelminthes.

Ibericancridae, a new dakoticancroid family (Decapoda, Brachyura, Podotremata) from the upper Campanian (Upper Cretaceous) of Spain

A small faunule of crabs from the upper Campanian (Upper Cretaceous) of Valencia, eastern Spain, is described as Ibericancer sanchoi n. gen., n. sp., and assigned to a new family, the Ibericancridae n. fam., which is placed in the Dakoticancroidea Rathbun, 1917, until now known to comprise a single family, Dakoticancridae Rathbun, 1917, restricted to the Upper Cretaceous of North America and northeast Mexico. The Ibericancridae n. fam. shares with the Dakoticancridae the general shape and size of the carapace, the arrangement of dorsal regions of the carapace, a pleural suture situated at carapace flanks, insertion of a sternal thoracic portion between abdomen and coxae of the pereiopods, and long P2 and P3. Ibericancer n. gen. differs from the four genera currently included in the Dakoticancridae (Dakoticancer Rathbun, 1917; Tetracarcinus Weller, 1905; Avitelmessus Rathbun, 1923 and Seorsus Bishop, 1988), in having P4 and P5 conspicuously reduced and subdorsal in position, a narrower thoracic sternum, and distinct frontal and orbital features. Because the male and female gonopores are located on the pereiopods, P5 and P3 coxae, respectively, and the spermathecal aperture is at the extremity of the thoracic suture 7/8, the Dakoticancroidea conforms to the Podotremata Guinot, 1977. It is here interpreted as a carcinised podotreme superfamily, the broadening of the thoracic sternum being weak in the Ibericancridae n. fam., but distinct in the Dakoticancridae. Dakoticancroid crabs probably employed a carrying behaviour, as do most podotremes, and were characterised by an abdominal holding of the press button type. Morphological characters of the Ibericancridae n. fam. add significantly to our knowledge of the evolutionary processes within the Podotremata.

Protandric simultaneous hermaphroditism in the shrimps Lysmata bahia and Lysmata intermedia

Abstract. The sexual system of two peppermint shrimps, Lysmata bahia and Lysmata intermedia, inhabiting intertidal fossil coral terraces at Bocas del Toro, on the Caribbean coast of Panama, was examined. Dissections suggested that the population of each species consisted of functional males and functional simultaneous hermaphrodites. Males have cincinulli and appendices masculinae on the first and second pair of pleopods, respectively, gonopores located at the coxae of the third pair of walking legs, and ovotestes with a well‐developed male portion full of sperm, but an undeveloped female portion. Hermaphrodites lacked appendices masculinae and cincinulli. However, they have male gonopores and ovotestes with well‐developed ovaries full of mature oocytes and testes with sperm. When hermaphrodites were maintained in pairs, both molted and spawned eggs (to beneath abdomen) that continued developing after 3 d, demonstrating that hermaphrodites can reproduce as males and inseminate other hermaphrodites acting as females. The possibility of self‐fertilization or parthenogenetic reproduction was tested and disregarded, because hermaphrodites reared in isolation spawned oocytes that failed to develop, disappearing from the abdomen after 2 d. Males reared in pairs mature as hermaphrodites in <50 d, showing the ability of males to mature as hermaphrodites. These results demonstrate that L. bahia and L. intermedia are protandric simultaneous hermaphrodites, as reported for all species of this genus whose sexual system has been examined. However, the studied species featured a lifestyle, termed “tropical‐low abundance,” here not recognized previously for the genus; they occur in low abundances in tropical environments, they do not develop symbiotic associations with sessile invertebrates, and they are not conspicuously colored. Information on the sexual systems and lifestyles of more species needs to be examined before these observations can be placed into a comparative context within the genus.

Myogenesis in the basal bilaterian Symsagittifera roscoffensis (Acoela)

BackgroundIn order to increase the weak database concerning the organogenesis of Acoela – a clade regarded by many as the earliest extant offshoot of Bilateria and thus of particular interest for studies concerning the evolution of animal bodyplans – we analyzed the development of the musculature of Symsagittifera roscoffensis using F-actin labelling, confocal laserscanning microscopy, and 3D reconstruction software.ResultsAt 40% of development between egg deposition and hatching short subepidermal fibres form. Muscle fibre development in the anterior body half precedes myogenesis in the posterior half. At 42% of development a grid of outer circular and inner longitudinal muscles is present in the bodywall. New circular muscles either branch off from present fibres or form adjacent to existing ones. The number of circular muscles is higher than that of the longitudinal muscles throughout all life cycle stages. Diagonal, circular and longitudinal muscles are initially rare but their number increases with time. The ventral side bears U-shaped muscles around the mouth, which in addition is surrounded by a sphincter muscle. With the exception of the region of the statocyst, dorsoventral muscles are present along the entire body of juveniles and adults, while adults additionally exhibit radially oriented internal muscles in the anterior tip. Outer diagonal muscles are present at the dorsal anterior tip of the adult. In adult animals, the male gonopore with its associated sexual organs expresses distinct muscles. No specific statocyst muscles were found. The muscle mantles of the needle-shaped sagittocysts are situated along the lateral edges of the animal and in the posterior end close to the male gonopore. In both juveniles and adults, non-muscular filaments, which stain positively for F-actin, are associated with certain sensory cells outside the bodywall musculature.ConclusionCompared to the myoanatomy of other acoel taxa, Symsagittifera roscoffensis shows a very complex musculature. Although data on presumably basal acoel clades are still scarce, the information currently available suggests an elaborated musculature with longitudinal, circular and U-shaped muscles as being part of the ancestral acoel bodyplan, thus increasing the possibility that Urbilateria likewise had a relatively complicated muscular ground pattern.

Synalpheus paraneptunus (Crustacea: Decapoda: Caridea) populations with intersex gonopores: a sexual enigma among sponge-dwelling snapping shrimps

Summary Caridean shrimp populations are usually gonochoristic, i.e., composed of separate sexes; however, some carideans are protandric sex changers or simultaneous hermaphrodites. In this contribution we investigated the sexual composition and its determination in two sponge-dwelling Synalpheus species with different degrees of sociality. Because the usual external sexing methods (presence or absence of appendices masculinae in males) can not be used in Synalpheus spp., we sexed individuals by observation of male and female gonopores using scanning electron microscopy (SEM). We found that populations of two species of the Synalpheus paraneptunus complex consist almost entirely of individuals with both male and female gonopores (termed herein “intersexes”). Such a high incidence of intersexes has not been previously reported in other decapods. We performed morphological and behavioral observations to test various hypotheses explaining the presence of intersex gonopores. Whereas protandry and simultaneous hermaphroditism are not likely to occur in these two species, capacity of immature helpers to mature as either sex, or developmental anomaly without adaptive significance could explain the presence of both female and male gonopores in these shrimps.