Eoligiiscus tarraconensis, 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 : 5-12

Eoligiiscus tarraconensis , new species

Figures 2 , 3

DIAGNOSIS: As for the genus (above).

DESCRIPTION: Body (fig. 2A, C–D) oval, attenuated caudally, but with pleon not abruptly contracted, of “runner” habitus; small sized, total length 1.35 mm (from tip of cephalon to tip of pleon), twice as long as broad; dorsal surface only moderately convex, smooth; gland pores not visible as preserved.

Cephalon (fig. 2B) transversely semioval, fairly broad, not sunk into first pereonite; length 0.21 mm as preserved, about 0.15× of body length, maximum width 0.49 mm, with front evenly rounded, lacking lateral lobes; antennal lobes absent. Eyes large and convex, diagonal 0.10 mm, consisting of multiple ommatidia (at least 10 as preserved).

Pereon about 0.70× of body length; pereonites overlapping, lamellar; lateral parts of pereonites (i.e., epimeral plates) only moderately prominent, those of posterior pereonites with posterior corners acutely triangular. Pleon about 0.27× of body length, narrower than pereon, lateral parts of two anterior pleonites concealed; pleotelson short, subtriangular, with rounded apex and uropod insertions on posterior corners.

Mouthparts not visible as preserved.

Antennule not visible as preserved.

Antenna (fig. 3A) not very spinose in appearance, rather stout, with five peduncular articles and a multiarticulate flagellum, reaching posteriorly to middle pereonite 2, elbowed between fourth and fifth articles; first article partly obscured by head; second article short and stout, 0.07 mm long, about as long as broad, with two visible thick spines distally; third article short and stout, as long as preceding article, about as long as broad, with one visible thick spine distally; fourth article only slightly elongate, stout, 0.09 mm long, 1.29× length of preceding article, 1.50× longer than broad, with one visible thick spine distally; fifth article only slightly elongate, stout, 0.12 mm long, 1.33× length of preceding article, 3.00× longer than broad; flagellum short, with only four subequal articles, distal article tapering distally and without visible aesthetascs.

Pereopods all alike, slender and cylindrical, without sexual modifications; basis and ischium mostly obscured by body; merus with at least three short thick spines distally; carpus with at least four short thick spines distally; propodus longer than carpus, without visible spines; dactylus (fig. 3B) with large outer claw and smaller inner claw; dactylar setae unbranched, glabrous, very short and hirsute; ungual setae (usually arising between both claws) not visible as preserved.

Pleopods not visible as preserved.

Uropod greatly elongate, about 0.41× of body length, distinctly surpassing length of pleon, freely projecting caudally; protopod not produced inside pleotelson, subrectangular, long and stout, 0.18 mm long, 0.10 mm width, with endopod and exopod inserted at same level; exopod styliform, long and slender, 0.38 mm long, only slightly longer than endopod, 0.04 mm width, with one short slender seta apically (0.03 mm long); endopod styliform, long and slender, 0.34 mm long, 0.04 mm width, with one long slender spine apically (0.16 mm long).

HOLOTYPE: MCNA 9751 , sex unknown, virtually complete. Preserved in a 8.5×8.0×1.0 mm section of dark-orange amber (in an epoxy trapezoid 15.5×8.2× 1.1 mm), surrounded by numerous pseudoinclusions interpreted as droplets of emulsified phloem sap in Lozano et al. (2020), particles of detritus and fungal hyphae; no other major inclusions.

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 is taken from the Roman name for the province Hispania Tarraconensis, which encompassed the Peñacerrada I amber site.

REMARKS: The family Ligiidae comprises the extant genera Caucasoligidium Borutzky , Ligia Fabricius , Ligidioides Wahrberg , Ligidium Brandt , Tauroligidium Borutzky , and Typhloligidium Verhoeff.

Eoligiiscus tarraconensis may be placed clearly within the family Ligiidae on the basis of the following morphological features ( Sars, 1899): (1) oval-shaped body, somewhat convex, with lamellar segments; (2) cephalon without lateral lobes, with the front rounded and not distinctly defined from the epistome; (3) eyes well developed or wanting; and, (4) uropods freely projecting caudally, with both endopod and exopod styliform. Species of Ligiidae also share well-developed antennae, with a multiarticulate flagellum. However, E. tarraconensis is readily distinguished from the aforementioned genera in the possession of only four articles to the antennal flagellum (refer to Discussion, below). Unfortunately, no details of the antennulae, mouthparts, and pleopods are visible in the holotype of E. tarraconensis , preventing further comparison with extant Ligiidae until better preserved specimens are discovered.

Morphotype I

Figure 4

DESCRIPTION: Body (fig. 4) oval, attenuated caudally, but with pleon not abruptly contracted, of “runner” habitus; medium sized, total length 5.28 mm, about 2.54× longer than broad; dorsal surface only moderately convex, smooth, with very small semicircular scales; gland pores not visible as preserved.

Cephalon transversely semioval, partly flanked by side plates of first pereonite; maximum width 0.97 mm, with front evenly rounded, lacking lateral lobes; antennal lobes absent. Eyes not visible as preserved.

Pereon about 0.70× of body length; pereonites overlapping, lamellar; lateral parts of pereonites (i.e., epimeral plates) more pronounced than in E. tarraconensis , those of posterior segments with posterior corners acutely triangular, all edged with few very small triangular-shaped scale setae. Pleon poorly visible as preserved, narrower than pereon, with lateral parts of pleonites acutely triangular.

Mouthparts not visible as preserved.

Antennule not visible as preserved.

Antenna not very spinose in appearance, with very small semicircular scales visible in some articles, much longer and slender than in E. tarraconensis , with five peduncular articles and a multiarticulate flagellum, at least reaching posteriorly to middle pereonite 3 as preserved, elbowed between fourth and fifth articles; first article partly obscured by head; second article short, not measurable as preserved, with one short thin spine distally; third article short, 0.28 mm long, twice as long as broad, with one long thick spine distally; fourth article elongate, 0.50 mm long, 5.00× times longer than broad, with one long thin spine distally; fifth article elongate, 0.62 mm long, 8.86× longer than broad, with short thin setae sparsely distributed; flagellum long, 0.95 mm long as preserved, with at least nine subequal articles, each article with several short thin setae distally.

Pereopods poorly preserved, all similar in shape and chaetotaxy, slender; dactylus with large outer claw and smaller inner claw.

Pleopods and uropod not visible as preserved.

MATERIAL: MCNA 9513, sex unknown. Preserved in a 6.0×5.0× 2.2 mm section of darkorange turbid amber (in an epoxy trapezoid 14.5×5.5× 2.2 mm), surrounded by numerous pseudoinclusions ( Lozano et al., 2020) and particles of detritus; no other major inclusions.

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

REMARKS: The specimen is difficult to place accurately among Oniscidea due to the few observable characters. However, placement within the family Ligiidae seems most appropriate owing to the presence of long antennae with a multiarticulate flagellum. We have avoided formally describing the specimen as a new genus and species until more well-preserved material becomes available. At the least, the above description should permit positive association between this specimen and more completely preserved conspecifics, if they are discovered through future excavations.

Morphotype II

Figure 5

DESCRIPTION: Body (fig. 5A–B) oval, attenuated caudally, but with pleon not abruptly contracted, of “runner” habitus; medium sized, total length 3.09 mm; details of cephalon (including antennule, antenna, and mouthparts), pereon and pleon (including pleopods) not visible due to poor preservation of cuticle.

Pereopods poorly preserved, all similar in shape and chaetotaxy, slender; dactylus with large outer claw and smaller inner claw.

Uropod (fig. 5C) greatly elongate, about 0.47× of body length, distinctly surpassing length of pleon, freely projecting caudally; protopod not produced inside pleotelson, subrectangular, long and slender, with outer margin grooved in distal part, 0.44 mm long, 0.13 mm width, with endopod and exopod inserted at same level; exopod styliform, long and slender, 1.00 mm long, subequal in length to endopod but much slender, with one short slender spine apically; endopod styliform, long and slender, 1.00 mm long, 0.04 mm width, with one long slender spine apically.

MATERIAL: MCNA 14274, sex unknown. Preserved in a 12×14× 1.5 mm section of darkorange amber (in an epoxy trapezoid 21.5×15.5×2.0 mm), surrounded by numerous pseudoinclusions ( Lozano et al., 2020), particles of detritus, fungal hyphae, coprolites, and arthropod and plant remains; other inclusions include a hemipteran and the wing of a hymenopteran.

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

REMARKS: The wholly exposed, greatly elongate uropods may serve as an easily recognizable distinguishing character that clearly places specimen MCNA 14274 in the family Ligiidae ( Sars, 1899) . Among extant Ligiidae , it most closely resembles the genus Ligia by having both uropodal rami inserted at the same level. However, the exopod is distinctly slender than the endopod, the reverse of that occurring in Recent Ligiidae ( Schmidt, 2008) . As for the previous morphotype I, morphotype II is not named here as the number of diagnostic characters available seems insufficient. Nonetheless, this is a unique taxon quite distinct from the others in this deposit and further emphasizes the diversity of the woodlouse fauna in this ancient ecosystem.

Section Synocheta Legrand, 1946

Family Trichoniscidae Sars, 1899

The new genus and species described here (see below) is certainly a member of the clade Synocheta. The main apomorphies of the Synocheta are a fused male genital duct and reduction of the eyes to three or fewer ommatidia ( Tabacaru and Danielopol, 1996; Schmalfuss, 2005; Schmidt, 2008). Erhard (1997) also considered the presence of a single pereopod claw as a valid character, but it was not regarded as an autapomorphy of the Synocheta by Schmidt (2008). Among the Synocheta, the Trichoniscidae , spanning the Holarctic region, are assuredly paraphyletic. The new taxon fits in Trichoniscidae sensu stricto by having the first male endopodal pleopod prolonged and bearing a long subterminal seta evolved into an apparent second article of this appendage ( Schmalfuss, 2005; Schmidt, 2008). Based on Sars (1899) for the Trichoniscidae , it also has: (1) a more or less elongate body, with the lateral parts of the segments generally not much expanded; (2) cephalon with distinct—though not very large—lateral lobes, with the front more or less produced but scarcely marginate; (3) eyes small or absent; (4) pleon generally much narrower than the pereon, with pleotelson forming a thin projecting plate; (5) antennule minute, with the distal article well developed and tipped with sensory aesthetascs; (6) antenna moderately elongate, minutely spinulose throughout, the flagellum composed of only a restricted number of articles which are less distinctly defined than those in the Ligiidae , the last one terminating in a tuft of delicate setae; (7) pereopods moderately elongate, coarsely spinous, with simple dactylus (i.e., with only one claw); (8) opercular plates of pleopods exceptionally thin, without air chambers or any branchial structure, with the inner plate lobular except on the two anterior pairs; (9) sexual appendage of simple conic shape; (10) endopod of both first and second pairs of pleopods transformed for copulatory purposes; and, (11) uropods with the protopod broadly expanded inside, partly covered by the pleotelson, with the endopod and exopod conically tapered, generally terminating in a tuft of slender setae.

Below the family level, placement in the Haplophthalminae is unsupported due to the new genus’ highly developed ornamentation and well developed epimera of pleonites 3–5 or 4–5 ( Vandel, 1960), and in the Buddelundiellinae due to their ability to roll into a ball ( Vandel, 1960). Placement in the Trichoniscinae is more likely owing to the combination of a smooth or tuberculate body (without longitudinal ridges), and the pleon distinctly narrower than pereon (usually abruptly contracted) due to the reduction of the epimera of pleonites 1 to 5 ( Vandel, 1960). Nevertheless, this subfamily is certainly an artificial group in need of phylogenetic clarification.

Figures

FIGURE 2. Eoligiiscus tarraconensis, new genus and species, family Ligiidae (holotype, MCNA 9751, sex unknown). A. Microphotograph in dorsal habitus. B. Camera lucida drawings of dorsal (top) and ventral (bottom) habitus. C. Microphotograph of head in dorsal view. Figures made with consecutive photographs taken at successive focal planes. Scale bars = 0.5 mm.

FIGURE 3. Microphotographs of Eoligiiscus tarraconensis, new genus and species, family Ligiidae (holotype, MCNA 9751). A. Detail of antenna in dorsal view; note five peduncular articles pointed with arrowheads. B. Detail of dactylus of left pereopod 1 in ventral view; note small inner claw of dactylus pointed with an arrowhead. Figures made with consecutive photographs taken at successive focal planes. Scale bars: A = 0.1 mm; B = 0.05 mm.

FIGURE 4. Morphotype I, family Ligiidae (MCNA 9513, sex unknown). A. Microphotograph in dorsal habitus. B. Camera lucida drawing in dorsal habitus. Figure made with consecutive photographs taken at successive focal planes. Scale bar = 1 mm (both panels to the same scale).

FIGURE 5. Morphotype II, family Ligiidae (MCNA 14274, sex unknown). A. Microphotograph in ventral habitus. B. Camera lucida drawing of uropods. C. Microphotograph in dorsal habitus. Figures A and C made with consecutive photographs taken at successive focal planes. Scale bars: A, C = 1 mm (both panels share the same scale); B = 0.25 mm.