Myrmarachne colombiana, Poinar, 2024

Poinar, George, 2024, Myrmarachne colombiana sp. n. (Araneae: Salticidae), a new species of ant-mimic spider in copal from Colombia, South America, Historical Biology CLXVI (CLXVI), pp. 1-6 : 1-3

Species: colombiana sp. n.

Characters that align Myrmarachne colombiana sp. n., to the genus Myrmarachne are the distinct posterior margin (pedicel) of the abdomen visible from above, the quadrangle of the eyes less than ½ the length of cephalothorax and the eight eyes arranged in two front rows of four each ( Comstock 1948; Levi and Levi 1996).

Etymology

The specific epithet is based on the geographic location of the fossil Type strata and locality

.

Colombian Quaternary copal; Santander province, Andes region, Colombia, South America.

Material examined

Holotype female (C-10-272) deposited in the Poinar amber collection maintained at Oregon State University, Corvallis, OR, U.S.A. Male unknown.

Diagnosis

Myrmecomorphic spider genera related to Myrmarachne were also examined, however none had generic features closer to those of the fossil than Myrmarachne . The related Synemosyna Hentz 1846 has the hind part of the thorax narrow and parallel-sided ( Comstock 1948) while species of Peckhamia Simon 1900 are small spiders that have the quadrangle of the eyes more than ½ the length of the cephalothorax ( Comstock 1948; Levi and Levi 1996). Species of Zuninga Peckham and Peckham have only a single tooth at the lower margin of the chelicerae, members of Synemosyna Hentz , including the Central American S. americana Hentz and the eastern United States S. formica Hentz , are either smaller than Myrmarachne colombiana sp. n., have a bulbous petiole, the posterior portion of the cephalothorax is very narrow, or the eyes extend to the posterior portion of the head. There are ant mimic spiders in the family Corinnidae that have some features of the present fossil, such as eight eyes in two rows. However members of this family have two tarsal claws, not one or none like the present fossil. Many species of Myrmarachne have recently been placed in new genera ( Prószyński 2016). In reviewing these various genera, the present author could find no representatives that fit the description of Myrmarachne colombiana sp. n.

In their study of ant-mimicking spiders, Hashimoto et al. (2020) divide this group into the ‘broad mimics’ and the ‘slender mimics’. Myrmarachne colombiana sp. n., is clearly a ‘slender mimic’. Along with other slender ant-mimicking spiders of the genus, Myrmarachne colombiana sp. n., displays a long body divided into three distinct regions now appearing antlike rather than the original two spiderlike regions. Another unique feature of the fossil is the long ‘pedicel’ clearly visible from above, an eye quadrangle less than ½ the length of the thorax, the lower margin of the chelicerae armed with 3–4 teeth and the upper row of eyes positioned on short pedicles.

While there are no published keys separating the described species of Myrmarachne , only two species of fossil spiders in copal have been described previously from Colombia ( Wunderlich 2004a, 2004b). These are non-mimetic spiders and include a member of the Oonopidae and another of the Dictynidae . Since neither of these are ant mimics, they can easily be distinguished from Myrmarachne colombiana sp. n. The single species of Myrmarachne in Britain and northern Europe, M. formicaria (De Geer) , has its head abruptly raised from the thoracic part of the carapace ( Roberts 1996), which clearly separates it from Myrmarachne colombiana sp. n.

With the accompanying eggs and absence of enlarged palps, there is no doubt that the specimen is a female.

Description

Holotype female

( Figures 1–10 ). Body length, 6.67 mm. Head, thorax and petiole dark brown; thorax elongated with constriction in middle. Head large, 2.2 mm in length; two horizontal rows of eyes present, lower row of four eyes with central two largest, positioned flat against the head while the two lateral smaller eyes are positioned at the tips of short peduncles ( Figures 7 , 8 ). Chelicerae furrow with 4 teeth and many bristles; mandibles with central serrula portion ( Figure 7 ). Legs and abdomen light brown to tan; foreleg segments narrow, reflexed, appearing as elbowed antennae ( Figures 1– 3 ). Tips of legs variable. Pretarsus of last (4th) leg with a single large claw bearing four accessory claws and terminal hairs ( Figure 4 A ). Bulbous tip on second pretarsus bearing short, thick setae ( Figure 4 B ). Ventral side shows pedipalps, wide labium; sternum and eggs ( Figures 5 , 6 ). Two thick bristles, each with a small flap, are attached to the femur of the pedipalps ( Figure 7 ). Lower portion of mandibles showing scopula with bristles and finely toothed keel (serrula) ( Figure 9 ). Abdomen with wide lung slit and three or more spinnerets ( Figure 10 ).

Comments

The eggs are loosely attached to the ventral side of the fossil spider ( Figures 5 and 6 ). These eggs are spherical, white, smooth and range in diameter from 212 to 230 µm; all of which are features of extant spider eggs ( Comstock 1948). Many of the eggs appear to be embryonated. They may have originally been carried in very loose sacs, since any sign of webbing now is very faint.

The internal border of the endite of Myrmarachne colombiana sp. n., along with the crushing part of the coxa of the pedipalp, bear a brush of hairs (scopula). Adjacent is a finely toothed keel (serrula) that lacerates the prey to release the juices. These structures are well developed on Myrmarachne colombiana sp. n. ( Figure 9 ). The function of the two thick bristles, each with a small flap, attached to the femur of the pedipalps ( Figure 7 ), is unknown. The small lateral pedunculated eyes, presence of the fossil in Colombia and current lack of other fossil ant-mimicking spiders in that country, can be considered additional diagnostic characters of the species.,

The club-shaped setae that cover the dorsum of the thorax of Myrmarachne colombiana sp. n. probably served as tactile hairs. It has been stated that the cuticular surface (colour, hairs, etc.) of myrmecomorphic spiders can resemble that of their ant model (Cushing 1987, Ceccarelli 2013). Perhaps a later analysis of spiders in Colombia will reveal the model ant of Myrmarachne colombiana sp. n. Reiskind (1977) listed two species in the salticid genus Pachycondyla Latreille as serving as ant models for Myrmapana parallela (Fab.) in Panama. Cushing (1987) listed Camponotus compressus (Fab.) , Oecophylla sp. , Paratrechina longicornis (Latreille) , Pheidole indica Mayr and Polyrachis lacteipennis Smith as models for various other Myrmarachne spp.

Figures

Figure 1. Holotype female specimen of Myrmarachne colombiana sp. n., in a piece of copal from Colombia. Scale bar = 3.3 mm.

Figure 2. Dorsal view of Myrmarachne colombiana sp. n. Scale bar = 57 µm. Insert shows detail of club-shaped setae covering cephalothorax. Scale bar = 0.8 µm.

Figure 3. Lateral view of Myrmarachne colombiana sp. n. Arrow shows petiole.Scale bar = 700 µm.

Figure 4. Pretarsi of Myrmarachne colombiana sp. n. A. Tip fourth leg. Arrow shows single claw with four teeth and surrounding bristles. Scale bar = 123 µm. B. Tip second leg. Note bulbous tip with emerging thick setae but no claw. Scale bar = 53 µm.

Figure 5. Ventral view of Myrmarachne colombiana sp. n. E = eggs, L = labium, Pe = pedipalps, p = petiole, S = sternum. Scale bar = 440 µm.

Figure 6. Detailed view of eggs (some with faint embryos) loosely attached to ventral surface of Myrmarachne colombiana sp. n. Scale bar = 210 µm.

Figure 7. Chelicerae of Myrmarachne colombiana sp. n. B= thickened bristles, E= lower large central eyes, F= small flap attached to thickened bristle; T=teeth at tip of chelicerae, S=serrula, Scale bar = 440 µm.

Figure 8. Lower row of eyes of Myrmarachne colombiana sp. n. showing tips of outer eyes on short peduncles (arrows). Scale bar = 184 µm.

Figure 9. Lower portion of chelicerae of Myrmarachne colombiana sp. n. showing scopula with bristles on right side (two arrows) and the finely toothed keel (serrula) on the left (single arrow). Note teeth at base of chelicerae. Scale bar = 114 µm.

Figure 10. Posterior view of tip of abdomen of Myrmarachne colombiana sp. n. showing an elongate lung slit (LS) and spinnerets (arrows). Scale bar = 600 µm.