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. 

Contexts in source publication

Context 1

... teeth When from Dur- the at ing least dental each one plates. sampling item In from order event, a stomach to observe the specimens was the identified, internal were captured the calcite respective microstructure, from brittle the same star one was location tooth considered was by fractured. SCUBA ‘with diving stomach For comparative at content’, depths between purposes, including 2 and the unidentifiable 7 jaws m (depending and teeth and/ on or the digested tides) remains. and collected Only in those plastic ophiuroids bags. At the without laboratory, any stomach they were content fixed were in Bouin’s considered solu- tion ‘empty’. for 24 Some h and portions then preserved of the unidentifiable in 70 % etha- or nol. digested When remains individual were remaining examined particles with the were light found and scanning in the electronic collection microscope bags they (SEM). 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. 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 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. Stomach contents: RESULTS Of the 250 individuals examined, The remaining 31.2 % had particles stomachs from with the contents. indi- vidual Of these, collection 64.1 % bags presented resulted only to one be small food item, shell fragments and far lower mixed percentages with algal referred fragments to stomachs originat- ing containing from the two sediment. to five different These items particles (Table 1). were similar The most to frequent objects that item are found sometimes corresponded retained to or macroalgal hooked by fragments, the ophiuroid’s mainly arm from spines filamen- and other tous algae. body parts. Food In particle no case sizes there were were up signs to 0.5 of these mm with particles the exception being egested of two stomach larger structures: 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 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 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 (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- ...

Context 2

... were captured the calcite respective microstructure, from brittle the same star one was location tooth considered was by fractured. SCUBA ‘with diving stomach For comparative at content’, depths between purposes, including 2 and the unidentifiable 7 jaws m (depending and teeth and/ on or the digested tides) remains. and collected Only in those plastic ophiuroids bags. At the without laboratory, any stomach they were content fixed were in Bouin’s considered solu- tion ‘empty’. for 24 Some h and portions then preserved of the unidentifiable in 70 % etha- or nol. digested When remains individual were remaining examined particles with the were light found and scanning in the electronic collection microscope bags they (SEM). 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. 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 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. Stomach contents: RESULTS Of the 250 individuals examined, The remaining 31.2 % had particles stomachs from with the contents. indi- vidual Of these, collection 64.1 % bags presented resulted only to one be small food item, shell fragments and far lower mixed percentages with algal referred fragments to stomachs originat- ing containing from the two sediment. to five different These items particles (Table 1). were similar The most to frequent objects that item are found sometimes corresponded retained to or macroalgal hooked by fragments, the ophiuroid’s mainly arm from spines filamen- and other tous algae. body parts. Food In particle no case sizes there were were up signs to 0.5 of these mm with particles the exception being egested of two stomach larger structures: 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 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 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 (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 ...

Context 3

... was by fractured. SCUBA ‘with diving stomach For comparative at content’, depths between purposes, including 2 and the unidentifiable 7 jaws m (depending and teeth and/ on or the digested tides) remains. and collected Only in those plastic ophiuroids bags. At the without laboratory, any stomach they were content fixed were in Bouin’s considered solu- tion ‘empty’. for 24 Some h and portions then preserved of the unidentifiable in 70 % etha- or nol. digested When remains individual were remaining examined particles with the were light found and scanning in the electronic collection microscope bags they (SEM). 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. 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 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. Stomach contents: RESULTS Of the 250 individuals examined, The remaining 31.2 % had particles stomachs from with the contents. indi- vidual Of these, collection 64.1 % bags presented resulted only to one be small food item, shell fragments and far lower mixed percentages with algal referred fragments to stomachs originat- ing containing from the two sediment. to five different These items particles (Table 1). were similar The most to frequent objects that item are found sometimes corresponded retained to or macroalgal hooked by fragments, the ophiuroid’s mainly arm from spines filamen- and other tous algae. body parts. Food In particle no case sizes there were were up signs to 0.5 of these mm with particles the exception being egested of two stomach larger structures: 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 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 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 (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- ...

Context 4

... tides) remains. and collected Only in those plastic ophiuroids bags. At the without laboratory, any stomach they were content fixed were in Bouin’s considered solu- tion ‘empty’. for 24 Some h and portions then preserved of the unidentifiable in 70 % etha- or nol. digested When remains individual were remaining examined particles with the were light found and scanning in the electronic collection microscope bags they (SEM). 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. 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 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. Stomach contents: RESULTS Of the 250 individuals examined, The remaining 31.2 % had particles stomachs from with the contents. indi- vidual Of these, collection 64.1 % bags presented resulted only to one be small food item, shell fragments and far lower mixed percentages with algal referred fragments to stomachs originat- ing containing from the two sediment. to five different These items particles (Table 1). were similar The most to frequent objects that item are found sometimes corresponded retained to or macroalgal hooked by fragments, the ophiuroid’s mainly arm from spines filamen- and other tous algae. body parts. Food In particle no case sizes there were were up signs to 0.5 of these mm with particles the exception being egested of two stomach larger structures: 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 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 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 (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. ...