Amphiodia (Amphispina) obtecta Mortensen, 1940

Stöhr, Sabine, Çinar, Melih Ertan & Dagli, Ertan, 2010, Brittle stars (Echinodermata: Ophiuroidea) from the southern coast of Turkey (eastern Mediterranean): new records and revision of Amphiodia obtecta Mortensen, 1940, Zootaxa 2483, pp. 45-57 : 47-51

Amphiodia (Amphispina) obtecta Mortensen, 1940

Figure 2

Amphiodia obtecta Mortensen, 1940:88 -90

Amphiodia (Amphispina) clarki Liao, 2004: 159 –160, 425

Material examined. ESFM-ECH/2005-5, 10.9.2005, Iskenderun Bay, G5, 25 m, muddy sand, 2 specimens; ESFM-ECH/2005-6, 19.9.2005, Iskenderun Bay, D14, 25 m, muddy sand, 2 specimens; ESFM-ECH/2009-1, Mersin Bay, 3.2.2009, Sta. 10, 72 m, muddy sand, 3 specimens; ESFM-ECH/2009-2, Mersin Bay, 3.2.2009, Sta. 17, 13 m, muddy sand, 2 specimens, ESFM-ECH/2009-3, Mersin Bay, 4.2.2009, Sta. 34, 9 m, muddy sand, 80 specimens; ESFM-ECH/2009-4, Mersin Bay, 28.4.2009, Sta. 2, 20 m, muddy sand, 12 specimens; ESFM-ECH/2009-5, Mersin Bay, 28.4.2009, Sta. 14, 47 m, muddy sand, 7 specimens; ESFM-ECH/2009-6, Mersin Bay, 30.4.2009, Sta. 17, 13 m, muddy sand, 11 specimens; ESFM-ECH/2009-7, Mersin Bay, 30.4.2009, Sta. 27, 38 m, muddy sand, 3 specimens; ESFM-ECH/2009-8, Mersin Bay, 29.4.2009, Sta. 34, 9 m, muddy sand, 70 specimens; ESFM-ECH/2009-9, Mersin Bay, 3.8.2009, Sta. 2, 20 m, muddy sand, 2 specimens; ESFM-ECH/ 2009-10, Mersin Bay, 3.8.2009, Sta. 10, 72 m, muddy sand, 1 specimen; ESFM- ECH / 2009-11, Mersin Bay, 4.8.2009, Sta. 17, 13 m, muddy sand, 5 specimens; ESFM-ECH/ 2009-12, Mersin Bay, 5.8.2009, Sta. 27, 38 m, muddy sand, 2 specimens; ESFM-ECH/ 2009-13, Mersin Bay, 5.8.2009, Sta. 34, 9 m, muddy sand, 100 specimens; ESFM-ECH/ 2009-14, Mersin Bay, 19.10.2009, Sta. 2, 20 m, muddy sand, 7 specimens; ESFM-ECH/ 2009-15, Mersin Bay, 19.10.2009, Sta. 14, 47 m, muddy sand, 5 specimens; ESFM- ECH / 2009-16, Mersin Bay, 19.10.2009, Sta. 17, 13 m, muddy sand, 17 specimens; ESFM-ECH/ 2009-17, Mersin Bay, 19.10.2009, Sta. 34, 9 m, 71 specimens.

Comparative material. Amphiodia obtecta syntypes; ZMC Oph 34, 4.3.1937, Persian Gulf sta. 6, 12 miles NE of the NE-point of the isle of Kharg, 10 m, brown clay, Petersen grab, 2 specimens; ZMC Oph 227, 4.3.1937, Persian Gulf, sta. 7, 6 miles NE by E of the NE-point of the isle of Kharg, 20 m, brown clay, Petersen grab, 15 specimens; ZMC Oph 35, 11.3.1937, Persian Gulf, sta. 20, outer road off Bushire, 8.5 m, gray clay, Petersen grab, 1 specimens; ZMC Oph 36 + 37, 18.3.1937, Persian Gulf sta. 29, about 3 miles S by E of the outer light buoy, Bushire, 10 m, gray clay, Petersen grab, 1 + 12 spms,.

Amphiodia microplax Burfield, 1924 , NHM 1938.12.1.1, 1 syntype, Sudanese Red Sea, Khor Dongola; NHM 1938.12.1.2, 1 syntype, Sudanese Red Sea, SE Shubuk. Ophiophragmus duplicatus Koehler, 1930 (currently placed in Amphiodia ), ZMUC OPH-140, 27.2.1922, syntypes, Amboina bay, sandy beach.

Description. Several specimens lack the dorsal disk. The largest specimen with intact disk has a dd of 3 mm; the arms are about 15 times the dd long (at least 45 mm). The dorsal disk is covered with small, thin, round to oval scales among which the primary plates are not distinguishable. In fully scaled individuals the scales at the dorsal margin are extended into fork-like thorns at their proximal edge. These scales are slightly erect, with the thorns pointing towards the disk centre, slightly elevated above the disk surface. The extent of these thorny scales varies between individuals, from an almost full circle around the disk to just a few scales. Some individuals lack scales in the interradii or even the centre of the disk and these usually also lack the marginal spines except at the radial shields.

Of the radial shields only narrow, bar-like strips are visible, contiguous, about half the disk radius long. Most of the radial shield surface is covered with scales, obscuring their triangular shape. Distal and proximal ends of the radial shields are narrow, their greatest width is just distal to their mid-length, where they are so wide that only a narrow strip of interradius is left between neighbouring radii. Distal to each radial shield a small scale is present, with at least three long diverging thorns, similar to the marginal disk scales, but here the thorns arise from the centre of the scales, not on the edge. In individuals with naked interradii, lacking the marginal spines, also the radial spines may be reduced to flat scales without any trace of a spine. The naked ventral disk bulges outwards and forms the actual edge of the disk, displacing the scaled dorsal part inwards.

The dorsal arm plates are contiguous, wider than long, rounded, with convex distal and lateral edges and narrower proximal edge. There are three conical pointed arm spines, slightly longer than an arm joint, the middle spine slightly stronger than the others, all with minutely serrated edges.

The ventral disk is completely naked and the gonads are visible through the skin. The oral papillae consist of the block-like, paired, infradental papillae at the apex of each jaw and two lateral papillae to each jaw edge. The proximal lateral papilla is flat, longer than wide and pointed. The distal lateral papilla is wider than long, with wider outer edge and narrower base, but in some specimens similar to middle papilla. The adoral shields are wing-like, with round lateral lobe, reaching around the oral shield and separating it from the arm. The oral shield is longer than wide, with obtuse rounded proximal angle and convex lateral edges, abruptly narrowing at about two thirds of its length, forming a distal lobe with straight edges. The madreporite is distinctly larger than the other oral shields and lacks a hydropore. The ventral arm plates are pentagonal, about as long as wide, with straight edges, more or less contiguous or slightly separated on different arms in the same individual. A single narrow, bar-like tentacle scale is present at each tentacle pore, along almost the entire distal edge of the ventral plate. Live animals appear to have a dark red disk, which is caused by the stomach being visible through the thin disk scalation. The arms are light brown to beige with a dark brown longitudinal band, which may be less distinct on some arms and in different individuals. In alcohol the colours fade to a creamy beige.

Comparative type material. Mortensen (1940) listed 20 samples of A. obtecta from 19 localities in the Persian Gulf, with a total of 74 specimens. Most of these have lost the dorsal disk (Schiøtte, personal communication), a property common in amphiurids with naked ventral disk (Stöhr, personal observation). We requested a loan of specimens with attached dorsal disk and received five samples, with 31 specimens, of which six had intact dorsal disks. They ranged in size between 1.5 and 3 mm dd. In the dried sample ( ZMC Oph 227), three specimens had intact disks and large distal radial spines with multiple points. The two smallest specimens (1.7 mm dd) were fully scaled dorsally and had thorny marginal scales in addition to the radial processes. Their ventral interradii were naked only on the proximal part. The other two and three more specimens with intact disks from ethanol samples lacked marginal thorns. The size of the distal radial processes varied between specimens and was largest in the dried individuals. The dorsal and ventral arm plates also showed some variation between individuals in the width:length relationships and from contiguous to separate. In these and other characters the syntypes were indistinguishable from the Turkish specimens and we conclude that our material belongs to A. obtecta .

The syntypes of A. microplax are in worse condition than those of A. obtecta , most arm spines are lost, the second sample (1938.12.1.2) appears to have been dry at some point in its history and then rehydrated with poor result. That specimen appears to lack the radial processes and any other disk spines. Its ventral disk is covered with fine scales. The other syntype of A. microplax possesses the radial processes and has a likewise scaled ventral disk. Other characters fall within the variability of A. obtecta .

Remarks. Mortensen (1940) remarked that Amphiodia microplax is hardly distinguishable from A. obtecta , when the dorsal disk is lacking. The main difference between both species is supposed to be that A. microplax has spiny extensions on the marginal dorsal scales all around the disk, whereas A. obtecta has only the two spinose scales distal to the radial shields ( Mortensen, 1940). Cherbonnier and Guille (1978) suggested that both species may be conspecific, but did not actually revise them. Later, Liao and Clark (1995) and Liao (2004) still apparently treated both as separate species, since they did not mention A. obtecta when reporting A. microplax from South China. The condition of the ventral disk (scaled in A. microplax , naked in A. obtecta ) has hardly been mentioned by these authors. Re-examination of the type material of A. obtecta has revealed that two specimens have obvious spines along their disk edge, but taking into account that most specimens have lost the dorsal disk, the true frequency of this character in the population cannot be assessed. Nevertheless, it can no longer be maintained that the absence of marginal spines is a distinguishing character. Instead, the scalation of the ventral disk appears to be crucial.

The subgenus Amphispina is characterized by spiny marginal disk scales and currently includes five species: A. digitata Nielsen, 1932 (type species), A. urtica ( Lyman, 1860) , A. duplicata , A. microplax , and A. clarki . Amphiodia obtecta has never been included in Amphispina , probably because it was assumed to possess only the radial processes, which this study shows to be a variable character. Liao (2004) erected A. clarki for specimens that differ from A. microplax only in naked ventral interradii and digits distal to the radial shields. The fact that the distal radial spiny processes are actually separate structures (= digits) from the radial shields may have eluded previous researchers, since no SEM studies have been performed before. The fact that distal digits are present in type material of both A. microplax and A. obtecta , which differ in that the latter has a naked disk, strongly suggests that A. clarki is in fact conspecific with A. obtecta , since there is no character distinguishing them. It is well known that some amphiurid species with usually naked ventral disks show great variability from partially to fully scaled [e.g. Amphiura filiformis ( O.F. Müller, 1776) , Boos, unpublished results]. Therefore, we cannot exclude the possibility that A. microplax and A. obtecta may be conspecific, but we propose to maintain these species until more information, preferably including molecular data, is available.

Clark (in Clark & Rowe 1971) suggested that Amphiodia (Amphispina) duplicata ( Koehler, 1930) may also be conspecific with A. microplax , because the supposedly single difference between them is that Amphiodia duplicata has bifurcated marginal spines, while those of A. microplax are supposed to be singlepointed. As we now know, this character does not hold true. However, the ventral disk in A. duplicata ( Koehler 1930) (Ophiophragmus) syntypes is fully scaled and at 4 mm disk diameter they are larger than the other nominal species. Also, the spiny scales at the disk edge are much larger than the overall disk scalation and very obvious in this species, the dorsal arm plates are wider and shorter, the oral shield is narrower and the ventral arm plates have a notch in their distal edge. Thus we find that A. duplicata is a distinct species, separate from all others.

Another species with spiny radial processes is Amphiodia digitula H.L. Clark, 1911 , currently placed in Amphiura by Clark (1970) on the grounds of its oral papillae. At 6 mm disk diameter it is a much larger species, with fully scaled ventral disk and four arm spines. Curiously, Clark (1911) describes the radial processes as part of the distal end of the genital plates.

Spiny radial digits are known also from Amphioplus (Amphioplus) cyrtacanthus H.L. Clark, 1915 , Amphioplus (Amphioplus) lucidus Koehler, 1922 ( Liao & Clark, 1995) , Amphioplus (Amphioplus) ancistrotus ( H.L. Clark, 1911) ( Dyakonov 1954; Liao 2004) and possibly other species. None of these appear to have spiny disk scales though and they all show the typical Amphioplus formula of the oral papillae.

Distribution. Amphiodia obtecta is the first member of its genus found in the Mediterranean Sea. It is an Indo-Pacific species that is not known from the Atlantic Ocean and probably originated from Red Sea populations. It may have migrated through the Suez Canal, but most likely it was transported as a larval stage in the ballast water of ships or perhaps as part of the fouling community on ship bottoms. The presence of large international harbours located in Mersin and Iskenderun Bays, where this species was found, might support this hypothesis. The invasive species Strombus persicus ( Swainson, 1821) and Caulerpa taxifolia (Vahl) C. Agardh, 1817 were known to have been introduced to the southern coast of Turkey from the Indo- Pacific area by ballast water of ships (Çinar et al., 2005; Cevik et al., 2007). It has not yet been found in the southern Levantine countries, such as Israel or Lebanon, although ophiuroids have been collected regularly in Lebanese waters in recent years (Stöhr, Zibrowius & Bitar, unpublished results). An interrupted distribution may support the hypothesis of human- mediated transport via ships that travelled from the Red Sea directly to Turkey and unloaded their ballast water there. However, these collecting efforts were somewhat biased towards a coral dwelling fauna and A. obtecta may have been overlooked. The species may also have been confused with other amphiurids by other workers and thus not been identified. Amphiodia obtecta has also been reported from Thailand by Bussarawit and Hansen (in: Putchakarn & Sonchaeng 2004), which suggests a continuous distribution from the Red Sea to China, now extended to the eastern Mediterranean Sea.

Ecology. A total of 402 individuals of A. obtecta were collected in Iskenderun (stations G5 and D14) and Mersin Bays. The majority of specimens (398 individuals) were found in seasonal samples taken from Mersin Bay in 2009 and four individuals from Iskenderun Bay in September 2005. The species occurred at depths ranging from 9 to 47 m in the area.

The density and biomass of A. obtecta in Mersin Bay ranged from 10 (stations17 and 10 in) to 420 ind.m -2 (station 34, in summer), and from 0.004 (station 14 in fall) to 36 gm -2 (station 34, in summer), respectively ( Figure 3 ). No individual was found at station 43 (21 m). Station 34, which is shallow (9 m depth) and under the influence of the Seyhan River [salinity range: 34.5 psu (spring) to 38.8 psu (winter)], supports dense populations of A. obtecta ( Figure 3 ). Its density did not change seasonally (ANOVA test, p>0.05) at station 35, ranging from 280 ind.m - 2 in spring to 420 ind.m - 2 in summer. The biomass of this species significantly changed seasonally (p<0.05) and attained its maximum level (36 gm -2) in summer and its minimum level (9.3 gm -2) in fall. In fall and winter, juvenile specimens dominated the population. The mouth of Seyhan River seems to provide suitable environments for alien species. Çinar (2006; 2009) and Dagli & Çinar (2009) reported relatively dense populations of eight alien polychaete species [ Nereis persica Fauvel, 1911 , Glycinde bonhourei Gravier, 1904 , Onuphis eremite oculata Hartman, 1951 , Laonome triangularis Hutchings & Murray, 1984 , Hydroides elegans ( Haswell, 1883) , H. operculatus ( Treadwell, 1929) , Prionospio (Aquilaspio) krusadensis Fauvel, 1929 and P. (A.) sexoculata Augener, 1918 ] in the area.

The main environmental factors affecting the density of A. obtecta in the area were temperature (ρ r=-0.58) and silica (ρ r=0.52) in winter; depth (ρ r=-0.77) and temperature (ρ r=0.61) in spring; depth (ρ r=-0.76), total nitrogen (ρ r=0.76) and Chlorophyll a (ρ r=0.81) in summer; depth (ρ r=-0.81) and total phosphorus (ρ r=0.81) in fall. As overall seasonal data are concerned, the density of A. obtecta was negatively affected by depth (ρ r=- 0.59) and positively affected by total phosphorus (ρ r=0.51), Chlorophyll a (ρ r=0.41), silt percentage in sediment (ρ r=0.33) and silica (ρ r=0.31). It is well known that the Red Sea migrants prefer shallow water benthic habitats and occasionally inhabit deeper waters ( Ergev et al. 2003; Çinar et al. 2005; Çinar 2006). In the disturbed environments, it was found that silica and nitrogen concentration were positively affecting the density of alien species (Çinar et al. 2006).

The biomass of A. obtecta was mainly affected by temperature (ρ r=-0.51) and total phosphorus (ρ r=0.52) in winter; depth (ρ r=-0.52) and silt percentage in sediment (ρ r=0.43) in spring; depth (ρ r=-0.64), silica (ρ r=0.76) and silt percentage in sediment (ρ r=0.76) in summer; depth (ρ r=-0.82), total phosphorus (ρ r=0.82), total nitrogen (ρ r=0.70) and silica (ρ r=0.59) in fall. As overall seasonal data are concerned, the biomass of A. microplax was negatively affected by depth (ρ r=-0.53) and positively affected by silica (ρ r=0.43) and silt percentage in sediment (ρr=0.43).

The density of A. obtecta was positively correlated with that of Polychaeta (r=0.23) Crustacea (r=0.50), Mollusca (r=0.32) and Nemertini (r=0.04), but negatively correlated with that of other Echinodermata (r=- 0.24) and Sipuncula (r=-0.15). The biomass of A. microplax was positively correlated with that of Nemertini (r=0.26), Polychaeta (r=0.20), Crustacea (r=0.34), Mollusca (r=0.21), but negatively correlated with that of Sipuncula (r=-0.16) and other Echinodermata (r=-0.05). It seems that this species and other benthic groups benefit from inputs via the Seyhan River and no obvious competition was determined between A. obtecta and other species.

Figures

FIGURE 3. Seasonal variation of density and biomass of Amphiodia obtecta in Mersin Bay, southern Turkey, eastern Mediterranean Sea.

FIGURE 2. A – G, Amphiodia obtecta, SEM images. A, dorsal aspect; B, spiny marginal scales; C, distal radial spiny digits; D, ventral aspect; E, dorsal arm; F, ventral arm; G, tentacle scale. H, I, Ophiophragmus duplicatus Koehler, 1930, syntype, digital images. H, dorsal aspect, note the large marginal scales; I, ventral aspect. AS, adoral shield; DAP, dorsal arm plate; MS, marginal spines; OS, oral shield; RD, radial digit; RS, radial shield; TS, tentacle scale; VAP, ventral arm plate. Scale bars in millimetre.