XITOMITRIDAE

Family XITOMITRIDAE

O’Dogherty, Goričan & Gawlick, 2017

Xitomitridae O’Dogherty, Goričan & Gawlick, 2017 : 60.

TYPE GENUS. — Xitomitra O’Dogherty, Goričan & Gawlick, 2017: 62 [ type species by objective designation: Stichomitra ? tairai Aita 1987: 72].

INCLUDED GENERA (CENOZOIC ONLY). — Dictyomitrella Haeckel 1887: 1476 (= Parvimitrella n. syn.).

DIAGNOSIS. — A multisegmented Nassellaria whose cephalis is both small and poreless. All of its segments, except for the cephalis, are covered with a latticed meshwork of uniform sized pores. The distal end of the test is open or nearly closed, without distal projections or appendages. The cephalic initial spicular system present at least a MB, A-, V-, D- and double L-rods. MB is rises obliquely to the A-rod side. Thus, the basal ring of the cephalis is also oriented obliquely. The A-rod extends upright in the cephalic cavity to attach itself to the cephalic wall or even penetrate the wall. An amphipyndacid-like divider is visible in the cephalis. The divider in the proximal upper-section is constructed by the MB, D- and double L-rods.

STRATIGRAPHIC OCCURRENCE. —Early Aalenian-late Middle Eocene.

REMARKS

The Xitomitridae were related with the Canoptidae , Parvicingulidae and Xitidae ( O’Dogherty et al. 2017) . The cephalic structure of the type species of Xitomitra O’Dogherty et al. 2017 (the Middle-Late Jurassic Stichomitra ? tairai Aita, 1987) is well recognized in its paratypes ( Aita 1987: pl. 3, fig. 8a). Referring to this photo, “the divider” in the proximal top is constructed by MB, D- and double L-rods. This does not correspond to the characteristics of the divider in Amphipyndacoidea . The proximal top of the Xitomitra tairai consists of a cephalis and thorax. The divider in Xitomitra is poorly developed in comparison to the basal ring of the cephalis in the Eucyrtidiidae . Conversely, Dictyomitrella , and the Paleogene member of the Xitomitridae appear to have a well-developed cephalis basal ring such as in the Eucyrtidiidae ; however, the MB of Dictyomitrella is obliquely oriented. The cephalic view of the type species ( lectotype) of Dictyomitrella is also shown in pl. 22, figs 1e and 1f of Ogane et al. (2009b).

Phylogenetic Molecular Lineage II ( Sandin et al. 2019)

DIAGNOSIS. — Anatomically, one or two segments, but usually one segment, is observed. This is true for most cases except Lampromitridae and some members of the Artostrobiidae .If a subsequent shell develops, the final segmented part is not divided by an inner ring. This is unlike the Eucyrtidiidae . No common characteristics in the cephalic structure are recognized among the members. No feet are observed except in some members of the Acanthodesmioidea and Diacanthocapsidae .

REMARKS

Lineage II includes the Plectopyramidoidea (originally Acropyramioidea), Carpocanioidea (originally Carpocaniidae ), Artostrobioidea , and Acanthodesmioidea (originally Acanthodesmoidea in Sandin et al. 2019). Although the independency of the Lineage II from the other Lineages is supported with 100% PhyML bootstrap values with 10 000 replicates (BS) and>0.99 posterior probabilities (PP); the independency of superfamilies inside Lineage II is only supported for the Acanthodesmioidea with 100% PhyML bootstrap values with 10 000 replicates (BS) and>0.99 posterior probabilities (PP). The trees of the remaining three superfamilies have not been agreed upon within Lineage II. As for the Carpocaniidae and Artostrobiidae , both families have a common structure with very complex arches around the V-rods. Thus, it may not be necessary to separate them at the superfamily-level (see remarks for the Carpocanioidea , Carpocaniidae and Artostrobiidae ). However, this possibility should be carefully examined in consideration of the Mesozoic members.