Taxonomic Review of the Orders Mysida and Stygiomysida (Crustacea,Peracarida)

The order Mysida (2 families, 178 genera, 1132 species) contains species across a broad range of habitats, such as subterranean, fresh, brackish, coastal, and surface to deep-sea habitats. The Stygiomysida (2 families, 2 genera, 16 species), however, are found primarily in subterranean waters, but always in waters with a marine influence. The Mysida and Stygiomysida body is divided into three main regions: cephalon, thorax, and abdomen. They are shrimp-like in appearance, containing morphological features earlier referred to as defining a "caridoid facies". The shrimp-like morphology was to some extent diagnostic for the historic Decapod taxon Schizopoda, containing the Nebalia, Mysida, Lophogastrida, and Euphausiacea. In 1904 the concept of Schizopoda was abandoned, and the Mysidacea (Mysida and Lophogastrida) along with Cumacea, Amphipoda, Isopoda, and Tanaidacea were placed in a new taxon, the Peracarida. Later discoveries of groundwater mysids led to the establishment of Stygiomysida, but placement to either Lophogastrida or Mysida remained unclear. The presence of oostegites and absence of podobranchiae, coupled with non-statocyst bearing uropods have been used to classify the Stygiomysida as a primitive Mysida family, comparable to Petalophthalmidae. On the other hand, equally suggestive characters, but for a Lophogastrida affiliation, was suggested for the archaic foregut characters and again, non-statocyst bearing uropods. With the inclusion of DNA sequence data of ribosomal genes, sister group relationships between Stygiomysida, Lophogastrida, and Mictacea within the Peracarida are observed, which supports a classification of the Stygiomysida as a separate order removed from the Mysida.     

The disunity of "Mysidacea" (Crustacea)

New studies on malacostracan relationships have drawn attention to issues concerning monophyly of the order Mysidacea, manifested in recent crustacean classifications that treat the taxon as two separate orders, Lophogastrida and Mysida. We present molecular phylogenies of these orders based on complete sequences of nuclear small-subunit ribosomal DNA (18S rRNA), and morphological evidence is used to revise the classification of the order Mysida to better reflect evolutionary history. A secondary structure model for 18S rRNA was constructed and used to assign putative stem and loop regions to two groups of partitions for phylogenetic analyses. Phylogenies were estimated by maximum-likelihood, Bayesian inference, and maximum-parsimony. The analyses gave strong support for three independently derived lineages, represented by three monophyletic groups, Lophogastrida, Stygiomysida, and Mysida. The family Petalophthalmidae is considered as sister group to the family Mysidae, and Boreomysinae and Rhopalophthalminae are the most early derived of the Mysidae. The tribes contained in the current classification of the subfamily Mysinae are not well-supported by either molecular data or morphology.     

Limb articulation in caridoid crustaceans revisited - new evidence from Euphausiacea (Malacostraca)

The propodial articulation of thoracopods in Malacostraca is revisited. Two major joints at the base of the limb, a thorax-coxa joint and a coxa-basis joint permit promotion-remotion and abduction-adduction, respectively. In representatives of Decapoda, Anaspidacea and Euphausiacea, the coxa forms proximally a dicondylic articulation with the thorax, permitting promotion-remotion, and distally another dicondylic joint with the basis, permitting abduction-adduction. In Lophogastrida and Mysida, the thorax-coxa hinge line is antero-posteriorly oriented, as is the coxa-basis hinge line. Promotion-remotion in Mysida and Lophogastrida is possible because of the presence of an intrabasal joint which is also present in Euphausiacea and Anaspidacea. In Mysida, Lophogastrida and Euphausiacea, the intrabasal joint is only present anteriorly, just distally of the anterior coxa-basis joint between a small, triangular proximal part of the basis and a larger distal part. In Anaspidacea, the intrabasal joint is also present posteriorly and permits abduction-adduction. Homology with the intrabasal joint of the other taxa seems doubtful. Limb articulation in Anaspidacea shows, nevertheless, correspondences with that in Euphausiacea, Lophogastrida and Mysida: the coxa is posteriorly invaginated and has an open ring-like structure very different from the solid coxa in decapods. Despite the high level of structural correspondence between the intrabasal joint in Euphausiacea and that in Lophogastrida and Mysida, their different functional roles make homology implausible. In Lophogastrida and Mysida the intrabasal joint is thought to replace the promotion-remotion movement of the thorax-coxa articulation, which in these taxa permits abduction-adduction only, probably in connection with the evolution of the marsupium. In Euphausiacea, the intrabasal joint might play a role in feeding mechanisms. Neither the feeding basket nor a marsupium can reasonably be suggested for any common ancestor of Euphausiacea and Mysidacea (or Peracarida).     

The foreguts of the primitive families of the Mysida (Crustacea, Peracarida): a transitional link between those of the Lophogastrida (Crustacea, Mysidacea) and the most evolved Mysida

De Jong-Moreau, L. and Casanova, J.-P. 2001. The foreguts of the primitive families of the Mysida (Crustacea, Peracarida): a transitional link between those of the Lophogastrida (Crustacea, Mysidacea) and the most evolved Mysida. — Acta Zoologica (Stockholm) 82 : 137–147
The morphology of the foregut, which is a good indicator of phylogenetic relationships, has been studied within the two suborders of the Mysidacea. Special attention has been focused on rare species belonging to the Lophogastrida and the three primitive families of the Mysida, i.e. Stygiomysidae, Lepidomysidae and Petalophthalmidae. It appears that the foregut of Gnathophausia gracilis (Lophogastrida) is the most primitive in the Mysidacea, and that in the Petalophthalmidae the foregut exhibits transitional stages between that of the Lophogastrida and of the evolved Mysidae. Moreover, in the four families of Mysida, ancestral characteristics of the foregut remain, thus strengthening the hypothesis of the unity of this order.     

A new species of Gastrosaccus Norman, 1868 (Mysida,Mysidae, Gastrosaccinae) from a sandy shore of Indonesia

A new species of the mysid crustacean genus Gastrosaccus Norman, 1868 (Mysida, Mysidae, Gastrosaccinae) is reported from a sandy shore of Lombok Island, Indonesia. These specimens resemble G. sorrentoensis Wooldridge & McLachlan, 1986 and G. yuyu Bamber and Morton, 2012 by the possession of an articulated process on the fifth abdominal somite together with a fringe of spine-like filaments on the posterodorsal margin of the carapace. The Lombok population differs from the known congeners by having comparatively fewer numbers of carpopropod segments on the endopod of the third to eighth thoracic limbs and the conformation in the telson and in the male third pleopod. Hence, G. lombokiensis sp. n. is proposed herein as a third species of “G. sorrentoensis” species group.     

Phylogenetic relationships within the Mysidae (Crustacea, Peracarida, Mysida) based on nuclear 18S ribosomal RNA sequences

Species of the order Mysida (Crustacea, Peracarida) are shrimp-like animals that occur in vast numbers in coastal regions of the world. The order Mysida comprises 1,053 species and 165 genera. The present study covers 25 species of the well-defined Mysidae, the most speciose family within the order Mysida. 18S rRNA sequence analysis confirms that the subfamily Siriellinae is monophyletic. On the other hand the subfamily Gastrosaccinae is paraphyletic and the subfamily Mysinae, represented in this study by the tribes Mysini and Leptomysini, consistently resolves into three independent clades, and hence is clearly not monophyletic. The tribe Mysini is not monophyletic either, and forms two clades of which one appears to be closely related to the Leptomysini. Our results are concordant with a number of morphological differences urging a taxonomic revision of the Mysidae.     

The circulatory system in Mysidacea--implications for the phylogenetic position of Lophogastrida and Mysida (Malacostraca, Crustacea)

The morphology of the circulatory organs in Mysida and Lophogastrida (traditionally combined as Mysidacea) is revisited investigating species so far unstudied. In addition to classical morphological methods, a newly developed combination of corrosion casting with micro computer tomography (MicroCT) and computer aided 3D reconstructions is used. Lophogastrida and Mysida show a highly developed arterial system. The tubular heart extends through the greater part of the thorax and is connected with the ventral vessel via an unpaired descending artery. It is suggested that a distinct ostia pattern supports the monophyly of Mysidacea. The cardiac artery system is more complex in Lophogastrida than in Mysida, consisting of up to 10 pairs of arteries that supply the viscera. In both taxa, an anterior and posterior aorta leads off the heart. In the anterior part of the cephalothorax the anterior aorta forms dilations into which muscles are internalized; these structures are called myoarterial formations. One of these myoarterial formations can also be found in all the other peracarid taxa but not in other Malacostraca.     

Reproduction in the Giant Isopod,Bathynomus giganteus

Summary

Aspects of the reproductive biology of the giant isopod, Bathynomus giganteus (Edwards) resemble those of other isopods. In females, the gonopores are located on the sternal midline of the eighth thoracic somite and the eggs are brooded in a marsupium. The reproductive tract of the males also resembles those of other isopods. The paired vasa deferentia open into two penes located on the sternal midline of the eighth thoracic somite. The vasa deferentia are formed of columnar epithelial cells with basal nuclei. The lumen is filled with seminal products consisting of aggregrates of spermatozoa surrounded by extracellular tubules. The sperm head consists of an acrosome and subacrosomal rod from which a pendant nucleus extends. The tails are composed of an amorphous core consisting of a dark band, two medium bands, two light bands followed by a dark band again. The tails are attached to the heads by a knob which is an extension of the core     

Gonopore development and sex change in the Antarctic shrimp Chorismus antarcticus (Caridea: Hippolytidae)

Chorismus antarcticus is the only protandrous hermaphrodite decapod species found on the Antarctic continental shelves. The morphological structures of the male and female gonopores were described and used to determine sex and to fix the size range at which the transition from male to female takes place. The parallel occurrence of male and female gonopores was found in all specimens. The presence of open gonopore flaps at both the third and fifth pair of pereiopods in individuals between 9 and 12 mm of carapace length (CL) is discussed as the morphological indicator of sex change. Few females occurred from 9 mm CL onwards, whereas all shrimps larger than 13 mm CL only had open female gonopores. This size corresponds exactly with the CL at which onset of oocyte development and female gonad production starts. Secondary sexual characters, the gonopore structures, seem to allow an accurate prediction of the size range at which hermaphrodite caridean decapods change sex. Received: 23 February 1996/Accepted: 15 July 1996     

Dermacentor variabilis and Dermacentor andersoni: Genital sex pheromones

There is evidence for the existence of a previously undescribed sex pheromone (or pheromones) in the ticks Dermacentor variabilis and D. andersoni. In addition to 2,6-dichlorophenol, which attracts mate-seeking males, a pheromone released on the cuticle of the female genital area enables the sexually excited male to locate the gonopore. The compound (or compounds) appears to act as a contact pheromone; male copulation responses are greatly reduced when the female genital surface is washed with solvents, especially hexane. It is also a potent excitant; males will puncture or dislodge barriers placed over the gonopore to copulate. However, the response is eliminated if the genital area is washed (hexane or acetone) prior to sealing the gonopore, suggesting the reproductive system as the source of the pheromone. A species specific copulation-eliciting pheromone appears necessary to excite the male to form and implant its spermatophore in the vulva of a conspecific female. Males encountering trans-specific females probe their gonopores, but mating attempts are almost always aborted within 5–10 min. The copulation-eliciting pheromone may be the same, or similar, to that used to locate the gonopore. Physical differences in the shape of the female gonopore in the two species, although slight, may contribute to the male's ability to identify conspecific females. Using this pheromone-guided process of attraction and identification, females present in mixed species populations will almost always be distinguished and inseminated by conspecific mate-seeking males.     

The cushion–star Parvulastra exigua in South Africa: one species or more?

The cushion–star Parvulastra exigua (Lamarck, 1816) is a widely distributed member of the temperate intertidal fauna in the southern hemisphere. In South Africa, it occurs in sympatry with the endemic Parvulastra dyscrita (Clark, 1923), the two species being differentiated predominantly by gonopore placement. Several recent studies have suggested that there may be additional cryptic species within the Parvulastra exigua complex in South Africa, based variously on color morphology, genetic evidence and the differential placement of the gonopores. This paper attempts to resolve whether one or more species are represented within Parvulastra exigua. A total of 346 Parvulastra exigua and 8 Parvulastra dyscrita were collected from sites on the west and south–west coasts of South Africa; morphological, anatomical and genetic analyses were performed to determine whether cryptic species and/or Parvulastra exigua specimens with aboral gonopores were present. Results show that neither cryptic species nor Parvulastra exigua specimens with aboral gonopores occur at these sites. This study thus refutes previous claims of the existence of aboral gonopores in South African Parvulastra exigua, and suggests that a single species is represented. The distinction between Parvulastra exigua and Parvulastra dyscrita is also confirmed, and features separating these two species are clarified and documented.     

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.     

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.     

Global diversity of mysids (Crustacea-Mysida) in freshwater

In this article we present a biogeographical assessment of species diversity within the Mysida (Crustacea: Malacostraca: Peracarida) from inland waters. Inland species represent 6.7% (72 species) of mysid diversity. These species represent three of the four families within the Mysida (Lepidomysidae, Stygiomysidae, and Mysidae) and are concentrated in the Palaearctic and Neotropical regions. The inland mysid species distributional patterns can be explained by four main groups representing different freshwater invasion routes: (1) Subterranean Tethyan relicts (24 spp.); (2) Autochthonous Ponto-Caspian endemics (20 spp.); (3) Mysis spp. ‘Glacial Relicts’ (8 spp.); and (4) Euryhaline estuarine species (20 spp.). The center of inland mysid species diversity is the Ponto-Caspian region, containing 24 species, a large portion of which are the results of a radiation in the genus Paramysis. Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Guest editors: E. V. Balian, C. Lévêque, H. Segers and K. Martens Freshwater Animal Diversity Assessment     

Male reproductive system of the red brocade hermit crab Dardanus insignis (Diogenidae) and its relationship to other family members

The reproductive system of hermit crabs shows species-specific morphology, which can be used in phylogenetic analysis. Here, we describe the male reproductive system of the hermit crab Dardanus insignis, including morphological and biometric analyses of the spermatophore, the gonopore, and sperm ultrastructure. The morphological analyses were based on 15 selected specimens and carried out by means of light and electron microscopy. Our results indicate a reproductive system composed of lobular testes attached to a simple straight vas deferens connected to the exterior via ventral gonopores. The gonopores are ovoid, surrounded by dense serrulate setae, and covered by a membranous operculum. The spermatophores exhibit a tripartite structure, with an elongate ovoid ampulla, a long narrow stalk, and a proximal foot. The spermatozoal ultrastructure shows three main regions: an ovoid-oblong acrosomal vesicle, a nucleus, and cytoplasm with three armlike extensions. Some of these characteristics can also be found in other species of Diogenidae within the genus Dardanus and in members of Coenobitidae, a closely related family. The available information on spermatophore and spermatozoal structure may indicate a closer similarity between the genus Dardanus and the Coenobitidae, compared with other members of Diogenidae.     

Erpobdella (Dina) parva complex (Annelida: Hirudinea: Arhynchobdellida: Erpobdellidae): additional description of Erpobdella parva, E. dubia, and E. lahontana and taxonomic revision

Erpobdella (Dina) parva complex (E. parva, E. dubia, and E. lahontana) were analyzed by species distribution, pigmentation, size, number and position of the labial eyes, tubercle presence, annulus width, gonopore position, and male genital atrium shape. I concluded that E. parva and E. dubia are conspecific, with the priority name of E. parva. The Lahontan basin species (E. lahontana), was found to be distinct by gonopore position, and now includes two additional basins (Granite Springs and Winnemucca). Endemism occurred in the Relict Dace basin complex (Butte and Steptoe basins) with respect to one form of gonopore positions. The variation in pigmentation, eye position and number, gonopore position, and male genital organ shape were highly variable in the Great Basin. Examination of the annular widths did not give any guidance to the taxonomic problem of the genera of this complex. It was noted that the Erpobdella parva complex did have some similarities with Nephelopsis obscura.     

Morphological and genetic variation indicate cryptic species within Lamarck's little sea star, Parvulastra (=Patiriella) exigua

The asterinid sea star Parvulastra exigua (Lamarck) is a common member of temperate intertidal marine communities from geographically widespread sites around the southern hemisphere. Individuals from Australian populations lay benthic egg masses (through orally directed gonopores) from which nonplanktonic offspring hatch and metamorphose without a dispersing planktonic larval phase. Scattered reports in the taxonomic literature refer to a similar form in southern Africa with aborally directed gonopores (and possibly broadcast spawning of planktonic eggs and larvae); such differences would be consistent with cryptic species variation. Surveys of morphology and mtDNA sequences have revealed cryptic species diversity in other asterinid genera. Here we summarize the taxonomic history of Lamarck's "Astérie exigu?" and survey morphological variation (the location of the gonopores) for evidence that some P. exigua populations include cryptic species with a different mode of reproduction. We found strong evidence for multiple species in the form of two phenotypes and modes of reproduction (oral and aboral gonopore locations) in populations from southern Africa and islands in the Atlantic and Indian oceans. Both modes of reproduction have broad geographic ranges. These results are consistent with previously published genetic data that indicate multiple species in African and island (but not Australian) populations.     

Sex‐specific differences in gonopore and gonadal growth trajectories in the brooding sea urchin,Abatus cavernosus (Spatangoida)

The heart urchin Abatus cavernosus shows sexual dimorphism characterized by the development of external brood pouches and the enlargement of gonopores in brooding females. Relationships between body size, gonopore size, and gonadal maturation in each sex were examined for inflection points using piecewise regression models (PRM). Opening of the gonopore occurred at 15.5 mm test length. Inflection points in the gonadal growth and gonopore diameter trajectories were clustered at smaller sizes in males (23 and 24.2 mm, respectively) than in females (25.1 and 25.9 mm), indicating sex‐specific differences in sexual maturation. Gonopore growth showed positive allometry at pre‐adult stages of development in both sexes, but isometry and negative allometry in adult females and males, respectively. Gonadal growth was initiated at smaller sizes and proceeded at a higher rate with increasing body size in males than in females. Identification of inflection points in gonopore and gonadal growth trajectories, using objective PRM, allows the determination of life stages and sexual maturation for individuals, thus providing a complementary tool for population studies.     

Evidence for the presence of serotonin in Mysidacea (Crustacea,Peracarida) as revealed by fluorescence immunohistochemistry

In crustaceans, serotonin (5-HT) exerts a wide range of physiological actions on many tissues. However, 5-HT has not been detected to date in Mysidacea (Crustacea, Peracarida). We have investigated the presence of 5-HT in the brain and the eyestalks of two Mysida (Leptomysis lingvura, Hemimysis margalefi) and one Lophogastrida (Lophogaster typicus) species by using the immunohistofluorescence technique. 5-HT-like immunopositive areas exhibit a similar pattern in the three species. 5-HT-like immunostaining is present in the retinular photosensitive cells, except in the deep-living species L. typicus. 5-HT-like cell bodies and fibres are observed in the lamina ganglionaris and in the three medullae. In the sinus gland, only 5-HT-like endings are detected. In the eyestalks, 5-HT-like fibres detected in the optic tract link with the protocerebrum, in which 5-HT-like somata and their extensions are found. Some neurones are detected in the anterior median cell cluster, in the protocerebral bridge and in the central body. In the deutocerebrum, the paracentral lobes are connected by immunoreactive fibres that run along the deutocerebral commissure. The glomeruli of the olfactory lobes exhibit strong diffuse immunostaining. Beside and in the median part of the deutocerebrum, at least two large serotoninergic neurones project their axons into the olfactory lobe cell cluster. Immunoreactive fibres are also found in the antennular neuropiles. Our results demonstrate the presence of 5-HT-like cell bodies and fibres in Mysidacea. The distribution patterns of the 5-HT immunoreactivity found herein are compared with those of other peracarids and decapods.     

Spermatophore transfer in the hermit crab Clibanarius vittatus (Crustacea,Anomura, Diogenidae)

Although mating has been described in several hermit crab species, the mechanics of spermatophore transfer have not previously been demonstrated. Evidence from pleopod and gonopore morphology, video observations, and inseminated females indicates that in Clibanarius vittatus the male applies a spermatophoric mass directly onto the female via the gonopores rather than with modified pleopods 1-2 (gonopods) and/or genital papillae as in many other decapods. The single second pleopod of males of C. vittatus has a simple endopod with no apparent modifications for sperm transfer. There are no genital papillae extending from the male gonopores. The globular spermatophores are aligned in rows surrounded by a seminal secretion in the male ducts (vasa deferentia that terminate in ejaculatory ducts opening to the exterior via the gonopores). During copulation, described from time-lapse video recordings, the ventral surface of the last thoracic segment of the male, bearing the gonopores, was apposed to the ventral cephalothorax of the female. A massive amount of seminal secretion containing spermatophore ribbons, termed here the spermatophoric mass and described for the first time in a hermit crab species, was observed covering the sternites and coxae of pereopods 1-5 of a recently copulated female. It is suggested that during copulation the male emits the contents of the ejaculatory ducts directly onto the female without the aid of gonopods or genital papillae. Although spermatophore transfer is simple in C. vittatus, the presence of modified anterior pleopods or elongate genital papillae (sexual tubes) in other paguroidean species suggests the possibility of a more complex insemination process in these other hermit crabs.