Keratella Bory de St. ID; Synonym Anuraea Ehrenberg, ref. ID; or ref. ID; , reported year? ID; , [ref. ID; ] Dorsal surface of lorica with a pattern polygonal facets.

Author:Kigataur Akibar
Language:English (Spanish)
Published (Last):26 January 2018
PDF File Size:14.22 Mb
ePub File Size:2.18 Mb
Price:Free* [*Free Regsitration Required]

Keratella Bory de St. ID; Synonym Anuraea Ehrenberg, ref. ID; or ref. ID; , reported year? ID; , [ref. ID; ] Dorsal surface of lorica with a pattern polygonal facets. With one, two or no posterior spine and with six short to medium anterior spine. Highly variable plankton and limnetic species. Very common species. ID; [ref. ID; ] The genus contains, to date, approximately 16 known species which are placed in recognized, defined morphological groups principally on the basis of the variable lorica form.

There are three broad Formenkreis recognized: quadrata, valga-tropica and cochlearis, however there are as well several species groups which, although they show a certain morphological stability, are not, without further study, able to be ranked, e.

The taxonomy of most polymorphic species at present, is based on morphological lorica markings, particularly the foundation pattern facettation , the dorsal lorica, relative length of lorica spines and the surface structure.

ID; ] Mode of Egg-carrying ref. ID; Quote from ref. ID; ] This genus is divided into several species based upon the following characters Ahlstrom ; Gillard : 1. The presence or absence of posterior spines, their number and position. The pattern of dorsal sculpture on the lorica. The proportions of the body, especially as regards size, shape, width and depth. The number of anterior spines. The ornamentation of the ventral plate. The ornamentation of the dorsal plate rather than the fundamental pattern of the dorsum.

Position of the posterior spines terminal for cochlearis group, lateral for quadrata-valga group. Features of the dorsal sculpture on the lorica as the difference between americana and cochlearis, cochlearis and irregularis, serrulata and cochlearis, or testudo and quadrata. General shape or proportions of the lorica as the difference between K. Features of the occipital spines as the difference between taurophala and cochlearis. Such characters as presence or absence of the posterior spines, the ornamentation except for sculpture of the dorsal plate, however, have no taxonomic value.

The number of anterior spines is so constant in this genus contrary to Brachionus, that it might serve for generic separation when it is different cf. ID; ] Brachionid rotifers with loricate body, separated into a dorsal and ventral plate. Dorsoventrally ore or less compressed. Anterior margin usually with six spines. Posterior spines often present, one or two in number, single posterior spine usually median.

Dorsal plate with sculptural pattern, with or without areolate network, postulation, or fine spines. Many species in fresh water, only a few in brackish water. Keratella cruciformis cruciformis, cr. ID; Keratella ahlstromi Russell, ref.

ID; , , original paper Keratella americana Carlin, ref. ID; , , , , , , , , , reported year? ID; , ; Keratella gracilenta Ahlstrom, ref. ID; ; Keratella stipitata Harring, ref. ID; , Keratella americana f. ID; Keratella americana nhamundiensis Koste, ref.

ID; original paper Keratella australis Berzins , ref. ID; , , , Quote from ref. ID; Syn; Keratella quadrata australis Berzins, ref.

ID; Keratella bostoniensis Rousselet ref. ID; Keratella canadensis Berzins, ref. ID; , original paper or ref. ID; See; Keratella javana Hauer ref. ID; , , Keratella cochlearis-group [ref.

ID; ] Keratella cochlearis and related species have very important problem of their morphological variability and possible transitions between different forms. Lauterborn , has put forward his theory explaining different forms of the Keratella cochlearis group by step-by-step changes in morphology and splitting of a uniform winter Keratella into a number of successively separating strains of forms during summer, all of then ending up in the winter form again at the end of the season.

Apart from minor objections and corrections the theory is still generally accepted in Europe, although it has never been proven experimentally. According to Lauterborn, the three main strains deriving from the winter form, Keratella cochlearis fa. Even in the "hispida" and the "irregularis" strains, the posterior spine is successively reduced.

Besides the variable strains, a non-variable, "robusta" group may be found throughout the year, with basically the typical cochelaris characters. Ahlstrom, on the basis of many thousands of careful measurements on material from all over the continent, from Mexico to Alaska, and comparison also with material from Europe and other places, calls into question the direct connection between K. While he accepts, the definition of the robusta as a varieties and does not call into question the same rank for the hispida, he raises the irregularis to the level of an independent species.

Further he describes a new species, Keratella earlinae, obviously the North American equivalent to the European K. They occur widely spread over the continent but have been mistaken without doubt, for K. ID; ] Keratella cochlearis is probably the commonest planktonic rotifer. Carlin proposed to throw the familiar name K.

These animals may be assignable to K. The macracantha series belongs to the typical K. In the specimens of the United Sates, the median line on the dorsum has a slight jog on the right-side at a point between the first and the second plaques, while the median line is straight in most cases of European specimens. Both types are also found in Japan. A new combination of names was proposed by Ahlstrom to the typical form of the irregulars series which should be a species separate from the present species.

This is seldom seen in Japan. The robusta series is a large-sized group, in which the median line does not jog. This type is rare in Japan. The variety hispida, too, is larger size; the whole surface of lorica is hispid, and sometimes the fundamental patterns of dorsum are indistinct. This is rarely met with in Japan.

The forma leptacantha Lauterborn was considered by Ahlstrom to be a local variant of the typical K. Keratella cochlearis is one of the commonest rotifers in Japan. The size of body proper varies considerably, the length of hind spine deviating from nothing to as long as or more than the body proper.

It will be realized that variation seem to be caused not only by the conditions of localities but also by the seasonal factors. Generally speaking longspined individuals occur in early season and the progress of generations through repeated parthenogenesis makes the reduction of the length of hind spine.

The cyclomorphosis may, however, not occur due to the conditions of habitat water; an acyclic generation is resulted. A good samples of such as acycly due to a large body of water is seen in K.

The length of hind spines and the hind spine indices do not vary in accordance with the climates. In North America, a small-sized K. On the contrary, a remarkably large type of K. The size of individuals from the Shiga Heights exceeds that of var. Moreover, it is a particular interest that the length of the hind spine is considerably longer than the body proper.

It would, therefore, be called as the megacantha type in the macracantha series. The measurements made on more than one thousand individuals of this series revealed us the following facts worthy to be described. A gap is clearly observed between the megacantha type and the macracantha type, and also between the macracantha type and the tecta type, in the latter of which the hind spine is entirely lacking.

On the other hand, individuals of intermediate types are continuous in regard to the features which are measured, either the length of body proper and hind spine or the hind spine indices.

Anyhow, there can be seen a tendency that the larger the body size, the longer the hind spine. ID; ] For reasons of priority Carlin , p. In view of the different opinions expressed the author has referred the question, in accordance with the decision of the Zoological Congress in Paris of , to the International Commission on Zoological Nomenclature see Bull.

Pending the decision of the Committee the author uses the, up to now, most current name, viz. Keratella cochlearis. ID; ] The Keratella species with one posterior spine and size anterior spines, and a marked median keel was, without doubt, Keratella cochlearis Gosse.

It is difficult, however, to classify the form within the 8 varieties and 6 forms described Voigt The identification of varieties and forms is based on the following characteristics: total length of posterior spine, macro- and micro-sculpture dorsally on lorica, thickness and colour of lorica and the angle between posterior spine and ventral list of the lorica. Different varieties may show cyclomorphosis. The angle between the posterior spine and the ventral list of lorica varied.

The total length and the length of the posterior spine were measured on 40 individuals at different seasons.



Description[ edit ] Keratella cochlearis has an oval lorica , a shell-like protective outer cuticle. At the anterior end are three pairs of spines. The central pair curve towards the ventral surface, the next pair diverge slightly and the outer pair converge. There is a single red eye [3] There is also a central funnel-shaped mouth and on either side of this are rings of cilia which twirl and help waft food particles into the mouth. They are also used for locomotion.


Keratella cochlearis subsp. cochlearis


Related Articles