Archaemecys arcantiensis, Saupe & Selden, 2009

Saupe, Erin E. & Selden, Paul A., 2009, First fossil Mecysmaucheniidae (Arachnida, Chelicerata, Araneae), from Lower Cretaceous (Uppermost Albian) amber of Charente-Maritime, France, Geodiversitas 31 (1), pp. 49-60 : 56

Archaemecys arcantiensis n. sp. ( Figs 1-3 )

Arachnida Salticidae – Néraudeau et al. 2002: fig. 6.8.

TYPE LOCALITY. — Archingeay-Les Nouillers, Charente- Maritime, south-west France .

ETYMOLOGY. — The specific epithet is based on Arcantiatum, former Latin name of the locality Archingeay from which the fossil originates.

DIAGNOSIS. — As for the genus.

DESCRIPTION

Body length 3.10. Carapace 1.31 long, 0.94 wide, ≥ 0.66 high; pars cephalica highly elevated so that carapace, when viewed from side, appears subrectangular in outline; without tubercles.Only AME visible on anterior face of carapace. Chelicerae with ≥ 11 peg teeth on promargin ( Fig. 3 ); peg teeth ≈ 0.17 long, chelicerae 0.71 long; fang ≥ 0.35 long; chelicerae appear to originate from a foramen, although this is not certain; sclerotized lip/projection above where chelicerae originate ( Fig. 3 ). Sternum 0.34 wide, 0.57 long, lateral margins project slightly between coxae. Maxillae converge slightly, almost circular in shape. Petiole encircled by sclerotized plate ( Fig. 2A ); rugose epigastric plate, flanked by book lung covers ( Fig. 2B ). Opisthosoma 1.42 long, approximately 1.10 wide, height uncertain; likely sub-globular in life; dorsal surface not preserved so presence of scutum not known. Opisthosomal cuticle wrinkled in subparallel lines, bearing short, plumose setae, each originating from a prominent follicle.Four spinnerets and anal tubercle surrounded by well-developed chitinous ring ( Fig. 2B ); ALS well defined in two segments ( Fig. 1D ), posterior spinnerets smaller; patch of cuticle with short setae in front of ALS, possibly a colulus. Spiracle situated well anterior to spinnerets; well fortified with cuticle ring ( Fig. 1 A-C).

Leg formula 1423; leg 1 cx 0.23, tr 0.16, fe 0.57, pt 0.25, ti 0.39, mt 0.39, ts 0.39, total 2.38; leg 2 cx 0.18, tr 0.19, fe 0.52, pt 0.20, ti 0.38, mt 0.33, ts 0.33, total 2.13; leg 3 cx 0.17, tr 0.18, fe 0.45, pt 0.21, ti 0.39, mt 0.33, ts 0.28, total 2.01; leg 4 cx 0.25, tr 0.16, fe 0.54, pt 0.20, ti 0.44, mt 0.41, ts 0.33, total 2.33. Plumose setae on all leg segments; no spines; each metatarsus with single trichobothrium, most likely on dorsal surface (trichobothrium located seven-tenths of way along metatarsus from proximal end in legs 2-4); tibiae 2-4 with at least one (up to three) trichobothria ( Fig. 2 ). Legs relatively short and stout. Tarsi with unsclerotized constriction at the base of the tarsus ( Fig. 1E ). Three tarsal claws on unsclerotized onychium; paired claws with four, possibly five teeth, unpaired claw simple. Pedipalp rounded and bulbous, 0.37 long, 0.16 wide.

REMARKS

While we are only able to view four spinnerets, we cannot completely rule out the possibility of six, as there may be a very small median pair (this is unlikely since we are able to view inside the opisthosoma to the point of spinneret attachment). Regardless, even if the specimen possesses six spinnerets, this would not change its placement within the Mecysmaucheniidae . Although the archaeids and pararchaeids have six spinnerets, these families do not share the other characters found in our specimen (see family remarks).Additionally, losing spinnerets is a fairly common phenomenon within the Araneae . Extant mecysmaucheniids have lost four spinnerets in the reduction to the two the family currently possesses; given this, it seems quite possible that a primitive mecysmaucheniid would have four, or even six, spinnerets.

Figures

FIG. 1. — Archaemecys arcantiensis n. gen., n. sp. (MNHN ARC11R): A, dorsal view; B, ventral view; C, opisthosoma, notice the pronounced wrinkling of the cuticle and the sclerotized rings around the tracheal spiracle and the spinnerets; D, lateral view of the spinnerets, anterior to the left; the anterior two spinnerets (left) are relatively large, with two segments, while the posterior two spinnerets (right) are smaller; E, close-up of metatarsus and tarsus third leg segment showing the unsclerotized portion at the base of the tarsus (arrowed). Scale bars: A, B, D, E, 0.5 mm; C, 0.2 mm.

FIG. 2. — Interpretive drawings of Archaemecys arcantiensis n. gen., n. sp.: A, dorsal view; B, ventral view. See text for explanation of abbreviations. Scale bar: 0.5 mm.

FIG. 3. — Archaemecys arcantiensis n. gen., n. sp., anterior view of the chelicerae and pedipalps. Notice the peg teeth on the chelicerae and the heightened profile of the carapace. Scale bar: 0.1 mm.