The semi-aquatic pondweed bugs of a Cretaceous swamp

Systematic palaeontology

Genus Iberovelia Sánchez-García & Nel gen. n. urn:lsid:zoobank.org:act:9093AD2B-3AFC-4345-B35B-08139856ECFA

Type species Iberovelia quisquilia Sánchez-García & Nel sp. n.

Etymology. Derived from ibero-, in reference to the Iberian Peninsula from which the amber originates and -velia, a common suffix for Mesoveliidae genera.

Diagnosis. The genus is distinguished from all other Mesoveliidae genera by its unique combination of the following characters: small-sized apterous female form, length 1.6 mm. Head not deflected, extended in front of the eyes, slightly shorter than thorax, and clearly narrower than pronotum; anteclypeus with a pad of long erect hairs; eyes large; ocelli absent; antennae flagelliform, very long, clearly surpassing the abdominal apex, the first segment with two ante-apical spinous hairs; rostrum reaching metacoxae. Pronotum without collar and longer than mesonotum; metafemur long and clearly surpassing the abdominal apex; pro-, meso-, and metafemur with one, two, and one spinous hair, respectively; metatibia covered with scattered spinous hairs; first segment of tarsus the shortest, second segment shorter than third except in the metatarsus (second metatarsal segment almost twice the length of the third). Female genital segments only slightly protruding from pregenital abdomen; gonapophyses elongate and laciniate; gonoplacs small. Male unknown.

Iberovelia quisquilia Sánchez-García & Nel sp. n. urn:lsid:zoobank.org:pub:5EBBDE3B-9A12-4476-BC96-776651350175

(Figs. 2–5, Table 1)

Type material. Holotype MCNA 12804, female, virtually complete, dorsolaterally and ventrolaterally exposed. Preserved in dark yellow turbid amber trimmed to 0.8 ×0.6 × 0.2 mm (in a trapezoid resin measuring 2.0 ×1.6 × 0.2 mm) and containing many impurities and bubbles. The amber is also darkened near the inclusion. The entire head, rostrum, and even antennae are preserved, as are the thorax and abdomen (including genitalia). Most of the left protarsus (missing from the third segment) and left mesotarsus (missing from the second segment) are lost at the surface of the amber, while the right mesotarsal segments are not distinguishable due to preservation. The right metathoracic leg is also missing below the distal third of the tibia. Ventral head details and thorax and abdomen segmentation cannot be assessed due to preservation. Syninclusions comprised the holotype and allotype of Glaesivelia pulcherrima (MCNA 12805 and MCNA 12806, see below) and one Diptera Dolichopodidae (Microphorites sp., MCNA 12807).

Age and locality. Lower Cretaceous (Upper Albian); Peñacerrada I amber site (Peñacerrada I = Moraza), eastern area of the Basque-Cantabrian Basin, Burgos, northern Spain.

Etymology. The specific epithet quisquilia is Latin for litter, and makes reference to the putative habitat (leaf litter in moist terrestrial environments) of the specimen.

Diagnosis. Same as for the genus (vide supra).

Description of the holotype. Female (Figs. 2–5). Apterous form. Body (Figs. 2 and 3) suboval and elongate, very small, length 1.64 mm, greatest width (across abdomen) 0.39 mm, length 4.20× the greatest width. Body surface and appendages covered with fine to coarse recumbent to semi-erect long setae.

Head (Fig. 3) relatively long, not deflected, clearly extended in front of the eyes, length 0.31 mm, much longer than wide, greatest width (across eyes) 0.15 mm, with sides nearly parallel; slightly shorter than thorax and clearly narrower than pronotum; anterior part slightly declivent in side view; ventral lobes and ventral head details not visible; anteclypeus with a pad of long erect setae. Three pairs of trichobothria on dorsal head surface, long, apparently not equally spaced in the longitudinal direction; one of the pairs occurs towards the base of the head, just before the posterior margin of the eyes, while the other two are inserted into the anterior part of the head, well in front of the eyes. No distinct median groove on head.

Compound eyes (Fig. 3) spherical, large, diameter 0.12 mm, that are not touching and only slightly separated from the anterior margin of the pronotum, with more than 30 ommatidia; ocular setae not visible. Ocelli absent (as typically occur in extant apterous forms).

Antennae (Fig. 4A) very long, length 1.81 mm, surpassing the length of the body when directed backwards, flagelliform, with segments 3–4 much longer and thinner than segments 1–2; antennal tubercles moderately prominent, slightly projected laterally, and situated near apex of head; first antennal segment longer than second, lengths 0.35 and 0.24 mm, respectively, the first segment with two ante-apical spinous hairs (Fig. 4B); third segment 0.59 mm long; fourth segment the longest, length 0.63 mm, uniformly sclerotised throughout.

Rostrum (Fig. 3) long and slender with apex reaching metacoxae.

Thorax (Fig. 3) not prolonged, length 0.36 mm, greatest width 0.29 mm; pronotum without collar; pro-, meso-, and metanotum only visible in side view, thus impeding measurements; pronotum longer than mesonotum; intersegmental sutures poorly visible, the posterior margin of metanotum apparently curved. Metathoracic scent gland not visible.

Legs (Fig. 3) inserted close to the ventral midline of the body, long, rather slender, and with strong spinous hairs; metathoracic leg the longest; coxae relatively long; femora moderately incrassate in the middle, nearly twice as thick as the corresponding tibiae; metafemur the longest, clearly surpassing the abdominal apex; anterior margin of pro-, meso-, and metafemur with at least one, two, and one ante-apical spinous hair, respectively; tibiae slender; metatibia the longest and covered with scattered spinous hairs, viz., with only two spinous hairs on the inner margin and a series of spinous hairs on the outer margin, plus up to four spinous hairs distally; lengths of profemur and protibia: 0.49 and 0.50 mm; mesofemur and mesotibia: 0.64 and 0.55 mm; metafemur and metatibia: 0.99 and 1.21 mm; tarsi with three segments; tarsal segments increasing in length from first to third segment (Fig. 5A) except in the metatarsus (Fig. 5B) (second metatarsal segment almost twice the length of the third); basitarsomere of all legs very short and subcylindrical; lengths of protarsal segments 1–3: 0.03, 0.05, and 0.07 mm; length of mesotarsal segment 1: 0.03 mm; lengths of metatarsal segments 1–3: 0.05, 0.21, and 0.12 mm; claws simple, slender, and inserted apically into the distal tarsal segment; arolia not visible.

Abdomen (Fig. 3) long, length 0.97 mm, greatest width 0.39 mm, clearly widened at the middle, with broadly concave sides; mediotergites tapering in width towards the abdominal apex. Abdominal scent gland not visible. Genital segments (Fig. 5C) large and only slightly protruding from pregenital abdomen; gonocoxae large and plate-shaped; gonapophyses elongate and laciniate, slightly sclerotised apically; tergum 9 relatively small; proctiger cone-shaped; gonoplacs small.

• Male unknown.

• Macropterous adult form unknown.

Observational notes. Direct sexual determination of the holotype was possible given the preservation of the female genital segments composed of gonocoxae, gonapophyses, gonoplacs, and the cone-shaped proctiger in the distal part of the abdomen. The gonoplacs are primitively large in mesoveliids, but have become smaller in some taxa such as Cryptovelia, Mniovelia, and Phrynovelia. Furthermore, there are differences in the ovipositor serration (from slightly to distinctly serrated), although this could not be assessed in Iberovelia due to preservation. It should be noted that Recent mesoveliids have a well-developed ovipositor that is functionally associated with the unique egg structure of mesoveliids and their habit of embedding eggs into living or dead plant tissues or narrow crevices and holes in the soil litter layer, instead of placing them on top of the substrate (Andersen, 1982).

Genus Glaesivelia Sánchez-García & Solórzano Kraemer gen. n. urn:lsid:zoobank.org:act: DAC68787-5F0A-462A-BCBB-2CDD1E6991D6

Type species Glaesivelia pulcherrima Sánchez-García & Solórzano Kraemer sp. n.

Etymology. Derived from Latin glaesum to mean ‘of amber’ and -velia, a common suffix for Mesoveliidae genera.

Diagnosis. The genus is distinguished from all other Mesoveliidae genera by its unique combination of the following characters: small-sized apterous form, length 1.6 mm. Head not deflected, extended in front of the eyes, subequal in length to the middorsal length of thorax in the female, but longer than thorax in the male, clearly narrower than pronotum; anteclypeus with a pad of long erect hairs; ventral surface of head laterally bordered by ridged longitudinal carina; eyes large; ocelli absent; antennae flagelliform, long, not reaching the abdominal apex, the first segment with three ante-apical spinous hairs in the female and two ante-apical spinous hairs in the male; rostrum reaching metacoxae. Pronotum without collar and longer than mesonotum, the posterior margin slightly pointed medially; metanotum with the posterior margin weakly curved; metafemur short and not surpassing the abdominal apex; pro-, meso-, and metafemur with one, two, and two spinous hairs, respectively, in the female but without spinous hairs in the male; metatibia covered with scattered spinous hairs in the female and with an inner row of spinous hairs in the male; first segment of tarsus the shortest, second segment shorter than third except in the metatarsus (second metatarsal segment subequal in length to the third). Female genital segments clearly protruding from pregenital abdomen; gonapophyses elongate and laciniate; gonoplacs small.

Glaesivelia pulcherrima Sánchez-García & Solórzano Kraemer sp. n. urn:lsid:zoobank.org: act:64147FCE-2C91-4611-B62C-82858801C5AA

(Figs. 6–10, Table 1)

Type material. Holotype MCNA 12806, female, virtually complete, dorsally and laterally exposed. Preserved in dark yellow turbid amber, trimmed to 0.5 × 0.1 × 0.2 mm (in a trapezoid resin measuring 2.2 × 1.5 × 0.2 mm), which contains many impurities and bubbles obscuring some features of the specimen, especially the cuticular surface. The right mesothoracic leg is missing below the distal third of the tibia, while the metatarsi are lost at the surface of the amber. The entire head, rostrum, and even antennae are preserved, as are the thorax and abdomen (including genitalia).

Allotype MCNA 12805, male, virtually complete, dorsolaterally and ventrolaterally exposed. Preserved in dark yellow turbid amber, trimmed to 0.6 × 0.4 × 0.1 mm (in a trapezoid resin measuring 2.2 × 1.4 × 0.1 mm), containing many impurities and bubbles. Most of the antennae (missing from the base of the third segment) and right protarsus are lost at the surface of the amber. The left protarsal segments are not distinguishable due to preservation. Both type specimens were preserved as syninclusions with the holotype of I. quisquilia (MCNA 12804) and a Microphorites sp. (MCNA 12807).

Age and locality. Lower Cretaceous (Upper Albian); Peñacerrada I amber site (Peñacerrada I = Moraza), eastern area of the Basque-Cantabrian Basin, Burgos, northern Spain.

Additional material. MCNA 13326 (Figs. 8E–8F), male, poorly preserved in Lower Cretaceous Álava amber, Peñacerrada II amber site.

Etymology. The specific epithet pulcherrima is Latin for beautiful, and makes reference to the gorgeous habitus of the holotype.

Diagnosis. Same as for the genus (vide supra).

Description of the holotype. Female (Figs. 6, 7A–7C). Apterous form. Body (Figs. 6, 7A) suboval and rather stout, very small, length 1.61 mm, greatest width (across abdomen) 0.71 mm, length 2.27× the greatest width. Body surface and appendages covered with fine to coarse recumbent to semi-erect long setae.

Head (Fig. 7B) relatively long, not deflected, clearly extended in front of the eyes, length 0.29 mm, much longer than wide, greatest width (across eyes) 0.25 mm, with sides nearly parallel; subequal in length to the middorsal length of thorax and clearly narrower than pronotum; anterior part slightly declivent in side view; ventral lobes weakly-developed; ventral surface of head laterally bordered by ridged longitudinal carinae; anteclypeus with a pad of long erect setae. Three pairs of trichobothria on dorsal head surface, long, apparently not equally spaced in the longitudinal direction; the posterior pair is the longest and occurs towards the base of the head, just before the posterior margin of the eyes, while the other two pairs arise from swellings in the anterior part of the head, well in front of the eyes. No distinct median groove on head.

Compound eyes (Fig. 7B) spherical, large, diameter 0.17 mm, that are not touching and only slightly separated from the anterior margin of the pronotum, with more than 30 ommatidia; ocular setae not visible. Ocelli absent.

Antennae (Figs. 6, 7A) long, length 1.37 mm, just reaching the sixth abdominal segment when directed backwards, flagelliform, with segments 3–4 much longer and thinner than segments 1–2; antennal tubercles moderately prominent, slightly projected laterally, and situated near apex of head; first antennal segment slightly longer than second, lengths 0.22 and 0.17 mm, respectively (measurements possibly underestimated due to fossilization position), the first segment with three ante-apical spinous hairs; third and fourth segments subequal in length, lengths 0.48 and 0.50 mm, respectively, the fourth segment uniformly sclerotised throughout.

Rostrum (Figs. 6, 7A) long and slender, with apex reaching metacoxae; first labial segment slightly longer than second; third segment very long, 4.02× the length of fourth, lengths 0.64 and 0.16 mm respectively, the third segment swollen at base and clearly tapering towards the apex.

Thorax (Figs. 6C, 7B) not prolonged, length 0.28 mm, greatest width (across metanotum) 0.58 mm; pro-, meso-, and metanotum visible from above as transverse plates, with lateral margins rounded; pronotum without collar, longer than mesonotum, lengths 0.12 mm and 0.09, respectively; metanotum the shortest, length 0.06 mm; intersegmental suture between pro- and mesonotum slightly pointed in the middle; intersegmental suture between meso- and metanotum slightly curved; metanotum with posterior margin weakly curved. Metathoracic scent gland not visible.

Legs (Figs. 6B, 6D) inserted close to the ventral midline of the body, short, relatively robust, and with strong spinous hairs; metathoracic leg the longest; coxae relatively long; femora moderately incrassate in the middle, nearly twice as thick as the corresponding tibiae; metafemur the longest, not surpassing the abdominal apex; anterior margin of pro- and mesofemur with at least one and two ante-apical spinous hairs, respectively, metafemur with at least two ante-apical spinous hairs on the outer margin and at least seven on the inner margin; tibiae slender; metatibia the longest, covered with scattered spinous hairs and up to four spinous hairs distally; lengths of profemur and protibia: 0.44 and 0.44 mm; mesofemur and mesotibia: 0.51 and 0.38 mm (measurements underestimated due to fossilization position); metafemur and metatibia: 0.56 and 0.76 mm; tarsi with three segments (not preserved at both metathoracic legs and the right mesothoracic leg); tarsal segments increasing in length from first to third segment in pro- and mesotarsus; basitarsomere of all legs very short and subcylindrical; lengths of protarsal segments 1–3: 0.03, 0.07, and 0.09 mm; mesotarsal segments 1–3 (measurements underestimated due to fossilization position): 0.02, 0.07, and 0.08 mm; claws simple, slender, and inserted apically into the distal tarsal segment; arolia not visible.

Abdomen (Figs. 6, 7A) long, length 1.04 mm, greatest width 0.71 mm, clearly widened at the middle, with broadly concave sides; mediotergites tapering in width towards the abdominal apex. Abdominal scent gland not visible. Genital segments (Fig. 7C) large and clearly protruding from pregenital abdomen; gonocoxae large and plate-shaped; gonapophyses elongate and laciniate; tergum 9 well developed; proctiger rounded; gonoplacs small and triangular in shape.

Macropterous adult form unknown.

Description of the allotype. Male (Figs. 7D, 8A–8D, 9, 10). Apterous form, very similar to female, but somewhat shorter (Figs. 8A–8D), length 1.56 mm, width measurements not available due to fossilization position. Other differences with the female are listed below.

Head (Fig. 9A) length 0.32 mm and longer than thorax. Three pairs of long trichobothria on dorsal head surface, their exact distribution obscured by preservation. Eyes (Fig. 9A) diameter 0.11 mm. Both antennae (Fig. 9A) polished off at base of third segment, with segment 3 much thinner than segments 1–2; first antennal segment subequal to or slightly longer than second, lengths 0.28 and 0.24 mm, respectively, the first segment with two ante-apical spinous hairs.

Thorax (Figs. 8A–8D) length 0.28 mm; pro-, meso-, and metanotum only visible in side view, thus impeding measurements; pronotum longer than mesonotum; intersegmental sutures poorly visible, the posterior margin of metanotum apparently curved. Legs (Figs. 8A–8D) with strong spinous hairs (although with a different pattern to that in the female, see below); lengths of profemur and protibia: 0.46 and 0.46 mm; mesofemur and mesotibia: 0.51 and 0.28 mm (measurements underestimated due to fossilization position); metafemur and metatibia: 0.55 and 0.65 mm; femora without strong spinous hairs; mesotibia with a grooming comb apically (Figs. 9B, 9C); metatibia with a row of spinous hairs along the inner margin; tarsi with three segments (not distinguishable in protarsus due to preservation); tarsal segments increasing in length from first to third segment (Figs. 9B, 9C) except in metatarsus (Figs. 10B, 10C) (second metatarsal segment subequal in length to the third); lengths of mesotarsal segments 1–3: 0.05, 0.06, and 0.09 mm; metatarsal segments 1–3: 0.04, 0.10, and 0.10 mm.

Abdomen (Figs. 8A–8D) length 0.97 mm. Genital segments (Figs. 7D, 10A) large and clearly protruding from pregenital abdomen; proctiger very prominent, distally widened, length 0.24 mm, width 0.20 mm; claspers large and slender, symmetrical, shallow sickle-shaped, with the blade slightly curved and narrowing apically and displaying a series of thick setae; each clasper placed in the lateral margin of the pygophore.

Observational notes. Two morphotypes representing a male and female of the same species belonging to the rare family Mesoveliidae were observed in the same piece of amber together with the holotype female of Iberovelia. Morphological details of both the male and female genitalia of Glaesivelia were assessed using infrared microscopy. Male genital segments are often more conspicuous than female ones, which might be concealed or even retracted into the pregenital abdomen. Some important characters of the Glaesivelia male genitalia have not been included in the diagnosis of the new genus, but in the description because they are unknown in Iberovelia. However, these characters are remarkably different from those observed in all other males belonging to extant genera and are thus of potential diagnostic significance. One of these characters is the well-developed sickle-shaped male claspers of Glaesivelia, which probably had a functional role during copulation.

Extant mesoveliids often exhibit secondary sexual dimorphism in body size (males are usually shorter), certain body proportions (e.g., the relative lengths of the thoracic segments), and in the presence/absence of spines and their distribution. In this regard, the Glaesivelia allotype differs from the female holotype by the slightly smaller size and the different ratio of head to thorax lengths. Andersen & Polhemus (1980) reported similar observations in Recent Cryptovelia, with the length of the head being subequal to the middorsal length of the pro- and mesonotum in males and the length of the whole thorax in females. Other minor differences between Glaesivelia males and females include the distribution of the spines on the legs and antennae, as well as the presence of a comb of modified macrotrichia on the apexes of male mesotibiae.

Regarding wing dimorphism, most Recent Mesoveliinae are only known from apterous specimens, such as the fossil genera described herein. Madeovelia Poisson, 1959 and Mesoveloidea Hungerford, 1929 are the only known monomorphic macropterous specimens, while some Mesovelia species have been described as wing-dimorphic comprising both macropterous and apterous forms (Damgaard et al., 2012).

Infrared microscopy. The severely darkened cuticle of the specimens, hidden behind the occluded amber, rendered it impossible to resolve some detailed characters with light microscopy. Therefore, some details of the head, such as the ventral lobules and lateral carinae, the segmentation of the thorax and abdomen, the density of body setae, and the female and male genital structures were examined using infrared microscopy (Fig. 7). Infrared microscopy is still not widely applied in the study of inclusions in amber; however, in accordance with previous studies, our results show that this technique is promising and a good alternative to the systematic study of organisms preserved in amber that are not clearly visible.

Subfamily assignment

Andersen (1999) and Andersen & Polhemus (2003) investigated the phylogenetic relationships among extant Mesoveliidae genera, describing three major clades: (1) Madeovelia and Mesoveloidea in the subfamily Madeoveliinae; (2) Mesovelia Mulsant & Rey, 1852, Speovelia Esaki, 1929, and Cavaticovelia Andersen & Polhemus, 1980; and (3) Phrynovelia Horváth, 1915, Cryptovelia Andersen & Polhemus, 1980, Darwinivelia Andersen & Polhemus, 1980, Mniovelia Andersen & Polhemus, 1980, Austrovelia Malipatil & Monteith, 1983, and Nereivelia Polhemus & Polhemus, 1989 in the subfamily Mesoveliinae Douglas & Scott, 1867. The genus Seychellovelia Andersen & Polhemus, 2003 was later described and included in clade 3 (Andersen & Polhemus, 2003).

Damgaard et al. (2012) showed that the current classification of mesoveliid subfamilies and genera require revision, identifying Mesoveloidea, from the subfamily Madeoveliinae, as a sister group to Mniovelia, from Mesoveliinae, thus making the latter subfamily paraphyletic. Moreover, the genus Mesovelia was also shown to be paraphyletic, since several species were identified as sister groups to the genus Phrynovelia or Speovelia. Due to the high percentage of monotypic or species-poor genera, the limited number of diagnostic character combinations used for describing taxa, and the many clades diagnosed on putative convergences or homoplasies, Damgaard et al. (2012) rejected the subfamily classification. However, we have employed the clades in Andersen (1999) for clarity.

The placement of Glaesivelia and Iberovelia close to the extant genera Madeovelia and Mesoveloidea or the fossil genus Gallomesovelia (currently in Madeoveliinae) is clearly unsupported given the overall shape of the head (deflected in front of the eyes instead of extended in Glaesivelia and Iberovelia), the occurrence of winged adults (instead of apterous in Glaesivelia and Iberovelia), and the preapical insertion of claws (instead of apical in Glaesivelia and Iberovelia). Both apical pretarsal structures and extended heads are shared with other gerromorphan families, probably corresponding to plesiomorphic states.

The monophyly of the subfamily Mesoveliinae is supported by the shared apomorphic characteristics of an ejaculatory bulb of the male with a broad pump flange, the anterior end of the egg with a complete pseudopercular rim, and the tergal and stemopleural parts of the prothorax not usually being delimited by sutures (Andersen, 1999). We have refrained from formally including the genera described here in Mesoveliinae, as the listed characters are not known in our fossils and the diagnostic character combinations used for describing Mesoveliidae taxa are currently under revision. Table 1 shows the characters shared with some genera currently in Mesoveliinae.

The new fossil genera Glaesivelia and Iberovelia are most similar to the genera included in clade 3 through their flagelliform antennae (two distal segments much thinner and longer than the two basal segments and usually setose), a not simple ventral head, a mesonotum subequal to or shorter than the pronotum, and the relatively small gonoplacs of the female genitalia (except for the subflagelliform antennae and the large gonoplacs of Darwinivelia). Glaesivelia also shares with these genera (except Mniovelia) a head subequal in length to or longer than the thorax. Conversely, Mniovelia and the other new fossil genus Iberovelia share a head that is shorter than the thorax, although the difference in length is very small in Iberovelia. It has also been shown some variability in the relative lengths of the head and thorax in Cryptovelia, with C. terrestris males having a head that is shorter than the thorax (Table 1). As for the relative lengths of the metatarsal segments, the second segment is never longer than the third in Glaesivelia, as seen in almost all the genera in clade 3, whereas the second tarsal segment is longer than the third in the fossil Iberovelia as well as in Mesovelia, Speovelia and Cavaticovelia (clade 2), and Mniovelia (clade 3). Furthermore, Cryptovelia stysi males have a longer second metatarsal segment compared to the third. Glaesivelia and Iberovelia also share with most genera the spherical and large compound eyes. However, a trend towards smaller eyes has been observed in some species inhabiting caves or other secluded places (e.g., Austrovelia caledonica Malipatil & Monteith, 1983 and Darwinivelia fosteri Andersen & Polhemus, 1980), while the eyes are vestigial in the leaf litter-inhabiting Cryptovelia species. Remarkably, the two new fossil genera differ from all the genera in clade 3 by having strong antennal and femoral spines, as found in Mesovelia, Speovelia and Cavaticovelia (clade 2). Although antennal spines are not present in the clade 3 genera, some of them present a variable number of bristles in the first segment that are distinct from the surrounding setae (one in Seychellovelia, three in Cryptovelia, and two in Mniovelia). Similarly, thin femoral spines are present in Darwinivelia, while strong spines are either absent or present in Cryptovelia. Table 1 presents the other characters with taxonomic significance. However, there are additional features that can be used to easily distinguish the new fossil taxa from the Recent genera, such as the absence of the very short second antennal segment and small rounded male claspers diagnostic of Cryptovelia (male claspers are well developed and sickle-shaped in Glaesivelia), the absence of the tripartite first abdominal tergum of Phrynovelia, or the absence of a deep glabrous median furrow on the vertex of the head and the very large protruding eyes of Mniovelia.

The general habitus of our fossils is very close to those of the two fossil genera Emilianovelia and Malenavelia, currently assigned to Mesoveliinae (Solórzano Kraemer et al., 2014). They share relatively small bodies (around 1.4 mm long in Emilianovelia to 1.6 mm long in the other taxa) with moderately long heads and appendages, normal-sized eyes (not reduced), and flagelliform antennae. Emilianovelia and Malenavelia were originally described as having subflagelliform antennae, but it is now clear that the antennae are flagelliform. Iberovelia shares with Emilianovelia the following diagnostic characters, as listed in Solórzano Kraemer et al. (2014): a rostrum reaching the metacoxae; a pronotum longer than the mesonotum; and an anteclypeus with a pad of long erect hairs. We can add that they also share very long antennae surpassing the length of the body, the presence of two ante-apical spinous hairs on the first antennal segment, long metafemora reaching the abdominal apex, and a longer second metatarsal segment compared to the third segment (ca. twice the length). However, Iberovelia differs from Emilianovelia through some body proportions, its slightly declivent head (instead of abruptly declivent in Emilianovelia), different distributions of spinae on the femora (1:1:1 from pro- to metafemora in Emilianovelia and 1:2:1 in Iberovelia) and metatibiae (only a few spinous hairs on the inner margin and a series of spinous hairs on the outer margin in Iberovelia; and a few spinous hairs on the outer margin and a series of spinous hairs on the inner margin in Emilianovelia after Solórzano Kraemer et al., 2014, fig. 1), and the small gonoplacs (instead of large and elongate in Emilianovelia).

Glaesivelia shares with Malenavelia the following diagnostic characters (Solórzano Kraemer et al., 2014): a rostrum reaching the metacoxae; a pronotum longer than the mesonotum; a metanotum with a slightly curved posterior margin; and short metafemora not surpassing the abdominal apex. However, Glaesivelia has a slightly declivent head (instead of the abruptly declivent in Malenavelia), weakly developed ventral lobes (instead of the well-developed lobes in Malenavelia), and a venter of the head possessing a ridged longitudinal carina (instead of a simple one in Malenavelia). Other characters shared by Glaesivelia and Malenavelia include the short antennae not reaching the length of the body, the second metatarsal segment being as long as or slightly longer than the third segment (after Solórzano Kraemer et al. (2014), Fig. 3C and Fig. 4D), and the small gonoplacs. The male genitalia of Glaesivelia is clearly larger than that of Emilianovelia and Malenavelia, and has well-developed claspers. Although the male genitalia of the Emilianovelia holotype was described as having a pair of lateral spinous extensions, these are clearly smaller than those in Glaesivelia and it is unclear whether they correspond to a clasper. It should be noted that although the lack of spines in Malenavelia is likely to be an artefact due to scanning resolution, this, however, prevents its comparison with Glaesivelia.

Palaeoecology

Modern mesoveliids live in moist surroundings such as humid terrestrial (litter and moss) or marginal aquatic habitats, or on water surfaces extensively covered with floating leaves of water plants (Andersen & Weir, 2004). Humid terrestrial habitats (hygropetric) are not necessarily close to free water, consisting of different types of solid substrates covered by a thin film of water (Andersen, 1982; Andersen, 1998). The cosmopolitan genus Mesovelia contains both hygropetric species and surface-inhabiting species living on plant-covered water surfaces (Damgaard et al., 2012). However, mesoveliids are most frequently found in humid terrestrial environments, with some genera and species even occurring at a great distance from the nearest body of water (Andersen & Polhemus, 1980; Damgaard et al., 2012). The genera Phrynovelia (New Caledonia, New Guinea, and the Philippines) and Cryptovelia (Brazil and Borneo) inhabit soil and leaf litter in temperate and intertropical rain forests (Horváth, 1915; Andersen & Polhemus, 1980; Malipatil & Monteith, 1983), while Mniovelia (New Zealand) and Seychellovelia (Seychelles) live in moist terrestrial environments among mosses and litter on the floor of rain forests on misty mountains far from ponds or streams (Andersen & Polhemus, 1980; Andersen & Polhemus, 2003). The dependence on water varies. Austrovelia inhabits ground litter in rain forests in Australia and New Caledonia, but reproduces only in the wet season when water-filled leaves among the litter provide a habitat for early stages (Malipatil & Monteith, 1983). Moreover, there are two genera of Mesoveliinae—Speovelia (Japan and Mexico) and Darwinivelia (Galapagos Islands and Brazil)—that occur in narrow crevices and holes in an intertidal marine environment (Andersen & Polhemus, 1980), while Nereivelia and other members of Darwinivelia are found on mangrove flats (Polhemus & Polhemus, 1989) and the troglobitic Cavaticovelia aaa frequents lava tubes in Hawaii (Andersen & Polhemus, 1980).

There are no definite associations within Mesoveliidae between the physical nature of the environment and the diagnostic characters of the species inhabiting different types of habitats (from humid terrestrial to freshwater to marine). However, studies on aquatic Heteroptera have shown some variability in the structure and arrangement of setae (Perez-Goodwyn, 2009), with the highest densities of microthrichia occurring in marine taxa. Despite the descriptions not being usually precise regarding this feature, some typically humid terrestrial mesoveliid genera, such as Phrynovelia, Cryptovelia, Mniovelia, and Cavaticovelia, have been described as having glabrous abdominal sternites or sternopleuron. In Glaesivelia and Iberovelia, the body is covered with long setae that are not very dense, but as far it is possible to observe, do not leave any parts exposed (Fig. 7). It is also important to note the presence of a distal comb of modified macrotrichia on the mesotibiae of Glaesivelia males (Fig. 9C). Grooming is an important activity in semi-aquatic bugs, which use specialised structures to keep the hair layers of the legs and body tidy and free of dust and water drops (Andersen, 1982).

Thus, the fossil mesoveliids described herein probably lived in a humid terrestrial habitat (hygropetric), with entrapment in resin likely occurring out of water (Fig. 11). Andersen & Polhemus (1980) suggested that the most ancestral habitat of Mesoveliidae was ‘humid terrestrial and/or marginal aquatic including litter or wet soil, watersoaked, moss, and seeping rock faces’. This is consistent with the results in Damgaard et al. (2012), in which the terrestrial Austrovelia resolves as the sister group to all the other genera and could actually represent the original life style of the whole family. However, the preferred habitat of the Spanish fossil mesoveliids might also be characterized as marginal aquatic and therefore transitional between terrestrial and freshwater environments (Fig. 11). Indeed, the rest of the arthropod assemblage is consistent with such an environment, with numerous representatives of the ground habitat of humid forests preserved in ‘litter amber’ (Sánchez-García et al., 2015; Sánchez-García, Arillo & Nel, 2016; Arillo, Subías & Sánchez-García, 2016; Sánchez-García & Engel, 2016a; Sánchez-García & Engel, 2016b).

In this regard, the extreme scarcity of Mesozoic Mesoveliidae fossil records could be related to the confined microhabitats of primitive mesoveliids, which made their capture in tree resins unlikely. After actualistic experiments in a tropical forest in Chiapas (Mexico), Solórzano Kraemer et al. (2015) posed that the underrepresentation of several groups could be explained by their preferred habitats in leaf litter. The presence of mesoveliids in the arthropod fauna of Cretaceous Spanish amber strongly supports this hypothesis, as it probably stems from the unusual preservation of litter-inhabiting species in addition to organisms living on trees (Sánchez-García et al., 2015). More importantly, the discovery of three specimens in the same piece of amber indicates possible aggregative behaviour, thereby representing the earliest occurrence of such ethology for Mesoveliidae. Similarly, three and four mesoveliids, including males and females, have been reported fossilised in two pieces from Cretaceous French amber (Solórzano Kraemer et al., 2014). Naturally, there are many taphonomic factors that might cause individuals to be preserved together and that do not relate to a behavioural phenomenon. However, given the scarce fossil record of these bugs, it seems particularly unlikely that several specimens were repeatedly captured in the same small piece of amber due to chance alone, supporting the idea that the three specimens were in close association when engulfed in a resin flow very close to their habitat. Indeed, gregarious behaviour is common among Recent semi-aquatic bugs (Andersen, 1982).