Acineta Ehrenberg, 1833 (ref. ID; 2013) or 1834 (ref. ID; 3552), Ehrenberg, 1833 emend. Collin, 1912 (ref. ID; 3475) ,
Class Kinetofragminophora: Subclass Suctoria: Order Suctorida: Suborder Endogenina (ref. ID; 2013)

[ref. ID; 2013]
Body inverted conical shape within a cup-like lorica which in some species may be close fitting and difficult to observe. The body may or may not completely fill the lorica which is flattened and borne upon a stalk. The lorica opens apically usually as a dump-bell shaped slit. The body and tentacles protrude through this aperture. The tentacles which are commonly capitate are arranged in 2 (but may be in 3) distinct fascicles. The macronucleus is rounded to ovoid. A larva which has a ciliated band or is completely ciliated is produced by simple endogenous budding. Acineta is most easily confused with Acinetides, Canellana and Tokophrya. There are several species and the genus may be freshwater or marine.
Quote; Colin R. Curds "British and other freshwater ciliated protozoa Part I Ciliophora: Kinetofragminophora" Cambridge University Press, 1982 (ref. ID; 2013)


Acineta acuminata Stokes, 1887 (ref. ID; 2020)
Description; The shape of this form, found in "pond water" (probably in North America) is described by Stokes as follows; Lorica broadly vasiform, slightly longer than broad, the posterior border rounded, the anterior continuous, obliquely truncate on each side, and produced centrally in a prominent accumulation, the lateral angles also often acuminately prolonged; the anterior borders on each side separated by a slit-like aperture, and the front wall bearing two narrow, anteriorly converging fissures for the passage of the tentacles; pedicle hollow, from one-third to one-half as long as the lorica and communicating with it cavity; ... Length of lorica 1/500 inch (= 50.8 um)... The lateral angles are sometimes produced, sometimes rounded; and occasionally one will be rounded and the other slightly produced. The anterior central acumination has been present in all forms observed. That only one wall of the lorica should be pierced by two converging fissures is oteworthy. Corresponding lines on the opposite wall could not be perceived, although careful search was made for them". J. Rieder feels embarassed by this text as well as by the appertaining figure, which both could not give him a clear idea of the lorica, in particular the exact disposition of its clefts. It seems very possible that the aspect described and depicted by Stokes could be the optical consequence of an oblique position of the animal with respect to the direction of observation. This is imaginable because something quite alike can often be seen under this condition also in "normal" types of Metacineta mystacina, especially such with a relatively broad and short anterior part of the lorica, when the valves of the latter are fairly strongly vaulting inwards and thus resemble spherical triangles. Opposite such valves, touching each other with their apical borders, look then as a protruding central acumination and the basal ends of opposing clefts can appear situated on more or less pronounced prominescences. In fact, it is evident that at least the individual shown in Stokes has been drawn in an oblique orientation, because this is the only simple explanation for a crossline simulating a membranous separation between the proximal and the distal part of the lorica, which would be in discrepancy with the real construction in Metacineta. There remains the positive ascertance by Stokes that the lateral wall of the lorica was pierced by only two fissures. This signifies only one plane of symmetry parallel to the long axis, whereas in principal and according to the general experience the genus Metacineta shows radial symmetry parallel to the long axis. Slight approximations to bilateral symmetry or even to asymmetry frequently occur due to the fact that the fissures may be somewhat different in length or that some of the valves may be more trapezoidal, others more triangular in shape. The cross section too of the widened part of the lorica may then slightly deviate accordingly from a regular polygon. But such commonly seen deviations from the ideal are phenomena of the individual variability within a population, not features of all the members of this population. If pronounced bilaterality or severe asymmetria is present equally and simultaneously in multitude of Metacineta, such animals should, in the opinion of J. Rieder, not be considered as representing a separate normal species. If their structure is unstable in successive generations, they are most probably an abnormal form resulting from a disturbance of the secretion of the lorica by an endogeneous or exogeneous factor. If the peculiarity prooves stable over many generations, it can be admitted sufficient importance to determine a separate variety. In the case of "Acineta acuminata" not even the erection of a new variety can be accepted, because on the base of Stokes documentation the animals cannot be identified securely. For the same reason it is also not possible, to transfer to these animals the clearer description and the better drawing given by Penard (1920) of a form of Metacineta mystacina studied by him in the locality of Florissant and which he supposed to correspond to, but was not shure to be identical with "Acineta acuminata Stokes (1887)". (ref. ID; 2020)
Acineta cuspidata Stokes (ref. ID; 1618)
Description; Lorica cup-shaped; front end with two opposing sharp points; on Oedogonium in fresh water. (ref. ID; 1618)
Measurements; Lorica 32-42 um high. (ref. ID; 1618)
Acineta lacustris Stokes (ref. ID; 1618)
Description; Lorica elongate ovoid; flattened; on Anacharis in pond. (ref. ID; 1618)
Measurements; Lorica 75-185 um high. (ref. ID; 1618)
Acineta nitocrae (ref. ID; 3552)
Description; Acineta nitocrae is a commensal suctorian ciliate that lives on the exoskeleton of harpacticoid copepods. Its life cycle is composed of a free-swimming larval stage (swarmers, or tomites) and a sessile adult stage (trophonts). Trophonts adhere to the integument of substance organisms by means of a stalk and an adhesive disc situated on its base. Swarmers, which develop in a brood pouch of the maternal cell, are mouthless and possess a ciliary field used for swimming. Swarmers form the stalk to attach to a substrate suitable for settlement. Shortly after settling, they undergo further metamorphosis involving resorption of the cilia and differentiation of tentacles from the tentacle anlages. A. nitocrae possesses a rigid lorica, covering the cell body, and a series of clavate tentacles positioned on the actinophores at the body end opposite the podite. (ref. ID; 3552)
Comments; Acineta nitocrae differs from other members of the genus Acineta Ehrenberg, 1834 by its possession of a more elongated and less depressed body, more extensively developed triquetrous actinopores and a short, curved stalk (Dovgal 1984, 1996, Curds 1985). The ratio of the lorica length to the lorica width averaged nearly 2.9:1 (n=70) in A. nitocrae. Another important feature, making separation of this species from North American congeners straightforward, is that its trophonts are specialized for epizooic existence with harpacticoid copepods and colonize predominantly the caudal rami. (ref. ID; 3552)
Acineta periacinetoides Nozawa, 1938 (ref. ID; 3475 original paper)
Description; The test is cup-shaped, with the height about 1.5 times the median breadth, strongly compressed, and its contour is of an elongated ellipse in the apical view. A fibrillose short stalk is attached to the cup; at the other end the stalk is somewhat dilated. In texture the test is thin, transparent and may show two or three lines of growth. The body is closely fitted to the test, leaving no space between. The macronucleus is single, ovoid, and situated in the middle of the body. Near the anterior end of the body is one contractile vacuole, which opens to the outside by a distinct leading canal. The sucking tentacles are distinctly capitated, as long as the body, and spring from the anterior end of the body is two fascicles, each comprising from 6 to 10 tentacles. (ref. ID; 3475)
Comments; This animalcule closely resembles Periacineta linguifera (Claparede & Lachmann) described in Kent (1880-82) in its general appearance. However, it may be distinguished from the latter by the present of a single contractile vacuole and by the minuteness of the body. While Kent gives a figure of a stalk in Periacineta by mistake, this species is furnished with a distinct stalk. In this respect this species belongs not to Periacienta but to Acineta. (ref. ID; 3475)
Type locality; On the shells of Viviparus found in a small pond in Kitasirakawa, Kyoto (May, 1937) (ref. ID; 3475)
Measurements; Length of body 42, anterior breadth 34, posterior breadth 20, length of stalk 7, its thickness 6 um. (ref. ID; 3475)
Acienta speciosa Maskell, 1887 (ref. ID; 2020)
Description; Maskell has called Acineta elegans, 1886 in the first and Acineta speciosa, 1887 in the second of his publications mentioned, which might possibly evoke the question, whether it is a special kind of Metacineta. (ref. ID; 2020)
Acineta stagnatilis Stokes, 1886 (ref. ID; 2020)
Description; [Stokes's original description]; Lorica subcircular in outline, rounded and inflated posteriorly, compressed anteriorly, the frontal border irregularly convex; pedicle short, hollow, from one-forth to one-fifth as long as the lorica, widest at its junction with the sheat, tapering thence and terminating in a button-like point of attachment; frontal margin pierced by a slit-like fissure, and two anterior converging, narrow fissures on the front and rear walls, for the exit of the tentacles; the enclosed animalcule occupying the centre of the lorica, apparently not attached to the walls, subsperoidal, the anterior border truncate; tentacles more or less fascicled, capitate; contractile vesicle single, postero-lateral; endoplasm granular. Length of the lorica, including pedicle 1/450 inch (= 56 um). Habitat: Pond-water; on Myriophyllum. (ref. ID; 2020)
[J. Rieder's opinion]; This form cannot be judged with full certitude, because neither the description nor the lateral view shown by Stokes are clear in essential details. It is especially unfortunate that a picture seen from the apex is lacking. Thus the configuration of the fissures remains doubtful. One can only assume that the animal belonged to the group of the short-footed Metacineta since it had a fissured lorica with the wall and cavity of which continuous with those of the foot. But it would be impossible to recognize it securely if it should be encountered again. There are also no indications on the number of specimens seen by Stokes and on the stability of these features in time. From his figure they look asymmetrically built. This would be absolutely strange for a Metacineta as for as Acineta. It appears possible that the form in question was inadequately examined or was disturbed in its development by abnormal genetical or external conditions. It has never been signalized since its discovery. For the reasons mentioned J. Rieder thinks, that the animals called by Stokes (1886) "Acineta stagnatilis" cannot be esteemed as representing a duly established separate species or variety. (ref. ID; 2020)
Acineta tuberosa (Pallas, 1766) Ehrenberg, 1833 (ref. ID; 4612) or Ehrenberg, 1838 (ref. ID; 1618, 1629) reported author and year? (ref. ID; 191, 3689)
Syn; Acineta tuberosa var. foetida Sand, 1901; Acineta tuberosa var. fraiponti Sand, 1901; Brachionus tuberosus Pallas, 1766 (ref. ID; 4612)
Description; With stalk; salt and brackish water. (ref. ID; 1618)
Measurements; Lorica 50-100 um high. (ref. ID; 1618)
Acineta variabilis Nozawa, 1938 (ref. ID; 3473 original paper)
Description; The test is thin, sub-quadrangular, compressed laterally, and is hexagonal in contour in the apical view. The hind border of the test is not tapering towards the stalk. The lateral walls are continuous over the free margin of the body, leaving two apertures at the anterior opposite angles. The stalk is short, cylindrical, and rather thick for the body. The protoplasmic body is closely fitted to the test except the front and hind ends. The macronucleus is ovoid, and central. There is one contractile vacuole in front of the nucleus. The tentacles are capitated, and as long as the test. They are 5 to 15 in number in each fascicle, and extruded from the anterior apertures. (ref. ID; 3473)
Comments; This species shows a high degree of variability in its form. The variations are manifested in two ways: the formation of wrinkles in the test, and the increase of the height of the body as compared with the breadth. The wrinkles may be longitudinal or transverse, and seem to be in larger numbers in old and large individuals. As Kahl has pointed out, these wrinkles seem to be no systematic significance. This new species is distinguished from A. corophii Collin in its habitat and in the situation of the contractile vacuole. The latter species which is found on the gills of Corophium living in half-brackish water is provided with a contractile vacuole situated on the posterior side of the nucleus. The present species also differs from A. foetida Maupas in its habitat, its much smaller size, and in the contour of the test in the apical view. The latter species which is found in brackish water has its test 50-80 um in length, and is not hexagonal in contour in the apical view. (ref. ID; 3473)
Type locality; On a kind of green algae attached to the shells of Viviparus found in a pond in Kitasirakawa, Kyoto (from spring to autumn). (ref. ID; 3473)
Measurements; Typical specimens: height of test 31 um, anterior breadth 38 um, and length of stalk 7 um. The height of the test varies from 23 um to 63 um, and the anterior breadth from 30 um to 45 um in adult individuals. So the ratio of anterior breadth to height varies from 1.5 to 0.7. On the other hand, the length of the stalk are less variable, being from 6 um to 8 um. (ref. ID; 3473)