Holoplanktonic Mollusca (Gastropoda) from the gulf of Aqaba, Red Sea and gulf of Aden (Late holocene-recent)

2007·32.4 MB·English

by  Arie W Janssen

THE VELIGER
(& CMS, Inc., 2006
The Veliger49(3):140-195 (October 1, 2007)
Holoplanktonic Mollusca (Gastropoda) from the Gulf of Aqaba, Red Sea
and Gulf of Aden (Late Holocene-Recent)
ARIE W. JANSSEN
Nationaal Natuurhistorisch Museum Naturalis (Palaeontology Department), P.O. Box 9517, 2300 RA Leiden,
XWK
The Netherlands, currently: 12, Triq taFHamrija, Xewkija 9033, Gozo, Malta; [email protected]
Abstract. Fifteen bottom samples, two from the GulfofAqaba, twelve from the Red Sea proper and one from
the Gulf of Aden, were analysed qualitatively for holoplanktic Mollusca. The basic material yielded 43 taxa (14
Heteropoda, 1 Janthinidae, 20 Euthecosomata, 4 Pseudothecosomata and 4 Gymnosomata). Eighteen species are
distributed all overthe Red Sea (9 ofthem also in the GulfofAqaba), another 16arepresent only in the southeastern
part of the Red Sea, and 10 species were exclusively found in the Gulf of Aden sample. The presence of several
further species in the Red Sea (1 heteropod, 4janthinids, 1 thecosome, 2 pseudothecosomes, 3 gymnosomes and 1
nudibranch) is assumed on the basis ofliterature data or unpublished observations. Northward increasing salinity is
considered to be the main cause for the differences in occurrence. Although all material studied originates from
bottom samples, all species are considered to form pazrt ofthe living holoplanktonic mollusc stock,judging on the
presence ofwell-preserved specimens. Only epi- and mesopelagic specieswerefound. Bathypelagic species areabsent.
Predominantly based on SEM-imaging additional data on morphology of especially the Heteropoda is given.
Taxonomical and/or nomenclatural notes are added for several species.
Key Words: Holoplanktonic Mollusca, Holocene, distribution, systematics. GulfofAqaba, Red Sea, GulfofAden.
INTRODUCTION lack of food explain the absence of Red Sea
bathypelagic species (Weikert, 1982; Hemleben et al.,
TheRed Sea (al-Bahr al-Ahmar, in Arabic language) is 1996).
the world's northernmost tropical sea, situated in Main currents in the Red Sea are influenced by
between the NE part ofthe African continent and the monsoons (Baars et al., 1998). As a result ofthe wind
Arabic peninsula. Its length is approximately 1900 km, system, surface currents flow from the Indian Ocean
NW
maximum width is around 350 km. In the the Red into the Red Sea during winter and the other way
Sea is subdivided by the Sinai Peninsula into two around in summer. Surface and nutrient-rich mid-level
bights, the western, relatively shallow (—75 m) Gulfof currents flow in opposite direction, resulting in an
Suez, leading through the Suez Canal to the Mediter- outflow of nutrients from the Red Sea during winter
ranean Sea, and the eastern, much deeper (—1850 m) and its enrichment during summer (most data from
Gulf of Aqaba [also referred to as Gulf of E(i)lat]. In Siddall et al., 2004; and Saudi Geological Survey,
the SE the relatively narrow (—35 km) Bab el-Mandab 2006). Sediment supply into the Red Sea is mainly by
Strait connects the Red Sea with the GulfofAden and desert dust, transported by strong winds (NASA,
the Arabian Sea, which form part ofthe Indian Ocean. 2006).
Sea depth of the Red Sea proper amounts to over Geologically theRed Seais a young(Oligo-Miocene)
2400 m in thecentral part, butis only —137m near the structure, originated as part of the Great Rift System,
southern passage to the Gulf of Aden (Hanish Sill as a result of which the Arabian peninsula separated
shallows). An isolated position and high temperature from the African mainland. The Red Sea was never
within tropical climate, with an average surface water part ofthe Tethyan Ocean.
temperature in the north of26°C, in the south of30°C An initially existing connection with the Mediterra-
(butrapidlydecreasingto c. 22°Cat a 'thermohalocline' nean was lost in the Middle Miocene (Boswerth et al.,
m
at 100 sea depth, Weikert, 1982, fig. 2), causing high 2005, fig. 11). During the Pliocene the connection with
evaporation, and lack of discharging rivers cause the Mediterranean was restored. Sea level fall during
a hypersaline environment (salinity northward to over the Pleistocene isolated the Red Sea from the
40%o), considerably higher than that in the Gulf of Mediterranean as well as from the Indian Ocean,
Aden and the Indian Ocean (approximately 35%o). afterwards only the southern connection was restored.
High temperature and salinity in the intermediatewater During the last glaciation maximum, holoplanktonic
column, together with reduced oxygen contents and organisms (nannoplankton, foraminifera and molluscs.
A. W. Janssen, 2006 Page 141
apart from the pteropod Creseis 'acicula' = C clava) H shell height.
W
did not survive the increasing salinity (>55%o) in the shell width.
Gulf of Aqaba and the northern part of the Red Sea
(Almogi-Labin, 1982 andinlitt., 2006). Afterwards, the MATERIALS AND METHODS
one and only source of species immigrating into the
Red Sea is the southern connection with the Indian Fifteen bottom samples, predominantly from deep
Ocean, through the Bab-el-Mandab Strait. It seems water (range 56-2120 m) and reasonably well-spread
that the Gulf of Aqaba was continuously connected over the entire length ofthe Red Sea (Text-fig. 1), were
during the last 150 kA with the Red Sea and the latter analysed qualitatively for holoplanktonic Mollusca.
with the GulfofAden (Reiss et al., 1984). Eight of these were donated by Dr. Frank P.
At present, immigration ofmollusc species from the Wesselingh, who joined a Meteor Red Sea and Gulf
Mediterranean through the Suez Canal, especially for ofAden collecting trip in 1995. Samples from the same
holoplanktonic molluscs, can be neglected, as the main trip were described and analysed by von Riitzen-
migration stream seemsto befromthe Red Sea into the Kositzkau (1999), who gave extensive additional in-
Mediterranean (so-called Lessepsian species). Also, formation, especially on the benthic mollusc material.
holoplanktonicmolluscsaremost probablynotcapable A further series of5 Red Sea samples, collected in 1981
ofsurviving transportation through the shallow canal. (1 sample Valdivia 29) and 1987 (4 samples Meteor 5),
Thus, the Red Sea holoplanktonic mollusc faunacan was donated by Dr. Ronald Janssen (SMF) in 1996.
be considered a young (holocene) assemblage, origi- Two samples from the Gulf of Aqaba were made
nated completely by immigration from Indian Ocean available by Dr. Ahuva Almogi-Labin (Geological
stock. Survey of Israel, Jerusalem, Israel). Locality data of
Theextant overall Red Sea mollusc fauna is very rich these samples are summarised in Table 1. Sample
and diverse in species, due to the presence of a wide locations are given in Text-fig. 1.
variety of environments (as e.g., a complex reef Most samples were collected by means of box cores
ecosystem). Dekker & Orlin (2000) listed no less than that take a bottom sample to a depth of 0.50 m or
1765 species by name and referred to a large number of (usually) less of the sea bottom sediments. The age of
as yet unidentified further species. Holoplanktonic such box core samples, as discussed by von Riitzen-
Mollusca from the Red Sea have been referred to in Kositzkau (1999, p. 49), is no more than maximally
a number of papers, but an up to date overview or ~6 kA (usually less) and can therefore without
systematic revision is not available yet from this area. exception be indicated as 'Late Holocene to Recent.'
The recent inventory of Dekker & Orlin includes Such samples, ofcourse, give no information whatso-
a number ofholoplanktonics (Heteropoda, Atlantidae: ever on seasonal fluctuations in the holoplanktonic
5 species; Janthinidae: 5 species; Thecosomata, Lima- mollusc stock. They just indicate which species
cinidae: 3 species; Cavoliniidae: 9 species; Desmopte- occurred at the sampling sites during the last few
ridae: 1 species; Gymnosomata, Pneumodermatidae: 1 thousand years. As quite fresh specimens were present
species). It should be realised, however, that these for all species, it may be safely assumed that they do
references are predominantly concentrated from scat- occur in the extant assemblages, occurring in the water
tered literature resources and are not necessarily based columns over the sampled sites.
on actual observations ofthese authors themselves. Samples taken and donated by Frank Wesselingh
were washed aboard ship on a 120 \im mesh and
Abbreviations: included small sediment samples. The Senckenberg
samples were obviously sieved on a 500 |im mesh and
NNM
NationaalNatuurhistorisch MuseumNat- therefore the smallest species and specimens are absent
uralis, Leiden, The Netherlands. (as e.g., Gymnosomata larval shells). The Gulf of
RGM
Nationaal Natuurhistorisch Museum Na- Aqaba samples were received as picked material. One
turalis, Leiden, TheNetherlands, Palaeon- ofthem contained only specimens >1 mm.
tology Department; formerly Rijksmu- All samples were analysed qualitatively after being
seum van Geologic en Mineralogie. separated in sieving fractions of 2000, 1000, 500, 300,
SMF Senckenberg Museum, Frankfurt am 200 and 100 |im. Isolating the smallest specimens
Main, Germany. (under 200 |j,m) was frequently hampered by the
ZMA Instituut voor Systematiek & Populatie- presence of overwhelming numbers of (mainly plank-
biologie, Zoologisch Museum, University tonic) Foraminifera, which madeconcentratingthe tiny
of Amsterdam, Department of Malacol- mollusc specimens laborious and very time-consuming.
ogy. Therefore the coarser three or four fractions usually
A
long diameter ofatlantid species (Janssen, were inspected completely, the finer ones only partially,
in press, text-fig. 6). until no further species were found. This method gives
Page 142 The Veliger, Vol. 49, No. 3
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Figure 1. Location ofsamples (compare Table 1).
A. W. Janssen, 2006 Page 143
Table
1
NW
Sample data (localities arranged from to SE, compare Text-fig. 1).
Nr Locality Coordinates Leg. Station Sea depth Date
1 GulfofAqaba offElat city unknown unknown 320 m unknown
2 GulfofAqaba Geziret Fara'oun 29"30'N;? E unknown unknown 380 m unknown
3 Red Sea 27^41'N; 34"35'E FS Meteor 31/2 unknown 1040 m 00.02.1995
4 Red Sea 26 44.97'N; 35^02.02'E Valdivia 29 746 KG 873 1377 m 09.03.1981
5 Red Sea 26=14.477'N; 35°21.033'E FS Meteor 31/2 DRZ dredge 1146 m 00.02.1995
6 Red Sea 22=35,2'-22°24,8'N to FS Meteor 5 85 772-779 m 07.02.1987
36=45.9'-36°46.2'E
7 Red Sea 20°57.7'N; 37=25.7'E FS Meteor 31/2 GKG 93-3 685 m 23.02.1995
8 Red Sea 20"57.5'N; 37=22.1'E FS Meteor 31/2 GKG 93-10 56 m 23.02.1995
9 Red Sea 19-35.0'N; 38=40.0'E FS Meteor 5 183 Ku 2120-2119 m 28.02.1987
10 Red Sea 19=33.2'N; 37=24.5'E FS Meteor 5 196 KG 757 m 28.02.1987
11 Red Sea 19=06.3'N; 38=36.6'E FS Meteor 31/2 GKG 100-1 393 m 27.02.1995
12 Red Sea 18=32.9'N; 38°59.4'E FS Meteor 5 unknown 431 m 23.02.1987
13 Red Sea 17°21.7'N;40°01.3'E FS Meteor 31/2 MC 101-1 475 m 28.02.1995
14 Red Sea 15=33.0'N; 41=41.1'E FS Meteor 31/2 MC 102-1 583 m 28.02.1995
15 GulfofAden 12=22.8'N; 44=31.5'E FS Meteor 31/2 GKG 105-3 321 m 04.04.1995
only scant information on the relative abundancy of Holoplanktonicmolluscs (heteropods,janthinidsand
species, the smaller forms always being underrepre- pteropods),concentratedfromthe 15 availablesamples,
sented, but the numbers of specimens included in the are specified in Table 2. Most species, especially so the
collection (as given in Table 2) give sufficient clue in pteropods, are well-known and sufficiently described in
this respect. the existing literature, but notes on distribution,
Most material is included in the RGM collection of systematics and/or morphology are added below.
fossil holoplanktonic molluscs, sample 2 is housed in All SEM-images were made by the author, using the
the Geological Survey of Israel. Registration numbers Jeol JSM-6480 LV instrument of NNM. The photo-
are: sample 1: RGM 540.338-540.345; sample 3: RGM graphs ofPlates 20-21 were kindly made by Mr Frank
540.141-540.162; sample 4: RGM 540.163-540.190; P. Wesselingh, with a Nikon DS-SM camera.
RGM RGM
sample 5: 540.191-540.206; sample 6:
RGM
517.980-518.000 and 540.135-540.140; sample 7: SYSTEMATIC PART
RGM
539.867-539.899, 540.207; sample 8: 539.900-
539.915; sample 9: RGM 540.080-540.111; sample 10: As synonyms for most taxa only the first valid
RGM 540.112-540134; sample 11: RGM 540.021- description is given, as well as a more recent reference
540.054; sample 12: RGM 540.055-540.079; sample 13: to a paper in which the taxon is described and well-
RGM 539.960-539.993; sample 14: RGM 539.994- illustrated. Extensive synonymy is to be found usually
540.020; sample 15: RGM 539.916-539.959. All illus- in van der Spoel (1967, 1976). For the Atlantidae some
trated specimens separated from these samples are more attention is paid to the morphology ofjuvenile
RGM specimens, especially also by SEM-images. In particu-
registered vv'ith nrs 540.347-540.464.
Benthic mollusc specimens were transferred to Mr. lar their protoconchs are still insufficiently known,
Robert G. Moolenbeek (Zodlogisch Museum, Uni- although in most cases indispensable for the recogni-
versiteit van Amsterdam, dept. of Malacology, Am- tion of the species.
sterdam). Teleostei otoliths found in many samples are Phylum MoUusca Linne, 1758
in the collection of Mr. Kristiaan Hoedemakers Class Gastropoda Cuvier, 1797
—
(Mortsel, Belgium). Note ClassificationofGastropoda,especiallyabove
Preservation of the planktonic mollusc specimens the rank of superfamily, is in a 'currently very active
varies from crystal clear to opaque or completely white phaseofreevaluation,'asBouchet&Rocroi(2005, p. 4)
because of recrystallisation or early stages of dissolu- putit.Topreventtheimpressionthatthepresentauthor
tion. In the four northwesternmost Red Sea samples hasapronounced opinion on highterclassification only
(nrs 3-6), however, part of the material, sometimes ranks ofsuperfamily and lower are given here.
even more than half the number of specimens, shows
distinct dissolution ofthe aragonite and specimens are Superfamily Pterotracheoidea Rafinesque. 1814 [=
preserved as internal calcitic moulds, with or without Heteropoda Lamarck, 1812 (partim); Carinarioidea
their shells preserved. de Blainville, 1818]
Page 144 The Veliger, Vol. 49, No. 3
Table 2
Holoplanktonic mollusc distribution in the GulfofAqaba (samples 1-2), Red Sea (samples 3-14) and GulfofAden
(sample 15). Numbers ofspecimens per sample locality (m = >50 specimens).
Sample
Species 10 11 12 13 14 15
Heteropoda —__— _—_—_—_—_—__— __ — —
Atlanta echinogyra Richter, 1972 4 1 32 — — 10 10
Atlantafrontieri Richter, 1993 — — m m m10 m —4 14
Atlantafusca Souleyet, 1852 — — 23 5 21 6 50 26 29 3
AAttllaannttaa hienlcilciinnatoaideSsouSloeuyleety,et1,8512852 —6 —10m—34 —mm —m6 —m5 —4m7 —135 3m9 m13 mm 4m0 mmm m150 2106
m
AAttllaannttaa loleisguoegwyiraSoTuelsecyhe,t,11980562 —— —— —48 m —17 30 m —10 3mm9 m3163 mm m3m5 mm m—m1190
Atlantaplana Richter, 1972 —__— __1 __12 _m _______
Atlanta tiiniculala d'Orbigny, 1836 3 13 1 1 39 1 10 2 23 26 20 6 33
Oxygyrus kerauclreni (Lesueur, 1817) ______________ 1
Carinariidae sp. 1 __________
Carinariidae sp. 2 — — 1
Carinariidae sp. 3 m2 4m5 mm19
Pterotrachea coronata Niebuhr, 1775 — — — — Re—d Sea—, fromm l5iterature dat—a
Firoloida demurestia Lesueur, 1817 6
Janthinidae
Janthina exigiia Lamarck, 1816 GulfofAqaba, from literature data
Janthinajantliina L., 1758 Red Sea, from literature data
Janthina umbilicata d'Orbigny, 1840 R—ed S—ea, f—rom li7tera—ture da—ta — — — 18— —
Janthina sp. 1 4 8
Recliizia erythraea Jickeli, 1882 mmmRemd Sema, frmom lmiteratmure dmata mmmmm
Thecosomata, Euthecosomata
Heliconoides inflata (d'Orbigny, 1836) —5 — — —
LLiimmaacciinnaa bturlocihmiofiodremsis(d('dO'rObribgingyn,y,1813863)6) —— —117 —2m4 —— —m18 —7 mm m 25m490 2m68 mmm m25550 m94m0m6368mmm
Creseis chierchiae (Boas, 1886) — — mmmm13mm5 mmm14 mmmm14
f constricta Chen & Be, 1964 7 16 1 30
Creseis clava (Rang, 1828) —19 —371 mm— m—m—mm70—35 mmmmmmlm 2mm
Creseis conica Eschscholtz, 1829 1 30 28 50 25
HCyraesleoicsylviisrgsutlraia(tRaa(nRga,ng1,82188)28) _—5 _— _m _— _7 _li_m _— _19_17_m_m_m_22 m
Styliola subula (Quoy & Gaimard, 1827) — —21— m— m—m—m—m—m—m—mm— mmmm3
Clio (Bellardiclio) ciispidata (Bosc, 1802) _______^_ ___liter_ature_data 29
Clio (Clio) convexa cyphosa Rampal, 2002 24 —
Clio (Clio) pyramidata f. lanceolata 1
(Lesueur, 1813)
m8—
Cavoliniaglobulosa (Gray, 1850) __— ___— ___sout_he1rn1_R2ed_Sea1,_l5iterma_turme_d5ata
Cavolinia uncinata (Rang, 1829) 7 3 12 6
DDiiaaccaavvoolliinniiaafalnegxuilpaetsav(aSnoudleeryeStp,oe1l85e2t)al., _1 _— _1 _3 _— _28 _14 _— _m _6 _36_m_16_11 m1
1993 ____________
Diacavolinia longirostris (Blainville, 1821) m34mmmmm31m36mmmm_m9
Diacavolinia sp. _____________1 _ 7
Diacria erythra van der Spoel, 1971 ____________
Diacria qiiadridentata (Blainville, 1821) _ 4
Diacria trispinosa (Blainville, 1821) — — m — — — — m m m 3p
Cavoliniidae sp. 3 3 24 13 13
Thecosomata, Pseudothecosomata
Cymbulia sibogae Tesch, 1903 ____ ______ southern R—ed Sea, lit—erature data
Cymbulia sp. 1 3 40 14 2 —1 — 27 — 40 —1
Cymbulia sp. 2 19 2 1 3
Desmopteruspapilio Chun, 1889 southern Red Sea, literature data
PeraclismoluccensisTesch, 1903
Peraclis reticulata (d'Orbigny, 1836) m m m m 40 40 m 31 15
—
A. W. Janssen, 2006 Page 145
Table 2
Continued.
Sample
Species 7 8 10 11 12 13 14 15
Gymnosomata
Gymnosomata sp. 43 36 7
Gymnosomata sp. 1
Gymnosomata sp. 2
Gymnosomata sp. 1
Gymnosomata Typ I sensu Kunz, 1996 Red Sea, literature data
Gymnosomata Typ Ila sensu Kunz, 1996 Red Sea, literature data
Gymnosomata Typ lib sensu Kunz, 1996 Red Sea, literature data
Nudibranchia
Glaucus atlanticus Forster, 1977 southern Red Sea, K. Bandel (in litt.)
incertae sedis — — m9___— _m _— _m_m_
veliger larvae? 10 9 15
'beaked larva' sensu van der Spoel & 1
Newman, 1990
Family Atlantidae Rang, 1829 subsutural zone, on which further spiral lirae may be
—
Notes Identification ofAtlantidae species solely on present. Sometimes the shell wall is slightly angular at
shell characteristics remains hazardous. In several this place, giving the whorl a shouldered appearance. I
A
papers the importance of soft part anatomy (eyes, indicate this spiral here as 'shoulder spiral." further
radula, operculum)isstressedandconsideredofutmost spiral is often seen lower on the whorl, separating
importance for the distinction of species, especially a middle peripheral and a lower umbilical zone. This
within the so-called 'species groups' [note the very spiral developes on the teleoconch whorl into the
differentmeaningofthis wording, contrary to the same flange-like keel, and is therefore here called the "keel
termused in the ICZN Code (1999)]. Still, careful study spiral.' In some species, however, one or both are
ofespeciallyjuvenile specimens (protoconchs-1 and -2) entirely absent.
enables recognition of the species beyond doubt in Genus Atlanta Lesueur, 1817
most instances, albeit that application of SEM-images Type species Atlantaperoni Lesueur, 1817 (Recent).
usually is requisite. Specimens with missing apical
whorls (which occur frequently in bottom sample Atlanta echinogyra Richter, 1972
material) in most cases cannot be identified with any
degree ofcertainty. PI. 1, figs. 1-3; PI. 2, figs. 1, 2
For every species in this family one of the larger 1972 Atlanta echinogyra n. sp.; Richter, p. 90, figs. 3,
specimens is measured, giving the shell's long diameter 5, 7. —
(A), the shell height (H) and the whorl formula, as 1987 Atlanta echinogyra Richter 1972 Richter,
developed by Tokioka (1955), see also Janssen (in
p. 182, pi. 1, figs. 5, 6; pi. 2, fig. 14; pi. 4, figs. 31,
press, text-fig. 6). 32; pi. 5, figs. 36 (as A. echninogyra, sic\), 42; pi. 6,
Occurrences and distributions of heteropod species fig. 47; pi.—7, fig. 57.
in the Red Sea are still largely unknown, as is clear Discussion This species was only found in small
from van der Spoel's (1976) distribution charts. The numbers in the southeastern part ofthe Red Sea and in
one and only heteropod species mentioned by him for the Gulf of Aden (samples 9-15). Apparently it is
the Red Sea is Pterotrachea coronata Niebuhr, 1775. sensitive for increasing salinity and therefore does not
Larval shells of that species, or even genus, were not reach further to the NW.
recognised during the present study. This species was The early protoconch whorls are ornamented with
also listed by Dekker & Orlin (2000, p. 24), probably a variable number of spirals. The shoulder spiral is
based on van der Spoel (1976). distinct, but may be partly covered by the next whorl.
In many atlantid species two main spirals can be Frequently an interrupted line ofslightly curved spiral
distinguished on protoconch-2. One is found in the segments is seen just below the shoulder spiral (PI. 1,
upper half of the whorls, situated at or near the place fig. 2a, b). The peripheral zone of the protoconch
where the next whorl will attach. It separates an upper. whorls is covered with regularly spaced spiral lirae
—
Page 146 The Veliger, Vol. 49, No. 3
(PI. 1, fig. 2a; PI. 2, fig. 1). The keel spiral is weak or Discussion A. fusca is an easily recognisable
indicated as a slight angularity on early whorls, species, present in almost all samples of the Red Sea
developing more strongly on later whorls. The base and the Gulf of Aden (except samples 1-2 and 14),
ofthe adult shell (PI. 1, fig. 4) shows very fine growth- sometimes in considerable numbers, even in the
lines only. The complete protoconch, nucleus included, northwesternmost samples ofthe Red Sea. It is absent,
is covered with an extremely fine granulation (visible at however, in the Gulf of Aqaba material (but was
magnification c. X 2k, PI. 1, figs. 2b, 3b). The spiral recorded from that area by Yaron, 1977: 75). It co-
ornamentation on the subsutural whorl part of the occurs with the less common second species from the
protoconch is more weakly developed than in the same species group, A. turriculata, in all samples. Only
specimen illustrated by Seapy (1990, fig. 8E-H). in the Gulf ofAden (sample 15) A. turriculata is more
Measurements ofa large specimen (sample 15): A = frequent than the present species.
1.72 mm, H = 0.57 mm, whorl formula 1:0.29:0.17. The protoconch is relatively high conical, initially
even clearly highter than wide (PL 2, fig. 5a). The
Atlanta frontieri Richter, 1993
whorls are covered with an irregular spiral ornament
PI. 11, figs. 1-3 (PL 3, fig. 2a), in between which the shoulder and keel
spirals sometimes are difficult to distinguish. Especially
1993 Atlantafrontieri n.sp. Richter, p. 192, pi. 1, fig. on the early whorls the spirals show a zigzag-structure
3; pi. 2. fig—. 7, pi. 3, fig. 9, pi. 4, figs. 18, 21. (PL 3, fig. la). In adult specimens the boundary
Discussion Onlyjuvenile specimens were found, in between proto- and teleoconch is distinct and situated
the southeasternmost part ofthe Red Sea and the Gulf at the place where the spiral ornament disappears
ofAden (samples 11, 14 and 15). Richter recorded the (PL 2, figs. 3b, 4b). In fully grown specimens the spiral
species from the Indian and western Pacific oceans. ornamentis still visible on theumbiHcal side ofthe shell
The protoconch has four whorls, together forming (PL 2, fig. 4a, b). The nucleus ofthe protoconch (PL 2,
a low cone with concave tangents (PI. 11, fig. 2a). The fig. 5b; PL 3, fig. 2b)and theearly whorls (PL 3, fig. lb)
subsutural zone has a single spiraljust below the suture are covered with an extremely fine granulation
on the earliest whorls (PI. 11, figs, lb, 2b, 3), and is (magnification c. X 2k). The ultimate one third ofthe
separated by a well-developed shoulder spiral, shaped teleoconch separates from the penultimate whorl. Most
as a lamella (PL 11, fig. 3), and situated at orjust above specimens retain their reddish-brown colour.
the place where the next whorfs suture will attach. In Measurements ofa large specimen (sample 12): A =
juvenile specimens it is visible that the shell wall is 2.16 mm, H = 1.00 mm, whorl formula 1:0.32:0.14.
slightly angular at the place of the shoulder spiral
(PI. 11, fig. 2a). The peripheral zone is slightly convex Atlanta helicinoides Souleyet, 1852
and procuredwith very thin, regularlydistributed spiral
lirae in the smallest specimens. The keel spiral is clear, PI. 3, figs. 4-6; PI. 4, figs. 1-5
but does not cause an angularity of the shell wall. In
just one specimen it can be seen that the whorl 1852 Atlanta helicinoides, nobis; Souleyet, p. 384, pi.
expanding rapidly is the fifth (PI. 11, fig. la). These 20, figs. 23-30. —
characteristics agree with A. frontieri, even if insuffi- 1987 Atlanta helicinoides Souleyet 1852 Richter,
cient material is available. Also in this species the p. 179, pi. 1, figs. 5, 6; pi. 2, figs. 15, 16; pi. 4, figs.
nucleus of the protoconch is very finely granulated 31, 32; pi. 5. figs. 33, 40; pL 6, figs. 43, 44, 51, 52, 54;
(PI. 11, fig. 2c). pi. 7, figs. —58-60.
Measurements of the largest (but still juvenile) Discussion Specimens of this species were isolated
specimen: A = 1.22 mm, H = 0.56 mm (shell height from all Red Sea and Gulf of Aden samples (but not
in this specimen is not, as usual, the height of the from the Gulf of Aqaba), albeit sometimes in rather
aperture, as the protoconch's apex still reaches beyond low numbers independent from the sampling position.
the height of the aperture), whorl formula = Recorded alivefrom Red Sea planktonhaulsby Bandel
1:0.38:0.22, which also indicates that the shell is still et al. (1997, p. 162, fig. 4G-H).
juvenile, with just half a teleoconch whorl present. Most of the specimens still possess their original
brownish colour, strongest in the larval shell part and
Atlantafusca Souleyet, 1852
on the keel basis. The protoconch has a regular spiral
PI. 2, figs. 3-5; PL 3, figs. 1-3 ornament all over the height of the whorl. Above the
shoulder spiral, which usually is clearly recognisabe
1852 Atlanta fusca, nobis; Souleyet, p. 389, pi. 21, (but covered by the suture of the next whorl), the
figs. 15-29. — ornament may be slightly weaker. The keel spiral is
1990 Atlanta fusca Souleyet, 1852. Seapy, p. 123, developed as a slight angularity around the base ofthe
figs. 6G, lOA-D. juvenile shell (PL 4, figs, la, 2) and becomes only more
A. W. Janssen, 2006 Page 147
significant after tlie boundary with the teleoconch. The scribed by Richter (1990, p. 261), occurring in the
spiral ornament of the shell's base is visible on the related species A. inclinata and A. tokiokai van der
umbilical side of adult specimens (PI. 3, fig. 6). The Spoel & Troost, 1972, could be observed in several
nucleus and early protoconch whorls are covered with fresh specimens with the light microscope, but is of
an extremely fine granulation (PI. 4, figs, lb, 4b, c). course invisible in a SEM-image. Dissolution of inner
Very characteristic in the present material is the shell wall parts, also characteristic for these two species
strikingly low keel (PI. 3, fig. 5) of adult specimens, (Richter, 1990, pi. 3, figs. 21, 22), could only be seen in
distinctly lower than in the specimen illustrated by some specimens of which protoconch whorls were
Richter (1987, pi. 1, fig. 5) or even Seapy (1990, fig. broken, as most specimens are insufficiently trans-
HE) and agreeing better with van der SpoeFs (1976, parent or filled with matrix.
fig. 140a, b) illustration. In several well-preserved Red Measurements of large specimen (sample 5): A =
Sea specimens this low keel shows short radial folds 6.64 mm, H = 2.16 mm, whorl formula 1:0.31:0.07.
directed backward, whereas in van der Spoel's drawing
these folds are perpendicular on the shell's periphery. Atlanta lesueiiri Souleyet, 1852
Richter (1987), among others, stressed the resem-
blance ofAtlanta inflata Souleyet, 1852 and the present PL 5, figs. 6, 7; PL 6, figs. 1-3
species. Still, the differences in height/width-propor-
tions ofjuvenile shells (compare Richter, 1990, pi. 5, 1852 Atlanta Lesueurii, nobis; Souleyet, p. 380. pi. 20,
figs. 33, 34 and 37, 38) are significant and cannot be figs. 1-8. —
overlooked. Also the adult keel is much wider in A. 1990 Atlanta lesueiiri Souleyet, 1852 Seapy, p. 118,
inflata (see Seapy, 1990, fig. 11A). This latter species, figs. 5B, 6A—, 7A-D.
however, could not be recognised in any ofthe samples Discussion This species is a common constituent of
studied here. Apparently it does not occur in the Red the holoplanktonic mollusc stock in the SE part ofthe
Sea, although the species was mentioned (but not Red Sea and theNGWulf of Aden only (samples 9-15).
described or illustrated) by Bandel et al. (1997, p. 162). Further to the it is completely absent. It was
Measurements of a large specimen (sample 4): A = already recorded from the Red Sea by Richter (1986,
1.72 mm, H = 0.72 mm, whorl formula 1:0.28:0.17. p. 21).
Atlanta lesueuri can only be confused with the other
Atlanta inclinata Souleyet, 1852 species from the same species group, A. oligogyra (see
below). Both have a protoconch ofjust three whorls
PI. 5, figs. 1-5 without any ornament, and a teleoconch rapidly
1852 Atlanta inclinata, nobis; Souleyet, p. 375, pi. 19, increasing in width. In the former, however, the
figs. 9-15. — protoconch whorls are separated by incised sutures
1990 Atlanta inclinata Souleyet 1852 Richter, (PL 6, figs. 2, 3), whereas in the latter the sutures ofthe
p. 261, pi. 1, figs, 3, 4, 10; pi. 2, figs. 15, 16; pi. 3, early whorls are superficial (PL 7, figs. 1-3).
figs. 22, 26,—30; pi. 4, figs. 32, 37, 39. Juvenile specimens of^. planain the presentmaterial
Discussion This is the most abundant atlantid are easily mistaken for A. lesueuri, as the shape ofthe
species found in the Red Sea samples, present in most early whorls is quite similar. In A. plana, however, the
samples in more than 50 specimens. It is only less protoconch has onewhorl more and a distinct shoulder
common in the Gulf of Aqaba, in sample 8 (the spiral is always present. The second and third whorl of
shallowest sample, from a sea depth ofjust 56 m) and that species bear faint spirals on the subsutural zone,
in samples 14 and 15, in the southwestern Red Sea and sometimes difficultly seen with a normal binocular
the GulfofAden, respectively. microscope, but clearly present in SEM-images. A
The material studied here is characterised by the shoulder and keel spiral are hardly or not developed in
possession of a protoconch of 4-4'A whorls, clearly A. lesueuri, the lower one occasionally is visible in
inclined with respect to the teleoconch's axis. Identifi- juvenile specimens as a very faint line (PL 6, fig. 3). In
cation ofthe species as A. inclinata is already apparent specimens ofthree or less whorls the peripheral zone of
because ofthe size ofthe shell, reaching to over 6 mm the whorls is flattened, giving the shell a more or less
shell width in the largest specimens from the Red Sea. rectangular shape (PL 6, figs. 2, 3). In completely adult
In such large specimens the last complete whorl specimens one third of the body whorl separates from
separates from the preceding one, the space is filled the preceding whorl.
by the keel (PI. 5, figs. 1, 2). On the protoconch whorls The taxa 'Atlanta Lesueurii'' d'Orbigny, 1836 (pres-
a shoulder spiral is vaguely indicated by a very slight ently Limacina lesueuri) and Atlanta Lesueurii Sou-
angularity of the shell wall (PI. 5, fig. 3), whereas the leyet, 1852 (now Atlanta lesueuri) are primary homo-
keel spiral ismore significant (PL 5, fig. 5). Theinternal nyms (ICZN art. 53.3 and 57.2). Thejunior homonym,
radial wall structure of the protoconch whorls, de- however, is not automatically to be replaced, but the
——
Page 148 The Veliger, Vol. 49, No. 3
case should be referred to the Commission, for ruhng distincly present (PI. 8, figs. 2a, 3a, 4) all over the
underits plenary powers (ICZN art. 23.9.5) (Janssen & protoconch and disappears after the boundary with the
Seapy, in press). teleoconch. It is also visible in more adult specimens,
Measurements ofa large specimen (sample 12): A = but at places it can be covered by the suture of the
2.76 mm, H = 1.0 mm, whorl formula 1:0.16:0.07. In subsequent whorl. Very juvenile shells are slightly
the measured specimen the last third part of the body angular on the place of the shoulder spiral. The keel
whorl separates from the penultimate whorl. spiral is much less distinct, at this place the whorl is
Richter (1986, p. 22) refers to considerably larger gradually rounded. On the subsutural zone of the
specimens (4 mm), and Souleyet (1852, p. 381) even second and the third whorl two very fine and slightly
reported specimens with a 'diametre antero-posterieur' irregular spiral lirae are present (PI. 7, fig. 4c; PI. 8, fig.
of6 mm, but even in such large specimens only a small 3b). These are sometimes difficult to be distinguished
part of the last whorl separates from the preceding under a light microscope. In specimens of less than
whorl. The Red Sea specimens clearly remain smaller. three whorls the peripheral zone bears regularly spaced
spiral lirae (PI. 8, figs. 2a, 3a, 4), that disappear soon
Atlanta oligogyra Tesch, 1906 adaperturally. Also in this species the nucleus of the
protoconch is covered with an extremely fine granula-
PI. 6, figs. 4^7; PI. 7, figs. 1-3 fion (PI. 8, figs. 2b, 3c).
Measurements ofa large specimen (sample 10): A =
1906 Atlanta oligogyra n. sp.; Tesch, p. 54, pi. 8, figs. 4.40 mm, H = 1.52 mm, whorl formula = 1:0.26:0.07.
14-18.
—
1990 Atlanta oligogyra Tesch, 1906 Seapy, p. 118, Atlanta turriculata d'Orbigny, 1836
figs. 7E-H.
Discussion Atlanta oligogyra is a common species PI. 9, figs. 2, 3; PL 10, figs. 1-3
in almost all samples, inclusive of the northwestern- 1836 Atlanta turriculata, d'Orb.; d'Orbigny, p. 173,
maonsdtinojnuesst.oInteissaabmspelnet,(nhrow1e4)vefrr,ominthteheRGeudlfSeoafpArqopaebra. 199pi0. 20A,tlfaignst.a5-t1u1r.riculata d'Orbigny—Seapy, p. 123,
It TishilsessspcecoimesmoisndiinsttihneguGiushlefdoffrAodmeAn.slaemspueluer.i, ofthe fDiigss.cu5sCs,io9nE—, TFh,islOsEp-eHc.ies is absent in the Gulf of
same species group, by the very superficial sutures of Aqaba, but present all overthe Red Sea andin theGulf
the earliest whorls (PI. 7, figs. 1-3). In very juvenile of Aden (samples 3-15), but usually in rather low
specimens (less than three whorls) the shoulder and numbers. This species was recorded alive from the Red
keel spirals are absent, or just barely visible as faint Sea by Bandel et al. (1997, p. 162, figs. 4E, F, 5).
lines, without any further ornament being present. The Theprotoconchconsists off. 3-3V2 whorls. It is high
shape of such juvenile shells differs significantly from conical, juvenile shells with this number of whorls
A. lesueuriofthesamesize, astheperipheralzoneisnot (PI. 10, fig. 3a) are twice as high as wide. The fourth
flattened, but regularly curved (PI. 7, figs. 1-3). In the and later whorls expand rapidly (PI. 10, figs. 1, 2a),
largest specimens here too the last whorl separates resulting in a planispiral adult shell, on which the
shghtly from the penultimate whorl (PI. 6, fig. 4). protoconch protrudes almost as a small cylinder. The
2.4M8eamsmu,reHme=nts0.9o6fmaml,argwehosrplecfiomremnul(asa1m:p0l.e15:6)0:.0A5. = asshoaulddiesrtisnpcitraclairsipnraesienntthferommidtdhleefiorfsttwhheorplrootnowcaorndcsh
Atlanta plana Richter, 1972 whorls. It becomes less obvious only onthe first rapidly
widening whorl (PI. 10, fig. 1) and after the boundary
PI. 7, fig. 4; PI. 8, figs. 1^: PI. 9, fig. 1 with the teleoconch. On very juvenile specimens the
keel spiral is not very clear (PI. 10, figs. 1, 3a), but gets
1972 Atlantaplana n. sp.; R—ichter, p. 90, figs. 4, 6, 8. stronger on later protoconch whorls (PI. 10, fig. 2a).
1990 Atlanta plana Richter Seapy, p. 120, figs. 3A, The subsutural zone ofthe protoconch whorls seems to
B, 6E, 8A-D, 9A, B. be smoothunder a light microscope, but sometimes has
Discussion Atlantaplana is a very common species an ornament ofan irregular spiral (PI. 9, fig. 2c; PL 10,
in the southeastern part of the Red Sea (samples 6 to fig. 3a, c). The peripheral zone is ornamented with
14) and is also present in the GulfofAden sample. In regularly spaced spiral lirae, frequently in a zigzag-
the more northwestern part it is virtually absent (just shape. Also the base ofthe juvenile shell bears spirals,
one specimen in sample 4). Living specimens were that touch the peripheral ornament at an angle (PL 10,
mentioned from the Red Sea by Bandel et al. (1997, fig. 3b). The complete protoconch, nucleus included, is
p. 162). covered with a very fine granulation (PL 10, figs. 2, 3).
The protoconch ofthis species has 3Va ratherconvex The spiral ornamentation is visible on the umbilical
whorls in a conical shape. The shoulder spiral is side of adult specimens (PL 9, fig. 3a, b). Most
A. W. Janssen, 2006 Page 149
specimens still have their original reddish-brown colour and no sufficiently well-preserved Recent material was
preserved. available to identify the specimens to species level.
Measurement of a large specimen (sample II): A = None of the four Carinariidae protoconchs illustrated
1.62 mm, H = 0.64 mm, whorl formula = 1:0.26:0.12. by Seapy & Thiriot-Quievreux (1994, figs. 2-13)
resembles the present material completely. Their
Ge—nus Oxygyrus Benson, 1835 illustration of Carinariajaponica Okutani, 1955 resem-
Type species Oxygyrus inflatus Benson, 1835 bles the present specimens most, but differs by more
O. keraudreni (hesueur, 1817) (Recent) developed radiating lines on the early whorls and
Oxygyrus keraudreni (Lesueur, 1817) a much wider umbilicus.
Measurements ofa large specimen (3V^ whorls): H =
W
1817 A(tlanta) Keraudrenii; Lesueur, p. 391.— 0.69, = 1.06, height ofaperture = 0.54 mm.
1990 Oxygyrus keraudreni (Lesueur, 1817) Seapy,
p. Ill, fig.—3E-H. Carinariidae sp. 2
fouDinsdcuisnsitohne GJuulstf oaf sAidngelne jsuavmepnliel.e Tshpeecismpeecnieswaiss Discussion—Just PaLsi1n2g,lefigv.er3y juvenile specimen,
absent in all samples from the Red Sea proper and the diameter barely more than 0.3 mm, from sample 15
GulfofAqaba.
(GulfofAden) differs from the two other Carinariidae
The shell has a diameterofjust 1.12 mm, its height is types found by the absence of any spiral ornament on
0.80 mm. The protoconch ornament of spiral lines is thefirstprotoconchwhorl. Thesurfaceofthe nucleusis
rather worn, but just before the damaged apertural covered with a nice granulation, the separate elements
minadrigciantetdhebyshtahrepsbuodudnednardiyswaiptphertahneceteolfeotchoencshpiriaslwse.llA- ohaflwfhwihcohrlt,entdotwoadredvseltohpe troatshpeirralasbratuptthebeonudndofartyhewfiirtsht
peripheral belt is clearly indicated on the body whorl, protoconch-2. Radiating riblets appearjust behind the
suddenly widening at the boundary with the tele- nucleus. This little shell might belong to the genus
oconch. Thevery short teleoconch shell part is smooth. Pterosoma, as it basically agrees with the illustration of
Family Carinariidae de Blainville, 1818 Pterosoma planum Lesueur, 1827 in Seapy & Thiriot-
Genus incertae sedis Quievreux (1994, fig. 2). It is toojuvenile, however, to
be identified with more certainty.
Carinariidae sp. 1
Carinariidae sp. 3
DiscussioPnI.—1P1r,otfiogc.on4;chPsI.of12C,arfiingas.rii1,da2e sp. 1 were — PL 13, figs. 1-3
present in the GulfofAden sample (18 specimens), but Discussion Carinariidae sp. 3 demonstrates a simi-
thespecies doesnot seemto survivein thesouthwestern lar distribution as Carinariidae sp. 1: 19 protoconchs
part ofthe Red Sea (3 protoconchs in sample 13, and were found in the Gulf of Aden sample, and in
just 1 in sample 11). More adult specimens or addition,just 2 specimens in sample 11, and 5 in sample
fragments were not found. 13.
The specimens are easily recognised as a carinariid The juvenile specimens differ clearly from Carina-
species, bytheirpeculiarshellform: one and a halftime riidae sp. 1 by their somewhat more flattened apical
wider than high, with the greatest width above the plane (PI. 13, fig. la), the more convex whorls,
horizontal midline. The apical part of the shell is very separated by incised sutures, a more rounded aperture,
slightly conical, with flat whorls, separated by super- and a weaker ornament, with a subsutural spiral and
ficial sutures. All specimens are of an opaque whitish very faint radial lines on the first two whorls. Here too,
colour, but the nucleus in all specimens is brown. The the nucleus ofthe protoconch has a similar granulated
wohronralmse,ntonexisbtosthofsaidseusbsusteupraarlatsepdirablyonathgerofoivrset-ltiwkoe rsuersfeamcbele(PPLte1r3o,sfoimg.a2p)l.anIunm,theassihlalpuestroaftetdhbeyshSeellaptyhe&y
structure (PI. 11, fig. 4b; PI. 12, fig. 2b), disappearing Thiriot-Quievreux (1994, figs. 2-A), but in that species
adaperturally. Theupperpartofthefirstwhorl in some the first whorls have no spiral ornament, and the
4ssbtp)ae.rctiTimnhgeensbfarbsoeemarosfthtsehoemusemhbelirllaidhciauasstidniagsntidgnrcotaloyvenrsoatdi(PaIvt.eirn1yg1,fwofelildgls. u0.m5bM1ielamiscmuu,sreimsWednitsts=inocft0l.ay76wliamdregmre,.spheeciigmhetn (o3fwhaoprelrst)u:reH ==
0.46 mm.
developed circum-umbilical spiral (PI. 12, fig. la, b).
Thenucleus ofthe protoconchis beautifully granulated Family Pterotracheidae Rafinesque, 1814
(PI. 11, fig,4b; PI. 12, fig, 2b), markedlycoarserthan in Genusd Firoloida Lesueur, 1817
the Adanta-SY)QC\QS.
Carinariid protoconchs are not very well known yet. Firoloida demarestia Lesueur. 1817