Bekomidae Dumitrica in De Wever, Dumitrica, Caulet, Nigrini & Caridroit 2001

Family BEKOMIDAE Dumitrica in De Wever, Dumitrica, Caulet, Nigrini & Caridroit, 2001

Bekomidae Dumitrica in De Wever, Dumitrica, Caulet, Nigrini & Caridroit, 2001: 284. — Matsuzaki et al. 2015: 63-64.

Bekominae – Afanasieva et al. 2005: S296. — Afanasieva & Amon 2006: 145.

TYPE GENUS. — Bekoma Riedel & Sanfilippo, 1971: 1592 [type species by monotypy: Bekoma bidarfensis Riedel & Sanfilippo, 1971: 1592].

INCLUDED GENERA. — Bekoma Riedel & Sanfilippo, 1971: 1592. — Bekomiforma Sanfilippo & Riedel, 1974: 1020. — Lamprotripus Haeckel, 1882: 431. — Orbula Foreman, 1973a: 437.

NOMINA DUBIA. — Stichocampe, Stichopterium.

DIAGNOSIS. — Bekomidae consist of two-segmented Lithochytridoidea (exclusive of Orbula) with six collar pores that form the basal ring of the cephalis, two free A- and V-rods in the cephalic cavity, and three feet. Except in the case of Lamprotripus, the cephalis is covered with a thick siliceous wall. The cephalic initial spicular system consists of A-, V-, D-, double l-, and double L-rods. A combination of A- and V-rods, or solely A-rod, forms one or more significant cylindrical apical horn(s). D- and double L-rods protrude from the cephalis and form three feet or rims on the thorax. The MB is located in the center of the basal aperture of the cephalis. The basal ring is directly connected to the D-, double l- and double L-rods. The basal ring tends to be located horizontally in the cephalic cavity. Although the basal ring is generally merged to the shell wall, it is well visible in older forms (Bekoma and Bekomiforma) but degraded in a younger form (Lamprotripus).

A protoplasm is observed in Lamprotripus. The endoplasm is opaque dark grey, filling the upper part of the shell at the level where three rod wings are separated from the shell. No algal symbionts are present.

STRATIGRAPHIC OCCURRENCE. — Middle Paleocene-Living.

REMARKS

The Bekomidae are distinguishable from the Lithochytrididae. The latter lack the double l-rod and have four collar pores instead of six and their MB is oblique to the collar stricture.The cephalic initial spicular system was illustrated for Bekoma (Nishimura 1992: pl. 5, figs 4, 5, 9, 11; pl. 8, fig. 5?), Bekomiforma (Sugiyama et al. 1992: pl. 20, fig. 1) and Lamprotripus (Nishimura & Yamauchi 1984: pl. 31, fig.1; Nishimura 1990: figs 26.6, 26.7, 29.6; Sugiyama et al. 1992: pl. 22, fig. 1). The diagnosis written above excludes the characteristics of “ Lamprotripus ” mawsoni (Riedel 1958). As this species lacks the double l- and V-rods (Sugiyama et al. 1992: pl. 16, figs 4, 5), it cannot be placed in Lamprotripus. This species is also grouped with Dictyopodium (= Pterocanium in original) but not Lamprotripus in the Clade I (Sandin et al. 2019). “ L.” mawsoni has three collar pores as opposed to four.Sugiyama et al. (1992: 18-19) conceptualized it as a new genus. The living appearance of Lamprotripus is documented (Suzuki & Not 2015: fig. 8.10.15).