Morphology and dynamic behavior of anal pores during defecation in the ctenophore Pleurobrachia pileus

Defecation in the lobate ctenophore Mnemiopsis leidyi was recently shown to occur periodically with an ultradian rhythm through a single transient anal pore which suddenly appeared, expelled waste, and disappeared afterward. To discover whether this novel method of defecation occurs in other kinds of ctenophores, I examined individuals of Pleurobrachia pileus and Beroe cucumis. Both ctenophores were found to have two identical and permanent anal pores as described in the scientific literature and textbooks. In P. pileus, both anal pores commonly participated in a defecation, but they did so asynchronously with independent and irregular opening and closing kinetics. Individuals of P. pileus defecated with an ultradian rhythm. Closed anal pores in P. pileus and B. cucumis consisted of a continuous ectodermal epithelium overlying a continuous endodermal epithelium with a cup-shaped group of thickened endodermal cells bearing a tuft of cilia which beats into the anal cavity. The rims of opening or closing pores were smooth and uniform without encircling muscles or fibers. This morphology and the continuity of the epithelial layers between defecations suggest that anal pores may not operate by a contractile sphincter, but by a reversible ring of tissue fusion between apposed ectodermal and endodermal epithelia to create an adjustable hole to expel waste.     

Functional morphology of the developing alimentary canal in the holothurian Eupentacta fraudatrix (Holothuroidea, Dendrochirota)

Development of the digestive tract of the holothurian Eupentacta fraudatrix was examined using light and transmission electron microscopy. After the blastopore closes, the gut rudiment loses its connection with the blastoderm and becomes an enclosed, tubular chamber, ending blindly at both ends. The differentiation of the digestive and coelomic epithelia is mainly completed by day 12. Since no transient cell types are observed, this differentiation is definitive. By day 20, the mouth and anal openings appear. The cuticular lining in the anterior part of the gut rudiment has an endodermal origin and differentiates before the mouth is formed. The rest of the gut lining is composed of enterocytes typical of holothuroid intestine. At the early stages of development, mitotic figures are encountered among nonspecialized cells of the gut primordium. In more developed digestive epithelium, vesicular enterocytes are capable of mitotic division. Dividing enterocytes retain secretory vacuoles; thus mitosis occurs in actually differentiated cells. After mouth and anus formation, the oesophagus, stomach, intestine and rectum can be distinguished. In the wall of the stomach, powerful musculature is formed.     

Spreading and physico-biological reproduction limitations of the invasive American comb jelly Mnemiopsis leidyi in the Baltic Sea

Hydrodynamic drift modeling was used to investigate the potential dispersion of Mnemiopsis leidyi from the Bornholm Basin in the Baltic Sea where it has been observed since 2007 further to the east and north. In the brackish surface layer dispersion is mainly driven by wind, while within the halocline dispersion is mainly controlled by the baroclinic flow field and bottom topography. Model runs showed that the natural spreading via deep water currents from the Bornholm Basin towards north and east is limited by topographic features and low advection velocities. Based on the information on ranges of salinity and temperature, which limit survival and reproduction of this ctenophore within the Baltic Sea, areas have been identified where the American comb jelly, M. leidyi could potentially survive and reproduce. While, we could show that M. leidyi might survive in vast areas of the northern Baltic Sea its reproduction is prevented by low salinity (<10 psu) and temperature (<12°C). Thus, due to the combined effect of low salinity and temperature, it is not probable that M. leidyi could establish permanent populations in the central or northern Baltic Sea. However, it seems that in the southern parts of the Baltic Sea environmental conditions are suitable for a successful reproduction of M. leidyi.     

Seromucous anal gland in a New World hystricognath rodent Thrichomys apereoides (Lund, 1839)

New World species of the Hystricognathi comprise a group of rodents that exhibit poorly understood social behaviour. One such species, the echimyid Thrichomys apereoides, has a behavioural and social repertoire which suggests the use of its eversible anal gland in communication between individuals; however, no information on the morphology of this gland is available. In this study, the anal gland of nineteen adult individuals (11 males and 8 females) was analysed through histological and histochemical techniques. The gland was located in the submucosal of the anal region, cranial to the anus, and had an opening located dorsally in the rectum mucosa at approximately 1 mm from the anus. The gland was characterized as seromucous, secreting neutral glycoprotein. Not all individuals studied presented secretion in the glandular ducts, indicating a possible functional variation in the gland. This was the first record of an anal gland of the seromucous type in rodents.     

Potential pathways of invasion and dispersal of <Emphasis Type="Italic">Mnemiopsis leidyi</Emphasis> A. Agassiz 1865 in the Baltic Sea

The rapid spread of Mnemiopsis leidyi across the entire Baltic Sea after its first observation in 2006 gave rise to the question of its invasion pathway and the possible vector of its transport. To investigate pathways of M. leidyi invasion, the years 2005–2008 have been simulated by a three-dimensional coupled sea ice-ocean model of the Baltic Sea. In addition, a Lagrangian particle-tracking model has been utilized to test possible transport routes of this invader for 2006/2007. Based on the model, we exclude advection from the Kattegat as the main area of origin of M. leidyi and further spreading through the entire Baltic Sea. To explain the dispersion of M. leidyi in 2007 an earlier invasion already in 2005 is most probable. Alternatively, an invasion originating from main harbors with high ship traffic could also be a potential pathway. Drift simulations with drifter release in the main harbors are in good agreement with the observed distribution pattern of M. leidyi.     

Ultrastructure of the anal sacs in <Emphasis Type="Italic">Thalassema</Emphasis><Emphasis Type="Italic">thalassemum</Emphasis> (Annelida,Echiura)

The anal sacs of Thalassema thalassemum consist of an elongate tubular invagination (end sac) that is uniformly covered with numerous sessile ciliated funnels. While the funnels are composed of multi-ciliated, non-muscular cells and possess a ciliated neck-like constriction, the end sacs are lined by a simple epithelium of large, irregularly formed and sparsely ciliated cells that include masses of secretory granules. Podocytes are incorporated in the peritoneum that surrounds the anal sacs. A muscle grid consisting of inner longitudinal, outer circular and additional diagonal fibres that branch off of the circular fibres is embedded in the matrix between the end sac epithelium and peritoneum. Major structural differences between the hindgut and anal sacs support the hypothesis that the anal sacs are not gut derivatives but are instead part of a modified metanephridial system. Comparison of the anal sac morphology in Echiura reveals that T. thalassemum shares a tubular end sac with all known members of Thalassematinae and Ikedaidae, as well as with some members of Bonelliidae and Echiurinae, while the sessile funnels are apomorphic for the Thalassematinae.     

Comparing fish assemblages and trophic ecology of permanent and intermittent reaches in a Mediterranean stream

Mediterranean streams are characterised by seasonal droughts, the frequency and intensity of which vary spatially and are expected to increase with global change. We studied the potential effects of drought and climate change on the fish assemblage and its trophic ecology in a Mediterranean stream by comparing an intermittent tributary with two more permanent neighbouring reaches. Although the three sites were dominated by the same two fish species, Mediterranean barbel (Barbus meridionalis) and chub (Squalius laietanus), the intermittent tributary had a lower overall fish density and fewer eel (Anguilla anguilla). The intermittent tributary had macroinvertebrates with lower density, smaller taxa and higher diversity. Fish in the intermittent tributary had significantly lower biomasses in their gut contents (adjusted for fish length) and more negative electivities than those in the permanent reaches, as well as significantly lower taxonomic diversity. These results indicate that there was reduced resource availability in the intermittent tributary, which resulted in significantly lower condition and gonadal weight (adjusted for length) of barbel and chub. The data obtained in this Mediterranean stream support the observation that reduced water flow may affect fish at both individual and assemblage levels.     

Two new species and a new record of the genus Sinogastromyzon (Teleostei: Balitoridae) from Yunnan, China

Two new species and a new record of Sinogastromyzon are described from Lixianjiang River of Yunnan province, China. Sinogastromyzon lixianjiangensis, new species, can be distinguished from its congeners by the following characters: pectoral fin with XIII–XIV, 15–17 rays; pelvic fin with X–XI, 10–12 rays; 60–65 lateral-line scales; no scales on the dorsum of paired fins or the region between axilla of pectoral fin and pelvic-fin origin; tip of pelvic fin close to anus; tip of anal fin close to caudal-fin base; anal-fin origin nearer to the caudal-fin base than to the posterior pelvic-fin base; anus nearer to anal-fin origin than to the posterior pelvic-fin base; dorsal side of the body with 9–11 black blotches. Sinogastromyzon macrostoma, new species can be distinguished from its congeners by the following characters: pectoral fin with XII–XIV, 12–15 rays; pelvic fin with VII–IX, 11–13 rays; 48–56 lateral-line scales; mouth extremely big, slightly arched; no scales on the dorsum of paired fins or the region between axilla of pectoral fin and pelvic-fin origin; tip of pelvic fin far beyond anus; tip of anal fin far from caudal-fin base; anal-fin origin about midway between the posterior pelvic-fin base and caudal-fin base; anus nearer to posterior pelvic-fin base than to anal-fin origin; dorsal side of the body uniformly gray, without regular blotches in formalin preserved specimen. Sinogastromyzon cf. multiocellum is firstly recorded in China.     

Role of musculature during defecation in a particle‐feeding arachnid,Archegozetes longisetosus (Acari,Oribatida)

Most extant Chelicerata are characterized by external digestion and the ingestion of fluid food. Exceptions include the marine taxa, most Opiliones, and the mite groups Opilioacarida (Parasitiformes) and Sarcoptiformes (Acariformes), which ingest particulate food. This leads to different physiological and morphological adaptations for food processing, including the production and extrusion of solid fecal pellets, which are rather large in sarcoptiform mites. Few studies have investigated the defecation of such large fecal pellets, and available information is contradictory. We use a combination of non invasive microscopical techniques and in vivo examination to investigate the complex functional morphology of the anal region of the oribatid mite Archegozetes longisetosus Aoki. The opening of the anus is at least initiated by indirect muscular action via an increase of hemolymph pressure, through the action of dorsoventral muscles (dvm). Extrusion of the fecal pellet is accomplished by the prerectal muscle collar, with full opening of the anus and rotation and bowing of the plates probably resulting from pressure of the pellet. The sequential nature of these actions was demonstrated by many observations in which the anus opened only partially; these were concomitant with dmv contraction but pellets were not being extruded. All muscles directly connected to the anal and adanal regions assist in keeping the anus closed; they are antagonists to hydrostatic forces that are necessary for normal activity. Based on the literature, no obvious similarities were noted with defecation musculature in other particle‐feeding chelicerates, but most muscles can be homologized with those of more specialized oribatid mites. The function of the outer anal muscles has been modified in both Euphthiracaridae and Brachypylina to assist in providing general hemolymph pressure. J. Morphol., 2009. © 2008 Wiley‐Liss, Inc.     

龟足消化系统形态和组织学特点

应用光学显微镜观察龟足（Capitulum mitella）消化系统的形态和组织结构。龟足的消化系统包括消化腺和消化道。消化腺一对,呈长囊状,含有分泌细胞（B细胞）、吸收细胞（R细胞）、储存细胞（F细胞）和胚细胞（E细胞）4种类型细胞。消化道呈U型,由口、食道、胃、肠、直肠和肛门组成,各部分的结构由内到外可分为黏膜层、黏膜下层、肌层和外膜4层。口器为咀嚼型,包括一片上唇、一对触须、一对大颚以及两对小颚。食道细短,具几丁质层但无基膜,管壁向腔内突起形成明显的纵褶突;食道前段的环肌特别发达,同时独有放射肌。胃略呈球袋状,肠较长;胃和肠的组织结构相似,没有几丁质层,上皮细胞都有发达的微绒毛。直肠细长,外膜分布有16组纵肌;直肠前段的组织结构与胃、肠相似,而直肠后段有几丁质层覆盖,黏膜层、黏膜下层、肌层和外膜渐退化,16组纵肌渐发达。肛门16组更加发达的纵肌挤入上皮细胞下方,在外膜外另出现一层明显的环肌。龟足消化道各部分的组织结构差异明显,反映了它们功能的差异。     

Association between Hyperoche martinezii (Amphipoda: Hyperiidae) and ctenophores from the Buenos Aires coast,Argentina (South-western Atlantic Ocean)

This survey examined the association between the hyperiid amphipod Hyperoche martinezii and ctenophores off the Argentinian coast (38°08′17″S, 57°31′18″W) through the evaluation of seasonality, prevalence and intensity of infection during an annual cycle. Medusae were also examined but only the ctenophores Mnemiopsis leidyi, Pleurobrachia pileus and Beroe ovata showed this association during the austral mid-spring to mid-summer. A total of 502 hyperiids were obtained; most (422 individuals) were larval stages, 53 juveniles and 27 adults. Mnemiopsis leidyi had the highest number of hyperiids with 98.6%, followed by P. pileus (0.80%), and B. ovata (0.60%). Total prevalence was 2.0 and intensity of infection ranged between 1 and 17 hyperiids per ctenophore. The host with highest prevalence was B. ovata (4.54), followed by M. leidyi (3.76) and P. pileus (0.1). Prevalence values had some correlations with the increase in the total length of B. ovata (r?=?0.480, P?=?0.006) and M. leidyi (r?=?0.501, P?B. ovata (r?=?0.425, P?=?0.017). The hyperiid was found in different parts of the host body: larval stages were found in the canal close to the subtentacular comb row and the stomodeum, whereas juvenile/adult stages were observed with a resting posture on the external surface of the ctenophores. The known geographic distribution of H. martinezii was extended; this finding represents the addition of three new hosts for this hyperiid.     

Anal uptake of water in terrestrial pulmonate snails

Summary The uptake of water was examined in 35 central European terrestrial pulmonate snail species from 15 families (Table 1) by giving the inactive, withdrawn animals dyed water and observing its bulk flow microscopically.During emergence, 32 of the species studied normally take up water through the pneumostome. A rectal pump (Figs. 1 and 2) rapidly conveys this water through the anus into the gut and stomach.In 7 species, anal water-uptake during emergence was quantified and found to be equivalent to 20–40% of the total body water of the inactive snails before water uptake (Table 2).After emergence, the rectal pump allows re-uptake of urine from the ureter or the lung cativity into the alimentary tract.The anal mechanism permits rapid uptake of large quantities of water into an extrasomal compartment. This helps terrestrial pulmonate snails to exploit short wet spells and presumably helps to stabilize blood concentration during activity under dry conditions.     

Predator-induced vertical behavior of a ctenophore

Although many studies have focused on Mnemiopsis leidyi predation, little is known about the role of this ctenophore as prey when abundant in native and invaded pelagic systems. We examined the response of the ctenophore M. leidyi to the predatory ctenophore Beroe ovata in an experiment in which the two species could potentially sense each other while being physically separated. On average, M. leidyi responded to the predator’s presence by increasing variability in swimming speeds and by lowering their vertical distribution. Such behavior may help explain field records of vertical migration, as well as stratified and near-bottom distributions of M. leidyi.     

Spatio-temporal overlap of the alien invasive ctenophore <Emphasis Type="Italic">Mnemiopsis leidyi</Emphasis> and ichthyoplankton in the Bornholm Basin (Baltic Sea)

In 2007 the alien invasive ctenophore Mnemiopsis leidyi A. Agassiz 1865 was recorded for the first time in the Bornholm Basin, an area which serves as important spawning ground for Baltic fish stocks. Since M. leidyi is capable of preying upon early life stages of fish and further might act as food competitor for fish larvae, it is of major concern to investigate the potential threat that this non-indigenous species poses to the pelagic ecosystem of the Baltic Sea. The present study investigates the temporal and spatial overlap of M. leidyi with eggs and larvae of Baltic cod (Gadus morhua L.) and sprat (Sprattus sprattus L.) in order to assess the potential impact of this new invader on two of the most important Baltic fish stocks. Results show variable inter-seasonal distribution and overlap dynamics and thus different seasonal threat-scenarios for the early life stages of cod and sprat. The spatial overlap between M. leidyi and ichthyoplankton was low for most of the period observed, and we conclude that M. leidyi presently does not have a strong impact. However, we detected situations with high overlaps, e.g. for sprat larvae and cod eggs in spring. As the population dynamics of M. leidyi in the central Baltic are not yet fully understood, a future population explosion of the alien ctenophore with possible effects on fish recruitment cannot be ruled out. Furthermore, a possible shift in peak spawning of cod to the early season, when ctenophore abundances were relatively high, might increase the impact of M. leidyi on cod.     

Feeding and the control of volume within the tests of regular sea-urchins

The rigid, fluid filled, echinoid test presents problems of internal volume control when the vital functions of the animal involve the introduction of material, from outside the test, into the internal fluid systems. The volume of food in the guts of echinoids can be shown to vary considerably in the short term, to an extent which demands considerable capabilities for internal volume compensation. This is achieved by adjusting the quantity of fluid held within the gut so that, although the volume of food may vary widely, the total volume of the gut remains constant within narrow limits. The volume of gut fluid varies inversely with the quantity of food, and ingestion of food through the mouth is compensated by ejection of an equal volume of fluid from the anus. Defaecation is compensated by intake of fluid into the gut. On starvation, the gut becomes completely fluid filled and free from food.
The food of regular urchins is habitually compacted into regularly sized subpherical pellets covered with a tough mucus coating. The formation of coated pellets takes place in the buccal cavity and pharynx. The pellets remain discrete throughout their passage along the gut. The mucus coating resists digestion and remains intact even after defaecation. The functional morphology of the buccal cavity and pharynx is described in detail.
It is suggested that the functional significance of the pellets is associated with the gut fluid, volume compensation mechanism, which requires free flow of fluid throughout the length of the gut. It is also suggested that the siphon may be implicated in volume control, where fine adjustment of gut volume can be achieved by balancing ejection of fluid from the anus with intake of water through the mouth, but that the water intake is by the siphonal route, thus avoiding the necessity of flushing and diluting the enzyme rich digestive stomach region.     

Blooms of the invasive ctenophore, <Emphasis Type="Italic">Mnemiopsis</Emphasis> <Emphasis Type="Italic">leidyi</Emphasis>, span the Mediterranean Sea in 2009

Blooms of the invasive ctenophore, Mnemiopsis leidyi, occurred in 2009 along the Mediterranean Sea coasts of Spain and Israel. This voracious zooplanktivore spread throughout the Black Sea basin after its introduction in the early 1980s, throughout northern European coastal waters, and now occurs throughout the Mediterranean Sea. M. leidyi occurred throughout the summer along the entire Catalan Spanish and Israeli coasts in 2009. Those locations had high temperatures (18–26°C) and salinities (37–38) during the blooms. The patterns of abundance of large jellyfish along the Catalan coast were unusual in 2009, with low numbers during July, August, and September when ctenophores were abundant. Small populations of those potential predators and food competitors of M. leidyi could have contributed to the ctenophore bloom. The identity of the ctenophores from Spain and Israel was confirmed as M. leidyi by molecular analysis based on DNA sequencing of the nuclear internal transcribed spacer (ITS) regions. This is the first molecular confirmation of M. leidyi in the Mediterranean Sea. Most ctenophores had an ITS genotype previously found in M. leidyi from other invaded regions (the Black, Azov, and Mediterranean seas), as well as native regions in the United States, suggesting common ancestry. Based on the circulation patterns of Mediterranean surface waters and shipping activities, we conclude that the spread of M. leidyi in the Mediterranean probably resulted from re-introductions by ballast water transport and subsequent distribution by currents. We also conclude that the near-simultaneous blooms in opposite ends of both the Mediterranean basins indicate that M. leidyi is resident around the Mediterranean. We discuss environmental conditions, food, and predators of M. leidyi in both regions that would influence the future effects of this voracious consumer on the pelagic food web of the Mediterranean Sea.     

Life-stage dependent, in situ dietary patterns of the lobate ctenophore Mnemiopsis leidyi Agassiz 1865

Analysis of in situ gut contents of the ctenophore Mnemiopsisleidyi collected during summer months of 1998 at Woods Hole,MA, USA indicates that dietary changes accompanied developmentof this zooplankter. The transition from cydippid to lobatemorphologies involved a shift from a microplanktonic diet dominatedby protists to a metazoan-based diet. Dietary diversity increasedrapidly during the transition from cydippid to lobate stagebut remained essentially similar through most (>3.0 cm totallength) of the lobate stage. These stage-dependent dietary differencesmay have important implications for understanding populationdynamics of M. leidyi.     

The Exceptional “Blind” Gut of Appendicularia sicula (Appendicularia, Tunicata)

In this work, we studied for the first time the histology and ultrastructure of the gut of Appendicularia sicula and demonstrated the absence of any trace of anus. Appendicularians are small holoplanktonic tunicates, characterised by very fast ingestion and quick food transfer along their gut. The high production of faecal pellets released in the aqueous environment, associated with a high filtration rate, highlights their important role in marine ecosystems. Due to the absence of an anus, in contrast with other appendicularians, A. sicula, one of the smallest species, accumulates undigested faecal material within its body, with consequent extreme enlargement of its rectum. The gut, the epithelium of which is generally extremely reduced, is formed of an oesophagus, a globular stomach, thin proximal and mid-intestine, and a huge rectum. The latter, when filled with faecal material, may occupy most of the volume of the trunk in fully grown specimens. Although profoundly altered, the gut of these animals does show several similarities to that of Fritillaria (a genus of the same family, Fritillariidae), with which it has in common many features such as specialised mitochondrial pump cells. In A. sicula, the structural simplifications of organs seem to reach their extreme condition in comparison to other appendicularians.     

Invaders Ctenophores Mnemiopsis leidyi (A. Agassiz) and Beroe ovata Mayer 1912, and Their Influence on the Pelagic Ecosystem of Northeastern Black Sea

We analyzed the state of pelagic ecosystem of northeastern Black Sea affected by invasion of a new settler Beroe ovata in 1999–2001. Development of B. ovata considerably decreased the population of another invader, Mnemiopsis leidyi, that deformed the Black Sea ecosystem for over a decade. Reduction of M. leidyi population limited its influence on the ecosystem and, consequently, we observed recovering of the main components of the Black Sea pelagic ecosystem—zooplankton and fish as well as their eggs and larvae. The relationships between annual and seasonal variability of the population development and size of the both invaders M. leidyi and B. ovata are discussed.     

Transport-active organs within the ’ano-genital’ capsule of Craterostigmus tasmanianus (Chilopoda, Craterostigmomorpha)

 In Craterostigmus tasmanianus, first results of the cellular organization of anal organs within the ’ano-genital’ capsule are presented. Each valve of the ’ano-genital’ capsule bears four pore fields ventrally, each of them consisting of several pore openings of the anal organs. The pores lead into a cuticle-lined pore channel, the base of which is surrounded by a single-layered epithelium that is composed of three different cell types. The main epithelium consists of radially arranged transport-active cells surrounded by exocrine cells, and the cells of the pore channel. The cells of the transporting epithelium show deep invaginations of the apical and basal cell surfaces and plasmalemma-mitochondrial complexes. These cells are covered by a specialized cuticle with a prominent subcuticle. Exocrine glands secrete a mucous layer on the cuticle of the main epithelium. The type of anal organ present in Craterostigmus tasmanianus shows similarities to coxal and anal organs found in other Pleurostigmophora in the chilopods. The possible function of the anal organs in uptaking water vapour is discussed. It is appropriate to call the organs within the ’ano-genital’ capsule of Craterostigmus tasmanianus ”anal organs”, as components of the genital segments are not involved. Accepted: 17 November 1996