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Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 63 (Suppl. 2): 353-360, June 2015
Tooth microstructure and feeding biology of the brittle star
Ophioplocus januarii (Echinodermata: Ophiuroidea)
from northern Patagonia, Argentina
Martín I. Brogger1,2, Mariano I. Martinez2, María Pilar Cadierno3 & Pablo E. Penchaszadeh2
1. Laboratorio de Reproducción y Biología Integrativa de Invertebrados Marinos, CENPAT-CONICET, Blvd. Brown
2915, Puerto Madryn, Argentina; brogger@cenpat-conicet.gob.ar, mbrogger@bg.fcen.uba.ar
2. Laboratorio de Ecosistemas Costeros, MACN-CONICET, Av. Ángel Gallardo 470, Buenos Aires, Argentina; mmarti-
nez@macn.gov.ar, pablopench@gmail.com
3. Instituto de Investigaciones Bioquímicas de La Plata, UNLP-CONICET, Avenida 60 y 120, La Plata, Argentina; mpi-
larcadierno@yahoo.com.ar
Received 28-VII-2014. Corrected 10-X-2014. Accepted 20-XI-2014.
Abstract: Ophioplocus januarii is a common brittle star on soft and hard substrates along the Argentinian and
Brazilian coasts. Based on stomach contents, tooth microstructure and field observations we identified its food.
Opposed to previous suggestions, O. januarii appears to be a microphagous species feeding on macroalgal frag-
ments (found in 60.0 % of the analyzed stomachs with content), plant debris (28.0 %), animal cuticle structures
(13.0 %), and unidentifiable material (30.7 %). Less frequent items found were foraminiferans, ostracods, an
amphipod, a juvenile bivalve, and other crustaceans. Electronic microscope revealed digested material, diatoms
and small crustacean appendices. Thus, O. januarii is an omnivorous species, feeding mainly on algae, comple-
mented opportunistically with other items. Suspension feeding was observed in the field. It has an fenestrated
arrangement intermediate between the previously described uniform and compound teeth. Rev. Biol. Trop. 63
(Suppl. 2): 353-360. Epub 2015 June 01.
Key words: brittle star, stereom microstructure, stomach contents, Ophiolepididae, teeth.
Ophiuroids display diverse feeding strate-
gies, often combined, and ranging from preda-
tion and scavenging to deposit- and suspension
feeding (Warner, 1982; Harris et al., 2009).
Based on the size of the ingested particles,
Warner (1982) proposed the division between
macrophagous and microphagous species, with
the former acquiring large particles through
predation and scavenging while the latter
include suspension feeding and the acquisi-
tion of small particles from the substratum.
Some species exhibit high degrees of flex-
ibility in their feeding mechanisms and their
prey spectra (Fontaine, 1965; Warner, 1982),
and it has been proposed that for both, shal-
low water and deep-sea species, differences in
diets between species also reflect differences in
lifestyles. Hereby they may act as non-special-
ized opportunists with respect to diet (Pearson
& Gage, 1984).
Information available on the diet of brittle
stars has been established through field obser-
vations estimating the feeding preferences by
the observed feeding behavior (Warner, 1982),
or by stomach content analyses (Harris et al.,
2009). Depending on their behavior it is pos-
sible to identify active predators or suspension-
feeding species (Davoult & Gounin, 1995),
while is difficult to directly observe those
species that feed on deposited material from
the sediment surface or beneath it (Gielazyn et
al., 1999). Prey items that are found in stomach
content studies allow for the identification of
an ophiuroid being microphagous, but also
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Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 63 (Suppl. 2): 353-360, June 2015
for the general source of the respective food
particles: planktonic prey items suggest a filter
feeding mode on water-borne items, whereas
considerable amounts of sediment may indicate
a surface- or subsurface deposit feeding mode
(Ferrari & Dearborn, 1989; Dahm, 1999). A
third approximation of brittle star feeding pref-
erences is relatively poorly developed and is
based on the analysis of the stereom microstruc-
ture of the teeth (i.e. how calcite is arranged or
disposed in the teeth). Medeiros-Bergen (1996)
analyzed the stereom microstructure of teeth
from several ophiuroid species using light and
scanning electron microscopy. She defined
two tooth types: a uniform teeth, in which the
tooth stereom is completely fenestrated, and
compound teeth, where the base of the tooth is
fenestrated, while the distal edge is composed
of imperforated calcite. With a few exceptions,
macrophagous feeders possess uniform teeth,
while microphagous species reveal compound
teeth (Medeiros-Bergen, 1996).
The brittle star Ophioplocus januarii (Lüt-
ken, 1856) (Ophiolepididae) is distributed
along the Western Atlantic coast from Golfo
Nuevo, Argentina, to northern Brazil, with a
doubtful record from Barbados (Thomas, 1975;
Bernasconi & D’Agostino, 1977). It is found
from the tidal zones down to 74 meters depth,
both on hard substrates and on soft sediments
rich in detritus (Bartsch, 1982). To date very
little is known about the feeding biology of O.
januarii (Brogger et al., 2013). Bartsch (1982)
analyzed stomach contents of some individuals
finding only sediment grains. Medeiros-Bergen
(1996) observed the microstructure of the teeth
of O. januarii under a light microscope and
described it as completely fenestrated, similar
to those teeth she observed in Ophioplocus
esmarki Lyman, 1874 with the scanning elec-
tron microscope.
Here we report on the diet of O. janu-
arii and discuss its feeding biology based
on stomach content analysis, feeding mecha-
nisms observed in the field, and tooth stereom
microstructure analysis using scanning electron
microscopy. For comparison, we also describe
and discuss the microstructure of the teeth of
other brittle stars species and their relations to
the respective feeding habits.
MATERIALS AND METHODS
Ophioplocus januarii were collected
monthly from Playa Villarino (42º 24’ S - 64º
17’ W), Golfo San José (northern Patagonia),
from April 2005 to April 2007 comprising a
total of 25 consecutively taken samples. Dur-
ing each sampling event, the specimens were
captured from the same location by SCUBA
diving at depths between 2 and 7 m (depending
on the tides) and collected in plastic bags. At
the laboratory, they were fixed in Bouin’s solu-
tion for 24 h and then preserved in 70 % etha-
nol. When individual remaining particles were
found in the collection bags they were also
preserved in 70% ethanol for later observation.
While sampling, brittle stars were observed and
photographed in situ in order to identify and
determine feeding activities. All sampling and
observations were conducted during daylight.
Stomach contents: The discs were cut
off along with the stomach lining, and the
contents picked out. Stomach contents of 10
brittle stars from each month (total N = 250)
were examined under the light microscope,
and all content items were separated. When at
least one item from a stomach was identified,
the respective brittle star was considered ‘with
stomach content’, including unidentifiable and/
or digested remains. Only those ophiuroids
without any stomach content were considered
‘empty’. Some portions of the unidentifiable or
digested remains were examined with the light
and scanning electronic microscope (SEM).
Tooth microstructure analysis: The jaws
of O. januarii were dissected and placed for
a few minutes in a diluted solution of com-
mercial house bleach in order to remove the
epidermal layer. Longer maceration allowed
for the dissociation of individual teeth from the
dental plates. In order to observe the internal
calcite microstructure, one tooth was fractured.
For comparative purposes, the jaws and teeth
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Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 63 (Suppl. 2): 353-360, June 2015
of five other brittle star species were examined
as well. These included Ophiomyxa vivipara,
Amphipholis squamata, Ophiactis asperula,
Ophiacantha vivipara and Ophiocten amiti-
num. All jaws and teeth were prepared for
SEM observations. At least 7 adult individuals
of each species were dissected during the tooth
microstructure analysis.
RESULTS
The remaining particles from the indi-
vidual collection bags resulted to be small shell
fragments mixed with algal fragments originat-
ing from the sediment. These particles were
similar to objects that are sometimes retained
or hooked by the ophiuroid’s arm spines and
other body parts. In no case there were signs of
these particles being egested stomach contents
from prior to the animals’ fixation.
Typical passive suspension-feeding activi-
ties were observed in the field. While feeding,
the individuals raised two or three arms into the
passing currents. Small particles were trapped
by the tube feet and collected into a bolus that
was passed down along the arm to the mouth.
Stomach contents: Of the 250 individuals
examined, 31.2 % had stomachs with contents.
Of these, 64.1 % presented only one food item,
and far lower percentages referred to stomachs
containing two to five different items (Table 1).
The most frequent item found corresponded to
macroalgal fragments, mainly from filamen-
tous algae. Food particle sizes were up to 0.5
mm with the exception of two larger structures:
a macroalgal fragment of 6.0 mm, and a cuticu-
lar structure of 7.5 mm. The average number of
food items was 1.64 per individual.
Macroalgal fragments were present in 60
% of the stomachs with contents, and in 64 %
of the studied months. Other frequent items
found were unidentifiable material (31%) and
small terrestrial plant debris (28 %). Less fre-
quent items were cuticular animal structures
(13%), unidentifiable laminar structures (8
%), spicules (4 %), three foraminiferans, three
ostracods, one amphipod, other crustaceans,
one juvenile bivalve and one hydrozoarian col-
ony. No sediment particles were found inside
the stomachs.
Tooth microstructure analysis: All teeth
in O. januarii revealed a fenestrated stereom
microstructure (Fig. 1). However, it was pos-
sible to clearly identify two distinct regions:
the basal parts of the teeth which are in contact
with the dental plate, are more loosely perfo-
rated than the distal parts. There the calcite
is much more compacted, presenting a clear
different arrangement (Fig. 1 A, B, C, D). This
superficial distinction is visible also internally
in the calcite microstructure as can be seen in a
fractured tooth (Fig. 1 F, G). The basal surface
presents little serrated edges, but at the distal
portion these edges are less prominent because
of the tightly packed calcite (Fig. 1 E).
Under light microscope, the teeth of Ophi-
omyxa vivipara presented translucent crys-
talline edges with small spines protruding
from the distal edges; they are semicircle in
shape and are perforated apart from the dis-
tally protruding spines (Fig. 2 A). The teeth of
Ophiacantha vivipara and Ophiocten amitinum
presented spine like shapes with uniform fenes-
trated surfaces and sharply serrated edges (Fig.
2 D, E). Amphipholis squamata carried teeth
with a fenestrated base, but distally the calcite
was imperforate (Fig. 2 B). The tooth stereom
microstructure of Ophiactis asperula is similar
to that described here for O. januarii, and con-
sisted of two regions with differentiated calcite
compactions (Fig. 2 C). The tooth types of the
TABLE 1
Total number of stomachs with content and percentage of
stomachs with distinguishable amounts of food item
Number Percentage
Stomachs analyzed 250
With contents 78 31.2
With one food item 50 64.1
With two food items 13 16.6
With three food items 9 11.5
With four food items 5 6.4
With five food items 1 1.3
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Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 63 (Suppl. 2): 353-360, June 2015
six species analyzed presently are summarized
in the Table 2.
DISCUSSION
In the present study, Ophioplocus januarii
from Playa Villarino fed ingesting small-sus-
pended particles through suspension feeding
from the water-sediment interface. Contrari-
ly to previously made assumptions (Warner,
1982; Medeiros-Bergen, 1996), O. januarii is a
microphagous species. It fed opportunistically,
mainly ingesting fragments of macroalgae,
but also small plant and animal structures,
and other suspended material. When analyzing
stomach contents from a 60 meters depth O.
januarii population collected in a nearby loca-
tion on the continental shelf (42° S - 62° W),
Bartsch (1982) observed stomachs lacking food
but filled partly with sediment grains. In the
present study, no sediments were found, sug-
gesting differences in feeding preferences to be
Fig. 1. Scanning electron microscopy images of teeth in Ophioplocus januarii. A) Dorsalmost tooth. B) Mid-positioned
tooth. C) Proximal view of dorsal teeth. D) Proximal view of ventral teeth. E) Detail of B, showing the different calcite
compaction. F) Fractured tooth. G) Detail of F, showing the internal differentiation in microstructure. I and II indicate
regions of more compaction (I) and more porosity (II) of the calcite, respectively. Scale bars: A, B, C, D = 200 μm; E, G
= 50 μm.
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dependent of habitat diversity. This was also
observed for different populations of Ophiura
ophiura (Blegvad, 1914 in Warner, 1982) and
of Ophionotus victoriae (Dearborn, 1977). The
main distinction between feeding types in
brittle stars used to be drawn between car-
nivory and microphagy (Warner, 1982). Those
species that capture large particles –typically of
animal origin– and, thus, feed as microphagous
feeders, are generally described as carnivorous,
while microphagous species feed on a mixture
of minute animal and vegetal material. The diet
presently observed for O. januarii indicates
that this species is an unselective omnivorous
species. Others also feeding mainly on vegetal
origin material are mostly associated with sedi-
ments. Ophionereis reticulata, for example,
has been indicated as exclusively herbivorous
TABLE 2
Tooth stereom microstructure for six analyzed ophiuroid species: uniform (completely fenestrated), compound
(fenestrated base and imperforate calcite tip) and intermediate (fenestrated with two distinct regions) tooth types
Species Family Source Tooth type
Ophioplocus januarii (Lütken, 1856) Ophiolepididae 42º 24’ S; 64º 17’ W (2 - 7 m) intermediate
Amphipholis squamata (Delle Chiaje, 1828) Amphiuridae 44º 53 ’S; 65 º40’ W (0 m) compound
Ophiacantha vivipara Ljungman, 1870 Ophiacanthidae 38º 51’ S; 55º 39’ W (115 m) uniform
Ophiactis asperula (Philippi, 1858) Ophiactidae 38º 51’ S; 55º 35’ W (145 m) intermediate
Ophiocten amitinum Lyman, 1878 Ophiuridae 38º 51’ S; 55º 35’ W (145 m) uniform
Ophiomyxa vivipara Studer, 1876 Ophiomyxidae 43º 36’ S; 60º 05’ W (96 m) uniform
Fig. 2. Scanning electron microscopy images of tooth stereom microstructure in different ophiuroid species (mid-positioned
teeth). A) Ophiomyxa vivipara. B) Amphipholis squamata. C) Ophiactis asperula. D) Ophiacantha vivipara. E) Ophiocten
amitinum. Scale bars: A, C, D = 200 μm; B, E = 100 μm.
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(May, 1925 in Warner, 1982) and more recently
as an omnivore with algal feeding preference
(Yokoyama & Amaral, 2008). Algal and cal-
careous fragments are the most frequent items
in the diets of Ophiocoma wenditii, O. echinata
and O. pumila (Sides & Woodley, 1985).
In stomach contents analyses conducted
with different species, the percentages of empty
stomachs found were highly variable between
the species. For example, Harris et al. (2009)
observed 66 % of empty stomachs in Ophiura
sarsii, Yokoyama and Amaral (2008) 23 % in
Ophionereis reticulata, Hendler (1982) found
variations from 100 to 5% with a dependence
of the months under study, and Hendler and
Miller (1984) observed differences in percent-
age for Asteroporpa annulata according to
whether the individuals were captured during
day or nighttime. In the present study, the per-
centage of empty stomachs in O. januarii was
close to 70 % and included only samples that
were collected during the daylight. The fact that
brittle stars may egest their stomach contents in
response to collecting procedure or handling
(Pearson & Gage, 1984; Hendler, pers. comm.),
could explain the high proportions of empty
stomach found in some deep-sea investigations
(Warner, 1982). This, however, does not seem
to be the case in the presently investigated O.
januarii because no egested material was found
when analyzing the collection bags.
The tooth stereom microstructure in O.
januarii is distinctly different from that in teeth
of macrophagous as well as microphagous spe-
cies (Fig. 1; Table 2). The presently found inter-
mediate fenestrated arrangement of the stereom
was also here observed for Ophiactis asperula,
and confirmed as such when analyzing the
teeth with the scanning electron microscope
(SEM). The fact that SEM reveals structures
which might remain disguised under the light
microscope could explain that Medeiros-Ber-
gen (1996) did not recognize differences in
the tooth microstructure between Ophioplocus
esmarki and O. januarii. Therefore, it is pos-
sible that other species previously described as
carrying uniform teeth (macrophagous) could,
in fact, possess intermediate tooth types. In
the present study we identified the intermedi-
ate tooth type, and the previously described
uniform and compound types. However, it
would be interesting to analyze additional
species in order to recognize other possible
variations in the tooth stereom microstructure
previously overlooked.
The present results observed for the diet
of O. januarii represent, to our knowledge,
the first trustworthy report of microphagy in
the family Ophiolepididae. Dietary studies
on Ophiolepis elegans suggested this spe-
cies to be a macrophagous species (Warner,
1982), while Medeiros-Bergen (1996), based
on tooth microstructure, estimated three Ophi-
oplocus species and Ophiolepis impressa to be
microphagous as well. Two other species from
the same family (Ophioplocus incipiens and
Ophiomusium lymani) are reported to conduct
suspension-feeding activities (Warner, 1982),
and little information about their diets is avail-
able. Pearson and Gage (1984) suggested O.
lymani to have an omnivorous diet. Because
there are no records of passive suspension feed-
ing in macrophagous species, it is likely that
both O. incipiens and O. lymani being repre-
sentatives of the Ophiolepididae, are micropha-
gous as well.
Much progress on the knowledge of the
diet of ophiuroids has been made since War-
ner’s summary in 1982. Yet, much is still
obscure. For example, the role that brittle stars
play in trophic transfers of nutrients with-
in benthic communities and between benthic
and pelagic communities still remains highly
unknown (Gielazyn et al., 1999). The utility of
analyzing teeth microstructure may surpass not
only knowledge on feeding habits and diet in
ophiuroids, but may also provide a helpful tool
for phylogenetic issues, most likely in combi-
nation with tooth macrostructure analyzes as
proposed by Stöhr (2005), and with studies on
jaw morphology already used by Murakami
(1963), Smith et al. (1995) and Stöhr and
Muths (2010).
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ACKNOWLEDGMENTS
Thanks to the people from the Laboratorio
de Ecosistemas Costeros (MACN) and the
LARBIM (CENPAT) for their assistance dur-
ing collection and processing at the laboratory.
This work was funded by grants from the Con-
sejo Nacional de Investigaciones Científicas
y Técnicas (CONICET PIP-0253) and from
the Agencia Nacional de Promoción Cientí-
fica y Tecnológica (PICT 2012-0561 and PICT
2013-2504). We also thank three referees for
valuable suggestions, particularly to Karin
Boos for her helpful commentaries and recom-
mendations that improved considerably the
final manuscript.
RESUMEN
Microestructura dental y biología alimentaria del
Ophioplocus januarii (Echinodermata: Ophiuroidea) del
norte de Patagonia, Argentina. El ofiuroideo Ophioplo-
cus januarii se distribuye a lo largo de las costas de Argen-
tina y Brasil, encontrándose tanto en substratos duros como
blandos. En base al análisis de contenidos estomacales y
la microestructura de los dientes, junto a observaciones
de campo, se describe el comportamiento alimentario de
esta especie. Opuesto a suposiciones previas, O. januarii
es una especie micrófaga que se alimenta de fragmentos
de macroalgas (encontrados en el 60.0 % de los estómagos
analizados que presentaban contenido), detritos vegetales
(28.0 %), estructuras cuticulares animales (13.0 %) y mate-
rial inidentificable (30.7 %). Menos frecuente, se encon-
traron foraminíferos, ostrácodos, un anfípodo, un bivalvo
juvenil y otros crustáceos. Pequeñas porciones del material
inidentificable fueron analizadas en el microscopio electró-
nico de barrido, resultando ser material digerido, diatomeas
y pequeños apéndices de crustáceos. Así, O. januarii es una
especie omnívora, que se alimenta principalmente de algas,
complementando su dieta de manera oportunista con otros
ítems. Las observaciones de campo revelaron alimentación
suspensívora. El análisis de la microestructura del este-
reoma del diente resultó en un arreglo del tipo fenestrado
intermedio, que se encuentra entre los dos tipos de arreglos
descriptos hasta ahora, los dientes de tipo uniforme y los
compuestos. De estos últimos, el primero ha sido encon-
trado en especies macrófagas mientras que el segundo se
corresponde a ofiuroideos micrófagos. En el presente tra-
bajo, se propone la existencia de un nuevo tipo de arreglo
intermedio en la matriz dental de los ofiuroideos.
Palabras claves: Estrellas quebradizas, microestructura
estereoma, contenido estomacal, Ophiolepididae, diente.
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