A Sternophorid Pseudoscorpion (Chelonethi) in Dominican Amber, with Remarks on the Family

10 Pages·1998·10.4 MB·English

by  Mark L I Judson

1998. The Journal ofArachnology 26:419-428
A STERNOPHORID PSEUDOSCORPION (CHELONETHI) IN
DOMINICAN AMBER, WITH REMARKS ON THE FAMILY
Mark L. I. Judson: Museum national d’Histoire naturelle, Laboratoire de Zoologie
(Arthropodes), 61 rae de Buffon, 75005 Paris, France
ABSTRACT. The first known fossil of the pseudoscorpion family Stemophoridae is described from
Dominican amber. The specimen, an adult female, is tentatively assignedto the extant speciesIdiogaryops
pumilus (Hoff), known from Florida and Little Cayman Island. The incomplete state of the fossil is
probably the result of scavenging while the animal was trapped on the surface ofthe resin. The cuticular
parts have collapsed during fossilization and the golden appearance of the fossil is due to light being
reflected from the surface ofthe cast, rather than from the cuticle itself. A thin layer of cerotegument is
recorded in Stemophoridae. The morphology ofthe coxal area is reinterpreted. The so-called pseudoster-
num is delimited by the apparent internal borders ofthe coxae, which have moved laterally. A Y-shaped
canal mns from the openings of the coxal glands to the oral cavity, carrying their secretions, together
with those of the accessory glands of the coxae, to the oral cavity. The canal is covered by a series of
overlapping tecta on coxae I-III and posteriorly on the palpcoxae. The coxae are fused medially from the
posterior margin of coxa I to the anterior margin of coxa IV. The internal modifications of the median
and posterior maxillary lyrifissures ofpseudoscorpions are shown to be apodemes oftrochanteral muscles
of the palp. The suboral setae of the manducatory process of certain Stemophoridae are vestigial, sug-
gesting that they may be undergoing a regression. The parallel between the morphology ofthe vestitural
setae and that of setae b and sb ofthe chelicera is used to identify the missing seta of Stemophoridae as
sb.
The Stemophoridae are a small, homoge- tionable, if only because fewer of their char-
neous family of pseudoscorpions, strongly acters are visible. However, there is no reason,
adapted for life under the bark of trees. The otherthan age, to suppose that the presentfos-
twenty described species are currently placed sil belongs to a different species. Pseudoscor-
in three genera: Garyops Banks 1909 from pions are known to be an ancientgroup (Scha-
North and Central America and the Caribbe- waller et al. 1991) and the wide distribution
an; Idiogaryops Hoff 1963 from Florida and and morphological homogeneity of Stemo-
the Caribbean; and Afrosternophorus Beier phoridae (Chamberlin 1932; Harvey 1985)
1967 from eastern Africa, India, Nepal, Sri suggest conservative rates ofevolution within
Lanka, Southeast Asia and Australasia (Har- the family. Recent material of the three ster-
vey 1985). nophorid genera has also been examined for
Given their ecology and distribution, it is comparative purposes and some of the results
not unexpected to find a member of the Ster- are given at the end of this paper.
nophoridae in Dominican amber, which is rel- Idiogaryops pumilus (Hoff)
atively young (15-20 My; Iturralde-Vinent & (Figs. 1, 2)
MacPhee 1996). Schawaller (1980a, 1980b,
Garyops depressa (not Banks): Banks 1909: 305-
1981a, 1981b) recorded six pseudoscorpion 306; Hounsome 1980: 85 (in part: misidentifica-
genera from this fauna, all of which are rep- tions).
resented by extant species in the Caribbean Garyopspumila Hoff 1963: 7-10, figs. 5-6.
region or Central America. What is, perhaps, Idiogaryops pumilus (Hoff): Harvey 1985: 165-
surprising is that the fossil described here is 166, figs. 32, 38, 40, 46-50, map 2.
morphologically indistinguishable from Idi- ? Idiogaryops sp. Harvey 1985: 166-167, figs. 33,
40.
ogaryops pumilus (Hoff 1963), a Recent spe- —
cies known from Florida and Little Cayman Material examined. 19, amber fossil
Island (Harvey 1985). The assignment offos- (Miocene?) from Dominican Republic (exact
sils to extant species is almost always ques- provenance unknown). Deposited in the Nat-
419
420 THE JOURNAL OF ARACHNOLOGY
—
Figure 1. Idiogaryopspumilus (Hoff), female, dorsal view ofamberfossil (image ofleftpalpdistorted
by oblique edge of block).
ural History Museum, London (Dept, of Pa- Chelicerae with 4 setae on hand, b blunt,
laeontology; registration number JA 43). Pre- other setae acuminate. Spinneret difficult to
sented by R. Rontaler, 5 December 1996. The see clearly, but apparently long and with three
amber piece is clear, golden-yellow and has rami.
been ground and polished parallel to the dor- Palps as shown in Fig. 2. Femur and patella
sal plane ofthe specimen to facilitate accurate fairly robust; lateral surfaces with strong gran-
observations. — ulation, dorsal and ventral surfaces smooth.
Description of fossil. Palps and anterior Femur with a long tactile seta, proximad of
part ofcarapace deep reddish-brown; legs and middle. Chela with granulation at base of
posterior region of carapace yellowish-brown hand; hand broader than deep, with sides sub-
(probably darkened by process of fossiliza- parallel in dorsal view and parallel in lateral
tion). Vestitural setae of dorsal surfaces with view. Fixed finger with 7 trichobothria {isb
blunt tips. Cuticular parts smooth, apart from absent). Movable finger with three trichoboth-
granulation on lateral surfaces of palps. Most ria; St about one-third of distance from b to t.
parts ofbody covered by a thin, clear layer of Fixed finger with 4 and movable finger with
cerotegument, which seems to have expanded 6 thickened (presumably spatulate) setae on
into the resin. paraxial face. Distal teeth retrorse, proximal
Carapace strongly flattened, with a moder- teeth reduced.
ate, lateral constriction at level of leg I; pos- Coxae with ‘pseudosternum’ typical of
terior part weakly sclerotized; surface with ir- family. Legs short and robust; arolia fan-
regular transverse lines in anterior half; shaped, shorter than the claws, which are ro-
posteriormargin lost. Eyes absent. Setae small bust. Setae (including ‘tactile setae’) typical.
and sparse. Pleural membrane finely plicate Joint between femur and patella of all legs
(portion visible on right side). Opisthosoma vertical (slightly oblique dorsally) and im-
missing, only represented by cerotegument of mobile.
ventral surface and a few detached setae. Measurements (in mm; ratios in parenthe-
—
JUDSON—STERNOPHORID FOSSIL 421
—
Figure 2. Idiogaryopspumilus (Hoff), female, dorsal view offossil cast. Leftpalp omitted, apartfrom
trochanter. Right chela shown separate from rest ofpalp simply for reasons offormat (see Fig. 1 for true
position). Cerotegument indicated by dotted lines (only shown in part). Cracking ofcuticle only indicated
on hand ofchela. Granulation ofpalps only shown in part. Abbreviations: cer = cerotegument; gb = gas
bubble; gbi = imprint ofbubble in cerotegument. Scale line = 1 mm.
ses): Carapace (estimated) 0.84 X 0.61 (1.4). length 0.52-0.61, chela length without pedicel
Right palp: trochanter 0.41 X 0.20 (2.05), 0.95-1.07), butthese differences arejudgedto
‘heel’ 0.29 (1.48); femur 0.59 X 0.20 (2.95); be insignificant; the measurements of Recent
patella 0.46 X 0.20 (2.31); chela (including specimens are based on only five females
pedicel) 0.95 X 0.23 (4.10) length without from Florida and are unlikely to represent the
pedicel 0.93 (4.04); hand length (withpedicel) true range ofvariation in this species. Itis also
0.54 (2.34), without pedicel 0.51 (2.21), depth possible that the specimen has undergone
0.18; movable finger0.47 (0.97 lengthofhand some compression during fossilization (seere-
without pedicel). Leg IV: femur 0.24 X 0.19 marks under Taphonomy).
(1.3), patella 0.31 X 0.19 (1.6); femoropatella Harvey (1985) briefly described andfigured
length 0.51 (2.7). a male paratype of /. pumilus that differed
Remarks. The fossil is almost indistin- from the male holotype in having a greatly
guishable from the descriptions of /. pumilus reduced dorsal apodeme of the genitalia. Har-
given by Hoff (1963) and Harvey (1985). The vey concluded that the paratype belonged to
measurements of the palpal segments fall a new species, but did not name it due to the
slightly below those given for Recent /. pum- lack of sufficient material. In the absence of
ilus (e.g., femur length 0.62““0.72, patella any further information, it seems more rea-
422 THE JOURNAL OF ARACHNOLOGY
sonable to regard the small apodeme of the The absence of debris suggests that the
paratype as either an abnormality or part of specimen was only briefly exposed before be-
the normal range of variation in /. pumilus. ing covered by a second flow of resin. The
However, ifHarvey’s interpretation is correct, removal of the body left a concavity in the
it would not be possible to assign the fossil surface of the first flow, which trapped an air
described here to either /. pumilus or the un- bubble (Fig. 3: gb) just behind the carapace.
named species. At this point, the specimen was upside-down
TAPHONOMY in the resin: the pressure ofthe bubble created
a large bulge in the layer of cerotegument
At first sight, the remains of the pseudo- above it (Fig. 3: gbi). Before the resin solid-
scorpion seem to be in very good condition. ified, it was turned over, such that the remains
When examined more closely, however, it be- ofthe pseudoscorpion were dorsal side up rel-
comes clear that the cuticle has collapsed in ative to gravity. The bubble slowly rose away
many parts, resulting in extensive cracking from the cerotegument and came to rest just
(this is only indicated forthe hand ofthe chela below the tom margin of the carapace. From
in Fig. 2). Hence, what is really seen is the the size of the impression left in the cerote-
cast left in the resin before the specimen col- gument, it can be seen that the bubble de-
lapsed. Because they were embedded in the creased in volume. This could be due to dif-
resin, the hairs of the setae and trichobothria fusion, contraction of the resin or
remained in their original positions, giving the compression, either alone or in combination.
cast a very lifelike appearance. The collapse Because the cuticle cracked, rather than
of the cuticle explains the shiny golden ap- simply disintegrating, it was probably sub-
pearance seen in reflected light, which is also jected to a significantpressure afterbeing bur-
characteristic of other Dominican amber fos- ied. If so, the cast now observed must be
sils. Where the cuticle is no longer in contact smaller than the living animal. Grimaldi et al.
with the amber, the light is reflected from the (1994) discussed differences in the size ofcu-
surface ofthe cast, but where it is still in con- ticularparts ofinsects and theircasts in amber,
tact with the amber, it is seen as a drab patch. but concluded that “Since it is unlikely that
Fortunately, the cuticle only collapsed after the cuticular surface would shrink, even dur-
the resin had hardened, leaving a faithful rep- ing dehydration, it is more likely that the cast
resentation of the external surfaces. The resin surface represents expansion of the amber,
was able to diffuse through the cerotegument probably due to polymerization ofthe original
before hardening and seems to have caused it resin.” There is indeed a large difference in
to expand. size for the specimens they illustrate, without
The incomplete nature ofthe fossil was ini- any obvious damage to the cuticle, but the as-
tially rather puzzling. The loss of part of the sumption that cuticle cannot shrink during
left palp, the opisthosoma and part ofthe car- fossilization is questionable. If, as Grimaldi et
apace almost certainly occurred after the ani- al. suggest, an expansion ofthe amber has oc-
mal had become trapped on the surface ofthe curred, the original cuticle ought to show a
resin. This can be deduced from the fact that finer, less distorted preservation of detail than
the outline of the ventral surfaces has been the cast. From their scanning electron micro-
preserved in the form ofthe cerotegument and graphs (e.g., figs. 26, 27), it appears that the
a few detached hairs. There are no signs of opposite is the case, indicating that the cuticle
decay, and the specimen cannot be an exu- has shrunk. Baroni Urban! (1980) interpreted
vium because, in addition to being adult, re- the damage seen in certain ant specimens in
mains of the internal tissues can be seen. The Dominican amber as due to shrinkage andcol-
only plausible explanation is that the exposed lapse of the cuticle, probably as a result of
parts were scavenged shortly after the pseu- heating (D. Schlee in Baroni Urban! 1980).
doscorpion—became stuck in th—e resin. The The possibility of changes in size during
scavenger perhaps an insect must have fossilization has not been considered in pre-
been relatively large: it bit through the left vious studies of amber pseudoscorpions. Al-
palp at the base of the patella and tore the though the differences are probably small, it
opisthosoma from the prosoma, leaving the is evident that caution is needed when com-
cerotegument stuck in the resin. paring morphometric data for fossil and Re-
JUDSON—STERNOPHORID FOSSIL 423
cent specimens. In identifying the present fos- a membranization. The difference between
sil as /. pumilus, I have assumed that its these interpretations may seem slight, but it
dimensions have decreased slightly. Ifit could reflects an apparent incongruity between the
be shown that a significant increase in size observations made using light and scanning
was involved, this identification would be in- electron microscopy. When Hoff’s light mi-
correct. crographs (1963: figs. 1, 5) are compared with
Harvey’s scanning electron micrograph (1985:
MORPHOLOGICAL NOTES
fig. 7), the difference is striking. The expla-
The following notes are mainly based on nation lies in the presence of a previously
two adults (Idl?) o—f an undescribed Afro- overlooked series of plate-like expansions of
sternophorus species clos—ely related to A. the paraxial walls ofthe coxae, which are here
hirsti (Chamberlin 1932) from Australia termed the coxal tecta.
(Northern Territory, The Bark Hut, Arnhem The tecta are present on coxae I~III and the
Highway, under bark of Eucalyptus sp. 18 posteriorpart ofthe palp coxae. Theirextreme
MH
June 1984, M. Kotzman; 611.07-08; de- thinness (about 2 p.m where they meet) means
posited in MNHN). Additional observations that they are almost transparent and difficult
were made on type material of Garyops sini to observe in ordinary preparations. They are
(Chamberlin 1923) and Afrosternophorus cy- best seen in specimens cleared in lactic acid.
lindrimanus (Beier 1951) housed in MNHN, The following description is mainly based on
and on specimens of G. depressus (1$, Do- the material of A. aff. hirsti, but the general
minican Republic, Pedemales Prov., 10 kmN. form seems to be the same in other stemo-
Cabo Rojo, beating thorn scrub, 22 August phorids.
1988, M.L Me, TK. Philips & K.A. Johnson; The tecta of each side extend past the mid-
WM
7186) and /. paludis (Chamberlin 1932) line, which means that they overlap. In the
(1(32$, U.S. Virgin Islands, St. John, Great specimen shown in Fig. 3, the tecta of the
Lameshur Bay, East shore, under bark, 14 right coxae pass beneath those ofthe left cox-
WM
June 1980, W.B. Muchmore; 5705). ae. In addition to this transverse overlapping,
—
Cerotegument. -A layer of cerotegument the tecta overlap longitudinally, with the tec-
is present in Stemophoridae, but it is easily tum of one coxa lying beneath that ofthe fol-
overlooked because it is thin and closely ap- lowing coxa. The combination of these two
pressed to the surface of the epicuticle. It is types of overlapping results in three points at
most evident when it becomes damaged and which four tecta are superimposed. The sec-
detached, as can be seen in Harvey’s (1985: ond ofthese points has been marked q on Fig.
fig. 7) scanning electron micrograph of the 5. At this point (looking ventrally), the exter-
coxal region ofA. hirsti. In transmitted light, nal tectum is that ofright coxa I, below which
the cerotegument is transparent and shows a is the tectum of the right coxa I, followed by
very fine, irregular granulation. Harvey that of right coxa II and finally the tectum of
(1992) regarded the presence ofcerotegument left coxa II, which is nearest to the body. This
(“pseudoderm”) as a synapomorphy of the can be represented more concisely by the se-
Garypidae and Larcidae (Garypoidea), but it quence right I/left I/right Il/left II, going from
is more widespread, occurring sporadically in ventral to dorsal. Naturally, it is the postero-
at least the Cheliferoidea (e.g., Mahnert 1985) lateral margins of tecta I and the anterolateral
and Feaelloidea (pers. obs.). margins of tecta II that are involved at q.
Coxal tecta.—The presence of a ‘pseudo- The space between the coxae is therefore
sternum’ has traditionallybeenconsideredone completely covered anteriad of coxa IV and
of the most characteristic features of the Ster- would not normally be visible with scanning
nophoridae. Chamberlin (1923, 1931) defined electron microscopy. Inreflectedlight, the tec-
it as a secondary space between the coxae, ta give the ‘pseudostemum’ a slightly irides-
resulting from a “partial mesal membraniza- cent appearance, caused by diffraction effects.
tion of coxae I to IV.” Harvey (1985) failed When a stemophorid is examined in trans-
to find any indication of a membrane in A. mitted light, two sets of apparent borders are
hirsti, using scanning electron microscopy, evident. The first and most obvious of these
and therefore interpreted the pseudostemum are the internal walls of the coxae (to which
as a desclerotization of the coxae, rather than the leg muscles are attached). These borders
424 THE JOURNAL OF ARACHNOLOGY
—
Figures 3-10. Coxal region and cheliceral setae of Stemophoridae. 3-7, Afrosternophorus aff. hirsti,
female (MH 611.08). 3, Coxae, ventral view; 4, Coxal canal (most of posterior rim removed from right
coxa IV; arrows indicate inferred flow of secretions); 5, Overlapping of coxal tecta; 6, Right median
maxillary lyrifissure, with apodeme (hatched) and muscle; 7, Left suboral seta. 8-10, Garyops depressus,
female (WM 7186); 8, Left suboral seta; 9, Abnormal seta es ofleft chelicera; 10, Normal seta es ofright
chelicera. Abbreviations: I-IV = coxae I-IV; ac^, ac^ = ducts ofaccessory glands; be = border ofcanal;
ega — atrium of coxal gland; ibc = internal border of coxa; m = muscle; ml = median maxillary
lyrifissure; P — coxa of palp; pi = posterior maxillary lyrifissure; q = point at which four tecta overlap;
r = posterior rim ofcoxal canal; so — suboral seta. Scale divisions: 0.1 mm (Figs. 3-5); 0.01 mm (Figs.
6-10).
—
JUDSON—STERNOPHORID FOSSIL 425
delimit the "pseedostemum’ and are the only into a large cavity in the posterior margin of
parts that have moved antiaxially. The cuticle coxa III (Fig. 4: ego). This cavity, here termed
between them (the pseudostern—um) is neither the coxal gland atrium, also contains the open-
membranous nor desclerotized -it is simply ings of smaller gland ducts (one inA, aff. hir-
thinnerthan that ofthe rest ofthe coxa. Closer sti two in A. cylindrimanus), which are as-
to the midline lies the second series of appar- sumed to belong to the anterior accessory
ent borders (be), which represent the edge of glands (ac^) (acinous glands ofcoxa IV; Heur-
a curve seen in tangent. These curves corre- tault 1973). The secretions of the accessory
spond to a furrow between the coxae or, more and coxal glands flow into the two branches
exactly, a canal. It is only once the nature of of the canal between coxae III and IV (Fig.
this canal is understood that the function of 4). The fluid continues along the unpaired me-
the tecta becomes clearer. dian canal, which receives the secretions of
Coxal canal. The coxal glands of most another pair of accessory glands (presumably
arachnids are associated with canals or ducts aci) at the anteromedian comers of coxa I.
that carry their secretions towards the oral re- The presence of small branches of the canal
gion. Pseudoscorpions are no exception, but between coxae I/II and II/III, suggests that se-
the course followed the secretions of their cretions from the accessory glands ofcoxae II
glands has received little attention. This may and III (not observed) may also flow into the
be due to the obscurity of the opening on the canal. The combined secretions then flow into
posterior margin ofcoxa III, which is covered the oral cavity, which marks the end of the
by the posterior margin of coxa IV. Heurtault canal.
(1973) even concluded that the coxal gland The course of the coxal canal is shown in
lacked an external opening and was solely en- Fig. 4. The drawing has been simplified by
docrine, based on histological studies ofNeo- omitting the tecta, the bases of which corre-
bisium caporiaccoi Heurtault 1966. spond to the apparent lateral borders of the
Hammen (1986: fig. 4B; 1989: fig. 115B) canal (be) in ventral view. The posterior
illustrated a tiny 'orifice’ associated with the branches of the canal are bordered by an ex-
intercoxal tubercle of Chthonius tenuis L. tended rim (or minitectum), which runs con-
Koch 1873. He interpreted the intercoxal tu- tinuously along the anterior borders of coxae
bercle as a vestigial stemapophysis and noted IV (Fig. 4: r). The fact that the rim crosses
that stemapophyses are often associated with the midline without intermption is significant
the ‘taenidia’ (canals) of coxal glands. Unfor- for two reasons. Firstly, it shows thatthe canal
tunately, the nature of this 'orifice’ is unclear. is closed posteriorly, removing any possibility
It is certainly not the opening of the coxal offluid flowingbackwards along the spacebe-
gland (which is larger and situated further tween coxae IV. Secondly, it shows that the
along coxa III) and I have not been able to anteromedian borders of coxae IV are fused.
find anything similar in Chthonius. Neverthe- In fact, the canal is sclerotized for much ofits
less, Hammen’s implication thatthe secretions length, which means that the other leg coxae
of the coxal glands flow between the coxae is are fused. This can be inferred from the po-
correct. This becomes evident when other rosity of the canal, which extends to the base
families are considered, many of which show ofcoxae 1. Pore canals are typical ofthe scler-
a well defined canal, running from the open- otized parts ofpseudoscorpions and are never
ings of the coxal glands to the oral region. found on the membranes. This fusion is prob-
The Stemophoridae are one of the most ably partial in the case ofcoxae I, which seem
convenient groups in which to study the to have retained faint traces of their original
course of the coxal canal. This is because the borders. It appears that the floor of the canal
flattening of the coxae reduces the three di- was formed by a simultaneous sclerotization
mensional nature ofthe canal, simplifying the of the original intercoxal membrane and in-
observations and their interpretation. Al- corporation ofthe original coxal margins. The
though this flattening also involves some un- paraxial borders ofcoxae IV are free for most
usual modifications, the basic form is similar oftheir length, being separated by an ordinary
to that found in other families and can there- intercoxal membrane (shown stippled in Fig.
fore serve as an example. 4).
Each coxal gland of Stemophoridae opens As yet, the presence of fluids in the canal
— —
426 THE JOURNAL OF ARACHNOLOGY
has only been directly observed in the cher- and may even become completely internal in
netid Lamprochernes savignyi (Simon 1881). some Prostigmata (Grandjean 1938).
Because the coxae are still relatively mobile Maxillary lyrifissures. Chamberlin(1931)
in this species, the movement of fluid can be noted that the median and posterior maxillary
observed ifa live specimen is trapped beneath lyrifissures ofcertain Cheliferoidea show spe-
a coverslip. As the animal struggles to free cialized internal processes, from which he in-
itself, the coxae move apart medially, reveal- ferred that they had evolved into a different
ing the fluid in the coxal canal. The fluid is sensory structure from the normal lyriformor-
clear and inconspicuous in transmitted light, gans. Although not mentioned in his text,
but its presence is evident from the meniscus Chamberlin (1931: fig. 20F) also figured an
that moves back and forth as the coxae open internal process of the median manducatory
and close. lyrifissure in Garyops sini. Similar modifica-
There can be little doubt that the secretions tions can also be found in Cheiridioidea, Gar-
of the coxal glands follow the same course in ypoidea and Neobisioidea, though their de-
all pseudoscorpions, even when there are no velopment is more variable and less well
obvious modifications of the coxal margins marked in the latter group.
(as Chthonioidea and most Neobisioidea). In- These internal structures are in fact apode-
direct evidence forthis is providedby the sim- mes. The median manducatory lyrifissure is
ilarity of the positions of the glands and the attached to one of the flexor muscles of the
presence of modifications facilitating the flow trochanter and the lateral lyrifissure is attached
between coxae I and the palpcoxae. It is al- to an extensor muscle (Figs. 3, 6). The apo-
ready known that ‘washing fluid’ moves from deme itself is a continuation of the plate of
and to the oral region along intercoxal space cuticle bounded by the lyrifissure and is at-
in the Chthonioidea and Neobisiidae (Wey- tached to the muscles via short tendons. As
goldt 1966, 1969; Judson 1990). Indeed, the the muscles contract, the plate will be pulled
assumption that this fluid is produced by oral inwards. Chamberlin’s interpretation is prob-
glands now seems questionable: it could ably correct, in the sense that the lyrifissure
equally be produced by the coxal glands. must be detecting contractions ofthe attached
Returning to the coxal tecta, it is evident muscle, rather than stresses across the cuticle.
that they serve to cover the canal, closing it It should be noted that an analogous curv-
off from the exterior. While it is possible that ing has occurred in the dorsal femoral lyrifis-
they form part ofthe canal (meaning that they sure of Chemetidae, Cheliferidae and Atem-
are in contact with the secretions), their pri- nidae (Harvey 1992). However, there is no
mary function is probably one of protection. indication of an apodeme associated with
Because Stemophoridae live in confined spac- these lyrifissures.
es, it is presumably important to prevent the Suboral seta. ^Judson (1985) briefly dis-
fluid from coming into contact with the sub- cussed the presence of a modified ‘sensory
strate or the canal from being blocked by de- seta’ at the mesal border of the manducatory
bris. Similar tecta are also present in Apo~ process in pseudoscorpions. Because the term
cheiridium Chamberlin 1924, another strongly ‘sensory seta’ is almost meaningless, it is here
flattened genus, adapted to living in tight replaced by suboral seta.
bark-crevices. The covering of the canal var- The suboral setae of Stemophoridae are
ies in other groups, ranging from a simple rim particularly interesting because they show the
to a membranous extension. most reduced form yet known. The suboral
The coxal canal of pseudoscorpions pro- setae ofGaryops depressus are small, but oth-
vides a remarkable parallel to the podoce- erwise unremarkable (Fig. 8). In contrast,
phalic canal of actinotrichid mites. Although those of Idiogaryops paludis and the Afro-
they occupy different positions (the podoce- sternophorus species examined have the hair
phalic canal runs laterally, above the anterior shortened to the point where its height scarce-
coxae), each receives the secretions of the ly exceeds its breadth (e.g.. Fig. 7). At low
coxal glands and accessory (non-nephridial) magnifications, it appears as a mere dot in the
glands. The podocephalic canal also shows the middle of its areole (Fig. 6) and could easily
same tendency to become covered by tecta be mistaken for the base of a broken hair.
JUDSON—STERNOPHORID FOSSIL 427
However, the seta has retained its lumen and the seta is enlarged at the node, but does not
tapers to a point. extend much further (c/ Figs. 9 and 10),
These reductions confirm that there is an which means that the hairis thinnerthanusual
evolutionary trend towards a decrease in the beyond this point. The factthatthebifurcation
size ofthe suboral seta. In view ofthe extreme occurred so farfrom the base suggests thatthe
reduction seen in stemophorids, it is possible anomaly was caused by mechanical defor-
that this regression can lead to the complete mation during ecdysis, rather than by a dou-
loss of the suborai seta. This might explain bling of the hair.
the curious absence of suboral setae in the Trichobothriotaxy.—Harvey (1985) showed
Pseudogar—ypidae, whose sister group—the that previous reports of stemophorids with a
Feaellidae- -have short suborai setae. full complement of eight trichobothria on the
CheMceral setae.—There is an interesting fixed finger of the chela were due to errors of
parallel between the form ofthe vestitural se- observation. Schawaller (1991) later illustrat-
tae and certain setae on the cheliceral hand in ed a female ofAfrosternophorus cylindriman-
pseudoscorpions. When the dorsal vestitural us (Beier) [possibly A. dawydoffi (Beier
setae are modified in a particular way, the 1951), according to Schawaller (1994)] as
proximal setae of the chelicerae tend to have having four trichobothria in the internal series
the same morphology, although it may be less of the fixed finger. However, the extra, distal
marked. This parallel differentiation is most trichobothrium in the internal series was
clearly seen in the Pancteeodactyli, partly be- drawn by mistake (W. Schawaller in iitL). The
cause they often have strongly modified ves- loss of trichobothrium isb therefore remains a
titural setae and partly because of the small synapomorphy of the Stemophoridae.
number of fundamental setae (five or less). ACKNOWLEDGEMENTS
Excluding cases of secondary multiplication
(neotrichy), it is setae b and sb that follow the The fossil of1. pumilus was generously do-
form of the vestitural setae, whereas setae is nated to the Natural History Museum, Lon-
and is remain simple and acuminate. Seta es don, by R. Rontaler; I am indebted to Andrew
is sometimes modified like b and sb, but is J, Ross (Dept, of Palaeontology) for bringing
more often simple, perhaps due to its lower it to my attention and making it available for
position (ventral vestitural setae also tend to study. Mark Harvey (Western Australian Mu-
be simple). seum) and Bill Muchmore (University of
Harvey (1985) noted that seta b {=bs) of Rochester) are thanked for their helpful com-
Stemophoridae differs from the other cheli- ments and for providing material of Recent
ceral setae in being blunt. This unusual form stemophorids. The manuscript was also im-
is found in the dorsal vestitural setae of all proved by comments from an anonymous ref-
Stemophoridae. Assuming that the rule ofpar- eree. I am grateful to Wolfgang Schawaller
allel differentiationholds in this family, itpro- (Staatliches Museum fur Naturkunde, Stutt-
vides a simple way of deciding which of the gart) for information concerning the tricho-
original five setae has been lost from the chel- bothriotaxy of A. cyiindrimanus from Nepal.
iceral hand. According to Chamberlin (1931) Photographic facilities were kindly provided
and Harvey (1985), it is Is that has been lost, by Jacqueline Kovoor and Arturo Munoz-
whereas Hoff (1963) interpreted the missing Cuevas (Museum national d’Histoire naturel-
seta as sb. Excluding es (the identity ofwhich le, Paris).
is not in question), if Is were missing, one
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