Hirsutisoma grimaldii BOTERO-TRUJILLO & DAVIS & MICHALIK & PRENDINI 2022, sp. nov.
Creators: name: BOTERO-TRUJILLO, RICARDO
name: DAVIS, STEVEN R.
name: MICHALIK, PETER
name: PRENDINI, LORENZO
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Arachnida
Ricinulei
Hirsutisomidae
Hirsutisoma
Hirsutisoma grimaldii

description: † Hirsutisoma grimaldii sp. nov.
(Figs 1–4; Tables 1, 2)
Type material. Holotype ♂ (AMNH _ IZC 00357137), Myanmar: embedded in an oval piece (18 × 12 × 5 mm) of Cretaceous Burmese amber (ca. 99 Ma).
Etymology. The specific epithet is a patronym honoring AMNH Curator, Dr David A. Grimaldi, in recognition of his work on extinct and extant arthropods. Dr Grimaldi’s assistance was instrumental in making this fossil available for study.
Diagnosis. Hirsutisoma grimaldii may be recognized by the presence of a distinct comb of 8–10 lamellate projections basally on the proventral surface of the pedipalp tarsus (Fig. 3D–F), a structure absent in the type specimens of other congeners. It differs further from H. bruckschi, the only other Hirsutisoma species for which the adult male is known, in the morphology of the male leg III and copulatory apparatus: in the male of H. grimaldii, the prolateral surface of the metatarsus of leg III is sharply expanded distally, the first tarsomere of leg III bears a pronounced longitudinal ridge retrodorsally, and the horn-shaped part of the copulatory apparatus is relatively long, reaching well past the midline of the first tarsomere (Figs 2C, D, 4D). In the male of H. bruckschi, the prolateral surface of the metatarsus of leg III is not expanded distally, no ridge is present retrodorsally on the first tarsomere of leg III, and the horn-shaped part of the copulatory apparatus is shorter, reaching to the midline of the first tarsomere.
Description. Male. Based on holotype (AMNH_IZC 00357137).
Measurements. Total length, approximately 3.91 mm (Table 1).
Inclusion. Complete specimen. Ventral aspect completely visible (Fig. 1B), amber matrix without significant imperfections; pedipalp coxae partially obscured by debris (Fig. 1D). Dorsal aspect of specimen, especially carapace, partly obscured by bubbles (Fig. 1A, C).
Colouration and hardness. Cuticle pale brown, uniformly coloured. Pedipalp tarsus and copulatory apparatus reddish. Colour of specimen and apparent compression of some leg segments (by pressure exerted by amber), suggest cuticle may be not heavily sclerotized.
Setation. Coxosternal region, opisthosoma dorsal surface (posterior half) and, especially, ventral surface covered with short to medium-sized, rather spinose macrosetae. Opisthosoma dorsal surface of anterior one- or two-thirds densely hirsute, long macrosetae (some about half opisthosomal length) obscuring anterior dorsal sclerites (Figs 2A, 3C); unclear whether macrosetae originate along anterodorsal external margin of opisthosoma or from surface of anterior tergites; external border of opisthosoma provisioned along entire length with dense array of medium-sized macrosetae (apparently originating from ventral sclerites). Cucullus and legs covered with bristle-like macrosetae of variable length (Figs 1, 2); leg III, dorsal surface of first tarsomere with brush-like array of brownish macrosetae (apparently clavate) distally (Fig. 2C, D). Pedipalps, setation similar to legs; tibia prolateral surface with distinct patch of dense, brownish macrosetae (Fig. 1C). Polygonal macrosetae absent.
Tegument surface macrosculpture. Tegument completely smooth, soma and appendages without single visible granule; cuticular pits absent.
Interlocking mechanism. Absent. Prosoma and opisthosoma not interlocked (Fig. 3A); coxae of legs IV unmodified, not hooked to opisthosoma ventrally; opisthosoma dorsal and ventral surfaces visibly oval (Fig. 2A, B), anterior margins not truncate; anterior part of opisthosoma extending dorsally over posterior part of prosoma, slightly obscuring the latter; exposed pedicel presumably connecting both tagmata (Fig. 3A).
Carapace. Carapace pear-shaped, narrower anteriorly (reminiscent of typical spider carapace), approximately as long as or slightly longer than wide; three pairs of ocelli in two triads laterally (Fig. 3B); sulci, if any, not visible.
Cucullus. Cucullus trapezoidal, slightly wider than long (Figs 1C, 3B); lateral margins slightly diverging ventrally; ventrolateral margins rounded; ventral margin sublinear in ventral aspect, slightly bilobate in anterior aspect; anterior surface slightly concave, almost flat (Fig. 1C), without remarkable structures or modifications; sulci, if any, not visible.
Coxosternal region. Sternum large, situated centrally on prosoma ventral surface (Figs 1D, 4C); drop-shaped, acute posteriorly; coxae of pedipalps and legs arranged concentrically around sternum; coxae of pedipalps abutting one another, forming floor of preoral cavity; coxae of legs I–IV short, separate from coxae of adjacent legs (i. e., lateral margins not fused along contact zone); sternum and coxae without remarkable structures or modifications.
Chelicerae. Chelicerae retracted into preoral cavity, not visible under light microscopy (micro-CT scanning revealed that fixed and movable fingers are long and similar in length, reminiscent of cheliceral fingers of Solifugae); finger dentition, if any, obscured; manus seemingly unmodified.
Pedipalps. Pedipalps positioned anteriad (Figs 1C, 3B); consisting of coxa, trochanters 1 and 2, femur, tibia, and tarsus; femur slightly longer than deep or wide; tibia length at most twice its maximum diameter, without fixed finger (not chelate); tarsus (movable finger) long and curved (Fig. 3D–F), about as long as tibia and at least half length of cucullo-carapacial commissure, laterally compressed, with sharp dorsal and ventral edges, basally with comb of 8–10 lamellate projections on proventral surface. Pedipalps without other remarkable structures or modifications.
Legs. Legs comprising seven segments (coxa, one trochanter, femur, patella, tibia, metatarsus, and tarsus), except leg IV with eight (i. e., two trochanters). Plane of flexion of tibia similar to (aligned with) plane of flexion of patella (Fig. 4B), axis of flexion at articulation of tibia and patella slightly rotated or not rotated. Leg femora unmodified. Leg I femur very narrow proximally, longitudinal axis crooked (Figs 1C, D, 3B, G, H); tarsus without dorsomedian lobe. Leg II longest; tarsus comprising five tarsomeres, all longer than wide and similar in length (Fig. 2C); laterodistal margins of first to fourth tarsomeres not overlapping adjacent tarsomere; fifth tarsomere without dorsomedian lobe. Leg III femur, patella, tibia, and metatarsus short and subspherical (Figs 2C, D, 4D); metatarsus prolateral surface with sharp, flat, glabrous expansion distally (Fig. 4D); metatarsal process forming curved, concave flap situated apically on metatarsus, near to and opposing tarsus; tarsus comprising four tarsomeres; first tarsomere markedly elongate, about four times longer than other tarsomeres, sinuous in dorsal aspect, shaped to accommodate copulatory apparatus that originates from its base, with pronounced retrodorsal longitudinal ridge; tarsomeres 2–4 short (each about as long as deep), similar in length and unmodified. Leg IV without remarkable structures or modifications; tarsus comprising five tarsomeres (Fig. 3I). Legs III and IV, terminal tarsomere apex margins not projected, ungues completely exposed in dorsal and lateral aspects (Figs 3I, 4D); dorsomedian lobe absent. Ungues acuminate and sharp on all legs, longer on III and IV.
Copulatory apparatus and associated structures. Comprising two parts not closely associated with one another (other components may be not visible) (Figs 2C, D, 4D); one part short, horn-shaped, lying prodorsally on first tarsomere; adjacent, in retrolateral position, hyaline, laterally compressed, lanceolate structure, apparently originating on metatarsus; other part, about twice length, narrower, and whip-shaped, curling around distal part of metatarsus. Based on morphology of modified leg III, horn-shaped part of copulatory apparatus presumably protected by various structures: ventrally by modified first tarsomere, dorsally by metatarsal process, prolaterally by metatarsal distal expansion, and retrolaterally by metatarsal(?) lanceolate structure.
Opisthosoma. Opisthosoma oval, longer than wide (Table 1), broadest at tergite XII. Dorsal surface divided transversally into separate tergites (Figs 1A, 2A, 3C); tergites without submedian depressions. Tergite X not visible, obscured by long macrosetae and matrix imperfections, segmentation unclear; XI–XIII each comprising median and lateral sclerites (visible for XII and XIII, revealed by micro-CT scanning for XI) (Fig. 3C); median sclerite of tergite XII only partially visible; of XIII cup-shaped, markedly wider than long (Table 1), lateral margins parallel. Sternites XI–XIII entirely fused, forming uniform ventral sternal plate without irregularities (Fig. 2B); submedian depressions absent. Pygidium not exposed (Fig. 2A, B), completely sheltered between dorsal and ventral opisthosomal sclerites, presumably retractile.
Female. Unknown.
description: Published as part of BOTERO-TRUJILLO, RICARDO, DAVIS, STEVEN R., MICHALIK, PETER & PRENDINI, LORENZO, 2022, Hirsutisoma grimaldii sp. nov., a ca. 99 - million-year-old ricinuleid (Primoricinulei, Hirsutisomidae) from Cretaceous Burmese amber with a corticolous, scansorial lifestyle, pp. 493-504 in Palaeoentomology 5 (5) on pages 495-500, DOI: 10.11646/palaeoentomology.5.5.11, http://zenodo.org/record/7333659