The mouthparts of the members of the Jaera albifrons group of species (Crustacea: Isopoda)

The mouthparts of Jaera albifrons Leach, Jaera ischiosetosa Forsman, Jaera praehirsuta Forsman and Jaera forsmani Bocquet were examined with the light microscope and the Stereoscan electron microscope, and were found to be identical in all species. The structure of the mouthparts indicate that all four species feed by scouring and abrading algal or bacterial films from rocks or Fucus. Food, therefore, does not seem to be an isolating factor involved in the microdistribution of the four species on a shore.     

Population dynamics and reproductive biology of the commensal isopod Colidotea rostrata (Crustacea: Isopoda: Idoteidae)

Colidotea rostrata (Benedict, 1898) is the only known commensal idoteid isopod, living on and mimicking the color of two northeastern Pacific sea urchins of the genus Strongylocentrotus. The population dynamics and reproductive biology of C. rostrata on its host urchins were studied at a low rocky intertidal area in southern California (33°40N; 118°30W) from December 1984 to December 1986. Isopod populations remained relatively stable throughout the 2 yr study, with isopods inhabiting an average of 56.1% of the urchins at 6.1±0.6 (x±2 SE) isopods per urchin. Female isopods reach sexual maturity at a length of 6.8 mm. Fecundity in C. rostrata averaged 11.8±0.9 (x±2 SE) embryos per brood, and increased with female body size. Breeding occurs all year long in C. rostrata, with a main reproductive period between the warmer spring and summer months. Newly released mancas and juvenile isopods were present during all months of the study. C. rostrata differs from the free-living Idoteidae in its smaller maximum size, reduced fecundity, 1:1 sex ratio, and low juvenile mortality. These features may represent adaptations to a commensal life style that reflect a reduced mortality pressure on these isopods.     

Mating system of the commensal marine isopod Jaera hopeana (Crustacea)

The commensal marine isopod Jaera hopeana Costa, 1853 was reared in the laboratory through 30 generations in the absence of its host, Sphaeroma serratum, to study its development and reproductive behaviour. It was found that adult males take virtually any opportunity to associate with a young conspecific in manca-I stage (first free-living stage) and carry it around in a characteristic position. This male-manca(I) amplexus ends during the manca's first postmarsupial molt (manca-I to manca-II) at an average age of about 9 d after hatching from the marsupium. Entry into amplexus does not alter a manca's molt timing, the duration of the amplexus thus depending exclusively on the manca's age when it joined by a male. Given a choice, males do not prefer manca-I close to molting over those just hatched. With the first postmarsupial molt, long before sexual maturity, female J. hopeana become receptive to mating. Before a female manca is released from amplexus, it is inseminated by its male partner. Sperm transferred to young immature females are stored within special sperm stores until they are needed for fertilization. The male-manca(I) amplexus seems to be a precopula, wherein males wait for their partners to molt and become sexually receptive. Nevertheless, it is inevitable that every second amplexus on average ends unsuccessfully: although manca-I have already been determined irreversibly (and probably genetically) as males and females in equal numbers, adult males are unable to predict which manca-I are potential mates and which are not. Males accept any manca-I as a precopula partner, and even when given a choice they do not prefer female over male manca-I. From the manca-II stage onward, females are continuously receptive to mating for the rest of their life, and mating can occur immediately upon contact of the partners without any significant investment in energy and time (en passant copulation).     

Comparative fecundity and reproductive strategies in seventeen species of the Cumacea (Crustacea: Peracarida)

The fecundity of 17 species of cumaceans belonging to 5 families from the eastern and western temperate regions of the Atlantic and the Canadian Arctic and Subarctic Oceans are discussed separately and then compared. The species range from 0.78 to 10.11 mm (mean carapace length) with fecundities ranging from 15.1 to 168.9 (mean number of eggs brood^-1 female^-1). Interspecific comparisons show that carapace volume versus volume of brood yields a very strong relationship (r=0.99). Therefore, it is a combination of carapace volume plus egg volume which determines the fecundity in the Cumacea. A discussion of the various life-history and reproductive strategies employed by the Cumacea is included.     

Cellulose digestion and phenol oxidation in coastal isopods (Crustacea: Isopoda)

In order to test three hypotheses on digestive constraints that may have affected the colonization of land by isopods, two marine isopods and one semi-terrestrial species were screened for their ability to oxidize phenolic compounds and digest cellulose in natural and artificial diets. Ligia pallasii (Isopoda: Oniscidea) and Gnorimosphaeroma oregonense (Isopoda: Sphaeromatidea) oxidized dietary phenolics, but Idotea wosnesenskii (Isopoda: Valvifera) did not, even though it feeds on seaweeds that are rich in phenolics. All three species were able to digest some cellulose, but this ability was least developed in the marine phytophagous species, Idotea wosnesenskii, and best developed in the semi-terrestrial L. pallasii. After reducing the number of endosymbiotic bacteria in the hepatopancreas (midgut digestive gland) by feeding antibiotics, cellulose digestion in L. pallasii was significantly reduced. Our results are consistent with the hypotheses that (1) the ability to oxidize phenolics is absent in phytophagous marine isopods, but present in saprophagous marine and semi-terrestrial species, (2) the ability to digest cellulose was an important pre-adaptation facilitating a fully terrestrial life-style in isopods, and (3) endosymbiotic bacteria in the hepatopancreas aid digestion in terrestrial isopods, and to a lesser degree in semi-terrestrial species, but not in marine isopods.     

Scanning electron microscope study of the modified spine characteristic for males of some Tisbe (Copepoda: Harpacticoida) species

The scanning electron microscope proved to be an ideal instrument for examining the species-specific spine (on the endopodite basal segment of male P2) in the group of sibling species Tisbe holothuriae, T. pontina and T. battagliai. Three other species: T. gracilis, T. cucumariae and T. biminiensis belonging to the gracilis group are included in the present study. A possible functional significance of the spine is discussed.     

Trophic diversity of idoteids (Crustacea, Isopoda) inhabiting the Posidonia oceanica litter

The coexistence of three idoteid species in Posidonia oceanica litter raises the question of trophic diversity and their role in the litter degradation process. Hence, diet composition of Idotea balthica, Idotea hectica and Cleantis prismatica was studied using a combination of gut contents and stable isotopes analysis. Gut content observations indicate that P. oceanica dead leaves are an important part of the ingested food for the three species, although their tissues are constituted of only a small to medium fraction of P. oceanica carbon. Our results also underlined the potential role of these species in the degradation of P. oceanica litter by mechanically fragmenting the litter and by assimilating a small to medium fraction of carbon. Moreover, we showed that there were considerable inter- and intra-specific differences in diet composition. Diet differed between juveniles and adults for I. balthica. Crustaceans are an important food source for adults of I. balthica, while I. hectica indicated a major contribution of algal material. C. prismatica showed an intermediate diet. This trophic diversity is probably one of the factors allowing these species to coexist in the same biotope.     

Symbiontic bacteria in the gut of the blood-sucking Antarctic fish parasite Gnathia calva (Crustacea: Isopoda)

Structure and ultrastructure of the digestive tract of the ectoparasitic stages of the Antarctic isopod Gnathia calva, collected in the Weddell Sea and around the Antarctic Peninsula in the 1984–1985 season, are briefly described. There are only two digestive glands, with an ultrastructure similar to that of other isopods. The gut is divided into six regions: oesophagus, stomach, dilatable reservior for sucked-in blood, sphincter, rectal vesicle with symbiontic bacteria, and rectum. The highly dilatable anterior hindgut (reservoir) takes part in the resorption of nutrients and stores lipids and glycogen. The rectal vesicle has an epithelium with all the features of an organ with high metabolism and the capacity for the transportation of small molecules. The surface is increased by irregular microvilli. A very thin intima and a basal labyrinth are present. The presence of symbiontic bacteria is discussed in correlation with the haematophagous nutrition of G. calva.     

Studies on digestion and the fine structure of digestive caeca in Eurydice pulchra (Crustacea: Isopoda)

In the carnivorous isopod Eurydice pulchra Leach the mid-gut caeca have a pH of 5.6 and produce a strong acid proteinase, a lipase and a carbohydrase. Electron microscope studies of the digestive caeca of starved and fed animals show that secretion is merocrine and may originate from a complex involving the basal cell membrane and associated mitochondria, producing lysosomes. Absorbed materials, in fed animals, appear to take the form of neutral lipid bodies, glycogen, and proteinaceous crystals, the latter forming within the golgi complex. Digestion of both lipid and protein inclusions was observed to occur intra-cellularly by fusion with free lysosomes. Secretion and absorption may occur in the same cell, and the scheme for the sequence of epithelial cell stages is proposed.     

Morphology of grooming limbs in species of Petrolisthes and Pachycheles (Crustacea: Decapoda: Anomura: Porcellanidae): a scanning electron microscopy study

The morphology of the grooming limbs, the 5th pair of pereiopods, was studied by scanning electron microscopy in six species of porcellanid crabs, Petrolisthes cabrilloi, P. cinctipes, P. armatus, P. galathinus, Pachycheles monilifer, and Pachycheles rudis, and their function was inferred by comparison with findings from previous studies. Grooming limb morphology was almost identical among the four Petrolisthes species and differed little compared to that of the two Pachycheles species. The 5th pereiopods bore a basal tuft of mechanoreceptive setae, three different types of grooming setae armed with setules or denticles, two types of smooth sensilla for location and identification of fouling objects, and a terminal, toothed chela for picking firmly attached objects off the gills and body. The grooming limb was extremely flexible and could reach most parts of the body, including the gill chamber on the opposite side. The grooming limb morphology in Petrolisthes cabrilloi is consistent with its wellknown effectiveness in preventing parasitism by the rhizocephalan Lernaeodiscus porcellanae. Grooming setae remove recently attached cyprids, while the chela can grip and remove the much smaller, firmly attached kentrogons. Porcellanid crabs not known to host rhizocephalans, however, had grooming limbs almost identical to those of Petrolisthes cabrilloi despite their previously demonstrated failure to prevent settlement and infestation by L. porcellanae larvae. The effectiveness of P. cabrilloi in removing kentrogons, therefore, seems also to depend on behavioral adaptations whereby this species recognizes the parasite larvae as high-threat objects.     

Hepatopancreatic endosymbionts in coastal isopods (Crustacea: Isopoda), and their contribution to digestion

Three isopod species (Crustacea: Isopoda), commonly found in the intertidal and supratidal zones of the North American Pacific coast, were studied with respect to symbiotic microbiota in their midgut glands (hepatopancreas). Ligia pallasii (Oniscidea: Ligiidae) contained high numbers of microbial symbionts in its hepatopancreatic caeca. Numbers of endosymbionts were strongly reduced by ingestion of antibiotics. By contrast, the hepatopancreas of Idotea wosnesenskii (Valvifera: Idoteidae) and Gnorimosphaeroma oregonense (Sphaeromatidea: Sphaeromatidae) did not contain any microbiota. Results of feeding experiments suggest that microbial endosymbionts contribute to digestive processes in L. pallasii, the most terrestrial of the three isopods that we studied. The acquisition of digestion-enhancing endosymbionts may have been an important evolutionary step allowing isopods to colonize terrestrial habitats where relatively indigestible leaf litter is the primary food source. By contrast, the ability to digest phenolic compounds was most developed in one of the more marine species, suggesting that this trait may have evolved independently in isopod species that consume a phenolic-rich diet, whether in marine habitats or on land. Received: 28 August 2000 / Accepted: 8 December 2000     

A light and electron microscope investigation of gametogenesis in Nicolea zostericola (Polychaeta: Terebellidae)

A light and electron microscope study was conducted on Nicolea zostericola (Oersted: Grube, 1860) to describe the processes of gametogenesis. N. zostericola is a monotelic species which spawns from 2 to 5 times over a period of 2 weeks at the end of its 1-year life span. The gonads consist of plates of cells bulging from beneath the peritoneum in the thoracic region of the body. Oogenesis has been divided into 3 phases: an ovarian phase in which gametogonia and primary oocytes are retained within the ovary, a follicular phase, in which oocytes are ovulated into the coelom surrounded by several layers of follicle cells and the vitellogenic phase, where individual oocytes rupture through the follicle cells and enter the coelomic fluid where cell growth and yolk synthesis occur. The combined ovarian and follicular phases have a duration of about 3 to 5 weeks and the vitellogenic phase about 5 to 6 months. Vitellogenesis is described on the ultrastructural level. Yolk synthesis involves the participation of the Golgi apparatus and endoplasmic reticulum of the oocyte in possible combination with nutrient absorption from the coelomic fluid. Spermatogenesis involves the rupturing of masses of spermatogonia into the coelom from the testis, surrounded by peritoneal cells. Smaller clusters of spermatocytes are later released into the coelomic fluid where mitotic and meiotic divisions eventually produce flattened plates of sperm. The mature spermatozoan possesses an elongate head, atypical for most polychaetes.     

Larval distribution and reproductive ecology of Thysanoessa macrura (Crustacea: Euphausiacea) in the Scotia Sea

In the Scotia Sea, the larvae of Thysanoessa macrura G.O. Sars, 1885 were scarce in spring (September 27 to October 6, 1971) and mainly present at the Calyptopis I stage, while in summer (December 17, 1974 to January 3, 1975) they were much more abundant and much further developed (up to Furcilia VI). The spawning season commences as early as September and, as indicated by the presence of numerous nauplii and metanauplii in summer, is rather long. T. macrura begins to spawn much earlier in West-Wind-Drift waters than in waters of the Weddell Sea. It starts to spawn simultaneously with Euphausia frigida and E. triacantha, but significantly earlier than E. superba. These timings of the breeding process are related to differential biogeographical characteristics of these species. Plankton collections made at depths of 500 or 1000 m have, for T. macrura, revealed a developmental ascent analogous to that of E. superba. Ontogenetical deep-water migrations are, consequently, characteristic not only for E. superba, but also for other Antarctic euphausiids (in particular E. frigida, but possibly not for inshore E. crystallorophias) and, as correctly postulated by several other investigators, for all oceanic euphausiid species.     

A scanning electron microscope study of the mandibular morphology of boreal copepods

Morphological details of the mandibular blades of 11 species of copepods were examined with scanning electron microscopy. The micrographs improved our understanding of the complex toothed edge of the mandibular blade, which in turn aids in identification of the copepod prey of chaetognaths by gut-content analysis. Beklemishev's discovery of siliceous tooth crowns in calanoid copepods was confirmed for most of the species examined. Long, sharp projections on the crowns of herbivorous species, and the deep grooves into which they fit on the teeth of the opposite mandible, suggest a cracking rather than a grinding function for these teeth.     

Orientation of Coenobita rugosus (Crustacea: Anomura): A field study on Aldabra

Experiments were designed to determine whether anemotaxis shown by the terrestrial hermit crab Coenobita rugosus H. Milne Edwards is (i) an orientational strategy leading the crabs to sea or (ii) a strategy improving rectilinear flight. In an arena with uniform landscape, hermit crabs from different beaches of the Aldabra atoll orientated during daylight in the direction of the sea of their own beach; this orientation was only slightly affected by wind direction. Under artificial wind conditions, at night, all hermit crabs displayed positive anemotaxis, independent of the orientation of the home beach, thus leaving little support for the first hypothesis. During the day, with the sea and beach both visible, all the hermit crabs on the beach moved landwards irrespective of wind and home beach direction.     

Scanning and transmission electron microscope study of specialized mantle structures in dorid nudibranchs (Gastropoda: Opisthobranchia: Anthobranchia)

Mantle surfaces of the dorid nudibranchs Rostanga arbutus and Jorunna sp. were examined using scanning and transmission electron microscopy, and two specialized structures are described. These are caryophyllidia and mantle rim organs; the latter being described for the first time. Caryophyllidia occur in large numbers (several thousand) uniformly distributed over the entire upper surface, while the mantle rim organs, numbering only 40 to 60, are restricted to the upper mantle margin. Caryophyllidia are minute (40 to 50 m diam), erect tubercles supported internally by 4 to 7, vertical, calcareous spicules which emerge in a crown surrounding an apical knob. Caryophyllidia display a high level of spicular organization and incorporate a complex muscle system at their base. The apical knob is formed from specialized epidermis capping a sub-epithelial ganglion. The highly organized structure of the caryophyllidium indicates its potential importance as a new character in dorid taxonomy and phylogeny. Mantle rim organs (80 to 300 m diam) contain large numbers of vacuolated cells and cells containing pellet-shaped nodules.     

A new species of Penaeus (Crustacea: Penaeidae) revealed by allozyme and cytochrome oxidase I analyses

 Penaeid shrimps comprise an important portion of the world's industrial fisheries and mariculture. In the Southwest Atlantic, Penaeus (Farfantepenaeus) subtilis, P. (F.) paulensis, P. (F.) brasiliensis and P. (Litopenaeus) schmitti are the most important commercially exploited species. Despite their high commercial value, there is little information available on the different aspects of their biology or genetics and almost no data on stock structure. Also, the taxonomic status of P. subtilis populations in relation to P. paulensis and their geographic ranges have been recently questioned. In this paper we used both nuclear (allozymes) and mitochondrial (cytochrome oxidase subunit 1) data to compare species of south-western Atlantic penaeids and to estimate their phylogenetic relationships. We could readily discriminate among the four main Brazilian penaeid species and detected a fifth, new, species of Penaeus. This new species corresponded to one of the described morphotypes of P. subtilis. Based on these analyses, the geographic ranges of P. subtilis and P. paulensis were clarified. Our data also support the conclusion of Baldwin et al. (1998) that the subgenus Farfantepenaeus is polyphyletic. Received: 6 January 2000 / Accepted: 13 June 2000     

Timing of copulation in the molting and reproductive cycles in a grapsid crab,Gaetice depressus (Crustacea: Brachyura)

From the seasonal changes in the amount of semen in the sperm ducts of males and in the fullness of spermatheca of females, the copulation season of Gaetice depressus in central Japan is considered to approximately coincide with the oviposition season, from March to October. The sperm ducts of all the large males examined contained semen, the amount of which did not vary obviously with stages of the molt cycle or with seasons. The genital apertures of females were normally covered with calcified immobile opercula in this species. The opercula decalcified after molting and again shortly before oviposition, and retained mobility for 1 to 3 d. Shortly after molting, soft-shelled females with mobile opercula did not have well-developed ovaries nor did they copulate with males even if they had a chance. In contrast, all of the hard-shelled females with mobile opercula had well-developed ovaries, and laid eggs within 2 d after the decalcification of opercula regardless of the occurrence of copulation. Laboratory experiments showed that the females normally copulated with males before oviposition. Crabs examined in this study were collected from Shirahama, Wakayama Prefecture, Japan between March 1988 and March 1989.