THE EVOLUTION AND COMPARATIVE PHYSIOLOGY OF TERRESTRIAL AND FRESHWATER NEMERTEANS

(1) Parallel evolution from separate marine ancestors has given rise to two groups of genera of terrestrial nemerteans, representative of at least two different family stocks. They have colonized land by the direct route, moving up the shore on widely separated oceanic islands. The relationships between the known terrestrial and semi-terrestrial nemerteans, comprising seven genera and 15 species, are defined and their geographic distribution is discussed.
(2) In fresh water, three heteronemertean and nine hoplonemertean species are known. The hoplonemerteans arise from two different families representing two different evolutionary routes to fresh water, one by way of estuaries and the other via land. The distribution of freshwater nemerteans and the characters common to all species are discussed.
(3) Very little is known about the comparative physiology of land and freshwater nemerteans. However, information about the physiology of marine forms is combined with morphological differences from them found in terrestrial and freshwater species to suggest profitable lines of future research.
(4) Water relations pose a major problem for both terrestrial and freshwater nemerteans. The role of the cerebral organs, the blood and the excretory system in the osmotic physiology of some littoral nemerteans is beginning to be understood. These systems in land and freshwater forms have clearly distinctive features which need to be thoroughly investigated.
(5) Suggestions are given for valuable lines of investigation of the mucous glands, digestive physiology and general behaviour of terrestrial and freshwater nemerteans.     

油菜菌核病菌生理生态研究

通过试验分析,结果得出,油菜菌核病菌生长温度范围在0～34℃之间,23℃以下菌丝生长速度与温度呈正相关,25℃以上则呈负相关,23～25℃最适宜,菌丝和菌核致死温度分别为45℃和75℃．该菌对酸碱度适应范围很广,PH1～14范围内只在PH_1条件下不能生长,其最适PH值为5～6。病菌利用铵态氮源能力最强,硝态氮源次之,不能利用亚硝态氮;对氨基酸利用能力以精氨酸最强,其次是酪氨酸、天门冬氨酸和谷氨酸,赖氨酸最差。植株内精氨酸和赖氨酸比值大的白菜型油菜“黄鳝籽”病情扩展最快。     

PARASITIC CRUSTACEANS OF AFRICAN FRESHWATER FISHES FROM THE NILE AND NIGER SYSTEMS

New crustaceans parasitie on African freshwater fishes of the Nile, or former Nile, and Niger systems are described. The taxonomy of a group of closely related species of Argulus is clarified, and errors in the older literature are corrected. Additional information on distribution is presented.     

GLOCHIDIA OF THE FRESHWATER MUSSEL LAMPSILIS OVERWINTERING ON FISH HOSTS

Largemouth Bass were infected with glochidia of the freshwatermussel Lampsilis cardium. Three fishes each were held at 4.5,10, and 15.5°C; five fish were held at 21°C.By 64 days,metamorphosed juveniles were found in the 15.5 and 21°Ctrials but not in the5.5 and 10°C trials, indicating thatthe lower threshold temperature for metamorphosis wasbetween10 and 15.5°C for the duration. In a second experiment,Largemouth Bass wereinfected with glochidia of L. cardium andheld at 10°C. A sample of fishes wasremoved monthly andbrought to 21°C. Numbers of glochidia that metamorphosedafterbeing warmed were compared to the number that metamorphosedwithout warming. Thepercentage that metamorphosed after warmingdecreased linearly with time. At one month, 100%of the glochidiametamorphosed after warming. This decreased to 80% by two months,to 30%by four months and 3% by six months. Although this post-warmingpercentage decreased withtime, the total percentage of metamorphosedjuveniles (at all temperatures) was not correlatedwith time.Controls kept at 21°C required three weeks to reach peakmetamorphosis, but testsubjects subjected to 10°C requiredless than nine days to metamorphose once warmed.Many overwinteringglochidia therefore complete a portion of their developmenton the host atwinter temperatures, but stop short of excystment.Some glochidia metamorphosed without beingwarmed, but thisphenomenon is not understood. This study confirms that glochidiamayoverwinter on hosts, with some glochidia persisting formore than six months beforemetamorphosing when warmer conditionsreturn. (Received 29 September 1998; accepted 18 January 1999)     

广西野生淡水鱼类的物种多样性及其资源的可持续利用

广西地形复杂,河流众多,适于不同鱼类的栖息和繁殖.经对分布于广西境内的各水系鱼类资源的调查、对相关馆藏标本的进一步鉴定以及对相关文献的整理,目前已知广西淡水鱼类15目37科143属290种和亚种,其中很多种类具有重要经济价值.对广西及其邻近省区鱼类多样性指数的计算、比较和分析表明,广西地区G指数最高,F指数和G-F指数除低于云南外,高于广东、海南、贵州和湖南.广西野生淡水鱼类的显著特点是物种多样性高,特有属、种多,很多物种分布区狭窄,区系成分表现出明显的东洋界特点,不同水系鱼类组成各具特色.近年来,广西自然水域的野生鱼类资源的破坏较为严重,本文对广西野生淡水鱼类资源的可持续利用进行了讨论.     

ANATOMY OF THE SWIMBLADDERS OF SEVEN FAMILIES OF TRANSVAAL FRESHWATER FISHES

SUMMARY

IN the genera Barbus and Labeo of the family Cyprinidae there is a typical twolobed, cylindrical swimbladder: a shorter anterior and a longer posterior lobe, connected by an isthmus. The pneumatic duct passes from the anteroventral end of the posterior lobe to the oesophagus. In the genus Labeo two spiral bands encircle the posterior lobe twice. No rete mirabile, nor any indication of a gas gland, was observed.

The species Hydrocynus vittutus of the family Characidae has a very similarly shaped swimbladder to that of the Cyprinidea. Inside the anterior lobe, however, there is a peculiar structure, which is evidently the gas glad, although a rete mirabile was not observed.

In the families of the Siluriformes, studied, with the exception of the Clariidae, a single lobed, heartshaped swimbladder is present. It is divided by a longitudinal and a transverse. septum into three chambers: an anterior, a right and a left posterior chamber. The pneumatic duct originates from the medial posteroventral part of the anterior chamber. In Clarias gariepinus the two-lobed, right and left lobed, swimbladder lies in a bony capsule, which is attached transversely to the posteroventral part of the skull. In all the Siluriformes, studied, no trace of a gas gland, nor of a rete mirabile was found.

The Cichlid swimbladder has no pneumatic duct, nor any other exit, hence it is physoclistic. In the Cichlids the retroperitoneal position of the swimbladder is accentuated, as the peritoneum and the outer tectum of the swimbladder have united to form a thick, tough membrane, which divides the body cavity into a distinct ventral, or visceral cavity, and a dorsal, or swimbladder cavity. The swimbladder cavity acts as an outer swimbladder. It contains an inner, smaller bladder whose internal ventro-anterior surface is covered with arborescently arranged patches of gas glands.

The attachment of the swimbladder to the tripus and also to the ossa suspensoris is discussed.     

酸性水对几种主要淡水鱼类的影响

在实验室条件下,研究了酸性水对几种主要淡水鱼类的毒性影响,结果表明,这几种淡水鱼的胚胎和鱼苗的死亡率与Ｈ的浓度呈现相关性,在低ｐＨ水平下,胚胎的发育进程明显地迟缓,要使鱼类受精卵正常孵化不受影响,水中的ｐＨ值应保持在６．５以上,在受试的几种鱼类中,没有发现对低ｐＨ敏感性有显著性差异,但在各自的发育过程中,其敏感性呈出现较大的差异,当ｐＨ〈６．０时,鱼的鳃组织就会受到损害,低ｐＨ加上铝,则对鱼类呈现     

EXPLORATORY STUDIES ON THE PHYSIOLOGY AND ECOLOGY OF A PSYCHROPHILIC MARINE DIATOM1

The effect of light, of 2 wavelengths, and of 3 temperatures on the uptake and evolution of O₂ by the antarctic marine diatom, Fragilaria sublinearis, has been examined with mass spectrometry. The responses of this organism to light, in terms of O₂ exchange, were qualitatively similar to those recorded by Hoch et al. with the blue-green Anacystis nidulans. In addition, distinctive temperature optima were indicated for O₂, production and uptake, which help to explain the psychrophilic character of the diatom. The possibility of varying rates of O₂ uptake in the light being associated with photoassimilation of organic substrates has been discussed.     

ADDITIONS TO THE CHECKLIST OF SOUTHERN AFRICAN FRESHWATER FISHES AND A GAZETTEER OF SOUTH-WESTERNANGOLAN COLLECTING LOCALITIES

SUMMARY

An additional 13 species of freshwater fishes recorded from south-western Angola, mainly from the Cunene Basin, are added to the checklist of southern African freshwater fishes, including five species of marine origin permanently resident in the fresh water of the Cunene River mouth. In addition, attention is drawn to a number of doubtful records from the region. A gazetteer of collecting localities in the region is presented.