Morphology and Differentiation of Non-sensory Cuticular Structures in Mysidacea, Cumacea and Tanaidacea (Crustacea, Peracarida)

The non-sensory cuticular structures of some peracarideans (Mysidacea, Cumacea, Tanaidacea) were examined by scanning electron microscopy. The various types of structures present in the adult specimens are listed and the relation amongst them is elucidated. Three ways of differentiation of the structures can be distinguished: 1) a differentiation in the complexity of the structures themselves, 2) a differentiation of their arrangement on the body. 3) a differentiation of their distribution on the various parts of the body. A highly differentiated type of arrangement (row) of a number of simple structures (e.g. teeth) may lead to a higher complex structure (comb), which is seen to be developed best on special regions of the body (e.g. the distal segments of thoracic legs). The function of the cuticular structures–by analogy with other taxonomic groups–is discussed.     

Larval development of the rhizocephalanSacculina polygenea (Crustacea: Cirripedia)

Larval development of the rhizocephalanSacculina polygenea (Crustacea: Cirripedia: Rhizocephala) parasitizing the coastal crabHemigrapsus sanguineus was studied in Vostok Bay, the Sea of Japan. At 22–23°C, the entire cycle of larval development takes 2.5 days and includes five naupliar stages and one cypris stage. Like other rhizocephalans, the larvae ofS. polygenea are lecithotrophic and only grow slightly in size in the course of development, and like all sacculinids, they have no flotation collar. The naupliar stages IV and V have a tubercle between the furcal rami; this tubercle is absent in the larvae of the genusPeltogasterella, but it has been described inS. carcini. The first seta of the antennule only disappears completely at the fourth stage, although it is markedly reduced at the third stage. No morphological differences, except differences in size, are found between male and female nauplii.     

Revision of the Genus BosminaBAIRD, 1845 (Crustacea,Cladocera)

The genus Bosmina can be differentiated into four subgenera: 1. Bosmina s. str. BAIRD , 1845, 2. Eubosmina SELIGO , 1900, 3. Neobosmina LIEDER , 1957, and 4. Sinobosmina LIEDER , 1957. Subgeneric discrimination is based upon several features of the females (postabdominal claw, serration of the mucro, patterns of the lateral head pores) and, mainly, upon certain differences in the morphology of the male (postabdomen and, according to LILLJEBORG 1900, BURCKHARDT 1924 and KOŘINEK 1971, the first leg). The distribution of the Bosmina subgenera throughout the world varies: Bosmina s. str. is distributed worldwide (except for Australia?), Eubosmina is holarctic, Neobosmina has been found in Africa, the neotropical zone, Australia and Oceania, and Sinobosmina occurs in East and South-East Asia.     

Morphogenesis Rate Variability and Modularity of Development in Jurassic Ammonites of the Genus Arcticoceras Spath, 1924

The high variability of ammonites is largely due to the diversity of combinations of individual heterochronies (bradimorphy, tachymorphy, bradygeronty, and tachygeronty) and the modularity of development. Using the genus Arcticoceras as an example, it was shown that heterochronies of various directions can be combined in any number of characters, and individual heterochronies differ from phylogenetic ones by their smaller range, and a larger number of combinations. The study of such combinations allowed intraspecific morphs to be recognized, and available Arcticoceras species to be revised. During the Early and Middle Bathonian, the family Cardioceratidae evolved through a series of paedomorphosis, and after the appearance of Cadoceratinae, through accelerations.     

The distribution and molecular diversity of the Eastern Atlantic and Mediterranean chthamalids (Crustacea, Cirripedia)

The three chthamalids Chthamalus stellatus , C. montagui and Euraphia depressa are common inhabitants of the intertidal zone in the Eastern Atlantic, Mediterranean Sea and Black Sea. In this study, we investigated the occurrence of these barnacles in a wide range of their distribution. Population divergences of these two species have been inferred using three molecular markers — internal transcribed spacer (ITS), elongation factor 1α (EF-1α) and cytochrome oxidase subunit I (COI). ITS sequences of C. stellatus were identical throughout the species range, whereas ITS sequences of C. montagui indicated that the Black Sea and Mediterranean populations are isolated from the Atlantic population. The COI and EF-1α sequences were the most variable and informative. They indicated a high genetic divergence between Atlantic, Mediterranean and Black Sea populations for C. montagui . In addition significant genetic structure was found among the populations of C. stellatus based on EF-1α but not COI. Interestingly, our molecular dating analysis correlated the pattern of diversification in C. montagui to major geological changes that occurred in the Mediterranean during the end of the Messinian and Pleiocene periods. We suggest that palaeohistory shaped the divergences between Chthamalus populations that have probably been maintained by current hydrographic conditions. Finally, COI phylogenetic analysis placed the genus Euraphia within the Chthamalus clade, suggesting the need for a taxonomic revision of Euraphia . This study represents the most detailed phylogeographical analysis of intertidal Mediterranean species to date, and shows that geological events have strongly shaped the current diversity pattern of this fauna.     

Phylogeny and evolution of life history strategies of the parasitic barnacles (Crustacea, Cirripedia, Rhizocephala)

The barnacles (Crustacea, Cirripedia) consist of three well-defined orders: the conventional filter-feeding barnacles (Thoracica), the burrowing barnacles (Acrothoracica), and the parasitic barnacles (Rhizocephala). Thoracica and Acrothoracica feed by catching food particles from the surrounding seawater using their thoracic appendages while members of Rhizocephala are exclusively parasitic. The parasite consists of a sac-shaped, external reproductive organ situated on the abdomen of its crustacean host and a nutrient-absorbing root system embedded into the heamolymph of the host. In order to resolve the phylogenetic relationship of the order Rhizocephala and elucidate the evolution of the different life history strategies found within the Rhizocephala, we have performed the first comprehensive phylogenetic analysis of the group. Our results indicate that Rhizocephala is monophyletic with a filter-feeding barnacle-like ancestor. The host-infective stage, the kentrogon larva, inserted in the lifecycle of the rhizocephalan suborder, Kentrogonida, is shown to be ancestral and most likely a homologue of the juvenile stage of a conventional thoracican barnacle. The mode of host inoculation found in the suborder Akentrogonida, where the last pelagic larval stage directly injects the parasitic material into the heamolymph of the host is derived, and has evolved only once within the Rhizocephala. Lastly, our results show that the ancestral host for extant rhizocephalans appears to be the anomuran crustaceans (Anomura), which includes hermit crabs and squat lobsters.     

Biodiversity and Biogeography of Chthamalid Barnacles from the North-Eastern Pacific (Crustacea Cirripedia)

The biogeography and ecology of the species of Chthamalus present on the west coast of America are described, using data from 51 localities from Alaska to Panama, together with their zonation on the shore with respect to that of other barnacles. The species present were C. dalli, Pilsbry 1916, C. fissus, Darwin, 1854, C. anisopoma Pilsbry 1916 and four species in the C. panamensis complex. The latter are C. panamensis Pilsbry, 1916, C. hedgecocki, Pitombo & Burton, 2007, C. alani nom. nov. (formerly C. southwardorum Pitombo & Burton, 2007) and C. newmani sp. nov.). These four species were initially separated by enzyme electrophoresis. They could only be partially separated by DNA bar coding but may be separated using morphological characters.     

Immunocytochemical studies on the naupliar nervous system of Balanus improvisus (Crustacea, Cirripedia, Thecostraca)

The nervous system of nauplii of the crustacean taxon Cirripedia was analysed in the species Balanus improvisus Darwin, 1854 using for the first time immunocytochemical staining against serotonin, RFamide and α-tubulin in combination with confocal laser scanning microscopy. This approach revealed a circumoesophageal neuropil ring with nerves extending to the first and second antennae and to the mandibles, all features typical for Crustacea. In addition, RFamidergic structures are present in the region of the thoraco-abdomen. A pair of posterior nerves and a pair of lateral nerves run in anterior-posterior direction and are connected by a thoracic nerve ring and a more posteriorly situated commissure. A median nerve is situated along the ventral side of the thoraco-abdomen. The innervation of frontolateral horns and the frontal filaments are α-tubulin-positive. Several pairs of large neurons in the protocerebrum, along the circumoesophageal connectives and in the mandibular ganglion stain only for serotonin. Due to the almost complete absence of comparable data on the neuroanatomy of early (naupliar) stages in other Crustacea, we include immunocytochemical data on the larvae of the branchiopod, Artemia franciscana Kellogg, 1906 in our analysis. We describe several characteristic neurons in the brains of the nauplius larvae of both species which are also found in decapod larvae and in adult brains of other crustaceans. Furthermore, our data reveal that the naupliar brain of cirripedes is more complex than the adult brain. It is concluded that this ontogenetic brain reduction is related to the sessile life style of adult Cirripedia.     

Synaptonemal polycomplexes in spermatocytes of the gooseneck barnacle,Pollicipes polymerus Sowerby (Crustacea: Cirripedia)

Polycomplexes are described for the first time in spermatocytes of a cirripede crustacean, Pollicipes polymerus Sowerby. Synaptonemal complexes of regular tripartite construction are seen from zygotene to mid-pachytene. Although some of the synaptonemal complexes are disrupted at late pachytene and may degenerate at this stage, some persist and by diplotene may form polycomplexes by the bending and self-fusion of their lateral elements. These polycomplexes are still encompassed by chromosomes and consist of four dense plates and intercalated central elements and transverse fibers. Other polycomplexes with five or six dense plates, all of which are considerably wider than lateral elements of mid-pachytene synaptonemal complexes, are also seen in diplotene nuclei. These may be attached to a chromosome at only one end or may be in the nucleoplasm, free of chromosomal involvement except for fine fibrous connectives. No polycomplexes are seen in meiotic cells after diplotene and their fate is unknown. It is suggested that poly-complexes serve as sequestra for synaptonemal material which could prevent normal chromosomal disjunction.     

Energy budget for the larval development ofElminius modestus (Crustacea: Cirripedia)

Biomass (CHN), respiration rate and food uptake were estimated for the larval development ofElminius modestus at three temperatures (12, 18, 24°C). Mean values of dry weight, elemental composition and energy equivalents increased exponentially with the development from nauplius II to VI. Dry weight, elemental composition and energy content exhibited the highest values at 18°C. Respiration rates increased with the larval stages expressed by a power function, but increased logarithmically with the dry weight of the larvae. The cypris larvae showed a reduced respiration rate compared with nauplius VI. The ingestion rate was measured at a concentration of 100 cells ofSkeletonema costatum μl⁻¹. At 12 and 18°C ingestion rates increased exponentially and at 24°C by a logarithmic function. The fittings were used to estimate the energy budget ofE. modestus during larval development. The energy content of the larvae increased during the development from nauplius II to VI by a factor of 21 at 12°C, 25 at 24°C and 31 at 18°C. The estimated energy content of the freshly metamorphosed barnacle is 100 mJ (12°C), 130 mJ (24°C) and 150 mJ (18°C). The assimilation- (A/I) and gross growth efficiencies (K₁) increased strongly during the development from nauplius II to VI (A/I: 6–14% in nauplius II to 50–90% in nauplius VI; K₁: 4% in nauplius II to 75% in nauplius VI). The net growth efficiency (K₂) showed a relatively constant level ranging between 57 and 83%.     

Comparative SEM Studies of Lattice Organs: Putative Sensory Structures on the Carapace of Larvae from Ascothoracida and Cirripedia (Crustacea Maxillopoda Thecostraca)

Putative sensory structures, called lattice organs, were studied with scanning electron microscopy from ascothoracid or cypris larvae representing a wide range of families of the Ascothoracida and Cirripedia. These organs, situated dorsally on the carapace were, with few exceptions, always found in two anterior and three posterior pairs. The lattice organ morphology displayed by the Ascothoracida, a seta–like structure with a terminal pore, is believed to be the most plesiomorphic condition. Within the Cirripedia lattice organ morphology varied from types resembling the Ascothoracida in the Acrothoracica and the lepadomorph Capitulum mitella, to an elongate pore field with a larger terminal pore in most Thoracica and Rhizocephala. Akentrogonid Rhizocephala seem to display the most apomorphic condition. While lattice organ morphology was generally constant at the family level, cases were seen where closely related species such as Chthamalus stellatusand Chthamalus montaguishowed minor, but clear cut differences. Lattice organs in 2 + 3 pairs are argued to represent a synapomorphy for the Ascothoracida and the Cirripedia. The results confirm that the cyprid morphology at the ultrastructural level will prove to be of high value in estimating phylogeny within the Cirripedia.     

Reproductive Stage of the Life Cycle in the Rhizocephalan Barnacle Polyascus polygenea (Crustacea: Cirripedia)

The specific features of the reproductive stage of the life cycle have been studied in the rhizocephalan barnacle Polyascus polygenea, a parasite of the coastal crab Hemigrapsus sanguineus. It is shown that a single crab can bear 1 to 8 externae of P. polygenea. The fecundity of the parasite depends on the size of the externae and their number on the host and may reach as much as 50000 eggs for one externa. In Peter the Great Bay, Sea of Japan, this species repeatedly reproduces during the entire spring–autumn period; externae with developing embryos in the mantle cavity occur from May to September, and planktonic larvae occur from June to October. One externa produces during the season of reproduction no less than three generations of larvae. Thus, the reproductive strategy in P. polygenea comprises a three-stage cascade of reproduction: asexual reproduction via budding of the interna; the development of several generations of one or several externae; and several reproduction cycles of each externa. This allows the parasite to produce a very great number of larvae and ensures the parasitization of a significant proportion of the host crab population. The structure of the ovaries and oogenesis in rhizocephalans and free-living cirripede barnacles have many common features, which provides evidence for integration of these two groups within one monophyletic taxon.     

The fine structure of the frontal filament complex of barnacle larvae (Crustacea: Cirripedia)

Cell and Tissue Research - The frontal filaments comprise two regions, the internal vesicles and the external filaments. Dendrites of extra-optic protocerebral origin pass ventrally from the brain,...     

Three new Verrucidae (Crustacea: Cirripedia) from the Upper Eocene of the Euganean Hills (Northeast Italy)

Marls with pillow lavas of Late Eocene age from Castelnuovo in the Euganean Hills (Padua, NE Italy) have yielded three new verrucid cirripede species, Verruca veneta nov. sp., Costatoverruca? seguenzai nov. sp., and Metaverruca euganea nov. sp. The stratigraphic distribution of these taxa is discussed in light of previous verrucid records and their geologic context is established. They represent the oldest known verrucids from Italy.     

External morphology of the burrowing barnacle shape Lithoglyptes bicornis (Crustacea: Cirripedia: Acrothoracica)

The external morphology of female and male Lithoglyptes bicornis was examined under SEM. The structure of the mantle, the thorax and, especially, the trophi were thoroughly examined. The data on the mantle and the thorax structures were compared with the previous data on the acrothoracican ultrastructure. The data on the structure and the character of trophi setation allow to speculate about a relationship with other cirripede taxa.     

The complete mitochondrial genome of Pollicipes mitella (Crustacea, Maxillopoda, Cirripedia): non-monophylies of maxillopoda and crustacea

The whole mitochondrial genome (14,915 nt) of Pollicipes mitella (Crustacea, Maxillopoda, Cirripedia, Thoracica) was sequenced and characterized. It is the shortest of the 31 completely sequenced crustacean mitochondrial genomes, with the exception of a copepod Tigriopus japonicus (14,628 nt). It consists of the usual 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes, and 1 relatively short non-coding region (294 nt). The thoracican cirripeds apart from Megabalanus volcano have the same arrangement of protein-coding genes as Limulus polypemus, but there are frequent tRNA gene translocations (at least 8). Some interesting translocation features that may be specific to the thoracican cirriped lineage are as follows: 1) trnK-trnQ lies between the control region and trnI, 2) trnA-trnE lies between trnN and trnS1, 3) trnP lies between ND4L and trnT, and 4) trnY-trnC lies between trnS2 and ND1. In P. mitella there are two trnL genes (L1 and L2) in the typical crustacean positions (ND1-L1-LrRNA and CO1-L2-CO2). The present result is compared and discussed with the other three cirriped mitochondrial genomes from one pedunculate (Pollicipes polymerus) and two sessiles (Tetraclita japonica and M. volcano) published so far. Mitochondrial protein phylogenies reconstructed by the BI and ML algorithms show that the thoracican Cirripedia is monophyletic (BPP 100/BP 100) and associated with Remipedia (BPP 98/BP 35). In addition, Oligostraca, including Ostracoda, Branchiura, and Pentastomida, is a monophyletic group (BPP 99/BP 68), and is basal to all the other examined arthropods. Remipedia + Cirripedia appears as an independent lineage within Arthropoda, apart from Thoracopoda (Malacostraca, Branchiopda, and Cephalocarida). The Thoracopoda is paraphyletic to Hexapoda. The present result suggests that the monophylies of Crustacea and Maxillopoda should be reconsidered.     

A Study of the Morphology and Biology of Thompsonia littoralis (Crustacea: Cirripedia: Rhizocephala)

Interna development within the intertidal tropical crab, Leptodius exaratus, requires up to 4.5 months; the roots become distributed from the CNS along the major nerves and, when the crab moults, results in emergence of numerous externae located symmetrically on the abdomen and bases of the thoracic appendages. As many externae drop off, their number is continuously reduced; the survivors reach sexual maturity and ovulate after 2.5 months and complete embryonic development after 2 more months. At the next moult a new and more numerous generation of externae appears, and this is repeated until the crab dies. Presence of externae significantly prolongs the host's normal intermoult period and minimizes its growth. The parasite has little effect on the host's sexual characters although females are normally sterilized. The cuticle of the externa is moulted once, leaving a distinct annulus around the stalk. Spermatogonia are presumably injected by male cyprids into the female externa and develop into sperm within one or more vesicular spermatogenic bodies in its mantle. The eggs are laid through a single oviduct into the mantle cavity where they become fertilized and develop into cyprids that are liberated at the disintegration of the externa.     

The cypris larvae of the parasitic barnacle Heterosaccus lunatus (Crustacea, Cirripedia, Rhizocephala): some laboratory observations

Heterosaccus lunatus parasitizes the portunid crab, Charybdis callianassa in Moreton Bay, Australia. With the host crabs maintained at 22.5 degrees C this sacculinid rhizocephalan released larval broods every 6-7 days. During July-August 1996 and particularly August 1999 such broods showed the change-over from male only larvae in the early broods to females only in the later broods. As the host crabs were maintained under similar aquarium conditions in both years it is concluded that the light/dark cycle is the principal cue triggering this larval sex reversal. Oogenesis in the parasite externa is somehow controlled to produce two different sized ova - male larvae develop from large ova and females from small ova. A working hypothesis outlining how sex is probably determined for the larvae of sacculinids is erected. H. lunatus is considered the ideal sacculinid for the further experimental work necessary to verify the proposed sex-determining mechanism and its control processes. Measurements of the maximum swimming speeds of H. lunatus male and female cyprids showed the larger males to be the faster in absolute terms (27.95 compared with 17.60 mm s(-1), respectively), however, the calculated relative speeds were almost identical at approximately 90 body lengths s(-1). Settlement experiments confirmed that female H. lunatus cyprids settle only on the gills of C. callianassa; these cyprids needed to be at least 2 days old before they were able to settle.