A new Devonian ophiuroid (Echinodermata: Oegophiurida) from New York state and its bearing on the origin of Ophiuroid upper arm plates

22 Pages·1993·11 MB·

by  F H C Hotchkiss

PROC. BIOL. SOC. WASH.
106(1), 1993, pp. 63-84
A NEW DEVONIAN OPHIUROID
(ECHINODERMATA: OEGOPHIURIDA) FROM
NEW YORK STATE AND ITS BEARING ON THE
ORIGIN OF OPHIUROID UPPER ARM PLATES
Frederick H. C. Hotchkiss
Abstract.—The genus Strataster Kesling and Le Vasseur, 1971, [Protasteri-
dae] is revised, and S. maciverorum, a new species, is reported from the Panther
Mountain Formation (Middle Devonian) near Cooperstown, New York. All
of the species of Strataster (amended) have upper arm plates; those of S.
maciverorum resemble the carinal plates of starfish. The prevailing view that
upperarm platesareabsentinthe Oegophiuridais abandoned. Thearrangement
ofthe alternating ambulacral plates in Stratasteris identical to the arrangement
in echinoids, and the madreporite is located in interradius III/IV of Loven's
system. These findings necessitate a revised diagnosis ofthe Oegophiurida. The
new data also clarify the history ofthe upper arm plates ofmodem ophiuroids.
These plates are serially homologous with the primary radial plates of the
ophiuroid calycinal system. Ophiuroid arm segmentation was perfected after
upper arm plates were brought into serial correspondence with the ambulacral
vertebrae.
The Devonian ophiuroids of New York ofthe origin ofophiuroid upper arm plates
State continue to provide important mate- and to the general question of homologies
rial for the investigation ofquestions at the between the crinoid arm and the somaster-
higher levels of echinoderm classification. oid ray is the topic of the general part of
Ophiuroid fossils collected by Dr. Monroe this paper. The first part concerns the sys-
A. Mclver and Elizabeth P. Mclver of tematic paleontology ofthe genus Strataster
Cooperstown, New York, and donated to Kesling & Le Vasseur, and the description
the New York State Museum are described ofS. maciverorum.
here as Strataster maciverorum, new spe-
cies. The starfish-like aboral appearance of
Systematic Paleontology
these specimens was, for a long time, an
impediment to their proper classification. Note on methods.—The Mclver fossils are
Eventually, the recognition of counterpart preserved as molds and were studied from
halves led to the discovery that the Mclver rubbercasts, utilizingeitherlatex or silicone
fossils belong to the well known family Pro- rubber. The "disc radius" (r) and "arm
tasteridae. The unusual aboral appearance length" (R) were measured from the center
is due to the presence ofa distinctive series ofthe disc. [Because many Paleozoic ophiu-
of carinal spines. Further review of pub- roids do not have a well defined circulardisc
lished descriptions of the Protasteridae led and have the general outline of a slender
todiscoveryofsimilarseriesofcarinal spines armed starfish, W. K. Spencer (1934:464,
&
inStratasterohioensisKesling Le Vasseur 468) established the practice of reporting
and Drepanaster wrighti Kesling. The im- disc radius, rather than disc diameter, for
portance ofthis morphology to the analysis measurements on Protasteridae.] The
64 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
"width of the arm" (w) is measured at the "newgenus".—Mclver&Mclver, 1955:159.
edge of the disc and does not include the
Type species.—Strataster ohioensis Kes-
width ofthe splayed arm spines. &
ling Le Vasseur by original designation.
The material has been closely examined
for evidence of Loven's law by recording Diagnosis (amended herein).—Frotaster-
the arrangement of the ambulacral plates id brittlestars with upper arm plates and
(Hotchkiss 1978). Examined from the oral carinal spines; upper arm plates are not in
surface, the ambulacral series on the anti- register with the ambulacrals, and their se-
clockwise side of each arm is either in ad- ries end before the arm tip. Uppermost ver-
vance (A) or behind (B) the series on the tical spines project at a high angle from the
clockwise side ofthe arm. Dataare recorded sides of the arms. Aboral outline of proxi-
as ifeach specimen presents an oral aspect. mal ambulacrals trapezoidal, accommodat-
The arrangement AABAB is Lovenian. If ing large dorsal longitudinal muscles. Disc
the madreporite is not identified, data are radius up to 8 mm; arm length five to six
recorded only ifit is possible to determine times disc radius. Where arms become free
which column is ahead of the other for at of disc, their width (not including splayed
least four of the five arms. If the madre- vertical spines) equals about half the disc
porite is identified on the specimen, the radius.
madreporic interradius is designated inter- Included species. —Strataster ohioensis
V &
radius III/IV and the labels I, II, III, IV, Kesling Le Vasseur, 1971, type species;
are applied to the arms. Data are recorded Strataster wrighti (Kesling, 1970) new com-
for each scorable arm (even ifonly one arm bination; Strataster maciverorum, new spe-
can be scored). cies; not Stratasterdevonicus Kesling, 1972,
The material has been closely examined referred to Eugasterella by Harper (1985).
for evidence bearing on the question ofori- Remarks. —No otherknown genera share
entation to substrate (cf. Schuchert 1915: the full set of characters in the revised di-
30, 1919:6, 7; Fell 1963:429, 430; Smith & agnosis. In particular, no others are known
Jell 1990:766, 775, fig. 53) and for other to have carinal spines. Hamling's Ophiu-
aspects ofbehavior in life. roid has upper arm plates, but it lacks ca-
rinal and disc spines (Hotchkiss 1980). The
Class Ophiuroidea Gray, 1840 splayed uppermost vertical spines and their
Order Oegophiurida Matsumoto, 1915 contribution to the overall appearance of
Suborder Lysophiurina Gregory, 1897 the arm is not known in any other genus.
Family Protasteridae S. A. Miller, 1889 Harper (1985:363) regarded Strataster as
& a subjective synonym of Eugasterella
Strataster Kesling Le Vasseur, 1971
Schuchert, 1914, which has proximal am-
&
Strataster Kesling Le Vasseur, 1971:305, bulacrals deeply excavated for insertion of
317. -Kesling, 1972:10 in part {S. dorsal longitudinal muscles. I accept Har-
ohioensis but not S. devonicus).—H2im- per's new combination Eugasterella devon-
mann & Schmincke, 1986:61. icus for Strataster devonicus, but Eugaster-
Drepanaster. —Kesling, 1970:74 in part (D. ella does not have carinal spines and upper
wrighti but not D. scabrosus, D. grayae, arm plates, anditisnecessaryto retainStra-
and D. schohariae). [Not Drepanaster taster as a distinct genus.
Whidbome, 1898] The arrangement ofthe ambulacralplates
Eugasterella. —Harper, 1985:361, 363 in of all three species conforms with Loven's
part (E. ohioensis but not E. logani and Lawforechinoids (see, e.g., Melville &Dur-
E. devonicus). [Not Eugasterella Schu- ham 1966:U221-U222). The hypothesis
chert, 1914] that the ophiuroid madreporite is located in
VOLUME NUMBER
106, 1 65
interradius III/IV (Hotchkiss 1978) is sup- caption to their plate 4, figure 2, designates
UMMP
ported by the new Strataster data. 58329a as the holotype.
Abouthalfthe specimens ona slab ofrock Loven's Law.—The remarkable preser-
are preserved with the oral side up, the oth- vation ofthe specimens, and the clarity and
ers with the oral side down. The carinal scale ofthephotographs, allowinvestigating
spines of Strataster are similar to those of whether Loven's Law applies to S. ohioen-
modem starfish such as Calliaster, Oreaster sis. Three specimens have four or five arms
and Asteropsis, all ofwhich have the usual that can be scored in oral view, and the
eleutherozoan orientation of mouth and madreporite is not identified on the pho-
ambulacra in contact with the substrate. The tographs:
orientation of Strataster in life is inferred Paratype L-25a A A B A ?
by the presence ofcarinal spines, to be "oral Paratype L-25f A A B A B
side down." Paratype L-25h A A B A B
As Strataster has upper arm plates, a re-
vised diagnosis of the Oegophiurida is re- Three specimens have arms that can be
quired. The origin of ophiuroid upper arm scored in oral view and the madreporite (*)
plates is discussed below in the general part is identified on the photographs:
ofthis paper. I II III * IV V
UMMP
Paratype
Strataster ohioensis 58332a A A B * A B
Kesling & Le Vasseur, 1971 Paratype L-25e A ? B * A B
A
& Paratype L-25i ? ? * ? 9
Strataster ohioensis Kesling Le Vasseur,
1971:305, 317, pis. 1-13.-Halpern, These data indicate that Loven's Law ap-
1972:8.-Kesling, 1972: 10.-Hotchkiss, plies to S. ohioensis and that the madre-
1978:542.-Hotchkiss, 1980:93. porite is located in interradius III/IV.
Eugasterella ohioensis. —Harper, 1985:369, Orientation and behavior. —Kesling & Le
371. Vasseur (p. 338) inferred that S. ohioensis
was a filter feeder and could hold nearly the
—
Diagnosis. Carinal spinesbegin nearthe full length ofthe arms vertical while holding
periphery of the disc; there are approxi- onto the substrate with the proximal tube
mately 13 spines in the space of four am- feetnearthe mouth. Theyhypothesized that
bulacrals. The carinal spines are not pre- the crest ofclosely spaced carinal spines may
served in a rigid erect position; instead they have been used to pull surface silt over the
are recumbent, usually all leaning in the brittle star's body and arms (negative pho-
same direction, and certainly not fused to totactic response). About half of the speci-
the upper arm plates. The splay of the up- mens were buried with the oral side up and
permost vertical spines nearly doubles the the others with the aboral side up (p. 330),
overall arm width so that it nearly equals and Kesling & Le Vasseur suggested that
the disc radius. The disc tends to have con- currents overturned the animals before
vex interradii, lacks spines, and is covered burial (pp. 338, 339).
above and below by minute granules which Remarks. —Many authors refer to the pa-
&
conceal underlying plates. [Partly based on per by Kesling Le Vasseur (1971) on S.
Kesling & Le Vasseur, pi. 7, fig. 2.] ohioensis when discussing ophiuroid com-
rype-^.-Type-bearing slabs in the Uni- munities, population densities, arm regen-
versity of Michigan Museum of Paleontol- eration frequency, and the fossil record of
&
ogy and in the collection of Le Vasseur are brittlestar beds (Meyer 1984; Aronson
listedby Kesling & Le Vasseur (p. 330). The Harms 1985; Aronson 1987; Aronson &
s
66 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
UMMP
Sues 1987, 1988; Meyer 1988; Aronson Holotype
1989, 1992). The size range is from about 57497 A A B A B
mm mm
1.2 disc radius to about 4 disc
Remarks.—ThQ disc radius of about 2.7
radius. Weathered specimens show that the mm
is in the middle ofthe size range for S.
proximal ambulacrals are trapezoidal in ab-
ohioensis. The count of about five carinal
oral outline, leaving large spaces for dorsal
longitudinal muscles. The arrangement of spines in the space of four ambulacrals is
the carinal spines suggests that in life they distinctly different from the count of 13 in
may have been interconnected by a web. fourin 5. ohioensis. It agreeswith S. ohioen-
& sis in the obviously loose attachment ofits
Kesling Le Vasseur report (p. 318) that
carinal spines. In fact, the spines are not
each spine articulates by a ball-and-socket
found on the holotype, but their former
joint, precisely like the spine ofan echinoid;
presenceis shown by aline ofvacant sockets
also, where spines are missing, the tubercles
which Kesling (p. 75) described as "pustular
on which they articulated are conspicuous
bases for attachment ofspines," and which
because they are larger than the papillae,
he noted extend from the aboral surface of
and are surrounded by a circular groove.
the disc [Note: typographical error in his
Age and locality. —EsltIy Mississippian,
text says "oral surface"] onto the aboral
Meadville Shale. Vicinity of Cleveland,
proximalpart ofthe arms. The spine sockets
Cuyahoga County, Ohio.
confirm the presence of upper arm plates.
The count offive carinal spines in the space
Strataster wrighti (Kesling, 1970),
offour ambulacrals is probably not reliably
new combination
different from the count in the new species
Drepanaster wrighti Kesling, 1970:75, pis. to be described next. The disc outline ofthe
l-2.-Hotchkiss, 1978:542.-Hotchkiss, holotype has generally concave interradii.
1980:93. The oral interradial spines are 0.3 to 0.4
mm
long. The shape of the aboral surface
Diagnosis.—CBxmdX spines (inferred from
of the proximal ambulacrals is hidden by
sockets) begin their series midway between
upper arm plates and granules (presumably
centerandedge ofdisc, extendontothearms,
the shape is trapezoidal, as in S. ohioensis).
and number about five in the space offour
Ageandlocality. —Middle Devonian, Ar-
ambulacrals (based on Kesling's plate 2, fig-
kona Shale. Vicinity ofArkona, Middlesex
ure 1). The carinal spines are not erect, and
County, Ontario, Canada.
are not fused to the upper arm plates. The
splay ofthe uppermost vertical spines near-
ly doubles the overall arm width so that it Strataster maciverorum, new species
nearly equals the disc radius. Aboral surface Figs. 1-5
ofdisc ornamented with granules and with "newgenus andspecies," Mclver&Mclver,
few scattered spines (presence inferred from
1955:159. Strataster, n. sp. Hotchkiss,
sockets). Oral interradii with numerous
1976:12.
spines. — &
Protaster logani. Mclver Mclver, 1955:
Types. —The holotype and only specimen
159. [Not Protaster logani (Hall, 1868)]
knownis inthe University ofMichigan Mu-
UMMP
seum of Paleontology, 57497. Diagnosis. —Carinal spinesbegintheir se-
—
Loven'sLaw. Theholotype has five arms ries at or near the center of the disc and
scorable in oral view (Kesling 1970:pl. 2, number approximately 13 in the space of
fig. 3), and the madreporite is not discern- eight ambulacrals. The carinal spines are
ible (p. 75). The specimen obeys Loven' preserved in a rigid erect position and are
Law: probably fused to the upper arm plates.
VOLUME 106, NUMBER 1 67
Fig. 1. Strataster maciverorum, new species. NYSM 13222, Holotype. Figured by Mclver & Mclver (1955).
mm
Counterpart halves. Latex pulls. Bar represents 5 and applies to both stereopair figures. 1.1. Aboral view.
Carinal spines are preserved in a rigidly erect position, probably indicating fusion with the upper arm plates.
Madreporic interradius at lowerleft. 1.2, Oral view. Groove spines completelyclose overthe ambulacral groove
on the oral surface. Madreporic interradius at lower right.
68 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
Fig. 2. Strataster maciverorum, new species. 2.1, NYSM 13225, Paratype. Aboral view. Carinal spines
number approximately 13 in the space ofeight laterals. Uppermost vertical spine short, splayed at a high angle
to the arm axis. Latex pull. Bar represents 2 mm. For less enlargement see Fig. 3.1. For counterpart see Fig.
NYSM
3.2. 2.2, 13223, Paratype. Aboral view. Carinal spines diminish in height distally. Latex pull. Bar
represents 4 mm.
VOLUME NUMBER
106, 1 69
Fig. 3. Strataster macivewrum, new species. NYSM 13225, Paratype. Counterpart halves. Latex pulls. 3.1,
Aboral view. Alternating ambulacrals visible through integument near arm tip at left. Madreporic interradius
atlowerright. Barrepresents 4 mm. Forgreaterenlargement see Fig. 2.1. 3.2, Oral view. Madreporic interradius
at lower right. Bar represents 2 mm.
70 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
Fig. 4. Strataster maciverorum, new species. NYSM 13226, Paratype. Counterpart halves. Latex pulls. Bars
represent 2 mm. 4.1, Aboral view. Most spines are missing; spine sockets locate theirformerpositions. The few
spines present are rigidly erect; evidently fusion ofspine to plate is not complete, 4.2, Oral view. Note groove
spines on arm at right.
VOLUME NUMBER
106, 1 71
Fig. 5. Strataster maciverorum, new species. NYSM 13224, Paratype. Latex pull. Bars represent 2 mm.
Aboral views. Disc radius (r) 7.5 mm. The disc surface is impressed onto the mouth frame. Note the plump
cylindrical arms. Carinal spines evident, but less distinct than in smaller specimens.
.
72 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
Table L—Measurements ofStrataster maciverorum, new species. NYSM, New York State Museum catalog
number; r, disc radius; R. distance from center ofdisc to the arm tip; w, width ofarm at edge ofdisc (does not
include the width ofthe splayed arm spines); DS, rock specimen number.
NYSM r R w R:r w.r Remarks
mm mm mm
13222 5.5 34 2.5 6:1 1:2.2 holotype; DS17
—
13223 8 26+ 4.5 1:1.8 paratype; DS9
—
13224 7.5 29+ 4 1:1.9 paratype; DS37
13225 5 24 2.5 5:1 1:2.0 paratype; DSll, DS24
—
13226 4.5 15+ 2 1:2.3 paratype; DSll, DS24
Similar plates and spines occupy the rest of University, who pointed out that the spec-
the aboral surface of the disc, diminish in imens may belong in a new genus and spe-
size toward the interradial margins, and are cies. Labels show that the ''Protaster lo-
smaller still on the oral interradii. Splayed ganV ofthe Mclvers' article are contained
uppermost vertical spines are very short, in rock specimens DSl DS2 (figured by the
,
less than halfthe length ofan arm segment Mclvers), DS3, DSl2, DSl8, DS25, DS30,
and do not materially contribute to the DS70, and DS75. These rocks contain im-
overall width ofthe arm. Interradial outline pressions ofthe oral surface ofa protasterid
of disc tends to be concave. brittlestar that resembles Eugasterella lo-
Types. —There are six type-bearingpieces gani(Hall), thesingletypespecimenofwhich
of rock, numbered DS9, DSll, DS17, is itself an impression of the oral surface
DS17a, DS24, and DS37, collected by without counterpart. These specimens are
Mclver and Mclver and given to the New most likely oral impressions of S. maciv-
York State Museum (NYSM). DSll and erorum, an inference based on the obser-
DS24 are counterpart halves ofa single piece vations (1) that the specimens which Prof.
ofrock, as are DS17 and DS17a. The single Wells distinguished as a new generic type
brittlestar (Fig. 1.1, 1.2) contained in rock are in every case impressions ofthe aboral
specimen DS17 and counterpart DS17a is surface, and (2) that counterpart impres-
now catalogued as NYSM 13222; it was il- sions oftheselastareindistinguishable from
lustrated by the Mclvers and is designated the oral impressions that do not have coun-
the holotype of Strataster maciverorum. terparts. Hence these specimens are iden-
There are four paratypes: one each in DS9 tified here as topotypes ofS. maciverorum.
(Fig. 2.2) and DS37 (Fig. 5.1, 5.2), now cat- Remains ofDevonaster are present in rock
alogued as NYSM 13223 andNYSM 13224, specimens DS3, DS4, DSl9 and DS24; re-
respectively, and two in DS1 1 and coun- mainsofEncrinastersp. arepresentinDS23.
terpart DS24. Ofthe latter two, one is oral Etymology.—The species is named in
side up and one is oral side down: NYSM memory ofDr. MonroeA. Mclverand Eliz-
13225 refersto theindividual (Figs. 2.1,3.1, abethP. MclverofCooperstown, NewYork,
3.2) preserved as an aboral impression in who donated these prize fossils to science.
rock specimen DS1 1, and NYSM 13226 re- [According to ICZN Code Recommenda-
fers to the individual (Fig. 4.1, 4.2) pre- tion 21a (1985), the prefixes "Mac," "Mc"
served as an aboral impressionin rock spec- or "M" should be spelled "mac," hence
imen DS24. ''maciverorum^'; I thank Dr. David L.
Additional material—ThQ asteroids and Pawson for pointing this out to me.]
—
ophiuroids foundbythe Mclverswere iden- Measurements. See Table 1
tified by Prof. John W. Wells of Cornell Loven's Law.—Two impressions of the