Sigmoopsidae

Ventral (upper) and right views of Winchellatia minnesotensis, from Benson et al. (1961).

Belongs within: Ostracoda.

The Sigmoopsidae are a group of dimorphic ostracods known from the Ordovician (Benson et al. 1961).

Characters (from Benson et al. 1961): Carapace nearly equivalved, with straight hinge line; valves subquadrate to subelliptical in outline and bi-, tri-, or quadrilobate, usually with gently convex posterior region forming extralobate area, lobes joined to ventral ridge that by its position usually corresponds to histium; S₂ uniformly present, generally long and sinuous, S₃ present in trilobate genera; marginal and one or two parallel structures developed in most species as low unornamented ridges. Dimorphism present, expressed in form of outermost ridge or flange-like structure (histium); ridge between marginal and histial structures sometimes present.

<==Sigmoopsidae [Sigmoopsidinae, Sigmoopsiidae]
    |--Sigmoopsis Henningsmoen 1953 BB61
    |    `--*S. platyceras (Öpik 1937) [=Ceratopsis platyceras] BB61
    |--Aulacopsis Hessland 1949 BB61
    |    |--*A. bifissurata Hessland 1949 BB61
    |    `--A. simplex (Krause 1892) TM02
    |--Brevibolbina Sarv 1959 BB61
    |    `--*B. dimorpha Sarv 1959 BB61
    |--Carinobolbina Henningsmoen 1953 BB61
    |    `--*C. estona (Öpik 1937) [=Ctenobolbina estona] BB61
    |--Disulcina Sarv 1959 BB61
    |    `--*D. perita (Sarv 1956) [=Ctenobolbina perita] BB61
    |--Ogmoopsis Hessland 1949 BB61
    |    |--*O. nodulifera Hessland 1949 BB61
    |    `--O. bocki (Öpik 19350 TM02
    |--Ordovicia Neckaja 1956 BB61
    |    `--*O. porchowiensis Neckaja 1956 BB61
    |--Pseudotallinnella Sarv 1959 BB61
    |    `--*P. scopulosa Sarv 1959 BB61
    |--Reigiopsis Sarv 1959 BB61
    |    `--*R. oepiki Sarv 1959 BB61
    |--Lomatobolbina Jaanusson 1957 BB61
    |    |--*L. mammillata (Thorsland 1940) [=Ctenobolbina mammillata] BB61
    |    `--L. craspedota BB61
    |--Oecematobolbina Jaanusson 1957 BB61
    |    |--*O. nitens Jaanusson 1957 BB61
    |    `--O. ctenolopha BB61
    |--Sigmobolbina Henningsmoen 1953 BB61
    |    |--*S. kuckersiana (Bonnema 1909) [=Entomis oblonga var. kuckersiana] BB61
    |    `--S. sigmoidea BB61
    |--Polyceratella Öpik 1937 BB61
    |    |--*P. kuckersiana (Bonnema 1909) [=Ulrichia kuckersiana] BB61
    |    |--P. bonnemai BB61
    |    `--P. tetraceras BB61
    `--Winchellatia Kay 1940 BB61
         |--*W. longispina Kay 1940 BB61
         |--W. lansingensis BB61
         `--W. minnesotensis BB61

*Type species of generic name indicated

REFERENCES

[BB61] Benson, R. H., J. M. Berdan, W. A. van den Bold, T. Hanai, I. Hessland, H. V. Howe, R. V. Kesling, S. A. Levinson, R. A. Reyment, R. C. Moore, H. W. Scott, R. H. Shaver, I. G. Sohn, L. E. Stover, F. M. Swain & P. C. Sylvester-Bradley. 1961. Systematic descriptions. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt Q. Arthropoda 3: Crustacea: Ostracoda pp. Q99–Q421. Geological Society of America and University of Kansas Press.

[TM02] Tinn, O., & T. Meidla. 2002. An enigmatic early ?palaeocope ostracode from the Arenig of NW Russia. Acta Palaeontologica Polonica 47: 685–690.