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R E S E A R C H P A P E R
Dehmicystis globulus, an enigmatic solute (Echinodermata)from the Lower Devonian Hunsru ck Slate, Germany
Imran A. Rahman Hermann Lintz
Received: 7 March 2011 / Accepted: 11 August 2011 / Published online: 28 August 2011 Springer-Verlag 2011
Abstract Dehmicystis globulus is a very poorly known
Lower Devonian solute echinoderm from the HunsruckSlate of Germany. To date, only the holotype has been
formally described; however, it is incomplete and does not
preserve important characters of the group. We report three
new individuals on the same slab of slate, one of which is
almost complete. This material informs a full systematic
redescription of the genus. The orientation and mode of life
of solutes are contentious; our new morphofunctional data
strongly suggest that Dehmicystis was oriented with the
ambulacrum on the upper surface. Such a position implies
a suspension feeding mode of life, with food particles
captured from the current using the ambulacrum. The stele
may have enabled limited movement on the sea floor but
was principally responsible for support, anchorage, and
(facultative) attachment.
Keywords Echinodermata Soluta Dehmicystis
Devonian Hunsruck Slate Germany
Kurzfassung Dehmicystis globulusist ein kaum bekann-
ter unterdevonischer Stachelhauter der Ordnung Soluta
aus dem Hunsruckschiefer in Deutschland. Bis heute ist nur
der Holotyp formal beschrieben worden. Dieser ist jedoch
unvollstandig. Wichtige Merkmale der Ordnung sind nicht
erhalten. Wir berichten uber drei neue Individuen auf einer
Schieferplatte, von denen eines nahezu komplett erhalten
ist. Das Material ermoglicht eine systematische Wieder-beschreibung der Art. Orientierung und Lebensweise der
Soluta sind umstritten. Die neuen funktionsmorphologi-
schen Belege weisen auf eine mit dem Ambulacrum nach
oben orientierte Lebensweise hin. Dies impliziert eine
filtrierende Ernahrungsweise unter Aufnahme von Nah-
rungspartikeln aus der Wassersaule. Der Stiel diente der
Fixierung, ggf. Anheftung des Tieres und hat begrenzte
Bewegungen auf dem Meeresboden ermoglicht.
Schlu sselwo rter Stachelhauter Soluta Dehmicystis
Devon Hunsruckschiefer Deutschland
Introduction
The Hunsruck Slate is a world-renowned fossil-Lagerstatte
from the Lower Devonian of Rheinland-Pfalz, western
Germany. It preserves a diverse fauna, including arthro-
pods, brachiopods, echinoderms, and vertebrates, with
more than 260 reported species (Bartels et al.1998,2002).
Despite extensive research on the deposit, which has been
studied for almost 150 years, several important taxa remain
incompletely known because initial descriptive work was
based on single, poorly preserved specimens. One such
fossil is the solute echinoderm Dehmicystis globulus
(Dehm,1934), which is the subject of this paper.
Solutes are aberrant extinct echinoderms without obvi-
ous radial symmetry. They comprise an asymmetrical body
(theca) with two appendages: an anterior ambulacrum and
a posterior stele (Fig.1). The ambulacrum consists of pairs
of small cover plates articulating with pairs of larger
flooring plates and is interpreted as having accommodated
elements of a water vascular system in life (Nichols1972;
I. A. Rahman (&)
School of Geography, Earth and Environmental Sciences,
University of Birmingham, Edgbaston, Birmingham B15 2TT,
UK
e-mail: [email protected]
H. Lintz
61194 Niddatal, Germany
e-mail: [email protected]
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Palaontol Z (2012) 86:5970
DOI 10.1007/s12542-011-0116-y
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Jefferies1990; David et al.2000; Smith2005). The stele is
long and tripartite; it was flexible in its proximal part and
stiff distally. Some workers have treated solutes as stem-
group chordates (e.g., Jefferies1990; Daley1992; Jefferies
et al. 1996; Rozhnov and Jefferies 1996), but their char-
acteristic stereomic calcite skeleton clearly places them in
the Echinodermatathe family of genes responsible for
forming such a skeleton is almost certainly unique to
echinoderms (Bottjer et al. 2006). Solutes are best con-
sidered as basal stem-group echinoderms (Caster 1968;
Ubaghs1975; Paul and Smith1984; Smith2005,2008) or
blastozoans (Parsley 1997; Sumrall 1997; David et al.2000; Sprinkle and Guensburg2004; Nardin et al.2009),
depending on the interpretation of their ambulacrum.
Fossils of solutes have been reported from the Middle
CambrianLower Devonian of Australia, Europe, Mor-
occo, and North America (Caster1968; Domnguez et al.
2002; Lefebvre and Fatka2003).
In 1934, the German palaeontologist Richard Dehm
published a description of a peculiar Hunsruck Slate
echinoderm based on one partial specimen, which he
provisionally named Dendrocystites (Dendrocystoides?)
globulus. He identified the fossil as a solute, grouping it
with the genera Dendrocystites Barrande, 1887; Dendro-
cystoides Jaekel, 1918; and Rhipidocystis Jaekel, 1901
(which was later reclassified as an eocrinoid). Gill andCaster (1960) were the next to consider this specimen in
detail, and they tentatively placed it in the genusRutroc-
lypeus Withers, 1933 (together with several other Lower
Devonian solutes characterized by a strongly flattened,
spinose theca with a circular outline). They did, however,
note the apparent absence of thecal spines on the specimen
(Fig.2a), suggesting that a new generic assignment might
be more appropriate. Most recently, Caster (1968), noting
an anal pyramid and interpreting the theca as inflated in life
(Fig.2b), erected the genus Dehmicystis to house the
taxon. Since this work, the animal has been only occa-
sionally briefly mentioned (e.g., Kutscher 1975; Haude1983; Parsley and Sumrall 2007). Bartels and Brassel
(1990) and Bartels et al. (1998) figured two additional
specimens; one of these (Bartels and Brassel 1990:
Fig. 162 right; Bartels et al.1998: Fig. 139) is clearly not a
solute, but more likely an individual of the poorly known
stylophoran Mitrocystites styloideus Dehm, 1934. The
other fossil (Bartels and Brassel1990: Fig. 162 left) might
represent a solute, but it does not preserve the anus or
ambulacrum and has not been formally described.
Fig. 1 Reconstruction of Dendrocystoides scoticus (Bather, 1913)
showing typical solute characters. Modified from Smith (2005: Fig. 3)
Fig. 2 Reconstructions of Dehmicystis globulus (Dehm, 1934).
a Drawing of the holotype by Gill and Caster (1960). b Drawing of
the holotype by Caster (1968). Modified from Caster (1968: Fig. 388)
60 I. A. Rahman, H. Lintz
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Because of the very limited treatmentDehmicystis has
received in the roughly 80 years since its discovery,
important characters of the genus have yet to be
described, for example the ambulacrum. Here, we report
three well-preserved, newly prepared specimens and
reconsider the holotype in light of this material. In this
manner, we are able to decipher the anatomy of the
animal in far greater detail than previously possible,thereby uncovering the mode of life of this hitherto
enigmatic fossil.
Geological setting
The material described herein was collected from the
Eschenbach-Bocksberg roof slate quarry, about 500 m
southwest of the village of Bundenbach, Hunsruck region,
Germany (Fig.3). This site contains some of the best-
preserved fossils of the Hunsruck Slate; it is characterized
by a coarsening upwards sequence with fine-grained
turbidites near the base and interbedded sandstones/silt-stones and claystones towards the top (Sutcliffe et al.
1999). Slate-producing lithologies were deposited on a
mud-rich slope apron as turbidites, and they include at least
four clay-rich levels that yield exceptional pyritized spec-
imens (Bartels et al. 1998; Sutcliffe et al. 1999). These
rocks form part of the Lower Devonian (middle Lower
Emsian) Kaub Formation; the stratigraphy of this unit is
discussed in detail in Bartels et al. (2002) and Schindler
et al. (2002).
The Eschenbach-Bocksberg quarry is highly fossilifer-
ous and contains abundant fossil echinoderms. Asteroids,
crinoids, and ophiuroids are especially common (Schmidt
1934; Lehmann1957; Kutscher1976; Bartels et al.1998;
Glass and Blake 2004; Glass 2006), but well-preserved
blastoids (Pentremitidea medusa and Schizotremites oso-
leae), echinoids (Porechinus prosus and Rhenechinus
hopstaetteri), edrioasteroids [Pyrgocystis (Rhenopyrgus)
coronaeformis], holothurians (Palaeocucumaria hun-
srueckiana), rhombiferans (Regulaecystis pleurocysto-
ides), and stylophorans (Mitrocystites styloideus and
Rhenocystis latipedunculata) have also been recovered
from the quarry (Jaekel 1895; Dehm 1932, 1934, 1961;
Lehmann 1949, 1958; Rievers 1961; Bartels et al. 1998;
Ruta and Bartels 1998). In a few very rare cases, direct
associations between ichnofossils and their echinoderm
tracemakers have even been reported (Sutcliffe et al.
2000; Rahman et al. 2009). Unusually for echinoderms,
fossils are often preserved articulated and relatively
complete; rapid burial in sediment prevented the disar-
ticulation of skeletal plates, while pyritization strength-
ened the skeleton and, in some cases, preserved soft
tissues (Bartels et al. 1998; Sutcliffe et al. 1999; Glass
and Blake2004).
Materials and methods
A slab of dark gray slate with three specimens ofDehmi-
cystis(termed individuals 13; Fig.4) was obtained from a
private collector by one of the authors (H. Lintz) in August
2004. The slab also preserves one stylophoran of uncertain
affinity (most likely Mitrocystites styloideus) and two
stelleroids: the leftmost specimen is the ophiuroid Chei-ropteraster giganteus; the right one probably belongs to the
asteroid genus Jaekelaster. One of the Dehmicystis fossils
(individual 1) overlies another (individual 2). The slab was
carefully prepared by hand with scrapers and an air-abra-
sive machine (using glass pearls as an abrasive) to enable
detailed morphological analysis. X-rays of the slab were
taken, but did not reveal additional features of the fossils.
The slab is currently housed in the private collection of
H. Lintz, Niddatal, Germany; a replica (SMF-HS 969) is
located in the Naturmuseum Senckenberg, Germany. The
holotype of Dehmicystis (SMF-HS 432) was studied for
comparison. Photographs of the specimens were takenusing a Canon EOS 300D with a 50 mm macro lens, and
figures were prepared with Adobe Photoshop CS2 and
Adobe Illustrator CS2.
Terminology
The anterior-posterior orientation of solutes is uncontro-
versial, with the stele marking the posterior pole (Caster
1968; Smith2008). In contrast, the dorsal-ventral orienta-
tion is debated; in the description below, the thecal surface
bearing the ambulacrum (and associated mouth) is referred
to as the oral surface, while the opposite face is the aboral
surface (as suggested by Kolata et al. 1977). Proximal
refers to points relatively closer to the proximal plane (the
junction between the stele and the theca), while distal
denotes points that are further away. Descriptive termi-
nology largely follows Bather (1913) and Caster (1968).
Systematic palaeontology
Phylum Echinodermata Bruguiere, 1791 (ex Klein,
1734)
Class Homoiostelea Gill and Caster,1960
Order Soluta Jaekel,1901
GenusDehmicystis Caster,1968
Dehmicystis globulus (Dehm, 1934) (Figs. 57)
Material The holotype, an incomplete articulated speci-
men preserved on a slab of slate; three additional articu-
lated specimens (one of which is almost complete) on a
single slab of slate. The holotype (SMF-HS 432) and a
replica of the newly prepared slab (SMF-HS 969) are
Dehmicystis globulus, an enigmatic solute 61
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housed in the Naturmuseum Senckenberg, Germany (the
original of SMF-HS 969 is in the private collection of
H. Lintz, Niddatal, Germany).
Occurrence Hunsruck Slate, middle Kaub Formation,
Lower Emsian, Lower Devonian. Eschenbach-Bocksbergquarry, near Bundenbach, Rheinland-Pfalz, Germany.
Amended diagnosis Solute with an irregularly rounded
thecal outline; theca comprises numerous polygonal plates,
some of which are ornamented with rounded bosses
(positioned centrally and at plate sutures); single large
adbrachial plate bearing a warty tumescence (probable
hydropore). Anus large and circular, covered by a pyramid
of elongate, radially imbricate plates and a pair of suranal
plates, situated on the same face as the ambulacrum, not
associated with thecal lobation. Ambulacrum non-terminal
and moderately long; ambulacral flooring plates meet
tightly along a zigzag suture. Proxistele with well-devel-
oped tetramerous rings; mesistele short; dististele long and
comprises pairs of rectangular ossicles, with the distalmost
aboral ossicles horizontally keeled.
Description
Theca The theca is irregularly rounded in outline and
measures approximately 70 mm in length and 67 mm in
width in the holotype (Fig.5). Lobation is absent or poorly
developed at either end of the theca. Thecal faces are
preserved strongly flattened and consist of numerous thin,
polygonal plates (Figs.57). Plating is asymmetrically
Fig. 3 Geographic map and
stratigraphic position of the
Hunsruck Slate sensu lato.
Modified from Sutcliffe (1997:
Fig. 1) and Gradstein et al.
(2004: Fig. 14.1)
62 I. A. Rahman, H. Lintz
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arranged, with firm sutures between plates; typical thecal
plates vary in size from 3 to 10 mm. External ornamenta-
tion occurs on some plates (Fig.6); this takes the form of
rounded bosses, which are usually positioned centrally, but
occasionally occur at plate sutures.
The thecal plates adjacent to the appendages are
specialized; this is most obvious in individual 1 (Fig.6).
The ambulacrum attaches to a single large adbrachial plate
on the oral thecal surface via a short contact zone
composed of small, polygonal plates (Fig.6). The large
adbrachial plate bears a distinctive warty tumescence in a
shallow, concave depression, which is located at the base
of the ambulacrum (Fig.6). This structure most likely
represents a hydropore. The stele attachment is bordered by
two or three large, thick adsteleal plates (Figs.6,7). In the
holotype, the posterior thecal margin is strongly invagi-
nated (by approximately 6.5 mm) where it articulates with
the stele, and plate boundaries are ambiguous (Fig.5).
The anus is located at the posterior of the theca and is
not associated with a well-developed thecal lobe (Figs.5,
6). In two of the new individuals, the anus occurs on the
left of the theca (Fig.6); in the holotype, it occurs on the
right (Fig.5). It is large and circular (ranging from 10 to
15 mm in diameter), with specialized plates covering the
anal aperture. Two large, subtriangular suranal plates,
which overlap at their rounded inner margins, are posi-
tioned centrally (Figs.5, 6); they average approximately
3 mm long and 6 mm wide. Laterally, the suranal plates are
bounded by multiple narrow, elongate (up to 5 mm long),
radially imbricate plates, which form a low pyramid (Figs.5,
6). A ring of small platelets surrounds the anus (Fig.6).
Ambulacrum The ambulacrum attaches to the theca just
left of the midline, around 70% along the total length of the
theca (Fig.6). It measures approximately 36 mm in length
in individual 1 and tapers distally to a rounded tip (Fig.6).
Fig. 4 Newly prepared slab with three specimens ofDehmicystis globulus (Dehm,1934), 90.5
Dehmicystis globulus, an enigmatic solute 63
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The exposed surface is disrupted in places but apparently
comprises an alternating biseries of large, curved plates
(the flooring plates or brachials) (Fig.6); there are at least
44 pairs of plates, which meet tightly at their inner margins,
giving a zigzag suture, but overlap at their proximal mar-
gins (Fig.6). These plates average approximately 0.7 mm
Fig. 5 Dehmicystis globulus
(Dehm,1934). a, b Photograph
and interpretative sketch of the
holotype, 91.5. An Anus, Di
dististele, PP pyramidal plates,
Prproxistele, SP suranal plates
Fig. 6 Dehmicystis globulus
(Dehm,1934). a, b Photograph
and interpretative sketch of
individuals 1 and 2, 91.5. Abp
Adbrachial plate, Am
ambulacrum,An anus, AnP anal
platelets, AsP adsteleal plate,
CZcontact zone between theambulacrum and the theca,
FP flooring plates,
Hy hydropore, Me mesistele,
Prproxistele, SP suranal plates,
TO thecal ornamentation
64 I. A. Rahman, H. Lintz
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long and 2 mm wide (decreasing in size distally). The
opposite surface of the ambulacrum (the presumed cover
plates) is not clearly visible in any specimen. The transition
between the ambulacrum and the theca is abrupt (Fig.6);
the internal detail of the ambulacrum is obscured by the
skeleton.
Stele The stele is at least 76 mm long and is divided intothree parts: (1) the proxistele, (2) the mesistele, and (3) the
dististele. The broad proximal region (the proxistele)
makes up around one-fifth of the total length of the stele; it
averages approximately 6.5 mm wide (tapering distally)
and consists of 1316 smooth, flexible, tetramerous rings
(Figs.57). Each ring is composed of four large, curved
plates, which imbricate laterally and axially (Figs.6, 7).
These plates average approximately 1.1 mm long and
3 mm wide, and they enclose a large lumen internally
(Fig.7). The insertion of the proxistele into the theca is
unclear in the three new individuals, but the morphology of
the holotype suggests that it was deeply excavated (Fig.5).The proxistele grades into the dististele via a short
transition zone: the mesistele (Figs.6, 7). This comprises
two thick, elongate, subtriangular ossicles, which are widest
at their concave proximal margins (where they articulate
with the proxistele) and taper distally. The mesistele plates
are tightly sutured and measure approximately 2.5 mm in
length and 2 mm in width in individual 2 (Fig.6).
The dististele occupies roughly three-quarters of the
length of the entire stele (Figs.5,7). It is stiff and consists
of pairs of short, rectangular ossicles, which articulate in
the horizontal plane and average 0.8 mm in length and
width (Fig.7). In the distal part of the dististele, one or
both sides of the aboral ossicles are horizontally keeled
(Fig.7). In one individual, the stele terminates in a hook-
like structure, with the tip of the dististele bent back on
itself at an angle of approximately 180 to the axis of the
rest of the stele (Fig.7).
Remarks
The presence of a single anterior ambulacrum, a tripartite
posterior stele, and an asymmetrical, polyplated theca
clearly establish the solute affinities of Dehmicystis glob-
ulus. Indeed, almost all of the characters displayed by the
species are also known from other solutes, with only their
combination unique, and hence the familial classification
of Dehmicystis is problematic. Caster (1968) assigned
Dehmicystis to the Dendrocystitidae Bassler, 1938, butthere are no characters that are exclusively shared with this
family. Moreover, the Dendrocystitidae was not recognized
as monophyletic in recent cladistic analyses (Parsley1997;
Parsley and Sumrall2007) and might not be a valid taxo-
nomic group. The flattened, circular theca ofDehmicystis
was used as evidence by Gill and Caster (1960) to ally the
genus with Rutroclypeus in the Rutroclypeidae Gill and
Caster,1960. However, the extremely flattened state of the
theca inDehmicystis is most likely a taphonomic artefact;
Fig. 7 Dehmicystis globulus
(Dehm,1934). a, b Photograph
and interpretive sketch of
individuals 2 and 3, 91.4. AsP
Adsteleal plate, Di dististele,
DiH distal hook-like structure,HK horizontal keel, Me
mesistele, Prproxistele
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flattening is uniform across the entirety of the exposed
surfaces of the fossils, strongly suggesting that it is the
result of compression due to burial by sediment and/or the
collapse of the skeleton following decay of internal soft
tissues, and not a genuine biological feature. The theca was
probably somewhat inflated in life (Dehm 1934; Caster
1968). The central, non-terminal position of the ambula-
crum recalls the situation in some belemnocystitids, butmembers of this family are otherwise rather different from
Dehmicystis, and a close systematic relationship is highly
doubtful. Because Dehmicystis is diagnosed by a unique
character combination that consists of only two putative
autapomorphies (an anus with a pair of suranal plates and
thecal ornamentation at plate sutures), which may not be
suitable characters for familial assignment within solutes,
we prefer to leave the genus unassigned at family level
pending future phylogenetic studies incorporating our new
morphological data.
Discussion
Position of the anus
As noted above, the position of the anus appears to vary
amongDehmicystisspecimens. In two of the individuals in
which the anus is preserved, it occurs on the left of the
exposed thecal surface (Fig.6), while in the holotype, it
occurs on the right (Fig.5). The location of the anus is
highly constrained at genus/species level in solutes and in
Palaeozoic echinoderms generally, and hence it is almost
certain that this difference does not represent intraspecific
variation.
One potential explanation for this apparent change is
that the anus is seen in interior aspect in the holotype or in
both of the new individuals 1 and 2i.e., thecal plates
have been displaced to partly reveal the opposing thecal
surface where the anus is locatedso that it appears to be
on the opposite side of the theca. However, this is extre-
mely unlikely because there is no evidence of missing or
broken thecal plates adjacent to the anus in any of the
specimens, and the specialized anal plates are preserved in
the same plane as the ordinary thecal plates (strongly
suggesting that they occur on the same face). Another
possibility is that this difference is a case ofsitus inversus,
where structures located on one side of the theca are
transposed to the opposite side, presumably as a result of
developmental abnormalities (Caster1968; Ubaghs1968;
Jefferies et al. 1996). Examples of situs inversus have
occasionally been reported in the solute genera Dendro-
cystites and Dendrocystoides, but are always associated
with a shift in the position of the ambulacrum (from the left
side of the theca to the right), with the anus remaining in
the same location (Caster1968). Therefore, this interpre-
tation is also highly doubtful. The most probable expla-
nation is that the supposed difference in the position of the
anus is related to the taphonomic orientation of the fossils;
if a Dehmicystis individual was buried while lying on itsside, and subsequently flattened so that it was preserved in
lateral view, this would cause the position of the anus (and
ambulacrum) to appear to shift sides on the theca (Fig.8).
The uneven, broken anterior thecal margin and the absence
of thecal invagination at the stele attachment in individual
1 (Fig.6) suggest that it is the thecas of individuals 1 and 2
which are being viewed in lateral aspect; the stele appears
to have rotated independently of the theca post-mortem, so
that it is oriented in a different aspect. Thus, the normal
condition inDehmicystis was for the anus and the ambu-
lacrum to be located on the right of the theca, like the
holotype (even though the ambulacrum is not preserved inthis specimen). This also agrees with the situation in an
additional unpublished specimen ofDehmicystis, in which
the ambulacrum is preserved on the right side of the
exposed thecal surface (K. Derstler pers. comm. 2010).
Current-induced orientation
The Dehmicystis fossils on the newly described slab of
slate show similar orientations, with the ambulacrum
Fig. 8 Schematic diagrams of Dehmicystis globulus (Dehm, 1934)
illustrating how changes in orientation during burial could cause the
anus and the ambulacrum to appear to shift to the left of the theca.
aOral view.b Right lateral view. c Right lateral view after flattening
66 I. A. Rahman, H. Lintz
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(where preserved), the theca, and the stele all approxi-
mately aligned (Fig.4). A similar trend has been reported
for the North American solutes Castericystis Ubaghs and
Robison, 1985 and Coleicarpus Daley, 1996; individuals
on the same slab typically face in the same direction
(Ubaghs and Robison1985; Daley1995,1996).
The parallel orientation of solutes on a slab almost
certainly reflects the direction of current flow (Daley1996),but in the case of Dehmicystis may not have been the
precise life position. Even though solutes were apparently
gregarious (Kolata et al.1977; Ubaghs and Robison1985;
Daley1995), it seems highly unlikely that they would have
lived overlying one another to the extent seen in individ-
uals 1 and 2 (Figs.4, 6). The extreme overlap of these
individuals is most probably the result of movement by the
current at the time of burial, presumably rapid downslope
transportation by turbidity currents. Furthermore, the am-
bulacra of individuals 1 and 2 are preserved overlying their
thecas such that the presumed cover plates would have
opened towards the animals; it is more likely that theambulacrum was positioned to the anterior of the animal or
at an acute angle to it in life, allowing the cover plates to
open away from the theca, and thereby enabling feeding
with the extensions of the water vascular system (i.e., tube
feet) thought to be located inside the ambulacrum (Jefferies
1990; Daley1995, 1996; David et al.2000; Smith2005).
The associated stelleroid and stylophoran fossils are ori-
ented in roughly the same direction as the solutes (Fig.4),
and their position may also have been influenced by cur-
rents during burial.
Life orientation and feeding strategy
The life orientation of solutes is contested and has impor-
tant implications for their mode of life. Some workers
prefer a position with the ambulacrum and associated
mouth on the upper thecal surface (e.g., Bather1913; Gill
and Caster 1960; Caster 1968; Parsley 1972), suggesting
that solutes were predominantly suspension feeders that
used their ambulacrum to capture food particles from water
currents. In contrast, others favor the opposite way-up, with
the ambulacrum situated on the lower surface (e.g., Kolata
1973; Sprinkle 1976; Kolata et al. 1977; Jefferies 1990;
Daley 1992, 1995). This would imply that solutes were
either very low-level suspension feeders (Sprinkle 1976)
or, more likely, deposit feeders using the ambulacrum to
actively browse on organic matter on the sea floor (Kolata
et al. 1977; Jefferies 1990; Daley 1995). Thus, resolving
the life orientation of solutes is key for inferring their
preferred feeding method.
Hunsruck Slate fossils are often preserved overturned
(Bartels et al.1998), and hence the taphonomic orientation
of Dehmicystis specimens is not necessarily indicative of
their life position. However, the functional morphology of
the genus, elucidated for the first time herein, is strongly
suggestive of life-style orientation. In Dehmicystis, the
anus occurs on the same thecal face as the ambulacrum and
the mouth; the oral surface (Fig.6). If this was the lower
surface in life, the anus would have opened directly onto
the substrate, forcing the animal to rest in its own waste.
Thus, it is much more likely that Dehmicystis lived oralsurface up, enabling the anus to release faeces into the
water away from the sea floor. Moreover, a structure on an
adbrachial plate adjacent to the ambulacrum (Fig.6)best
interpreted as a hydropore based on its morphology and
positionwould also have been unable to function prop-
erly if the oral surface had rested on the substrate. Such an
orientation for Dehmicystis appears to rule out deposit
feeding, and favors, instead, a suspension feeding mode of
life.
Contrary to Daley (1995), multiple branched feeding
structures are not essential for suspension feeding (Meyer
1979; LaBarbera1984; Riisgard and Larsen2010); solutes,with their single unbranched ambulacrum housing numer-
ous tube feet, were entirely capable of such a feeding
strategy.Dehmicystiswas most likely a passive suspension
feeder, like crinoids, with its anus and ambulacrum facing
away from the substrate. It presumably lived oriented
downstream of the prevailing current direction to ensure
efficient venting of the anus, with food particles captured
from the current using tube feet in the ambulacrum. Similar
to modern echinoderms, food was conveyed to the mouth at
the base of the ambulacrum via a large internal groove
(Nichols 1972; Jefferies 1990; Daley 1995, 1996; David
et al.2000).
It is unclear if other solutes followed the same mode of
life as Dehmicystis; even if thecal faces are homologous
across the Soluta (Caster 1968), their life orientations
need not be identical. In most genera (i.e., Castericystis,
Coleicarpus, Dendrocystites, Dendrocystoides, Heckeri-
cystis Gill and Caster, 1960, Myeinocytites Strimple,
1953, Rutroclypeus, Scalenocystites Kolata, 1973 and
Syringocrinus Billings, 1859), the ambulacrum is located
at the anterior edge of the theca and the anus (where
known) is marginal; such an arrangement does not appear
to impose a particular life orientation or feeding method.
The same may be true for Maennilia Rozhnov and Jeff-
eries, 1996 and Minervaecystis Ubaghs and Caster in
Caster, 1968, in which the ambulacrum is located on a
lateral margin. However, in some forms (i.e., Belemno-
cystites Miller and Gurley, 1894 and Iowacystis Thomas
and Ladd, 1926), the ambulacrum is nonterminal and
centrally positioned on the oral surface, with adjacent
hydropore/gonopore structures, and in all likelihood these
taxa lived oral surface up, similar toDehmicystis. Hence,
a suspension feeding mode of life seems most probable
Dehmicystis globulus, an enigmatic solute 67
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for these genera. In Girvanicystis Caster, 1968, the anus
occurs on the aboral surface of the animal, necessitating
an aboral face-up orientation. An alternative feeding
strategy (e.g., deposit feeding) may be more likely for
Girvanicystis.
Function of the stele
Like all solutes, the stele of Dehmicystis was flexible
proximally and stiff distally. The highly flexible proximal
part was most probably muscular, similar to stylophorans
(Caster1968; Smith2008) and glyptocystitid rhombiferans
(Kesling 1968; Paul 1984), and facilitated limited move-
mentfor example, to adjust the position of the animal
with the current to improve feeding efficiency. This differs
from the situation in crinoids, where the stem lacks mus-
culature and is not used for locomotion. The long, stiff
dististele, which is horizontally keeled in its distalmost part
(Fig.7), could have served to support the animal on the
soft substrate; moreover, it may also have functioned as ananchor to help maintain a position downstream of the
current (Daley 1995). In one Dehmicystis individual, the
distal end of the stele is strongly bent back on itself to give
a hook-like structure (Fig.7). Furthermore, in the holotype,
the dististele is preserved in close association with the
distal end of a crinoid stem, albeit a partly disarticulated
one (Fig.5). This suggests that the distal stele ofDehmi-
cystis may have sometimes been used to attach the animal
to the substrate and, possibly, to other organisms living on
the sea floor, as is thought to have occurred inCastericystis
and Coleicarpus (Daley1996; Smith2008).
Acknowledgments We thank Ulrich Jansen for the photographs
used in Figs.4,5,6,7 and Olaf Vogel for producing a replica of the
slab (both Naturmuseum Senckenberg, Germany). Bertrand Lefebvre
(Universite de Lyon, France) and Ron Parsley (Tulane University,
USA) are thanked for providing detailed reviews that greatly
improved the quality of this paper. We are also grateful to Ulrich
Jansen, Wouter Sudkamp (Bundenbach, Germany), Andrew Smith
and Samuel Zamora (both The Natural History Museum, London) for
helpful comments. This work was supported by the Natural Envi-
ronment Research Council (grant number NE/H015817/1).
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