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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)


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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


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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



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


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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;



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


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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


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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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