Heraclitus helenae, Sánchez-García & Peñalver & Delclòs & Engel, 2021

Sánchez-García, Alba, Peñalver, Enrique, Delclòs, Xavier & Engel, Michael S., 2021, Terrestrial Isopods from Spanish Amber (Crustacea: Oniscidea): Insights into the Cretaceous Soil Biota, American Museum Novitates 2021 (3974), pp. 1-32 : 21-25

Heraclitus helenae , new species

Figures 10 , 11

DIAGNOSIS: As for the genus (above).

DESCRIPTION: Body (fig. 10) more or less oblong, of “clinger” habitus; small sized, total length 1.76 mm, width not measurable due to orientation in amber; dorsal surface convex, rough, covered with large semicircular scales and densely crowded prominent triangularshaped scale setae arranged in transverse rows; gland pores not visible as preserved.

Cephalon rounded, rather arcuate, rough, with same ornamentation as described for body (fig. 11B); lateral lobes not visible as preserved (probably small); antennal lobes absent. Eyes not visible as preserved.

Pereon about 0.73× of body length; pereonites overlapping, lamellar; lateral parts of pereonites (i.e., epimeral plates) only moderately prominent, those of two posterior pereonites with posterior corners acutely triangular, all edged with small appressed spikes and distinctly prominent triangular-shaped scale setae (as a continuity to those of dorsal surface). Pleon about 0.24× of body length, distinctly narrower than pereon (abruptly contracted); pleotelson short, subtriangular, with rounded apex bearing two short distal setae.

Mouthparts considerably well developed but without visible details.

Antennule poorly visible; distal article with three short thick spines distally.

Antenna (fig. 11A) very spinose in appearance, packed with small scale setae and spines, rather stout, with five peduncular articles and a multiarticulate flagellum; articles 1–3 partly obscured by head, apparently short and stout; fourth article elongate, stout, 0.18 mm long, 2.25× longer than broad; fifth article elongate and much slender than fourth article, 0.22 mm long, 1.22× length of preceding article, 5.5× longer than broad; flagellum partially preserved, with at least three articles not clearly delimited.

Pereopods all alike, of moderate size; all pereopods without sexual modifications; basis and ischium mostly obscured by body; merus, carpus, and propodus with elongate, thick, nearly straight spines generally arranged in a longitudinal row on sternal margins giving them a rippled appearance; propodus and carpus length apparently subequal; dactylus with enlarged outer claw and minute inner claw; dactylar setae unbranched, glabrous, long, and slender, distinctly expanded distally; ungual setae not visible as preserved.

Pleopods not visible as preserved.

Uropod (fig. 11C) moderately elongate, about 0.28× of body length as preserved, freely projecting caudally; protopod produced inside pleotelson, subrectangular, long and stout, 0.15 mm long, with endopod and exopod inserted at same level; exopod styliform, long and slender, width not measurable due to poor preservation, 0.35 mm long as preserved (distal part not preserved), distinctly longer than endopod, with some very short thin setae sparsely distributed; endopod conical, maximum width at base 0.03 mm, tapering distally, 0.21 mm long (excluding terminal tuft of setae), with some very short thin setae sparsely distributed, and a tuft of long setae apically (0.10 mm long).

HOLOTYPE: MCNA 12546 , sex unknown, exposed dorsolaterally, ventrolaterally, and laterally. Preserved in darkened orange-colored amber, trimmed to 3.5×1.7× 1.2 mm (in an epoxy trapezoid 23.0×15.0× 1.5 mm), surrounded by numerous pseudoinclusions ( Lozano et al., 2020) and particles of detritus; no other major inclusions. The specimen is nearly complete, but some areas are poorly visible owing to the position of the animal during fossilization. The distal parts of the uropodal endopod and the antennulae are not preserved.

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

ETYMOLOGY: The specific epithet refers to Helen of Troy, a figure from Greek mythology known for her considerable beauty and having “launched a thousand ships” (à la Marlowe) as Menelaus and Agamemnon initiated the Trojan War to return her to Achaea.

REMARKS: Heraclitus helenae may be clearly differentiated from A. resinicola by the roughened cuticle, the spinose antennulae, the dactylus with two claws, and the longer uropodal endopod. It is perhaps a representative of Crinocheta: Detonidae ? owing to the antennule with a 5-jointed peduncle and a 4-jointed flagellum, the antennulae with conspicuous scaly tubercles, the inner claw small, the uropodal protopod surpassing the pleotelson, the exopodites leaf shaped, and the endopodites styliform ( Schmidt, 2002).

Oniscidea Indet.

SPECIMEN MCNA 14907: (fig. 12A) is preserved in darkened orange-colored amber, trimmed to 10.5×6.0× 1.5 mm (in an epoxy trapezoid 21.1×13.5× 2.2 mm), and surrounded by numerous pseudoinclusions ( Lozano et al., 2020), particles of detritus, fungal hyphae, and three coprolites. The specimen is exposed dorsally and ventrally, poorly preserved, with the cuticle virtually degraded except for the lateral parts of the segments, which are edged with small appressed spikes and some small triangular-shaped scale setae. Worthy of note are the oval-shaped medium-sized body (total length 4.27 mm as preserved, maximum width 2.27 mm), and the moderately large eyes composed of multiple ommatidia (only the left eye is visible). The specimen also possesses a partly preserved antenna (cut just below the articulation between the fourth and fifth articles) that is elbowed between the fourth and fifth articles. The first peduncular article is partly concealed by the head, whereas the measurements of the rest of articles are as follows: second article 0.22 mm long, about as long as broad; third article 0.25 mm long, 1.25× longer than broad, with one long, thick spine; fourth article elongate, 0.58 mm long, 4.83× longer than broad. Only some anterior pereopods are visible, but these are so thoroughly obscured owing to preservation as to provide no useful delineation of features. However, long, thick, nearly straight spines, a dactylus with two claws (the inner claw minute, distinctly smaller than in H. helenae ), and an unbranched, glabrous, long, and slender dactylar seta are visible on some pereopods. The specimen is difficult to place accurately among Oniscidea , but placement within the family Ligiidae seems most appropriate owing to the presence of large eyes composed of multiple ommatidia, the comparatively elongate antennae, and a dactylus with two claws. Interestingly, the specimen corresponds with the anterior half of an exuvia. Isopods perform a biphasic molt, which consists of the shedding of the posterior and then the anterior half of the body. The boundary between the two halves is between the fourth and fifth pereonites, which agrees with that observed in the fossil.

SPECIMEN MCNA 9458: (fig. 12B) is preserved in darkened yellow-colored amber, trimmed to 5.2×3.5×1.0 mm (in an epoxy trapezoid 19.1×14.1× 1.1 mm), and surrounded by numerous pseudoinclusions and particles of detritus; the amber is also darkened near the inclusion. The specimen is exposed dorsally and ventrally, and although a vague outline of the pereopods armed with long, stout, nearly straight spines can be seen, these are so thoroughly obscured owing to preservation and by the adjacent body mass as to provide no useful delineation of features. It possesses a more or less oblong, small body (total length 2.09 mm long as preserved, maximum width 0.87 mm), and some segments of the pereon with some small triangular-shaped scale setae.

SPECIMEN MCNA 9924.2: (fig. 13; previously figured in Delclòs et al., 2007, Broly et al., 2013, and Sánchez-García et al., 2015) is preserved in darkened orange-colored amber, trimmed to 18.0×14.5× 3.5 mm (in an epoxy trapezoid 22.5×15.0× 4.8 mm). Syninclusions include one acariform Bdellidae , one Blattodea, six Diptera (one Ceratopogonidae , two Dolichopodidae , one Phoridae , two Psychodidae ), one Tanaidacea ( Alavatanais margulisae Sánchez-García, Peñalver, and Delclòs ), two Archaeognatha, six coprolites (attributed to termites based on their general shape), and abundant fungal and plant remains (see details of syninclusions in Sánchez-García et al., 2015). The specimen is exposed laterally and partially complete (missing head), with the right side of the body and the right pereopods mostly polished off. The specimen possesses a medium-sized body (total length 3.78 mm as preserved), more or less oblong, only moderately convex dorsally. The pereon is about 0.73× the body length, with the lateral parts of the pereonites only moderately prominent, those of the four posterior segments with posterior corners acutely triangular, all edged with some small appressed spikes. The pleon is about 0.22× of the body length and distinctly narrower than the pereon (abruptly contracted). It also possesses spinous pereopods, a dactylus with two claws (the inner claw minute), and an unbranched, glabrous, long, and slender dactylar seta, distinctly expanded distally. Lastly, an elongate structure that could correspond to a short uropod is sticking out from under the pleon.

Figures

FIGURE 10. Microphotographs of Heraclitus helenae, new genus and species, family Detonidae? (holotype, MCNA 12546, sex unknown). A. Lateral habitus. B. Ventrolateral habitus. Figures made with consecutive photographs taken at successive focal planes. Scale bar = 1 mm (both panels to the same scale).

FIGURE 11. Detail microphotographs of Heraclitus helenae, new genus and species, family Detonidae? (holotype, MCNA 12546). A. Head and antenna in ventrolateral view; box indicates that section magnified in B. B. Prominent triangular-shaped scales in A, photographed from the other side. C. Uropods in dorsolateral view. Figures made with consecutive photographs taken at successive focal planes. Scale bars: A = 0.2 mm; B, C = 0.1 mm.