Alona stochi n.sp. – the third cave-dwelling cladoceran (Crustacea: Cladocera) from the Dinaric region

Nemerteans (phylum Nemertea) have been viewed by mostzoologists as descended from, or closely related to,the flatworms. This view is based mainly on theirsupposedly acoelomate body. Their ancestry, however,is a point of controversy and there is evidence for acoelomate, protostomous origin. Notwithstanding thesedifferent views, most zoologists consider nemerteansto be phylogenetically distant from the chordates.Four authors (Hubrecht, Macfarlane, Jensen, Willmer),however, have postulated that nemerteans instead areclosely related to the chordates and that they sharea most recent common ancestor with the vertebrates. We argue that this view is based on a flawed view ofhomology and of seeing evolution as a series ofprogressions, which has no support in modernevolutionary thinking. Since there are nomorphological synapomorphies supporting aChordata-Nemertea clade, these authors instead guesswhat characteristics in extant nemerteans gave rise tocharacters observed in recent chordates. For example,they propose that the nemertean proboscis sheath hasevolved into the notochord. This is mere speculation,lacking testable propositions and is hence void ofinformation, and thus becomes futile in our view. However, the idea of a nemertean-vertebrate sisterrelationship as such is a testable hypotheses, and wetest it by applying the parsimony criterion to a setof morphological characters, and a set of molecular(the 18S rRNA gene) characters. Both tests reject thehypothesis.     

Laboratory observations on the feeding behavior and feeding rate of the nemertean Procephalothrix simulus

The feeding behavior of the nemertean Procephalothrix simulus and the effects of extrinsic factors on the feeding rates of this nemertean were experimentally studied. Procephalothrix simulus showed a typical macrophagous feeding strategy and consumed various food items. When capturing freshwater Tubifex sp., the nemerteans successfully ingested prey in all attacks, and they did not evert the proboscis in 25% of capture events. When capturing marine Saccocirrus gabrillae, the nemerteans failed to consume prey in more than half of the attacks, and they always everted the proboscis. There was a positive relationship between nemertean body weight and the rate of successful attacks, and a negative relationship between nemertean body weight and the duration of feeding events. The feeding rate of P. simulus increased when the temperature was raised from 5 degrees C to 30 degrees C but was significantly inhibited at 32 degrees C. Food intake was significantly reduced in media diluted to a practical salinity of 20 and 10 and in medium with the salinity elevated to 45. Dark conditions induced higher food intake, but prey density had no significant effect on feeding rate. These results suggest that P. simulus is a predator successfully adapted to the variable environmental conditions of the intertidal habitat.     

Food, Feeding Behavior and Feeding Ecology of Nemerteans

The feeding biology of nemerteans is reviewed, new informationis presented, and the role of nemerteans in natural communitiesis discussed and evaluated. Most nemerteans are carnivorous,the majority feeding on live, often specific, prey, while someare scavengers. Macrophagous feeding is found in the Palaeonemertea,Heteronemertea and some of the Hoplonemertea; the more specializedsuctorial feeding is limited to five of the hoplonemertean families,and suspension feeding (omnivorous diet) occurs only in thehighly specialized symbiotic monogeneric Bdellonemertea. Feeding adaptations seem to be related to the nature and employmentof the proboscis, the dilatability of the mouth, and the structureof the anterior part of the digestive tract. The transport ofdissolved organic materials from seawater has been demonstrated,but its role in nemertean nutrition is just being contemplated.Present meager information on predation has shown nemerteansto have actually and potentially large effects on prey populationsand thus on the communities in which they live. As the feedingbiology of only a relative handful of species has been studied,much basic comparative research is needed before we can corroborateor refute our present ideas concerning the ecological rolesof nemerteans.     

Morphology of the proboscis of Hubrechtella Juliae (nemertea,pilidiophora): Implications for pilidiophoran monophyly

The proboscis of Hubrechtella juliae was examined using transmission electron microscopy, scanning electron microscopy, and confocal laser scanning microscopy to reveal more features of basal pilidiophoran nemerteans for morphological and phylogenetic analysis. The proboscis glandular epithelium consists of sensory cells and four types of gland cells (granular, bacillary, mucoid, and pseudocnidae‐containing cells) that are not associated with any glandular systems; rod‐shaped pseudocnidae are 15–25 μm in length; the central cilium of the sensory cells is enclosed by two rings of microvilli. The nervous plexus lies in the basal part of glandular epithelium and includes 26–33 (11–12 in juvenile) irregularly anastomosing nerve trunks. The proboscis musculature includes four layers: endothelial circular, inner diagonal, longitudinal, and outer diagonal; inner and outer diagonal muscles consist of noncrossing fibers; in juvenile specimen, the proboscis longitudinal musculature is divided into 7–8 bands. The endothelium consists of apically situated support cells with rudimentary cilia and subapical myocytes. Unique features of Hubrechtella's proboscis include: acentric filaments of the pseudocnidae; absence of tonofilament‐containing support cells; two rings of microvilli around the central cilium of sensory cells; the occurrence of subendothelial diagonal muscles and the lack of an outer diagonal musculature (both states were known only in Baseodiscus species). The significance of these characters for nemertean taxonomy and phylogeny is discussed. The proboscis musculature in H. juliae and most heteronemerteans is bilaterally arranged, which can be considered a possible synapomorphy of Hubrechtellidae + Heteronemertea (= Pilidiophora). J. Morphol. 274:1397–1414, 2013. © 2013 Wiley Periodicals, Inc.     

Monoamine- and peptide-containing elements in the body wall and nervous trunks of nemerteans

Localization and morphological peculiarities of cateholamine-containing (CA-C), serotonin-(5HTIR), neurotensin-(NT-IR) and FMRFamide-immunoreactive (FMRFa-Ir) cells and processes in the body wall and lateral nervous trunks of nemerteans were investigated. The following nemertean species from three orders occurring in the White Sea were studied by fluorescent histochemistry and by immunohistochemistry: Lineus viridis, Lineus ruber and Cerebratulus sp. (Heteronemertini), Cephalothrix linearis (Palaeonemertini), and Amphiporus lactifloreus (Hoplonemertini). The similarity and characteristics of morphological types of monoamine-and peptide-containing elements, their distribution and possible participation in regulation of some functions in different nemertean species and in other invertebrates are discussed. We suggest that 5HT-IR and CA-C bi-and multipolar intra-and subepidermal open-type cells prevailing in the body wall perform a receptive function, while the FMRFa-Ir and NT-IR neurons of the nerve trunks and body wall are responsible for efferent innervation of musculature and connections within the nervous system.     

Nemerteans of the genus <Emphasis Type="Italic">Ototyphlonemertes</Emphasis> (Enopla: Ototyphlonemertidae) from Van Phong Bay (South Vietnam)

Two species of the interstitial nemerteans from the intertidal zone of Van Phong Bay (southern Vietnam) are described. By the structure of the proboscis and statocysts, the nemertean Ototyphlonemertes ani sp. n. can be referred to the species group “Lactea” (sensu Envall, Norenburg, 2001), but it differs from other species of this group by the presence of cerebral organs and caudal cirri. The second species new for the region is very similar to O. martynovi, but differs from it in having 2 to 3 cephalic cirri in group C (instead of 4 to 6 cirri found in O. martynovi).     

Cephalic region damage in the nemertean Lineus ruber by the orthonectid Intoshia linei

Previous investigators believed, that the plasmodia of Intoshia linei can affect all part of nemerteans body except the cephalic lobe. Our results indicate that in strongly infected worms mature plasmodia can settle inside of the cephalic region and form the large conglomerates. Common places of plasmodia localization in hosts are not only the tegument, connective tissue, gonads, muscles of body wall and proboscis, but also the nervous tissue. We found a lot of the mature plasmodia in all four lobes of the nemerteans brain and in the lateral nerve trunks. Furthermore the plasmodia can settle in the cerebral organs, in the walls of blood lacunae and rhynchcoel. In spite of the strong invasion of the cephalic lobe we have never observed a plasmodial outgrowths in the tegument of this region. This phenomena can be explained by the assumption, that plasmodia usually intrude into the cephalic region relatively late and have no time to form outgrowths up to the moment when starts the emission of adult males and females in the rest parts of nemertean body. Moreover, single parasite cells were repeatedly found in the host tissue near the mature plasmodium. These cells had few cytoplasm and large vesicular nuclei, which were very similar in size to the nuclei of the host cells. General morphology of single cells was very similar to the generative cells of the plasmodium. At present, the function of these cells is not evident, but we believe, they appearance is concerned with the proliferation of plasmodiuma and agglomeration of the parasite in the body of Lineus ruber.     

Zur Nahrungsaufnahme vonTetrastemma melanocephalum (Nemertini)

The proboscis of hoplonemerteans is armed with a stylet apparatus, which is used for capturing prey.Tetrastemma melanocephalum (Johnston) is a common hoplonemertean in the littoral of the Baltic Sea and the North Sea. It lives in the phytal and on sand- and mudflats and occurs in large numbers in theCorophium belts in the waddenseas.T. melanocephalum feeds on arthropods, mainly on copepods and amphipods. The prey is caught with the proboscis, penetrated by the stylet and grows weak (reduction of movements) within a few seconds; it is then sucked out. During the summer, a 15–35 mm long nemertean captures about 3 specimens ofCorophium volutator of 3.5–6 mm length per day. In theCorophium belt at Sahlenburg, German Bight, North Sea, 29 nemerteans/0.25m² were found; they feed mainly onC. volutator, so that on average more than 10 000 specimens ofC. volutator/m²/month are sucked out by these nemerteans. Hence,T. melanocephalum is an important consumer ofCorophium.     

Ecological studies of the nemertean fauna in an estuarine system of the northwestern Gulf of Mexico

The distribution and abundance of nemerteans in the brackish-water lakes of Sea Rim State Park, Texas, near the Louisiana border, were studied and compared with other macrobenthos during one year. Six of 93 macrobenthic species collected were nemerteans (0.9% of the total number of specimens). Only one species of nemertean, Carinoma sp., was consistently present. This species is the most ubiquitous and, probably, the most abundant nemertean in the estuarine systems of the Texas coast. Carinoma sp. was collected at Sea Rim from a salinity range of 0–21 ppt and at other Texas estuaries from 2–26 ppt. Preliminary experiments with Carinoma sp. as predator and as prey indicated that it feeds on polychaete worms and in turn is fed upon by white (Penaeus setiferus) and brown (P. aztecus) shrimp.     

Food and feeding behavior of the hoplonemertean Oerstedia dorsalis

The monostiliferous nemertean Oerstedia dorsalis was collected from eelgrass (Zostera marina) beds located along the coast of New Jersey, and feeding responses to amphipods and isopods were observed in the laboratory. Tests with 46 worms showed that they fed suctorially on Ampelisca vadorum, Ampithoe longimana, Corophium acherusicum and C. tuberculata. Corophiids were preferred. Upon contact with an amphipod, the proboscis is everted and strikes the prey on the ventral side, immobilizing it in a few minutes. The worm probes the sternal region with its head and everts its proboscis one or more times during the process. The exoskeleton is eventually penetrated by the head, and the stomach is everted into the hemocoel as a flattened funnel-like structure. Peristaltic undulations of the body signify the suctorial action that removes the living contents from the exoskeleton. The actual feeding process (from head penetration to removal of the head) takes about 7 min. O. dorsalis is only the third species within the Prosorhochmidae for which the feeding behavior has been documented. The other two are terrestrial species, and are also suctorial.     

Temporal variation in abundance of the egg predator Carcinonemertes epialti (Nemertea) and its effect on egg mortality of its host,the shore crab,Hemigrapsus oregonensis

An outbreak of the nemertean, Carcinonemertes epialti, was observed on Hemigrapsus oregonensis during October, 1982 at Campbell Cove, Bodega Harbor, California. Mean worm intensity (296 worms/crab) was the highest recorded for this nemertean egg predator on H. oregonensis. During the outbreak, male crabs were found to harbor more worms than both non-ovigerous and ovigerous females. Crab egg mortality was substantial; 83% of the ovigerous females experienced 75–100% brood mortality. The seasonal peak in worm abundance coincided with the seasonal low in crab reproduction at this locality. A method for estimating the impact of C. epialti on H. oregonensis natality was developed using crab size and fecundity, and worm prevalence and intensity. For a non-outbreak sampling period, a mean of 5.6% egg mortality was experienced by infested crabs for the period selected. Thus, brood mortality during the outbreak was much greater than that experienced at non-outbreak periods. Heavy fishing pressure on some commercially important crab species has been suggested as a possible factor inducing worm outbreaks and facilitating their continued persistence. These observations suggest that fisheries are not necessarily responsible for the outbreaks of nemerteans on commercially important crab species. However, fishing pressure may still be a sufficient condition to promote nemertean outbreaks.     

Morphology and evolution of the nervous system in Gnathostomulida (Gnathifera,Spiralia)

Within Spiralia, Gnathifera may represent the deepest branching lineage comprising the jaw worms Gnathostomulida and their sister group Micrognathozoa + Syndermata. Yet, very few nervous system studies have been conducted on this lineage of microscopic, jaw-bearing worms, limiting our understanding of the evolution of this organ system in Spiralia. The nervous system of representatives from all major groups of Gnathostomulida was here mapped using confocal laser scanning microscopy and immunohistochemistry. Their intra-epidermal, unsegmented nervous systems comprise an anterior brain and three to five ventral and two to four dorsal longitudinal nerves, connected by few transverse commissures. Neurites of the stomatogastric nervous system were found lining the pharynx and connecting to a prominent buccal ganglion. Supposedly, sensory ciliated cells in the pharynx and the gut were documented for the first time. Based on these morphological results, primary homologies of neural structures in Gnathostomulida and other Gnathifera were hypothesized and thereafter tested using parsimony. This first neurophylogeny of Gnathostomulida resulted in a topology congruent with molecular data, supporting the monophyly of Bursovaginoidea, Conophoralia, and Scleroperalia. From this topology, the evolution of the gnathostomulid nervous system was reconstructed. It suggests a specialization and diversification of cords and serotonin-like immunoreactive cell patterns from a plesiomorphic neuroarchitecture of three unsegmented nerve cords and a compact anterior brain and buccal ganglion. These plesiomorphic states resemble the nervous system of Micrognathozoa, and possibly the ancestral states of Spiralia.     

NEMERTINES AS POSSIBLE ANCESTORS OF THE VERTEBRATES

1. Primitive vertebrates have many characters which do not appear to be immediately represented in any obvious precursor. 2. The hypothesis is put forward that creeping, or bottom-living worms, classifiable as nemertines, attempted to recolonize the water by acquiring buoyancy, by swimming or both. 3. Some of those that succeeded were able to do so by adopting a method of filter-feeding made adequate by the development of gill slits, and then converting the proboscis rudiment into a semi-rigid structure (the notochord) essential for oscillatory swimming movements. These were the precursors of the protochordates and the vertebrates. 4. The acquisition of the ability to swim efficiently depended on the simultaneous development of distance receptors and the co-ordination of the information that they provided with that provided by proprioceptors on the one hand and with the changing motor systems on the other. This entailed the development of a far more extensive nervous system, probably by incorporating into it much more of the dorsal ectoderm, and superimposing a primarily sensori-motor system on to the more vegetative system already present in nemertines. This was achieved by elaboration of the placodal folding of the ectoderm which is characteristic of many nemertine embryos of the present day. In this manner a new central nervous system was combined and integrated with the existing more primitive ‘autonomic’ system and the cephalic ganglia of the nemertines became incorporated in the hypothalamus. 5. The hypothesis suggests likely precursor tissues from which the following vertebrate structures could plausibly have developed: olfactory organ, lateral line system, anterior and posterior pituitary, thyroid, pineal organ, chloride-secreting cells, oxyntic cells, notochord, urinogenital system, liver, and several others. 6. The possible origins of the vertebrate eye, the somitic muscles, and some other fundamental features of the vertebrates are discussed. The evidence is still equivocal. 7. The acquisition of filter-feeding and swimming by nemertine worms would be expected to bring into operation a whole new system for the selection of appropriate genes and thus inaugurate a period of very rapid and probably divergent evolution, made even more rapid by the enormous advantages gained by animals acquiring efficient form-vision together with rapid and well co-ordinated movements. It is thought likely that the rapid evolution of this group of animals, which possessed few features conducive to clear fossil remains, accounts for the apparent break in the continuity of the story of animal evolution which has until now made the origin of the vertebrates such an enigma. 8. It is suggested that studies of the proteins and secretions of the various organs of the nemertines and their comparison with those of the organs of the more primitive vertebrates might lead to the establishment of some important homologies.     

A new species of Tetrastemma (Nemertea: Enopla: Monostiliferoidea) from Ria de Foz, north-western Spain, found living in the mantle cavity of the bivalve mollusc Scrobicularia plana

A new species of monostiliferoidean nemertean, Tetrastemmafozensis , from the mantle cavity of the bivalve mollusc Scrobicularia plana , in the Ría de Foz, north-western Spain, is described and illustrated. Other nemerteans from the mantle cavity of Scrobicularia collected in Poole Harbour, southern England, are provisionally identified as conspecific with the Ria de Foz material, but show certain anatomical differences whose taxonomic significance cannot at present be assessed.     

Aspects of the biology of Pantinonemertes californiensis,a high intertidal nemertean

I studied the distribution, feeding biology, and reproductive biology of Pantinonemertes californiensis, described as a semi-terrestrial nemertean, along the central California coast. At the sites used in this study, maximal tidal height is about 2 m, and P. californiensis typically occurred under boulders between 1.3 and 1.7 m tidal height. Worms fed primarily on the semi-terrestrial amphipod Traskorchestia traskiana. Distribution of nemerteans was similar to that of the prey, although prey extended higher on the beach than did the worms. Nemerteans were largest and most abundant at the site with highest abundance of T. traskiana and smallest and least abundant at the lowest prey abundance site. In laboratory feeding trials, nemerteans from the site with lowest prey abundance fed most readily. Non-reproductive nemerteans lived for at least a week when submerged in sea water; some prey died within a week of being submerged. Nemerteans only lived minutes when submerged in fresh water; 50% of prey lived 4.5 h. Eggs are approximately 90–100 μm in diameter and hundreds to thousands are shed per female. Larvae are planktonic and apparently planktotrophic, and are morphologically similar to other marine hoplonemertean larvae. At the sites studied life history characteristics of P. californiensis provided little evidence of adaptations to terrestrial life in these worms and were not helpful in elucidating the role of semi-terrestrial nemerteans in the evolution of terrestrial nemerteans.     

S.E.M. and polarization microscopy of nemertean stylets

The ultrastructure of the stylets produced by nine species of nemerteans has been examined by scanning electron microscopy (S.E.M.) and polarized light microscopy. Stylets are solid, nail-shaped structures that typically reach lengths of 50–200 μm. Each stylet is composed of a centrally located organic matrix surrounded by an inorganic cortex that contains calcium and phosphorus. When viewed at high magnifications, fine granules can be seen throughout the organic matrix, and the cortex appears to be composed of densely packed homo-geneous material. Fractured specimens and whole matrices isolated from decalcified stylets reveal a close correspondence between the shape of the organic matrix and that of the surrounding cortex. This similarity in morphology suggests that the organic matrix serves as a template during calcification of the stylet. The fact that abundant material can be seen in the core of incinerated stylets, and in the central region of stylets that had been soaked for several hours in sodium hypochlorite, supports the hypothesis that the organic matrix is also highly calcified. Polarization microscopy of nemertean stylets indicates that they are composed of a crystalline, rather than amorphous, form of calcium phosphate. The probable organization of the calcium phosphate crystals is discussed.