Burmisotoma spinulifera, Sánchez-garcía & Engel, 2016

Sánchez-garcía, Alba & Engel, Michael S., 2016, Springtails from the Early Cretaceous Amber of Spain (Collembola: Entomobryomorpha), with an Annotated Checklist of Fossil Collembola, American Museum Novitates 2016 (3862), pp. 1-48 : 5-8

Burmisotoma spinulifera , new species

Figures 1–2

DIAGNOSIS: Aside from the general traits of the genus (outlined by Christiansen and Nascimbene, 2006), the new species differs from the type species ( Burmisotoma lamellifera Christiansen and Nascimbene ) by the presence of a long, thick, and straight femoral spine, as well as a ventrally crenulate manubrium.

DESCRIPTION: Total body length as preserved 473 µm. Body slender, thickened in posterior half, of typical isotomid shape. Dorsal integument with distinct, fine reticulation; all body setae smooth.

Head length as preserved 122 µm, about 0.26× length of body; covered largely with sparse, somewhat curved, slender setae; antennae with four antennomeres; fourth antennomere not swollen, densely setaceous, with slender, mostly weakly curved, acuminate, long setae, accompanied by some thick, truncate, cylindrical, long setae on apical half of antennomere; first to third antennomeres mostly obscured preventing measurements. Ommatidia not visible. Postantennal organ not visible (likely not present).

Thorax highly distorted, maximum width 87 µm, without visible setae; prothoracic segment membranous; meso- and metathoracic segments subequal in length.

Legs with trochanter poorly visible, with a few short, weakly curved, acuminate setae; femur length 33 µm, bearing a thick and straight spine, about as long as femoral diameter; tibiotarsus length 43 µm, with several slender setae, setae apparently not clavate nor truncate; unguis and unguiculus not clearly visible, apparently simple, without serration or denticles; unguis length 23 µm, acuminate.

Abdomen swollen and somewhat ovoid, maximum width 153 µm, distinctly wider than thorax, with sparse, straight to somewhat curved, slender setae, such setae becoming longer and more numerous posteriorly; abdominal segments not fused; third and fourth abdominal segments subequal in length, fourth segment only slightly longer than third segment; lengths of abdominal segments III–VI in µm, approximately: III, 43; IV, 49; V, 27; VI, 20. Length, exclusive of appendages 107 µm.

Furcula long and slender (visible in lateral view); manubrium length 36 µm, ventrally crenulate, without visible setae; dens length 84 µm, tapering distally, without visible setae; mucro poorly visible, apparently bidentate.

HOLOTYPE: MCNA 12583 (fig. 1), virtually complete, visible dorsally, ventrally, and laterally. Preserved in a clear-yellow, turbid piece of amber trimmed to 1.05 × 0.80 × 0.05 cm (set into an epoxy trapezoid of dimensions 2.10 × 1.20 × 0.10 cm), and included with fungal hyphae, and many arthropod (e.g., scales) and plant remains (e.g., stellate hairs).

OCCURRENCE: Peñacerrada I amber site (Peñacerrada I = Moraza), Utrillas Group, eastern area of the Basque-Cantabrian Basin, Burgos, northern Spain; Early Cretaceous (Late Albian).

ETYMOLOGY: The specific epithet is from the Latin spinula (meaning, “small spine”) and fero (meaning, “bear” or “carry”), and refers to the femoral spine distinctive of the species.

REMARKS: The genus Burmisotoma was described originally from a single specimen in mid-Cretaceous amber from Myanmar ( Burma). Burmisotoma spinulifera , n. sp., shares with the type species, B. lamellifera , a well-developed furcula lacking ventral manubrial setae, strongly tapered dentes, and the antennae bearing stout, cylindrical, truncate setae. Unfortunately, the ommatidia, details of the setae and tubercles of the dens, and the morphology of the mucrones were not clearly visible in B. lamellifera , preventing comparison of these structures with the present specimen. In the new species, the body shape (slender and thickened in the posterior half), general chaetotaxy of the body, antennal structure, and the tarsal complex are all very similar to B. lamellifera as illustrated by Christiansen and Nascimbene (2006); therefore, the most reasonable is to consider them congeneric. However, B. spinulifera is remarkable in having a thick and straight femoral spine (fig. 2), and a ventrally crenulate manubrium. The dorsal reticulation of the integument is also distinctive of the new species. These features are, however, merely autapomorphic and the establishment of a separate genus based on these comparatively minor differences would serve only to proliferate the number of monospecific genera for otherwise quite similar Cretaceous springtails.

Genus Protoisotoma Christiansen and Pike, 2002a

Protoisotoma Christiansen and Pike, 2002a: 171 . Type species: Protoisotoma micromucra Christiansen and Pike, 2002a , by original designation.

Figures

FIGURE 1. Microphotographs of the holotype (MCNA 12583) of Burmisotoma spinulifera, new species, in Late Albian amber from northern Spain (images combining consecutive photographs taken at successive focal planes). A. Dorsal habitus. B. Ventral habitus. C. Detail of manubrial crenulation.

FIGURE 2. Camera lucida drawing of the holotype (MCNA 12583) of Burmisotoma spinulifera, new species, in dorsal habitus.