Morphological variation of <Emphasis Type="Italic">Keratella cochlearis</Emphasis> (Gosse) in Myanmar (Burma) in relation to zooplankton community structure

Keratella cochlearis was present in 27 of 35 water bodies sampled in Myanmar, and was the most abundant rotifer in 10. Measurements of lorica length and posterior spine length from 20 localities showed that posterior spine length varied both with lorica length and with the composition of the crustacean zooplankton. Long spines were associated with dominance by Heliodiaptomus. The shortest spines were found in samples dominated by cladocerans or cyclopoid copepods. Posterior spine length was positively correlated with the number of diaptomid copepods. Forms without posterior spines were found in 17 localities. The lorica lengths of these spineless forms were generally similar to those of co-occurring spined forms (r = 0.68), but in a few samples the loricas of the spineless forms were significantly larger. These larger forms are similar to the ‘aspina’ forms recently recognised in the River Thames in England. These samples were dominated by cladocerans or cyclopoid copepods. In one locality spineless forms were found without spined forms. The crustacean zooplankton in this locality was also dominated by cladocerans. Guest editors: S. S. S. Sarma, R. D. Gulati, R. L. Wallace, S. Nandini, H. J. Dumont & R. Rico-Martínez Advances in Rotifer Research     

Effect of Temperature on Fecundity,Life Span and Morphology of Long‐ and Short‐Spined Clones of Brachionus caudatus f. apsteini (Rotifera)

We investigated the effect of temperature (20, 25 and 30 °C) on fecundity, life span and morphology of the rotifer Brachionus caudatus f. apsteini. For each temperature, short posterior‐spined and long posterior‐spined clones of B. caudatus f. apsteini were individually cultured for up to six generations. The rotifers were fed Chlorella sp. at a density of 1 × 10⁶ cells ml^–1. Morphometric data (body size and spine length) were collected. Total number of offspring producing by a single female per life cycle at high temperature was higher than at low temperature. The duration of juvenile period, reproductive period, post‐reproductive period and life span of both clones of B. caudatus f. apsteini decreased with increasing temperature. All offspring of short posterior‐spined clone produce posterior spines at 20 and 25 °C, with an average length of 19.8 ± 6.6 and 11.9 ± 2.6 μm, respectively. In contrast, they cannot develop posterior spines at 30 °C, at which the average length of the posterior spine remnant was 6.4 ± 1.3 μm. On the other hand, all offspring of long posterior‐spined clone have long posterior spines with average lengths of 36.8 ± 6.1, 36.3 ± 5.2 and 36.6 ± 6.2 μm at 20, 25 and 30 °C, respectively. This study indicated that the production of posterior spines can be induced by low temperature and that short posterior‐spined and long posterior‐spined clones are genetically different. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Cyclomorphosis in Keratella tropica (Apstein) of Lake Asejire,Nigeria

Of one thousand, one hundred and four (1104), Keratella tropica collected with a 55 m mesh plankton net from the surface of Lake Asejire from February 1974 to February 1976 lorica length and width, and the lengths of the posterior spines were measured.Lake Asejire K. tropica are among the smallest in Africa. Variations in the patterns of spine length development were independent of season as individuals without left posterior spines and with relatively long left and right posterior spines occurred as commonly in the rainy as in the dry season months.Correlations between K. tropica dimensions and thirty environmental factors underscore the importance of physical environmental factors and point to biological and genetic factors as determinants of the patterns of cyclomorphosis in K. tropica.     

Periodic shedding and replacement of venomous caudal spines,with special reference to South American freshwater stingrays,Potamotrygon spp.

Synopsis The number of venomous caudal spines and their length and position relative to one another were determined in seven species of South American freshwater rays (Potamotrygonidae) and eight marine or euryhaline species of four families from the Caribbean Coast of South and Central America. Most species have two visible spines at certain stages in the shedding-replacement cycle and only one visible spine at other stages (following shedding). If we include the embryological beginnings of the spines before they erupt and become visible, the spine counts of most rays are actually 2 rather than 1 or 2. Since most species apparently follow this pattern, spine counts are of little use in distinguishing between species except in the relatively few that may have only one, or no spines. Eight captive Potamotrygon specimens maintained in simulated tropical temperature conditions over 12 months showed periodic shedding and replacement of spines. The molts were biannual for a given ray but annual for a given spine. They alternated between two spine loci and their cycles were approximately six months out of phase with each other. Recent studies on Dasyatis sabina by others report only one molt per year, with replacement spines forming always posterior to the primary spine rather than alternating between posterior and anterior. Supernumerary spines (counts of more than two, up to five) are also discussed, as are counts of one and zero.     

On the morphology of Acanthostomum spiniceps (Looss, 1896) and A. absconditum (Looss, 1901) (Digenea: Cryptogonimidae: Acanthostominae) with particular reference to the juvenile stage

The morphology of juvenile and adult stages of Acanthostomum spiniceps and A. absconditum, from bagrid fish of the river Nile in Egypt, was studied with both light and scanning electron microscopy. In early juveniles, circumoral spines are absent and the entire body surface is covered with tegumental spines. Late juveniles show gradual differentiation of the circumoral tegument into a collar of spines associated with a reduction in density of tegumental spines at the posterior extremity of the body. Genital primordia appear when juveniles are about 1.75 mm long. The distributions of tegumental spines on adult A. spiniceps and A. absconditum are similar. Spines are denser on the dorsal and ventral surfaces of the anterior and middle parts of the body and less dense towards the posterior end. The tegumental fold surrounding the ventral sucker of A. absconditum has spines while the fold of A. spiniceps lacks them. The most important morphological features differentiating both species are the number of circumoral spines, body shape, ratio of body length to width, sucker sizes, and the presence or absence of spines on the ventral sucker.     

A new species, Trichiurus australis (Perciformes: Trichiuridae), from Australia

Trichiurus australis, a new trichiurid fish, is described on the basis of four specimens collected off Burnett River mouth, Pialba and Thursday Island, Queensland, Australia. The new species strongly resembles Trichiurus brevis Wang and You, 1992 (distributed in the South China Sea), T. russelli Dutt and Thankam, 1967 (the northwestern Bay of Bengal and the northern Gulf of Thailand), and T. nickolensis Burhanuddin and Iwatsuki, 2003 (northwestern Australia) in having the highest point of the supraoccipital crest situated directly above the posterior margin of the eye and being relatively small in size (less than ca. 700mm in total length: TL). It differs from those three species in having spinescent gill rakers almost with 2 equally long cusps [vs. (1, rarely 2 but 1 of them clearly shorter than another)], posterior caudal peduncle vertebrae bearing neural spines (vs. neural spines absent), longer caudal peduncle length (mean 16% TL vs. 6% in T. brevis, 8% in T. nickolensis, and 8% in T. russelli), and shorter precaudal length (83% vs. 93%, 91%, and 91%), preanal length (26% vs. 33%, 31%, and 35%), and head length (9% vs. 12%, 11%, and 13%). We have tentatively classified this new species under the Trichiurus russelli complex because the foregoing diagnostic characters are identical to this species complex except for the presence of neural spines in the posterior caudal vertebrae.     

Doxomysis algoaensis, a new mysid species (Crustacea: Mysidacea) from Algoa Bay (South Africa)

Doxomysis algoaensis sp.nov. is described from Algoa Bay, South Africa where it is common in nearshore marine waters just beyond the breaker line. D. algoaensis sp.nov. is morphologically similar to D. australiensis, but can readily be distinguished by the shape and armature of the telson and the length of the exopod of the fourth male pleopod. The apical cleft is one fifth the telson length in the former species and one third the length in D. australiensis. The telson apex on each side of the cleft is also armed with five and four stout spines in the two species, respectively. In D. australiensis, the exopod of the fourth male pleopod is almost three times the length of the endopod; in D. algoaensis sp.nov., the exopod is only slightly longer than the endopod. Other distinctive features of D. algoaensis sp.nov. include the maxillary palp, which is only slightly broader than long and the greater number of spines on the endopod of the uropod.     

剪形臂尾轮虫形态的时空变化及其与生态因子间的关系

对芜湖市镜湖和汀棠湖中剪形臂尾轮虫(Brachionus forficula)的发生及其形态特征进行了一年的观察,并分析了其与环境因子间的关系。结果表明,镜湖中,剪形臂尾轮虫出现于7月至10月,且仅存在短后棘刺型个体;2样点内,除了前外棘刺长以外,轮虫的其他各形态参数均随季节显著变化,形态参数的样点间差异也因季节的不同而异;轮虫的各形态参数均随pH的升高而延长,随过滤水体中叶绿素a含量和水体中总叶绿素a含量的升高而缩短;体长和体宽均随晶囊轮虫密度的升高而增大。汀棠湖中,短后棘刺型个体出现于6月至10月,而长后棘刺型个体仅出现于6月至8月;2种形态型个体同时存在时,长后棘刺型个体在种群中所占比例始终高于短后棘刺型个体,并与水温、水体中总叶绿素a含量以及枝角类、桡足类和晶囊轮虫的密度均呈显著的正相关;2样点轮虫短后棘刺型个体各形态参数均随季节显著变化;长后棘刺型个体在1号样点内仅前外棘刺和后棘刺长有显著变化,而2号样点内仅体长、体宽和后棘刺长有显著变化;2样点内长后棘刺型个体的体长、体宽以及前外棘刺和后棘刺均显著长于短后棘刺型个体;同一形态型个体形态参数的样点间差异因季节的不同而异;短后棘刺型个体的前外棘刺和后棘刺长均与水体中总叶绿素a含量呈显著的正相关,后者与过滤水体中叶绿素a含量和枝角类密度也呈显著的正相关;长后棘刺型个体的后棘刺长与桡足类密度呈显著正相关,前内棘刺长与水温、溶氧量和晶囊轮虫密度呈显著负相关。两湖泊内剪形臂尾轮虫的后棘刺长和体长之间均呈显著的正相关,提示其后棘刺的延长并不是对体长的异速增长。     

Surface ultrastructure of the plagiorchid trematode Glossidium pedatum Looss, 1899 from bagrid fish in Egypt

The present study concerned the morphology and surface ultrastructure of a plagiorchid, Glossidium pedatum, from bagrid fish of the river Nile in Egypt. Adult G. pedatum have an elongate body, tapered towards the anterior and posterior ends. Their oral sucker is small, sub‐terminal and rounded, measuring 0.200 mm in diameter. Sensory papillae around the oral sucker usually occur in small clusters of three to eight each. The ventral sucker is large, situated at the anterior end of the second third of the body, 0.299 mm in diameter, and is surrounded by three pairs of sensory papillae. Both suckers have rounded rims covered by tegumental spines. On the anterior part of the ventral surface of the body tegumental spines are small, pointed and closely spaced. A small triangular area of tegument anterior to the ventral sucker is devoid of spines. Tegumental spines on the mid‐region of the body slightly increase in size and number, especially towards the lateral aspects and posterior to the ventral sucker. Towards the posterior end of the body the spines progressively decrease in both size and number. The dorsal side exhibits similar surface features but the spines are less numerous and slightly smaller.     

Further observations relating sex size ratios to mating success in calanoid copepods

Mating experiments using 153 pairs of Diaptomus leptopus Forbeswere video-taped in the laboratory. The following were measuredand scored: attempted capture of the female by the male, timeto successful capture and mounting, duration of copulation,spermatophore placement, time to clutch extrusion, prosome lengthsof all individuals and sex size ratios (female:male lengths)of all pairs. Mating success was not a function of sex sizeratio for D.leptopus at ratios commonly observed in nature inthe populations tested. However, this lack of relationship maynot be true of all populations. Photographic analysis of D.leptopusas well as D.birgei Marsh showed that males always held ontofemale genital segments in the vicinity of the spines with theirright fifth legs. Pearson correlations were calculated comparingprosome lengths to a variety of genital parts. The strongestrelationships were found with female genital segment width atthe level of the spines for both species, and male right fifthleg claw length for D.birgei. These data support the hypothesisthat the relationship between sex size ratio and mating successmay be species specific.     

Asymmetry and variation in keratella tropica

Keratella tropica usually has two posterior spines. Both may vary in length, but the left is always shorter than the right. Sometimes the left spine is absent. Spine length varies with the length of the lorica, but there are other, external, influences. Three separate lines of evidence indicate that factors which promote spine length are related in some way to the presence of calanoid copepods.     

<Emphasis Type="Italic">Lysmata rafa</Emphasis>, a new species of peppermint shrimp (Crustacea,Caridea, Hippolytidae) from the subtropical western Atlantic

Lysmata rafa n. sp. is described from freshly collected specimens from the Keys West Lakes, Florida Keys, and from a museum specimen collected at Bear Cut, Biscayne Bay, Florida. The new species is morphologically most similar to the western Atlantic Lysmata rathbunae Chace, 1970 and the eastern Pacific Lysmata gracilirostris Wicksten, 2000, but can be distinguished from them by the number of carpal segments in the second pereiopod; the length and dentition of the rostrum; the shape and number of spines on the dactylus of the third to fifth pereiopods; and the absence of a tooth on the pterygostomial margin of the carapace. Despite being a shallow-water species, L. rafa n. sp. has extremely elongate walking legs and third maxilliped that are more typical to deep-water or cave dwelling carideans.     

The effects of posterolateral spine length and body length on feeding rate in the rotifer,Brachionus calyciflorus

The length of the posterolateral spines in the rotifer, Brachionus calyciflorus, is variable. The effect of the length of these spines on the clearance rates of B. calyciflorus was examined under laboratory conditions using radioactively-labelled yeast (Rhodotorula) and bacteria (Aerobacter). The hypothesis that individuals with longer spines have higher clearance rates than those of similarly-sized individuals with shorter spines was rejected. The effect of body length (L) on the clearance rates (C) of short-spined and long-spined animals was also examined. Statistically significant linear regressions of the form log₁₀ C = aL + b, were derived for both types. The slopes of both regressions were similar and suggest that clearance rate in B. calyciflorus increases as a cube function of body length.     

Paleobiology of the Late Cretaceous sclerorhynchid sawfish,Ischyrhiza mira (Elasmobranchii: Rajiformes), from North America based on new anatomical data

Abstract

We describe seven associated skeletal remains of Ischyrhiza mira, a Late Cretaceous sclerorhynchid sawfish, from the Campanian?lower Maastrichtian of Tennessee and Alabama, U.S.A., to decipher its paleobiology. Ischyrhiza mira had about 16 or 17 functional spines and about the same number of replacement spines on each side of the rostrum in which tall erect spines occupied the anterior one-half to two-third of the rostrum followed posteriorly by smaller spines. Whereas small hat-shaped dermal denticles were distributed on the rostrum, large thorn-like dermal denticles were present on the dorsal side of the body characteristic of sluggish, benthic batoids. We concur with the interpretation that specimens previously identified as rostral spines of Peyeria are actually enlarged thorn-like dermal denticles of a sclerorhynchid. We suggest that the ratio between the rostrum length and total body length of sclerorhynchids was generally about 1:3.27. Our vertebra-based ontogenetic analysis of I. mira gives an age estimate of 12.4 years for a 190-cm-long individual, the size at birth of about 0.5 m, and the maximum possible length for the species of no more than 3 m. Compared to extant pristid sawfishes, I. mira probably became sexually mature much earlier with a slightly faster rate of rostrum development.     

Morphological Variation of <Emphasis Type="Italic">Keratella cochlearis</Emphasis> (Gosse) in a Backwater of the River Thames

The morphological variation of Keratella cochlearis in a Thames backwater has been studied over 4 years. There was a general inverse relationship between lorica length and temperature, but the annual cycle of change depended upon the rate of change of the temperature, and there was considerable variation between years. There was a similar inverse relationship between posterior spine length and temperature, and a shift in both relationships depending on whether the temperature was increasing or decreasing. As the water temperature increased from winter to summer the lorica and posterior spine were longer than at the same temperature as the water cooled from summer to winter. This shift can be modified by anomalous temperatures, such as a late spring or a cool summer.The form lacking a posterior spine usually, but not consistently, had a longer lorica than the typical spined forms. It usually disappeared from the samples at the end of November and did not reappear until March, although with a mild autumn and winter it persisted until January before disappearing. Forms without posterior spines did not all have the same origins.     

An early Cambrian chelicerate from the Emu Bay Shale,South Australia

The Emu Bay Shale Lagerstätte (Cambrian Series 2, Stage 4) occurs on the north coast of Kangaroo Island, South Australia. Over 50 species are known from here, including trilobites and non‐biomineralized arthropods, palaeoscolecids, a lobopodian, a polychaete, vetulicolians, nectocaridids, hyoliths, brachiopods, sponges and chancelloriids. A new chelicerate, Wisangocaris barbarahardyae gen. et sp. nov., is described herein, based on a collection of some 270 specimens. It is up to 60 mm long, with the length of the cephalic shield comprising about 30% that of the exoskeleton. The cephalic margin has three pairs of bilaterally‐symmetrical small triangular spines. A pair of small eyes is placed well forwards on the ventral margin of the cephalic shield. The trunk comprises 11 segments that increase in length while narrowing posteriorly, each possibly bearing a pair of biramous appendages; the most posterior segment is almost square whereas the others are transversely elongated. The spatulate telson is proportionately longer than in taxa such as Sanctacaris, Utahcaris and Leanchoilia. Up to eight (?four pairs) of 3 mm‐long elements bearing alternating inward‐curving short and long spines beneath the cephalic shield are interpreted as basipodal gnathobases, part of a complex feeding apparatus. A well‐developed gut includes a stomach within the cephalic shield; it extends to the base of the telson. In a few specimens there are shell fragments within the gut, including those of the trilobite Estaingia bilobata (the most common species in the biota); these fragments have sharp margins and extend across the gut lumen. The species may have been a predator or a scavenger, ingesting material already broken up by a larger predator/scavenger. The morphology of this taxon shares many overall body features with Sanctacaris, and some with Sidneyia, particularly its gnathobasic complex. These chelicerate affinities are corroborated by phylogenetic analyses.     

Distribution of <Emphasis Type="Italic">Calanus</Emphasis> populations in a glaciated fjord in the Arctic (Hornsund,Spitsbergen)—the interplay between biological and physical factors

The distribution and diversity of copepods of the genus Calanus were investigated in Hornsund Fjord (on the southwest coast of Spitsbergen) in summer 2001. The Bhattacharya method was used to sort individuals by species based on their prosome length. The established prosome length boundary values for the Calanus copepodid stages coincided with those defined for the Calanus species from Kongsfjorden (on the northwest coast of Spitsbergen). The predominant species in the main and inner fjord basins was Calanus glacialis, whereas Calanus finmarchicus was the prevailing species outside Hornsund. Younger copepodid stages (CI–CIII) of both species concentrated in the surface water layers (0–50∼70 m), while older copepodids (CIV–CVI females) that were ready for wintering stayed in deep layers (50∼70 m to bottom). Calanus hyperboreus was present in low numbers, predominantly as CIV, and in Hornsund deep water layers. The distribution and diversity of Calanus species complied with the notion that the marine fauna in Hornsund is of a more Arctic character than in Kongsfjorden, a fjord 260 km to the north on the west coast of Spitsbergen.     

The Effect of Abdominal Spines on Female Mating Frequency and Fecundity in a Water Strider

Conflict between the sexes over mating decision may result in antagonistic coevolution in structures that increase control over copulation. In Aquarius paludum both females and males have long abdominal spines. We tested the hypothesis that abdominal spines increase female ability to resist male mating attempts and reduce the costs of mating in A. paludum. We manipulated female spine length and observed female mating and egg-production rate in two different studies. We found that females with intact spines succeeded to reject male mating attempt more often than females with removed spines. Intact females also mated less often than females with removed or shortened spines. Male presence and mating rate increased female egg number. Our results thus support the hypothesis that abdominal spines help female to reject male mating attempts but contrary to predictions, we found that A. paludum females somehow benefit from multiple matings in spite of the sexual conflict.