Morphology and ecological setting of the basal echinoid
genus Rhenechinus from the early Devonian of Spain
and Germany
ANDREW B. SMITH, MIKE REICH, and SAMUEL ZAMORA
Smith, A.B., Reich, M., and Zamora, S. 2013. Morphology and ecological setting of the basal echinoid genus Rhenechinus
from the early Devonian of Spain and Germany. Acta Palaeontologica Polonica 58 (4): 751–762.
Based on new material from Germany and Spain, the echinoid “Lepidocentrus” ibericus from the Early Devonian (Emsian)
of northern Spain is shown to be congeneric with Rhenechinus from the Hunsrück Slate of south−western Germany. New in−
formation on the lantern, pedicellariae and internal structure of the theca is provided, and confirms this genus as a member of
the Echinocystitidae–Proterocidaridae clade and the most primitive of all Devonian echinoids. The two environmental set−
tings in which Rhenechinus is found are very different: the Spanish specimens come from a relatively shallow−water bryo−
zoan meadow setting while the German specimens are preserved in a deep−water setting. We deduce that the rare echinoid
specimens from the Hunsrück Slate are all allochthonous, whereas the Spanish material is preserved in situ.
Key words: Echinodermata, Echinoidea, morphology, phylogeny, Devonian, Spain, Germany.
Andrew Smith [a.smith@nhm.ac.uk] and Samuel Zamora [samuel@unizar.es], Department of Palaeontology, The Natu−
ral History Museum, Cromwell Road, London SW7 5BD, UK;
Mike Reich [mreich@gwdg.de], Geowissenschaftliches Zentrum der Universität Göttingen, Museum, Sammlungen &
Geopark, Goldschmidtstr. 1−5, D−37077 Göttingen, Germany.
Received 11 July 2011, accepted 27 February 2012, available online 8 March 2012.
Copyright © 2013 A.B. Smith et al. This is an open−access article distributed under the terms of the Creative Commons
Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original
author and source are credited.
Introduction
Although the fossil record of echinoids extends back to the Or−
dovician, Palaeozoic echinoids remain scarce and very poorly
known. This is because their skeleton is much less robust com−
pared to that of their post−Palaeozoic descendants, and they
are rarely well preserved. Whereas the great majority of
post−Palaeozoic echinoids have coronal plates that abut and
are firmly sutured together, all Palaeozoic echinoids have a
test constructed of imbricate plates that falls apart rapidly upon
death. Consequently, our knowledge of the early evolutionary
history of echinoids is patchy at best, and comes from a small
number of localities and horizons where sedimentary condi−
tions have favoured rapid burial.
The Devonian marks an important period in the diversifi−
cation of echinoids and saw the start of several lineages that
came to dominate in the upper Palaeozoic (Kier 1965: text−fig.
8; 1968). It is unfortunate, therefore, that so little is known
about the echinoids and their ecology at this period. This stems
from the paucity of well−preserved echinoids that have been
described. Just 17 species in ten genera have been recorded
from the Devonian, mostly from Germany or North America,
and half of these are based on isolated spines, disarticulated
plates or test fragments that are so incompletely known as to
be effectively indeterminate (Smith 2011). Yet, judging from
their morphological disparity, echinoids appear to have been
rather diverse at this time. Of the six genera for which ade−
quate material exists, three (Albertechinus Stearn, 1956, Nor−
tonechinus Thomas, 1924, and Deneechinus Jackson, 1929)
are members of the Archaeocidaridae, one (Lepidechinoides
Cooper, 1931) is a lepidesthid, another (Porechinus Dehm,
1961) a palaechinid, and a third (Rhenechinus Dehm, 1953) an
echinocystitid. The only Palaeozoic echinoids to have been
previously reported from Spain are some disarticulated plates
and spines that were referred to “Archaeocidaris sp.” (Barrois
1882; Sieverts−Doreck 1951), and the poorly known Lepido−
centrotus ibericus (Hauser and Landeta 2007). Newly col−
lected material of L. ibericus allows us to establish the true
identity of this species and reveals its close relationship to
Rhenechinus hopstaetteri Dehm, 1953, from the German
Lower Devonian Hunsrück Slate. R. hopstaetteri was estab−
lished on the basis of a single partial test. A second, well−pre−
served individual of this species has recently come to light and
we therefore take this opportunity to provide a detailed
redescription of the German species and review our under−
standing of this genus and its phylogenetic position.
http://dx.doi.org/10.4202/app.2011.0098Acta Palaeontol. Pol. 58 (4): 751–762, 2013
Institutional abbreviations.—BSPG, Bayerische Staatssamm−
lung für Paläontologie und Geologie, München, Germany;
DBM, Deutsches Bergbau−Museum, Bochum, Germany;
GZG, Geowissenschaftliches Zentrum, Universität Göttingen,
Germany; NHM, Natural History Museum, London, UK;
NM.PWL, Naturhistorisches Museum Mainz, Landessamm−
lung für Naturkunde, Mainz, Germany; SMF, Senckenberg
Forschungsinstitut und Naturmuseum, Frankfurt/M, Germany;
UO, Museum of Geology, Universidad de Oviedo, Spain.
Material and geological setting
Spanish material.—All the specimens come from the vicin−
ity of Arnao village, Asturias, on the northern side of the
Cantabrian Zone (North Spain) within the Somiedo−Corre−
cilla Unit (Fig. 1).
In this area a Lower Devonian (upper Emsian) succession
crops out in a series of old quarries between La Vela Cape and
752 ACTA PALAEONTOLOGICA POLONICA 58 (4), 2013
Undifferentiated Palaeozoic of the Cantabrian Zone
Somiedo-Correcillas
Esla-Valsurvio
La Sobia-Bodón
Aramo
Central
Asturian
Coalfield
Nappe (Ponga Nappe)
Province
Arnao
Oviedo
Fold and Nappe Province Units
Bay of Biscay
Picos de Europa
Province
Pisuerga-
Carrión
Province
Mesozoic–Tertiary
Cover
Unconformable
Stephanian
Narcea Antiform
(Precambrian)
50 km
Bay of Biscay
FRANCE
P
O
R
T
U
G
A
L
SPAIN
Iberian Massif
200 km
P
la
ya
B
a
in
a
s
E
l E
sp
in
El Escoyo
La Llada
E
n
se
n
a
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ta
M
a
ri
a
d
e
l m
a
r I
.
L
a
d
ro
n
a
Mar
Santa Maria
L
a
V
e
la
P
la
ya
d
e
A
rn
a
o
E
l M
u
g
a
ro
n
Punta Pical
La Pe onañ
Arnao
Las Chavolas
Playa de
Salinas
Mesozoic?
Stephanian
Naranco Formation
Moniello Formation
Aguion Formation
La Ladrona Formation
Ba guesñ Formation
Nieva Formation
Furada Formation
La Casta alonañ
200 m
D
e
v
o
n
ia
n
Naveces
El Puerto
30
50
40
40
70
5 10
20
30
10
40
30
20
10
30
30
20
90
10
85
50
70
30
65
40
40
70
35
50
40 50
80
70
80
60
60
80
50
75
30
40
Fig. 1. Map showing the geographical position and geological setting of the Aguión Formation and the echinoid bearing horizon (arrowed symbol), modi−
fied from García−Alcalde (1992).
Arnao beach. Here the lower 60 m of the Aguión Formation
are exposed and have been informally divided into three litho−
stratigraphic units (sensu Álvarez Nava and Arbizu 1986); a
lower calcareous unit, a middle marly−shaly unit and an upper
unit of green and red marls (Fig. 2). The upper unit is 24 m
thick and contains a rich fauna of pelmatozoans, fenestellid
bryozoans, and brachiopods. Crinoids are diverse and some−
times very common, especially Trybliocrinus flatheanus and
to a lesser extent Pterinocrinus decembrachiatus, Orthocrinus
sp., and Stamnocrinus intrastigmatus (Schmidt 1931; Breimer
1962). Blastoids include Pentremitidea lusitanica and Pleuro−
schisma verneuili (Johnny Waters personal communication,
May 2011). The commonest brachiopod is Anathyris and
there are abundant large fenestellid bryozoan colonies (Iso−
trypa sp.). Articulated specimens of Rhenechinus come from a
horizon towards the top of the upper unit (Fig. 2: arrow), al−
though isolated plates are found throughout.
Argillaceous content varies within the upper unit of the
Aguión Formation, indicating variability in the supply of
terrigenous material. Arbizu et al. (1995) suggested this was
a major factor in controlling the different fossil assemblages
encountered within the unit. Levels where the crinoid Trybo−
locrinus are common probably represent turbid palaeoenvi−
ronments where there was abundant mud in suspension,
whereas the level with echinoids has abundant fenestellids
and other crinoids (i.e., Pterinocrinus decembrachiatus) and
appears to have been deposited in a well−oxygenated and rel−
atively tranquil environment. Arbizu et al. (1995) interpreted
the entire unit as having been deposited in a typical platform
environment, with highly variable rates of terrigenous sup−
ply. The presence of marl−rich levels with well−preserved
echinoderm specimens alternating with tempestite encrinite
levels suggests an offshore setting, sporadically affected by
storm events.
The bed in which the echinoids are preserved is exposed on
the foreshore at 4334’44.6”N 559’02.2”W and is a firm−
ground with attached crinoid holdfasts in places. Echinoids are
preserved at the base of a red clay drape that covered this sur−
face and appear to have been relatively common at this level.
We deduce that echinoids were living in amongst the bryo−
zoan meadows in a firm−ground, level bottom community.
German material.—Both specimens of Rhenechinus hop−
staetteri come from the Lower Devonian (Early Emsian)
Hunsrück Slate in the Rhineland−Palatinate of south−western
Germany. The Hunsrück Slate is a Lagerstätte famous for its
soft tissue preservation (Bartels et al. 1998; Sutcliffe et al.
1999). These mudrocks were deposited in a shelf−basinal envi−
ronment separated by shallower swells on which a diverse
benthic marine fauna thrived. Arthropods dominate, but there
are also corals, sponges, brachiopods, gastropods, cephalo−
pods, and echinoderms (Mittmeyer 1980; Bartels and Brassel
1990; Bartels et al. 1997, 1998; Kühl et al. 2011). Asteroids,
ophiuroids and, to a lesser extent, crinoids dominate the
echinoderm assemblages, but there are also rare holothurians
and two monospecific echinoid genera (Porechinus Dehm,
1961 and Rhenechinus Dehm, 1953) as well as fragments of
the echinoid Lepidocentrus Müller, 1856 (Table 1).
Photographs and X−radiographs were taken at the Natural
History Museum, London.
Systematic palaeontology
Phyllum Echinodermata De Brugière, 1791
(ex Klein, 1734)
Stem group Echinoidea
Family Echinocystitidae Gregory, 1897
Genus Rhenechinus Dehm, 1953
Type species: Rhenechinus hopstaetteri Dehm, 1953, by original desig−
nation; Lower Devonian (Early Emsian), Hunsrück Slate from the
Rhineland−Palatinate of south−western Germany.
Diagnosis.—Ambulacral zones narrow and straight; plating
quadriserial throughout with every other plate a demiplate
occluded from the adradial suture. Pore−pairs uniform and
with a surrounding peripodial rim, alternately displaced to
left and right forming a biseries down the centre of each
half−ambulacrum. Interambulacral zones broad and com−
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SMITH ET AL.—EARLY DEVONIAN ECHINOIDS FROM SPAIN AND GERMANY 753
Fig. 2. Stratigraphical succession of the Aguión Formation at Arnao Plat−
form showing lithological units, their faunal composition and types of com−
munities. The level bearing echinoids is indicated by an arrow. From
Arbizu et al. (1995).
posed of a large number of small, polygonal plates forming
semi−regular en chevron rows; plates imbricate. Basicoronal
plate present adorally. Coronal plates with small secondary
tubercles or granules only, bearing short simple spines. Teeth
oligolamellar.
Remarks.—Rhenechinus closely resembles the late Silurian
Echinocystites, but in that taxon the interambulacral plates are
more scale−like and more irregular in arrangement, not form−
ing semi−organized rows, and the outer column of primary
ambulacral plates always extend to the perradius. Rhene−
chinus is distinguished from all other Devonian echinoids by
its quadriserial pore−pair arrangement and demiplates in the
ambulacra. In Albertechinus, Deneechinus, Nortonechinus,
Lepidechinoides, and Porechinus the ambulacral pore−pairs
are uniserial and there are no demiplates. Proterocidarids, such
as Proterocidaris and Pholidocidaris, differ from Rhenechi−
nus in having enlarged oral pore−pairs and more than four col−
umns of plates in their ambulacral zones.
Stratigraphic and geographic range.—Emsian, Lower De−
vonian; Spain and Germany.
Rhenechinus ibericus (Hauser and Landeta, 2007)
Figs. 3, 4, 5A–E.
2007 Lepidocentrus ibericus; Hauser and Landeta 2007: 66, text−figs.
2, 3.
Holotype: Specimen referred to by Hauser and Landeta (2007), housed
in a private collection and unnumbered in the original description.
Type horizon: Aguión Formation, Emsian, Lower Devonian.
Type locality: Cap la Vela, Arnao, Asturias, NW Spain.
Material.—Five specimens, UO DGO−23000–23003, NHMEE
13984, all from the type loclity and horizon.
Diagnosis.—A species of Rhenechinus with just four col−
umns of interambulacral plates in each zone. Surface of
interambulacral plates with pitted ornament.
Description.—All specimens have collapsed post−mortem
but are estimated to have been up to 45 mm in diameter.
They were almost certainly globular in shape. The apical
disc is not seen but in UO DGO−23002 there is a single geni−
tal plate in isolation (Fig. 5B). This has a single gonopore
and no hydropore openings and is pentagonal in outline.
Ambulacral zones are relatively narrow and composed of
four columns of plates throughout. In each half column a
large primary element extends from adradial to perradial
suture and alternates with a smaller demiplate, which is ex−
cluded from the adradial suture (Figs. 3B, 4B, 5A). In exter−
nal view the ambulacra are flush and each element has a sin−
gle rather large pore−pair with a subcircular tube−foot at−
tachment rim slightly less than 1 mm in diameter. The
pore−pairs are offset on the demiplates so that there are two
biserial columns of pore−pairs in each ambulacral zone.
There is usually one large mamelon (ca. 0.4 mm diameter)
without a boss on the lower adradial side of the pore−pair on
primary plates, accompanied by two or three small granules
(ca. 0.2 mm diameter). The occluded plates have just one or
two granules at most. On the internal surface each primary
plate thickens perradially, giving rise to a haft that arches
inwards towards the perradius forming a ridge (Fig. 4A3).
This internal ridge is more strongly developed on adoral
plates than on adapical plates. The perradial edge of these
plates is notched by a longitudinal groove for the radial wa−
ter vessel, which therefore lay enclosed within the ambulac−
ral plates. There is also a lateral canal that leads to the
pore−pair on the primary ambulacral plate, and which is also
therefore enclosed. Ambulacral elements close to the peri−
stome become narrower with long adradial projections, and
their pore−pairs become smaller (Fig. 3A). All plate edges
are bevelled, with the adradial edge of ambulacral plates
passing under the adjacent interambulacral plates.
754 ACTA PALAEONTOLOGICA POLONICA 58 (4), 2013
Table 1. Echinoid specimens from the Lower Devonian Hunsrück Slate.
Museum acronym
and number Original collection Species Locality Authors
BSPG 1955 I 585 leg. n. n. 1949; donated by Helmut
Hopstätter (Simmern), 1952
Rhenechinus hopstaetteri
Dehm, 1953
Quarry Kaisergrube,
Gemünden
Hopstätter 1952; Dehm
1953
BSPG 1960 I 164 donated by Maria Bodtländer−Gross
(Bundenbach), 1960
Porechinus porosus
Dehm, 1961 Bundenbach Dehm 1961
GZG.INV.19996 purchased in 1963 Lepidocentrus sp. Quarry Mühlenberg nearBundenbach –
SMF.HS.426 J. Schmitt, 1966 gen. et sp. indet. Quarry Eschenbach,Bundenbach –
private collection E. Halisch (Rotenburg W.) Lepidocentrus sp. Bundenbach Beyer 1979
private collection A. Seilacher (Tübingen) Lepidocentrus sp. ?Bundenbach –
DBM.HS.285 – Rhenechinus hopstaetteriDehm, 1953
Quarry Eschenbach−
Bocksberg, Bundenbach
Bartels and Brassel 1990;
Bartels et al. 1997, 1998
DBM.HS.337 – Lepidocentrus sp. Quarry Kreuzberg nearWeisel
Bartels and Brassel 1990;
Bartels et al. 1998
NM.PWL.1992/234−LS – Lepidocentrus sp. Quarry Eschenbach−Bocksberg, Bundenbach –
NHM.E76446 purchased from F. Krantz in 1905 ?Rhenechinus
hopstaetteri
Bundenbach –
http://dx.doi.org/10.4202/app.2011.0098
SMITH ET AL.—EARLY DEVONIAN ECHINOIDS FROM SPAIN AND GERMANY 755
A
B
3a 3c
3b
2b
2a
1
H
t
5 mm
5 mm
Fig. 3. Echinocystitid echinoid Rhenechinus ibericus (Hauser and Landeta, 2007). Aguión Formation, Emsian, Lower Devonian, Arnao, Asturias, NW
Spain. A. UO DGO−23001 showing adoral plating and elements of the lantern. B. UO DGO−23000 showing partially articulated plating of the upper sur−
face. Abbreviations: H, hemipyramid; t, tooth; 1, 2a, b, 3a–c, first three rows of interambulacral plates.
756 ACTA PALAEONTOLOGICA POLONICA 58 (4), 2013
B
5 mm
c
Ri
Re
H
5 mm
2 mm
2 mm
f
e
A1
3A2A
Interambulacral plates in the best−preserved specimen
form four columns towards the ambitus (Fig. 3B). The outer
columns are composed of irregularly pentagonal plates while
the middle two columns are composed of strictly hexagonal
plates (Fig. 5A). Plates are 5–6 mm in diameter and rather
thick (0.8 mm) compared to those of R. hopstaetteri. Plate
edges are bevelled with adradial faces overlapping ambulac−
ral plates and interradial faces underlapping adjacent plates.
Towards the apex the outer columns of plates are pinched out
leaving just two interambulacral columns. At the peristome
there is a single basicoronal plate followed by two equal−
sized plates, which in turn abut a large central hexagonal
plate plus two adradial plates (Fig. 3A). Externally inter−
ambulacral plates are ornamented by a dense circular pitting,
with pits approximately 0.2 mm in diameter (Fig. 4A1). In be−
tween the pits there are scattered small granules again ap−
proximately 0.2 mm in diameter.
Primary spines are preserved only in the ambulacral re−
gions. They are up to 2 mm in length, circular in cross−sec−
tion, and without a hollow core. There is a very short base of
fine stereom mesh and the exterior of the shaft has fine longi−
tudinal ridges of stereom. Smaller secondary spines up to 1
mm in length are also present and are the only spines found
on interambulacral plates.
There are two forms of pedicellaria present; large spinate
tridentate forms and short, bulbous tridentate forms (Fig. 5D,
E). The large spinate tridentate forms are 1.2–1.6 mm in
length and have a broad, expanded base (0.3 mm in width)
and long spine−like blades that meet for almost their entire
length and are subcircular in cross−section. Close to the base
is there a narrow gap between the blades, occupying no more
than one−third of the blade length. The interior structure and
appearance of the valves is unknown. These spinate tri−
dentates are found along the ambulacral zones. The second
type of pedicellaria is similar only smaller, between 0.3 and
0.6 mm in length, and with shorter, stubbier blades. They
have a rounded base without handles which grades into short
blades that contact along most of their length. Again there is
a narrow opening, much shorter than the length of the blades,
close to the base. Their interior structure is also unknown.
These small pedicellariae are found in association with both
ambulacral and interambulacral zones.
The lantern is preserved in two specimens, NHM EE13984
and UO DGO−23001. Large hemipyramids are present but are
always partially buried under other plates of the test so that
their overall shape is impossible to reconstruct. They taper
adorally and each has a deep, well−defined outer groove for re−
tractor and protractor muscle attachment (Fig. 3A). Rotulae
are of the hinge−construction type (Fig. 4A2). Both internal
(Ri) and external (Re) surfaces are clearly displayed and show
the articulation facets and symmetrical ligament insertion fur−
rows for attachment to the epiphyses. Adaxially the rotula is
notched and ends as two rounded projections while proxi−
mally there is a flattened condyle with a distinctive V−shaped
groove on its lower surface. Epiphyses were presumably pres−
ent but are nowhere clearly seen. A flat plate seen in Fig. 4A2:
e may be an epiphysis. This has only a weak lateral section un−
like the axe−shaped epiphyses of crown−group echinoids illus−
trated by Kroh and Smith (2010: fig. 19A–C). On one surface
there is a long median groove, presumably to house the rotula.
A single ossicle with a narrow subcircular shaft that ends in a
bent head with a double condyle (Fig. 4A2: c) is interpreted to
be a compass. Teeth are up to 3 mm wide with a flat axial face
and convex abaxial face. They are simple oligolamellar in
structure (see Reich and Smith 2009), constructed of a biseries
of stout lath−like elements (Fig. 5B). At any one point there are
some five laths abreast on each side of the tooth.
http://dx.doi.org/10.4202/app.2011.0098
SMITH ET AL.—EARLY DEVONIAN ECHINOIDS FROM SPAIN AND GERMANY 757
Fig. 4. Echinocystitid echinoid Rhenechinus ibericus (Hauser and Landeta, 2007). Aguión Formation, Emsian, Lower Devonian, Arnao, Asturias, NW
Spain. A. NHM EE13984; entire specimen (A1), detail of lantern elements (A2), detail of internal haft on ambulacral plates (A3). B. UO DGO−23000, show−
ing detail of ambulacral plating. Abbreviations: c, compass; e, epiphysis; H, hemipyramid; h, haft on internal face of ambulacral plate; Ri, rotula−internal
face; Re, rotula−external face.

2 mm
1 mm
(D–F)
(A–C)
Fig. 5. Camera lucida drawings of test plating, tooth, and pedicellariae.
A–E. Rhenechinus ibericus (Hauser and Landeta, 2007), Aguión Forma−
tion, Emsian, Lower Devonian, Arnao, Asturias, NW Spain. A. UO DGO−
23000, adapical ambulacral and interambulacral (shaded) plating. B. UO
DGO−23002, genital plate. C. UO DGO−23001, tip of oligolamellar tooth
seen in axial view. D. UO DGO−23001, spinate tridactylous pedicellaria.
E. UO DGO−23000, two small tridactylous pedicellariae (E1 and E2).
F. Rhenechinus hopstaetteri Dehm, 1953, DBM.HS.285, spinate tridacty−
lous pedicellaria with basal element.
Remarks.—This species differs from Rhenechinus hopstaet−
teri in having fewer more regularly polygonal interambulacral
plates with rather thicker and more upright sutures. Further−
more, the surface of interambulacral plates shows a distinctive
pattern of fine circular pits towards their centre, which is never
seen in R. hopstaetteri.
Stratigraphic and geographic range.—Emsian, Lower De−
vonian; Cap la Vela (Arnao), northern Spain.
Rhenechinus hopstaetteri Dehm, 1953
Figs. 6, 7.
1952 “Ein Seeigel aus dem Hunsrückschiefer”; Hopstätter 1952: 33.
1953 Rhenechinus hopstätteri; Dehm 1953: 93, pl. 5: 1–4.
1961 Rhenechinus hopstätteri Dehm, 1953; Kuhn 1961: 33, figs. 15, 16.
1966 Rhenechinus hopstatteri Dehm, 1953; Kier 1966: U303, fig. 224.2.
1970 Rhenechinus hopstätteri Dehm, 1953; Kutscher 1970a: 40.
1970 Rhenechinus hopstätteri Dehm, 1953; Kutscher 1970b: 96.
1980 Rhenechinus hopstaetteri Dehm, 1953; Mittmeyer 1980: 38.
1990 Rhenechinus hopstätteri Dehm, 1953; Bartels and Brassel 1990:
181, fig. 169.
1997 “Seeigel Rhenechinus hopstätteri mit erhaltenen Stacheln“; Bar−
tels et al. 1997: 49, fig. 61.
1998 Rhenechinus hopstaetteri Dehm, 1953; Bartels et al. 1998: 210,
fig. 188.
1999 Rhenechinus hopstätteri Dehm, 1953; Jahnke and Bartels 1999: 43.
2000 Rhenechinus hopstätteri Dehm, 1953; Jahnke and Bartels 2000: 43.
Holotype: BSPG. 1955 I 585.
Type horizon: Hunsrück Slate, Lower Emsian, Lower Devonian.
Type locality: Bundenbach, Rhineland−Palatinate, Germany.
Material.—One specimen, DBM.HS.285, Eschenbach−Bocks−
berg mine, Bundenbach, Rhineland−Palatinate, Germany.
Diagnosis.—A species of Rhenechinus with up to 8 inter−
ambulacral columns in a zone with plates of rather irregular
shape and size; surface of plates lacking pitted ornamentation.
Description.—The holotype (Fig. 6) shows an articulated
test in oral view and the new specimen (Fig. 7) is a complete
test squashed in lateral profile. The test must have been
subglobular in life and taller than wide, with a diameter up to
approximately 10 cm. Apical disc unknown but relatively
small, as the ambulacra converge adapically (Fig. 7A).
Ambulacral zones are narrow and biserial with a primary
element alternating with a small demiplate in each half ambu−
lacrum (Fig. 6B). Pore−pairs are prominent and offset forming
a double series in each column. The pore−pairs are about 1 mm
in width with an obvious periporal rim; the inner pore pierces
the plate rather than forming a marginal notch. There are small
granules scattered on the adradial and perradial sides of the
zone of pore−pairs. Towards the peristome plates become nar−
rower and wider, and pore−pairs become smaller. Ambulacral
plating appears to extend further onto the peristome than
interambulacral plates (Fig. 6C).
Interambulacral plates are up to 6 mm in width and irregu−
larly polygonal in outline. At the widest point there are some
nine plates abreast. Only the adradial series of plates form a
regular column and these may bear slightly larger tubercles
than other plates. Plates are relatively thin—not much more
than 0.6 mm in thickness, and have bevelled edges. A single
plate forms the adoral boundary to the peristome and this is
followed by two plates that just touch interradially and then by
three plates, a large central hexagonal plate and two adradial
pentagonal plates (Fig. 6C).
A membrane of small platelets covers the peristome (Fig.
6C), which is about 20 mm in diameter. While ambulacral
plates extend a little way onto this membranous region, they
are confined to the outer region.
Spines are up to 4 mm in length and are concentrated in the
peristomial and ambulacral zones (Figs. 6A, 7B). There are
several slender spines to each ambulacral plate, with some−
what longer spines being found adradially and shorter spines
perradially. Small spines are also found on interambulacral
plates but are not nearly as dense nor as long. Small spinate
tridactylous pedicellariae are present on interambulacral
plates (Figs. 5E, 7B). These are approximately 1 mm long and
have a swollen base and long spine−like blades that are in con−
tact along most of their length. The pedicellarial head rests on
a small element some 0.2 mm in width that is either a stem ele−
ment (as described by Haude 1998) or a small tubercle (preser−
vation is not adequate to distinguish).
The lantern is present but internal. Hemipyramid tips can be
seen (Fig. 7C) and show a deep abaxial groove for retractor and
protractor muscle insertion. The teeth that protrude have a flat
axial face and are simple oligolamellar in strucure with four or
five laths abreast on each half. They end at a simple point.
Remarks.—The original description given by Dehm (1953)
is detailed and largely correct. The new specimen provides
additional information about the test shape and about the dis−
tribution of spines and pedicellariae. This is a species that at−
tains almost twice the size of the Spanish species but we do
not think the diagnostic differences are simply size related.
Although R. ibericus may increase the number of inter−
ambulacral columns in each zone as it grows, the surface or−
nament in the two species is quite distinct with the Spanish
species having a strongly pitted surface and the German spe−
cies a smooth, unpitted surface.
One other echinoid, Porechinus porosus is known from the
same formation (Dehm 1961) and this does have a strongly
pitted ornament to its plate surfaces. However, it differs in
having distinctly thicker plating and ambulacral plates that are
uniserially arranged. All the other echinoid specimens of the
Lower Emsian Hunsrück Slate (Lepidocentrus spp.; Table 1)
are based on fragmentary material and need to be revised. This
is made especially difficult by the incomplete nature of the
type material of Lepidocentrus (Müller 1857).
Stratigraphic and geographic range.—Hunsrück Slate, Lower
Emsian, Lower Devonian; Gemünden and Bundenbach, Rhine−
land−Palatinate, Germany.
Discussion and conclusions
Rhenechinus was originally treated as a lepidocentrid by
Dehm (1953) and Hauser and Landeta (2007) also assigned
758 ACTA PALAEONTOLOGICA POLONICA 58 (4), 2013
their Spanish specimen to Lepidocentrus. Kier (1965: 450,
1966) transferred Rhenechinus to the Echinocystidae on the
basis of its plesiomorphic similarity to Echinocystites. How−
ever, much of its anatomy was at that time incompletely
http://dx.doi.org/10.4202/app.2011.0098
SMITH ET AL.—EARLY DEVONIAN ECHINOIDS FROM SPAIN AND GERMANY 759
A
B
C
5 mm
3a
3c
2a
1
2b
ps
t
5 mm2 mm
3b
Fig. 6. Echinocystitid echinoid Rhenechinus hopstaetteri Dehm, 1953, BSPG.1955 I 585 (holotype), Hunsrück Slate, Lower Emsian, Lower Devonian;
Gemünden, Rhineland−Palatinate, Germany. A. General view. B. Detail of ambulacral plating. C. Detail of oral region. Abbreviations: ps, peristomial
membrane; t, tooth; 1, 2a, b, 3a–c, first three rows of interambulacral plates.
known. The new specimens from Spain (Figs. 3–5) and Ger−
many (Fig. 7) provide important new information on the
morphology of Rhenechinus and help confirm its phylogen−
etic position as lying between Echinocystites and the Pro−
terocidaridae. Based on our new material we now confirm
that Rhenechinus retains many primitive features compared
to other Devonian echinoids. Firstly, as first noted by Jesio−
nek−Szymańska (1982), its teeth have a very primitive con−
struction−termed simple oligolamellar (Reich and Smith
2009), like those of Echinocystites but in marked distinction
to the teeth of archaeocidarids, lepidesthids, lepidocentrids,
and palaechinids, all of which have true lamellar teeth. Sec−
ondly, the radial water vessel in Rhenechinus is enclosed
within the ambulacral plates, at least adorally. Each primary
ambulacral plate has a large internal haft that projects per−
radially to underlie the radial water vessel (Fig. 4A3), again a
760 ACTA PALAEONTOLOGICA POLONICA 58 (4), 2013
A
B
C
amb
amb
5 mm
amb
ap
pst
amb
p
ps
p
2 mm 2 mm
Fig. 7. Echinocystitid echinoid Rhenechinus hopstaetteri Dehm, 1953, DBM.HS 285, Hunsrück Slate, Lower Emsian, Lower Devonian; Eschenbach−
Bocksberg mine, Bundenbach, Rhineland−Palatinate, Germany. A. General view. B. Detail of adoral plating showing pedicellariae and spines. C. Detail of
adoral ambulacral plating. Abbreviations: amb, ambulacral zone; ap, apical disc region; p, pedicellaria; ps, pedicellarial stalk element; pst, peristome.
feature seen in all Ordovician and Silurian echinoids, includ−
ing Echinocystites, but in none of the other Devonian forms
except Albertechinus. Thirdly, the lack of enlarged primary
tubercles and spines distinguishes Rhenechinus from other
Devonian echinoids with the exception of Porechinus.
Larger tubercles and spines are wanting from all Silurian and
Ordovician echinoids and it is only in the Devonian that
echinoids with larger articulated spines are first encountered.
Finally, the ambulacral plating in Rhenechinus is identical to
that seen in Echinocystites, and consists of a primary plate al−
ternating with a demiplate. This pattern of plating is not
found in any other Devonian echinoid. All these features
confirm the primitive status of Rhenechinus and its close
similarity to Echinocystites. However, compared to Echino−
cystites, Rhenechinus has more regularly organized inter−
ambulacral plating and distinct peripodial rims around its
pore−pairs, as in proterocidarids. Rhenechinus is therefore
phylogenetically intermediate between Echinocystites and
the Proterocidaridae.
Rhenechinus provides further information on the types of
pedicellariae present in Palaeozoic echinoids. It possessed
only tridactylous pedicellariae, although these were of two
forms, large and small. The large spinate pedicellariae are
similar in appearance to those that have been found in other
Devonian echinoids (Lepidocentrus; Haude 1998). They are
three−bladed and rest either on a small basal element or di−
rectly onto a tubercle. Ophicephalous and globiferous pedi−
cellariae, which have been reported from some Carbonifer−
ous taxa (Geis 1936; Coppard et al. 2012), are wanting. This
supports the view that ophicephalous and globiferous pedi−
cellariae evolved only in archaeocidarids. Larger pedicel−
lariae are more common along the ambulacra suggesting that
their primary role may have been to protect the tube−feet
from pests and parasites. Smaller pedicellariae are found
scattered over interambulacral plates and may have been
rather common, although they are now preserved only in
small patches.
Our new material also provides information on the struc−
ture of Palaeozoic echinoid lanterns. Specifically we recog−
nize for the first time that compass elements were present
(Fig. 4A2). These slender elements act to regulate the volume
of the peripharyngeal coelom as the lantern moves in and out
of the test during feeding. Although lanterns have been de−
scribed for a small number of Ordovician and Silurian echi−
noids (Aulechinus, Palaeodiscus, Echinocystites, and Apti−
lechinus) none have preserved compasses. Compasses are
slender and rather fragile elements by comparison to the
other elements that make up the lantern of sea urchins, so
their absence may be taphonomic rather than genuine. Their
definitive presence in Rhenechinus suggests that they must
also have been present in many of the other Palaeozoic
echinoids by phylogenetic implication.
It is unusual to find the same echinoid genus in two such
very different environmental settings and this requires com−
ment. The main difference between the Spanish and German
deposits is that the former were formed under normal shal−
low marine conditions on a terrigeonous−carbonate ramp
(Arbizu et al. 1995; see above), while the Hunsrück Slate
lacks carbonates and was deposited under deeper−water,
shelf−basin conditions (Bartels et al. 1998). The fact that the
echinoids are common, and preserved so well at Arnao, indi−
cates they are autochthonous. By contrast, after hundreds of
years of work on the fauna of the Hunsrück Slate there are
only two definite specimens of Rhenechinus known. Be−
cause echinoids preserved in the Hunsrück Slate are so rare
(around ten specimens only are known; Table 1) they are pre−
sumably allochthonous, washed into the basins from shal−
lower habitats in nearby local swells.
Acknowledgements
MR is grateful to Christoph Bartels (Deutsches Bergbaumuseum
Bochum, Germany), Herbert Lutz (Naturhistorisches Museum Mainz,
Germany), Martin Nose (Bayerische Staatssammlung für Paläonto−
logie und Geologie München, Germany), and Eberhard Schindler
(Senckenberg Forschungsinstitut und Naturmuseum Frankfurt/M.,
Germany), who kindly allowed us to study Hunsrück specimens in their
care. MR also thanks Reimund Haude (Göttingen, Germany) and Peter
Hohenstein (Lautertal, Germany) for fruitful discussions on Hunsrück
Slate echinoderms. This study was supported in part by a Synthesys
grant (http://www.synthesys.info/), a programme financed by Euro−
pean Community Research Infrastructure Action under the FP6 “Struc−
turing the European Research Area Programme” to MR (GB−TAF−
2446). We would like to thank Miguel Arbizu and Isabel Méndez−
Bedia (both Oviedo University, Spain) for providing work facilities in
Arnao and Jenaro García−Alcalde for some geological comments on
Arnao. Ms. Isabel Pérez (University of Zaragoza, Spain), produced our
Fig. 1. Johnny and Will Waters (Appalachian State University, USA)
provided invaluable help during the field work. SZ acknowledges a
postdoctoral fellowship from the Ministerio de Educación of Spain.
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