Polarisationsoptische Untersuchungen an Sagitta setosa und Sagitta hexaptera

Zusammenfassung Die doppelbrechenden Lipoide in der Körperwand der Sagitta setosa werden an Aufnahmen in polarisiertem Licht nach dem lebenden Objekt vorgeführt, und zwar sowohl die Lipoidstreifen und die Lipoidspindeln der Hauptmuskulatur als auch die nur polarisationsoptisch nachweisbaren Lipoideinlagerungen in den Fasern der lateralen Muskelfelder. Weiter wird die Lokalisation der Lipoide an Quer- und Längsschnitten durch die Körperwand der Sagitta hexaptera dargelegt.     

Complete mitochondrial genome sequences of the three pelagic chaetognaths Sagitta nagae,Sagitta decipiens and Sagitta enflata

The complete nucleotide sequences of the mitochondrial genomes were determined for the three pelagic chaetognaths, Sagitta nagae, Sagitta decipiens, and Sagitta enflata. The mitochondrial genomes of these species which were 11,459, 11,121, and 12,631 bp in length, respectively, contained 14 genes (11 protein-coding genes, one transfer RNA gene, and two ribosomal RNA genes), and were found to have lost 23 genes that are present in the typical metazoan mitochondrial genome. The same mitochondrial genome contents have been reported from the benthic chaetognaths belonging to the family Spadellidae, Paraspadella gotoi and Spadella cephaloptera. Within the phylum Chaetognatha, Sagitta and Spadellidae are distantly related, suggesting that the gene loss occurred in the ancestral species of the phylum. The gene orders of the three Sagitta species are markedly different from those of the other non-Chaetognatha metazoans. In contrast to the region with frequent gene rearrangements, no gene rearrangements were observed in the gene cluster encoding COII–III, ND1–3, srRNA, and tRNA^met. Within this conserved gene cluster, gene rearrangements were not observed in the three Sagitta species or between the Sagitta and Spadellidae species. The gene order of this cluster was also assumed to be the ancestral state of the phylum.     

Sperm emission in the chaetognath Sagitta crassa

Sagitta crassa which had just extruded a sperm ball, togetherwith a tube-like secretion, was obtained from Tokyo Bay forthe first time. The question of spermatophores in chaetognathsis discussed.     

长江口强壮箭虫和肥胖箭虫的丰度变化对环境变暖的响应

根据1959年和2002年在长江口28°00′～32°00′N,122°00′～123°30′E海域4个季节8个航次海洋调查资料,分析强壮箭虫(Sagitta crassa)和肥胖箭虫(Sagitta enflata)丰度的平面分布和季节变化特征,并结合同步的温度资料分析不同生态类群的强壮箭虫和肥胖箭虫对环境变暖的响应.结果表明:长江口水域春、夏、秋3季强壮箭虫平均丰度均小于1.00 ind/m3,出现率低,无集群性.1959年冬季平均丰度达3.24 ind/m3,出现率较高,有明显的集群性,而2002年冬季平均丰度锐减为0.001 ind/m3,几无分布.肥胖箭虫夏季平均丰度、出现率和集聚强度明显高于其它季节.2002年夏季平均丰度达16.06 ind/m3,较1959年增加3.71 ind/m3,且分布区明显扩大.可见,暖温种强壮箭虫和暖水种肥胖箭虫对长江口海域变暖的响应不同,可作为长江口海洋变暖长期变化的重要指示种.     

Copulation in the neritic chaetognath Sagitta crassa

The number of spermatophores found attached to Sagitta crassa,the dominant chateognath in Tokyo Bay, ranged from one to four.Individuals with one spermatophore were most abundant, accountingfor 70% of chaetognaths with spermatophores (A). Using the meanminimum body length of chaetognaths with spermatophores (A),those without spermatophores were subdivided into two categories:those >7 mm (B) were considered to be mature animals, andthose <7 mm (C) to be immature. The ratio of chaetognathswith spermatopbores (A) to all chaetognaths (A+B+C) varied withtime, with high values from 0040 through 0120 h as in a previousstudy. Variations in the ratio of chaetognaths with spermatophores(A) to all adults (A+B) showed a pronounced peak at 0100 h.Thus, it was confirmed that copulation of S. crassa is a periodicactivity with a peak soon after midnight. Most of the chaetognathpairs exchange one spermatophore. The frequency of copulationis considered to be two times per night at most because thechaetognaths have a single pair of seminal vesicles. However,the presence of chaetognaths with 3–4 spermatophores suggeststhat occasionally a reciprocal exchange of spermatophores doesnot occur. This could be called false copulation. It is suggestedthat copulation in S. crassa including false copulation occursat most four times per night.     

Further studies on the junctional complex in the intestine of Sagitta setosa

Summary The intramembrane structures of the pleated septate junction which occur in the junctional complex of the intestine of the chaetognath Sagitta setosa have been investigated.The pleated septate junction is made up of linear rows of irregularly shaped and sized particles, often fused into short rods, and pits which can be fused into furrows. The distribution of these structures on E and P faces depends upon the preparative methods used. Many of the morphological characteristics are the same as those of the lower invertebrate pleated septate junction type defined by Green (1981a). The physiological significance of this junction is obscure.On the basis of the presence of septate junctions (both of the paired septate junction and pleated septate junction types) which have mainly morphological characteristics of the lower invertebrate pleated septate junction we can add to the hypothesis that chaetognaths are not related to the molluscs and arthropods.     

Fine structure of the coelomic epithelium of Sagitta elegans (Chaetognatha)

Summary The coelomic space in the trunk of the arrow worm Sagitta elegans is lined by a thin epithelium, which may be termed coelomic epithelium. The visceral part of this epithelium is composed of flat cells characterized by thin and thick myofilaments, which constitute the circular musculature of the gut. In addition mitochondria, rough ER, and smooth walled cisterns, as well as vesicular and granular inclusions occur; the apical and basal plasma membranes exhibit no particular specializations. The parietal epithelium is exceedingly thin and covers the muscle cells of the body wall. In the lateral fields columnar ciliated cells are to be found which are rich in rough ER cisterns and which apparently are also coelomic epithelial cells.     

Zur morphologie,polarisationsoptik und chemie der greifhaken von Sagitta Hexaptera

Ohne Zusammenfassung     

The Sense Organs and Ventral Ganglion of Sagitta (Chaetognatha)

This paper describes some features of the chaetognath nervous system from ultrastructural observations and observations on material stained with specific techniques for nervous tissue, and from records of the activity of the locomotor muscles and ventral ganglion. Sensory cells grouped on the ventral surface of the head bear ciliary processes (some with multiple tubules), and are probably in connexion with the central nervous system by their own axons, unlike the sensory cells of the hair fan vibration receptors of head and body. The ventral ganglion is motor to the locomotor muscles of the body, and controls the rhythmic locomotor activity of the animal. Electrical events associated with contraction of these muscles are compound non-overshooting spike-like potentials. The ventral ganglion contains several large nerve fibres constant in position and connexions in different individuals. Some of these arise from cells in the ganglia of the head, and pass to the ventral ganglion, others from cells within the ventral ganglion, and probably supply the ciliary hair fan receptors of the body, whilst the motor axons issuing from the ventral ganglion are smaller in diameter. The ganglion is arranged on a ladder-like plan, and axons of the lateral cell bodies cross the central neuropil transversely before they contribute to the longitudinal tracts or pass out in the radial nerves. Synapses in the neuropil contain 30–40 nm electron lucent vesicles; the transmitter is unknown, but is unlikely to be either acetylcholine or l -glutamate. Occasional larger electron dense vesicles up to 70 nm in diameter are also found within nerve fibres of the neuropil. It is concluded that the arrangement of the peripheral nervous system is unlike that of several groups which have been suggested as related to chaetognaths.     

海洲湾强壮箭虫的生态学特征研究

根据海洲湾2006年8月—2007年11月的强壮箭虫(Sagitta crassa)调查数据,采用聚集强度指标、Iwao和Taylor模型分析了强壮箭虫的空间分布特征和丰度的时空变化。结果表明:强壮箭虫在调查海域呈聚集分布;强壮箭虫平均丰度的时空变化差异显著,空间上,中、北部海域的平均丰度高于南部海域,时间上,强壮箭虫春、冬季节的平均丰度明显高于夏、秋季节。     

Phylogeography of the planktonic chaetognath Sagitta setosa reveals isolation in European seas

Numerous planktonic species have disjunct distribution patterns in the world's oceans. However, it is unclear whether these are truly unconnected by gene flow, or whether they are composed of morphologically cryptic species. The marine planktonic chaetognath Sagitta setosa Müller has a discontinuous geographic distribution over the continental shelf in the northeastern Atlantic, Mediterranean Sea, and Black Sea. Morphological variation between these populations has been described, but overlaps and is therefore unsuitable to determine the degree of isolation between populations. To test whether disjunct populations are also genetically disjunct, we sequenced a 504-bp fragment of mitochondrial DNA comprising the cytochrome oxidase II region of 86 individuals. Sequences were highly variable; each represented a different haplotype. Within S. setosa, sequence divergence ranged from 0.2 to 8.1% and strong phylogeographic structure was found, with four main groups corresponding to the northeastern Atlantic, Mediterranean Sea (including Ligurian Sea, Tyrrhenian Sea and Gulf of Gabes), Adriatic Sea, and Black Sea. Two of these (Atlantic and Black Sea) were resolved as monophyletic clades, thus gene flow between disjunct populations of S. setosa has been extremely limited and lineage sorting has taken place. The deepest divergence was between Atlantic and Mediterranean/Black Sea populations followed by a split between Mediterranean and Black Sea populations. The Mediterranean/Black Sea clade comprised three groups, with the Adriatic Sea as the most likely sister clade of the Black Sea. These data are consistent with a colonization of the Black Sea from the Mediterranean. Furthermore, a possible cryptic species was found in the Black Sea with 23.1% sequence divergence from S. setosa. Two possibilities for the evolutionary origin of this species are proposed, namely, that it represents a relict species from the ancient Paratethys, or that it represents another chaetognath species that colonized the Black Sea more recently. Even though the exact timing of disjunction of S. setosa populations remains unclear, on the basis of the geological and paleoclimatic history of the European basins and our estimates of net nucleotide divergence, we suggest that disjunct populations arose through vicariance resulting from the cyclical changes in temperature and sea levels during the Pleistocene. We conclude that these populations have remained disjunct, not because of limited dispersal ability, but because of the inability to maintain viable populations in suboptimal, geographically intermediate areas.     

On the fine structure of the cerebral ganglion of Sagitta (Chaetognatha)

Summary In this study the fine structure of the cerebral ganglion of Sagitta setosa (Chaetognatha) is investigated. The ganglion is flat and superficially positioned dorsally, below the basal lamina of the cephalic epidermis. It is surrounded by a specifically differentiated sheath. This sheath is made up of cells, which are interpreted as representing glial cells, and can be divided into an outer and an inner zone. The outer zone is composed of flat sheath cells with pale nuclei and few organelles. The inner zone consists of densely packed, extremely thin lamellar cellular processes. These attenuated lamellae, which still contain cytoplasm, resemble the myelin sheath of vertebrate axons. The intercellular space between the lamellae contains electron-dense material. In the sheath specialized intercellular contacts occur. The inner zone of this sheath extends at definite points into the centre of the ganglion and separates a zone of perikarya from the neuropil, as well as the single perikarya from each other. The perikarya are relatively uniform and do not form a cortex, but are concentrated mainly in lateral parts of the cerebral ganglion. Within the neuropil are axonal endings which have synaptic contacts with several postsynaptic elements. These anatomical findings are discussed with respect to their functional significance.     

The liquid crystalline nature of the cytoskeleton in epidermal cells of the chaetognath Sagitta

The chaetognaths have a multilayered epidermis, which is not covered by cuticle, except in the head region. Two kinds of cells are found in the epidermis: the filament-rich cells, adjacent to the basement membrane, and superficial cells, which are filament poor. The filament-rich cells, which are linked by gap junctions and columnar junctions, are highly developed in the collarette region, which joins the head and the trunk. As elsewhere in the epidermis these cells are covered by the filament poor cells which are linked by zonulae adhaerentes, gap junctions and septate junctions. The filaments present in the inner cells of the collarette form a twisted fibrous arrangement, which shows parallel series of nested arcs when observed in oblique section. Such systems are well known in numerous skeletal materials and correspond to polymerized analogues of certain liquid crystals. The amount of connective tissue is extremely reduced in Sagitta. One can hypothesize that filament-rich cells are abundant in regions which undergo strong deformations. This is the case in the collarette, in contact with the basement membrane of the epidermis (which in turn is in contact with a myotendinous system), in a region where ingested prey must go through the general cavity where there is high internal pressure.     

Life history and population dynamics of the chaetognath Sagitta elegans in central Long Island Sound

One chaetognath species is found in Long Island Sound. Sagittaelegans. Individuals ranging in length from 1.5 to 22 mm werefound from March through August. Length at maturity ranged from13 to 22 mm. Maximum abundances. 67 ind m^–3 in 1982 and106 md m in 1983. occurred in early summer Two cohorts wereseen during both years, beginning as eggs produced in April-May.and in late June. The population is not endemic to Long IslandSound because temperatures during summer exceed 19C, whichseems to be lethal. The appearance of the first cohort in springis due to advection of animals from shelf waters. The secondcohort, however, is produced locally. The S. elegans populationin Long Island Sound is unique in two ways. First, the adultsare considerably longer than predicted by McLaren's (1963) Belhrdekfunction, and second, the total abundance of eggs, juvenilesand adults is at least two times higher than anywhere else.     

Vertical distribution of pelagic chaetognaths and feeding of Sagitta enflata in the Central Equatorial Pacific

The vertical distribution and feeding of pelagic chaetognathsat 5°S, 160°W in the Central Equatorial Pacific wereinvestigated using a series of 0–500 m vertical haulswith a VMPS net over a 24 h period between 6 and 7 October 1990.The total number of individuals per haul was between 370 and688. Fourteen species in four genera were found at this station.The most abundant species was Sagitta enflata which comprised32.4–61.1% of the individuals collected from the 0–500m layer. Mesopelagic species made up 9.3–15.1% of thetotal number of individuals. Sagitta enflata and Pterosagittadraco were found in the upper part of the thermocline both byday and at night. The fraction of the population containingfood items (FCF) of S.enflata in the 0–50 m layer variedbetween 4.8 and 12.5% (mean 10.8%) and feeding activity washighest between sunrise and noon. The percentages of Copepoda,Foraminifera, crustacean larvae, Chaetognatha, Pteropoda, Ostracoda,fish and unidentified material in the gut of S.enflata were51.9,6.7,3.8,2.9,1.9,1.9 and 30.9%, respectively. Sagitta enflataconsumed food organisms which were mainly between 0.5 and 1.0mm in length. The daily feeding rate of S.enflata was 1.81 preyper individual, which was equivalent to 8.06 mg C m^–2day^–1. This corresponded to     

温度、盐度对强壮箭虫耗氧率和窒息点的影响

研究了不同温度、盐度下强壮箭虫的耗氧率和窒息点.结果表明:温度和盐度均对强壮箭虫的耗氧率和比耗氧率有显著影响.试验温度在5℃-25℃,强壮箭虫个体耗氧率(IO)和比耗氧率(SO)开始随温度的升高而升高,之后呈明显下降趋势.其回归方程分别为y=0.0058x3 -0.2956x2+4.415x-8.7816(R2=0.99,P＜0.05)和y=0.0011x3 -0.0546x2+0.8161x-1.6232(R2=0.99,P＜0.05),数值分别为6.30～11.71μg·ind-1·h-1和1.22 ～2.16μg· mg-1·h-1,窒息点为4.18～6.87 mg·L-1.盐度10 ～40条件下,IO和SO随盐度的升高逐渐下降,回归方程分别为y=-0.0068x2 -0.1412x+21.702(R2=0.89,P＜0.05)和y=-0.0013x2-0.0261x+4.0114( R2 =0.89,P＜0.05),数值分别为4.98～17.73μg ·ind-1·h-1和0.92～3.56 μg·mg-1 ·h-1,窒息点为4.02～6.24 mg·L-1.对强壮箭虫与其他水生动物的耗氧率和窒息点进行比较得出,强壮箭虫是一种狭氧性浮游动物.     

Feeding of Sagitta enflata and vertical distribution of chaetognaths in relation to low oxygen concentrations

Zooplankton samples were collected in Mejillones Bay, northernChile (23°00'15'S, 70°26'43'W ). Sampling was conductedat 4 h intervals, for 24 h during three seasons, austral spring(October 2000), summer ( January 2001) and winter (August 2001)at three different strata (0–25, 25–50 and 50–100m). Five species of chaetognaths were collected. Sagitta enflatawas the most abundant species, representing up to 65% of allchaetognaths in total numbers, followed by Sagitta bierii, makingup 34% of the total abundance of chaetognaths. S. enflata wasdistributed mainly above the Oxygen Minimum Zone, while S. bieriiremained below this zone. Feeding rates were relatively constantwithin the upper layer (0–25 m depth), for each samplingdate, averaging 1.2 prey S. enflata day^–1, and decreasingwith depth. Gut content analyses demonstrated that predationwas principally focused on small copepods (<1500 µm),with greatest feeding activity occurring at night. The dailypredation impact on the total standing stock of small copepodsvaried seasonally between 6% in spring and 0.4% in winter. Thispercentage may represent a negligible impact on the entire copepodcommunity, but it is relevant at the species or genus level,since S. enflata removed more than 20% of the standing stockof Centropages brachiatus and Corycaeus sp. Thus, during someperiods of the year, chaetognaths may strongly influence theabundance and size distribution of copepods in coastal upwellingecosystems.