— This article by Jerry Cates and Marvin W., first published in November 2008, was last revised on 24 April 2016. © Bugsinthenews Vol. 09:11(01).
The photo on the right was taken by Marvin W., in Kempner, TX on 11.12.08. I have taken the liberty of applying image enhancement software to it and the other photos provided on this post to lighten the coloration and bring out some of the subtle features that would otherwise be lost. If you find a trapdoor spider like this in the field, it will be much darker, to the point of appearing almost entirely black.
Notice that the photos on this page, as with all the photos posted on bugsinthenews.info, can be enlarged for more detailed viewing by placing your cursor over the photo and left-clicking.
Marvin and his wife recently moved to Texas from the frigid northwest (Washington state). Not being familiar with the size of our Texas tarantulas, he first suspected this to be one. As both are orthognaths in the infraorder Mygalomorphae, they share a number of gross anatomical features. However, the leg span of this male (note the swollen distal palps) is about half that of the average Texas tarantula.
In the following narrative, replete with photos, we will refer to anatomical characters that bear on its identity, as described by a number of authorities, including the key provided in Ubick 2005, p. 25-37. Major changes to the taxonomy of the Mygalomorph spiders have recently taken place that must be taken into account before we can arrive at a conclusion regarding this spider’s taxonomical identity. In fact, because we do not have definitive images of this specimen’s genitalia, and no effort was made to find and examine its burrows, arriving at a firm conclusion in this regard is practically impossible. Regardless, much can still be said about this spider.
Marvin’s wife, a now-repentant arachnophobe, sprayed the first of these spiders–which she found on their back patio just after a cool, autumn rain–with a pesticide. The next morning Marvin found this one, on the same patio. He captured it and took several photos.
After looking Marvin’s photos over, I asked to borrow the spider for microscopic work, but this one had already been released. Marvin kindly retrieved the remains of the first for me to work with, and the micrographs that follow were taken from that specimen.
This photo, taken of the first spider Marvin’s wife found on their patio, shows the spider’s head and thorax, i.e., the cephalothorax, or dorsal prosoma, covered by a sclerotized plate, the carapace.
Also is shown the forward part of the dorsal abdomen, and the proximal three segments of the legs and pedipalps.
Notice the robust jaws (chelicerae) that project outward as a forward extension of the face.
This structure typifies spiders in the infraorder Mygalomorphae.
As noted in Ubick, 2005, pg. 25, such spiders also have two pairs of book lungs and eight eyes, are without the anterior median spinnerets (AMS) found in many araneomorphs, and have stout legs.
The cephalothorax is smooth and glabrous. Notice the deep, procurved thoracic furrow (an important, though not definitive, anatomical marker for the Ctenizidae) that separates the slightly bulging head (pars cephalica) from the thoracic region (pars thoracica) lateral and posterior to it.
The musculature for the spider’s sucking stomach attaches at the thoracic furrow, to the underside of the carapace.
A portion of the lateral anterior abdomen is a lighter color, due in part to a paucity of hairs over the spider’s anterior book lungs. The abdomen has no dorsal tergites, which rules out the Antrodiaetidae, Atypidae, and Mecicobothriidae.
The photo at left shows the spider’s ventral body. Notice that the chelicerae and fangs are paraxial, opening more like claws than scissors (as in the araneomorphs).
Most mygalomorphs burrow in the ground. Their claw-like fangs assist in excavating their burrows.
The palpal endites of this specimen are similar in structure to the coxae of the legs, longer than wide, and are lined medially with a loose row of bristles known as scopulae (not to be confused with the dense pads on the ventroapical surface of the legs of some spiders, which are also referred to as scopulae) that surrounds the mouth.
The entire anterior portion of the ventral abdomen is occupied by a pair of book lungs, whose lateral extension is visible on the dorsal abdomen in the photo just above this one.
A second pair of book lungs is positioned on each side of the ventral abdomen, posterior to the first pair, as indicated by the light-colored regions there.
Notice the spinnerets on the posterior abdomen.
Most mygalomorphs, including this specimen, have two pairs of functional spinnerets (the PMS and PLS), while araneomorphs have a third pair (the ALS) that is absent (lost) in the mygalomorphs.
The eye cluster of this spider is shown in the midsection of this photo, with the basal chelicerae, in the lower portion of the photo, out of focus.
The eyes are arranged in two rows, an anterior (foremost) row nearest the chelicerae, and a posterior (rearward) row behind it.
Each row is, by convention, divided into median (midmost) and lateral (outermost) eyes, and are referred to in coded form.
Notice the two anterior median eyes (AME) in the center of the face, facing forward and slightly upward. Flanking the AME, the anterior lateral eyes (ALE) face forward, angled to the side.
Notice that, in this spider, the posterior eyes form a triangle with the ALE, as the anterior eyes form one with the PME.
The posterior median eyes (PME) are brightly reflective. Notice also that the PME face upward, slightly back and toward a point above the centerline of the body. The posterior lateral eyes (PLE) face backward and to the side.
This eye arrangement does not provide acute vision, as found in jumping or wolf spiders, but does afford a wide field of view.
The lenses are fixed, but the retinas are moveable, so the spider can examine a large expanse of its environment without moving its head.
The eye cluster is now shown from the front.
Note the basal chelicerae in the lower portion of the photo.
Separating the eyes and chelicerae is a delicately delineated clypeus (the membrane connecting the basal chelicerae to the carapace).
Note that the head (pars cephalica) is not elevated behind the eye group, as in the Ummidia (Ctenizidae).
The anterior median eyes (AME) in the center of the face look forward and slightly upward.
Flanking the AME, the anterior lateral eyes (ALE) face forward, angled down and to the side.
The brightly reflective posterior median eyes (PME) are midway between, and behind, the ALE and AME.
The posterior lateral eyes (PLE), which face backward and to the side, are not visible but their tubercles appear as dark knobs, next to the PME.
A close-up view of the fangs, endites, and the anterior labium (the lip) of this spider is shown here.
Endites (the two leg-like structures forming a “V” at center left of the photo, which are actually the proximal segments of this spider’s pedipalps) are generally an expanded lobe of the palpal coxa, often referred to as gnathocoxa because, in most spiders, they play an active role in food mastication.
In the mygalomorphs, the endites are relatively long and simple.
They hold a morsel of prey in place while it is being masticated by the chelicerae and fangs before being sucked into the mouth.
The endites of this specimen have a thick brush of loose bristles (scopulae) along their medial margins.
The fangs are shown folded into their cheliceral furrows, and are flanked laterally by a row of denticles (diminutive teeth), and medially by a row of more substantial teeth that are barely visible in this perspective. The spider’s mouth is positioned where the distal fangs come together, at the labium, or lip, at the anterior median extension of the sternum (lower mid photo).
As food is masticated by the chelicerae, it is drawn into the mouth by the action of the spider’s sucking stomach.
This photo shows a close-up view of this spider’s distal chelicerae, with the fangs extended (and out of focus) so that the cheliceral furrows and their related denticles, and a rastellum (“little rake,” a rake-like structure near the cheliceral fang base, present in some mygalomorphae) can be examined.
Ubick 2005, p. 270, shows the rastellum as a patch of short spines, which appear to be present in this specimen in the form of hardened tubercles at the medial distal end of each jaw.
So, at least by that latter definition this specimen is positive for that anatomical feature.
This final photo shows a close-up view of the distal fangs, including the orifice through which venom is ejected (injected, actually, once the fangs have penetrated the spider’s prey). In many mygalomorphs, particularly the larger tarantulas, the venom glands are relatively small and reside entirely within the chelicerae.
It would be necessary to dissect this specimen to determine the extent of its venom glands. Many other anatomical features are easily depicted via imagery of the external body, however. These include, for this specimen, details of the distal palps.
- Kingdom Animalia (an-uh-MAYHL-yuh) — first described in 1758 by the Swedish taxonomist Carolus Linnaeus (1707 – 1778), using the Latin word animal = “a living being,” from the Latin word anima = “vital breath”, to refer to multicellular, eukaryotic organisms whose body plans become fixed during development, some of which undergo additional processes of metamorphosis later in their lives; most of which are motile, and thus exhibit spontaneous and independent movements; and all of whom are heterotrophs that feed by ingesting other organisms or their products;
- Phylum Arthropoda (ahr-THROPP-uh-duh) — first described in 1829 by the French zoologist Pierre André Latreille (1762 – 1833), using the two Greek roots αρθρον (AR-thron) = jointed + ποδ (pawd) = foot, in an obvious reference to animals with jointed feet, but in the more narrow context of the invertebrates, which have segmented bodies as well as jointed appendages;
- Subphylum Chelicerata (Kuh-liss-uh-RAH-tah) — first described in 1901 by the German zoologist Richard Heymons (1867 – 1943) using the Greek noun χηλη (KEY-lay) = a claw, talon, or hoof + the Greek noun κερας (SAIR-as) = an animal’s horn + the Latin suffix ata — which by convention is suffixed to the names of animal subdivisions — to refer to animals that have specialized appendages before the mouth that they use in feeding, capturing and securing prey and that — in the case of spiders — are further equipped to inject venom and digestive agents into their prey;
- Class Arachnida (uh-RAKH-nuh-duh) — first described in 1812 by the French naturalist and zoologist Jean Léopold Nicolas Frédéric Cuvier (1769 – 1832), usually referred to as Georges Cuvier, using the Greek noun αραχης (uh-RAH-kes) = a spider, in reference to all eight-legged arthropods, including such disparate animals as ticks, mites, scorpions, harvestmen, solpugids, and spiders;
- Order Araneae (uh-RAY-neh-ee) — first described in 1757 by the Swedish entomologist and arachnologist Carl Alexander Clerck (1709 – 1765), who used the Latin word aranea = a spider or a spider’s web, to refer to eight legged arthropods that spin webs;
- Suborder Opisthothelae (oh-PIS-thoh-THEE-lee) — first described in 1990 by the American arachnologists Richard C. Brusca and Gary J. Brusca, who used the Greek words οπισθεν (oh-PIS-thehn) = behind, at the back, yet to come + θηλη (THEE-lee) = nipple or teat, to distinguish this grouping of spiders from the more primitive spiders in the suborder Mesothelae, in that certain characters (e.g., tergite plates, ganglia in the abdomen, and — in particular, inasmuch as the suborder name is a direct reference thereto — median-positioned spinnerets) of the latter are absent in the former; thus spiders in this suborder have spinnerets positioned at the hindmost portion of the abdomen;
- Infraorder Mygalomorphe (my-GAL-oh-MOHR-fee) — spiders with paraxial chelicerae and two pairs of book lungs, as in the more primitive Mesothelae, but without the latter’s tergite plates and most of the latter’s abdominal ganglia, and having their spinnerets positioned at the abdomen’s hindmost portion rather than mid-ventrally as in the Mesothelae; presently comprised of fifteen families:
- Atypidae (Thorell 1870) — 3 genera, 49 species (Platnick WSCv13.5); commonly known as purseweb spiders; 8-27 mm, yellow-brown to dark purple-black in color; the legs of male specimens of Sphodros rufipes (Latrielle 1829) and S. fitchi (Gertsch & Platnick 1980) are bright orange-red;
- Antrodiaetidae (Gertsch 1940) — 2 genera, 33 species (Platnick WSCv13.5); commonly known as foldingdoor, collardoor, or turret spiders (Antrodiaetus), and trapdoor spiders (Aliatypus); 6-26 mm, tan to chestnut brown, with one or more tergites on the anterodorsal abdomen; live in burrows with a flexible collar, a rigid turret, or a trapdoor at the mouth;
- Mecicobothriidae (Holmberg 1882) — 4 genera, 9 species (Platnick WSCv13.5); no common name; mygalomorphs with two tergites on their anterodorsal abdomen (these sclerotized patches may be fused); build sheet webs with silk tubes from sheet to ground that lead into hiding places under terrestrial objects;
- Hexathelidae (Simon 1892) — 12 genera, 112 species (Platnick WSCv13.5);
- Dipluridae (Simon 1889) — 24 genera, 179 species (Platnick WSCv13.5); commonly known as mygalomorph funnelweb spiders; 3.5-17 mm, pale tan to purple-brown in color; thoracic furrow in the form of a short longitudinal groove or a shallow pit or rounded depression;
- Cyrtaucheniidae (Simon 1889) — 10 genera, 102 species (Platnick WSCv13.5);
- Ctenizidae (Thorell 1887) — 9 genera, 128 species (Platnick WSCv13.5); no common name; 10-30 mm or more in length, tan, dark chestnut brown, and black in color; the females lack scopulae, but are equipped with a number of robust lateral digging spines on their pedipalps, as well as on the tarsus, metatarsus, and tibia of legs I and II; carapace generally glabrous, with few distinct spines; thoracic furrow is transverse, typically very deep and procurved; burrows are covered with a thick cork-type trapdoor for all genera, except Cyclosmia Ausserer 1871, which have wafer-type trapdoors;
- Euctenizidae (Raven 1985) — 7 genera, 33 species (Platnick WSCv13.5);
- Idiopidae (Simon 1889) — 22 genera, 314 species (Platnick WSCv13.5);
- Actinopodidae (Simon 1892) — 3 genera, 40 species (Platnick WSCv13.5);
- Migidae (Simon 1889) — 10 genera, 91 species (Platnick WSCv13.5);
- Nemesiidae (Simon 1889) — 43 genera, 364 species (Platnick WSCv13.5); 16-30 mm, golden brown to dark gray, generally concolorous but sometimes with an indistinct chevron pattern on the dorsal abdomen;
- Microstigmatidae (Roewer 1942) — 7 genera, 16 species (Platnick WSCv13.5);
- Barychelidae (Simon 1889) — 44 genera, 307 species (Platnick WSCv13.5);
- Theraphosidae (Thorell 1869) — 124 genera, 946 species (Platnick WSCv13.5);
- Paratropididae (Simon 1889) — 4 genera, 8 species (Platnick WSCv13.5);
- Family not presently determined;
- Genus not presently determined;
- Species not presently determined;
- Beccaloni, Jan. 2009. Arachnids. Univ. Calif. Press.
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