Recent brachiopods from the Persian Gulf and their biogeographical significance

two brachiopod species Discradisca indica (dall, 1920) and Argyrotheca jacksoni cooper, 1973, together with Lingula sp., have been identified from the Persian gulf. these species, added to the two species Terebratulina retusa (linnaeus, 1758) and Megerlia truncata (linnaeus, 1767) previously identified by Jackson (1921), and Lingula anatina lamarck, 1819 by emig (1988) bring the total to 5 species for the region. the genera Discradisca and Argyrotheca are recorded for the first time from the Persian gulf. this fauna shows biogeographical affinities to the indian ocean and the Mediterranean faunas. the disjunct geographical distribution of Discradisca suggests this genus is a relict of an ancient tethyan fauna.

Scientia Marina 72(2) June 2008, 279-285, Barcelona (spain) issn: 0214-8358 introdUction recent brachiopods had not been recorded from the Persian (arabian) gulf until 1921, when J. Wilfrid Jackson described two species from four dead shells collected by F.W. townsend from dabai (dubai) on the west side of the ruus el Jibál peninsula, northwest coast of oman, depth unknown.the approximate position of this locality, which now lies in the United arab emirates, is shown in Figure 1. one specimen he identified as Terebratulina caputserpentis (now retusa) var.abbreviata Jackson and the other three as Mühlfeldtia (now Megerlia) truncata var.paucistriata Jackson.on the basis of these specimens Jackson equated the Persian gulf specimens with the typical lusitanian forms Terebratulina retusa (linnaeus) and Megerlia truncata (linnaeus) from the atlantic and Mediterranean and cit-ed them as additional evidence of a past connection between the atlantic and indian oceans by way of the Mediterranean.Unfortunately, none of the four specimens were figured by Jackson, although his descriptions of the two species are fairly detailed.the three Megerlia specimens (2 complete, one dorsal valve) are in the natural history Museum, london but we were unable to examine them, while the specimen of Terebratulina is not in either the natural history Museum or the Manchester Museum, where Jackson was based (s.l. long, pers. comm.; r. smith, pers. comm.) and is presumed to be missing.
the species Lingula anatina lamarck was mentioned by emig (1988) from a depth of 6-16 m in the Persian gulf but without any details of the exact locality.Undetermined Lingula was also found at several stations in the khor al Bazm and gulf of salwa (hughes clarke and keij, 1973).From the nearby gulf of oman an immature individual of Lingula was reported by Muir-Wood (1959).
this report describes and illustrates some of the recently-discovered Persian gulf specimens, from sediment samples kept in the Forschungsinstitut und naturmuseum senckenberg, Frankfurt, and from eberhard gischler's collection (institut für geowis-senschaften, J. W. goethe-Universität, Frankfurt), collected during expeditions over the last few years.

Material and Methods
Part of the investigated material comes from 6 shell-grit samples (Pg95-38-42, 44) collected by M. apel, U. Zajonz and a. Plaga around the karan and Jana islands (Fig. 1) during a german expedition in May 1995, and kept in the Molluscan section of the senckenberg Museum, Frankfurt.Brachiopods belonging to Lingula, Discradisca and Argyrotheca were sorted by one of us (MaB) during a visit to the Museum in autumn 2005.all these specimens are dead empty shells.
Most of the specimens of Discradisca indica come from a sediment sample (k119) from southern kuwait (Fig. 1) collected by e. gischler, using a lenz-type sampler operated from a small boat (see also gischler and lomando, 2005).all occurred in living position with soft parts preserved, and were attached to oyster shells.
the investigated specimens are housed in the senckenberg Museum, Frankfurt (sMF) and at the institute of Paleobiology, Warszawa (ZPal Bp.) Remarks. the material of only one immature specimen, 2.4 mm long and 1.4 mm wide, prevents any specific determination.however, this specimen belongs most probably to Lingula anatina already reported from the Persian gulf (emig, 1988).the specimens of Lingula collected in restricted environments in the khor al Bazm and gulf of salwa by hughes clarke and keij (1973)    Description.shell small (maximum length 4.1 mm) subcircular in outline, with margins often irregular.dorsal valve conical in profile with smooth apex, situated posteriorly, and ornamented by fine radial costae and numerous concentric growth lines.Ventral valve concave medially and slightly convex marginally.Pedicle region subcircular to heartshaped without ornamentation.rest of ventral valve ornamented by widely spaced, straight radial costellae.dorsal valve overlapping ventral valve.setae short in posterior and lateral regions but can be very long in anterior part (Fig. 2F).
Remarks. the name Discradisca was proposed by stenzel (1964) as a subgenus of Discinisca to distinguish those species having radial costae on the dorsal valve from those lacking costae.later cooper (1977) elevated Discradisca to generic rank. in the modern diagnosis Discradisca is described as "similar to Discinisca but with wide, transversely suboval pedicle track…" (holmer and Popov, 2000).the following species: D. antillarum (d'orbigny, 1845), D. cumingi (Broderip, 1833), D. strigata (Broderip, 1834), D. stella (gould, 1862), D. sparselineata (dall, 1920) and D. indica were transferred to Discradisca (see emig 1997; and http://paleopolis.rediris.es/Brachnet/class/discinidae/discradisca.html).D. indica was originally described from off Bombay and ceylon by dall (1920) and some of his types were figured by cooper (1973).Jackson and stiasny (1937) erected a new species, Discinisca keiensis for specimens collected at the depth of 90 m from off the kei islands, indonesia.We consider the latter species and D. indica as synonyms.in the ornamentation of dorsal and ventral valves D. keiensis is consistent with D. indica as indicated by Jackson and stiasny (1937).the difference, according to them, is in the longevity of setae. in the description presented by dall (1920) D. indica has short setae, and the specimens from indonesia possess long setae. in the studied material there are specimens with both short and very long setae, so this feature cannot be used to distinguish those two species.
the investigated specimens agree well with those hitherto described (dall, 1920;cooper, 1973;Jackson and stiasny, 1937) Ventral valve interior with short wide teeth lying parallel to hinge line.Pedicle collar well developed, supported by median septum that extends to about 2/3 of the length.anteriorly to the septum 3 shallow, ovoid depressions accommodate serrated crest of dorsal septum.dorsal valve interior with elongate sockets parallel to hinge line and short but high inner socket ridges.cardinal process prominent.crura thick, very short; crural processes massive, long directed medianly.descending branches extend down to unite with valve floor and emerge to join the median septum.Median septum triangular in profile, high with 3-4 serrations.Muscle scars marked as suboval depressions.
Remarks. this species was erected by cooper in 1973 based on one specimen, the holotype (UsnM 550432), from a shallow reef cave at ras Muhammad, southernmost sinai Peninsula, red sea.(it should be noted that cooper's measurements (1973, p. 17) of the holotype are incorrectly inflated by a factor of about two (d.levin, pers.comm.)). the species has since been identified from other areas in the red sea by logan et al. (2008), particularly the gulf of aqaba and around Port sudan.
in size, outline and ornamentation the investigated specimens resemble A. cuneata (risso, 1826), the species occurring in the Mediterranean and western atlantic (Brunton and curry, 1979;logan, 1979, 1993;logan et al., 2004;Álvarez and emig, 2005), but they differ in lacking a pink-red wash between the costae.in outline and ornamentation the specimens from the Persian gulf also display similarities to the specimen from southern africa described by hiller (1994a) as Argyrotheca sp. which may be a young representative of A. jacksoni.discUssion two brachiopod species Discradisca indica (dall, 1920) and Argyrotheca jacksoni cooper, 1973, together with Lingula sp., have been recognised in the material from the Persian gulf, collected during two german expeditions.these species, added to the two species Terebratulina retusa (linnaeus, 1758) and Megerlia truncata (linnaeus, 1767) previously identified by Jackson (1921), and Lingula anatina lamarck, 1819 by emig (1988) bring the total to 5 species known for this region.the genera Discradisca and Argyrotheca are recorded for the first time from the Persian gulf.
the Persian gulf is an epicontinental sea with shallow waters (maximum depth of 100 m), a very wide temperature range (13-52ºc), and high salinity (40-70) (Purser, 1973;emig, 1988, table 2;gischler and lomando, 2005).these conditions might be responsible for the low biodiversity of the brachiopod fauna when compared with brachiopods from the adjacent indian ocean (Muir-Wood, 1959;cooper, 1973, 1981a;hiller, 1986, 1994a, b;Zezina, 1987;logan et al., 2008).other peculiarities in the Persian gulf organisms have been observed among molluscs; all large species of indo-Pacific molluscs are absent (hughes clarke and keij, 1973).likewise, coral diversity in the gulf is low as compared to the indian ocean, and temperature tolerant taxa predominate, including one endemic species (Veron, 1995).the western parts of the Persian gulf have widespread areas of rock bottom which is covered by a thin layer (5-20 cm) of unconsolidated bioclastic sediment with a hard surface being exposed commonly between irregular patches of sand. the deeper iranian parts of the basin are generally muddy (Purser, 1973).
Biogeographically this fauna shows affinities to those of the indian ocean and the Mediterranean.although very rare in the investigated material Lingula is a widely distributed genus in the tropical and subtropical areas of the indian ocean (emig, 1997) but not known in the Mediterranean.Discradisca indica seems to be restricted to the indian ocean (cooper, 1973;Jackson and stiasny, 1937).Moreover, neither Discradisca nor any discinids are known from the Mediterranean, though a discinid brachiopod was recently noted from the red sea (logan et al., 2008).it is worth mentioning that a related species, D. antillarum (d'orbigny, 1845) occurs in the caribbean region (cooper, 1977).such disjunct geographical distribution of Discradisca suggests that the fauna is a relict of an ancient tethyan fauna.new findings and/or re-examination of the tertiary material in the Mediterranean region may fill this gap.
Argyrotheca jacksoni has so far been noted only from the red sea (cooper, 1973; logan et al., 2008) and the Persian gulf.however, Argyrotheca sp. from southern africa (hiller, 1994a) may appear to belong to A. jacksoni when more material becomes available.also, similarities of A. jacksoni to the Mediterranean and atlantic form A. cuneata suggest affinities of those species.
two species reported by Jackson (1921), i.e.Terebratulina retusa and Megerlia truncata, are very common in the Mediterranean and western atlantic (Brunton and curry, 1979;logan, 1979, 1993;cooper, 1981b;logan et al., 2004;Álvarez and emig, 2005).M. truncata (incorrectedly designated as M. gigantea; see also Bitner, 2007) was described from the area south of Madagascar, indian ocean (cooper, 1981a).acknoWledgeMents drs ronald Janssen and Joachim scholz (both senckenberg Museum, Frankfurt) supplied the samples from karan and Jana islands.dr.sarah long, natural history Museum, london and rebecca smith, Manchester Museum provided information on the whereabouts of Jackson's specimens, while daniel levin, national Museum of natural history, Washington dc supplied information on the holotype of Argyrotheca jacksoni.Prof. Fernando Álvarez (Universidad de oviedo, oviedo) and dr.christian c. emig (Marseille) are gratefully thanked for their critical reading of the manuscript.F. Álvarez also helped us with the spanish abstract.We thank Mrs. aleksandra hołda-Michalska (institute of Paleobiology, Warszawa) for help in the preparation of Figure 1. the seM micrographs were taken in the seM laboratory of the institute of Paleobiology (Warszawa) using a Philips Xl-20 scanning microscope.reFerences

Fig. 1 .
Fig. 1. -Map of the Persian gulf, showing the location of the samples where brachiopods were found; WJ -approximate position of Jackson's collecting locality.