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Chapter 50. Deep sea Ostracoda, taxonomy, distribution and morphology

Chapter 50. Deep sea Ostracoda, taxonomy, distribution and morphology

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700 G. HARTMANN

AND G. HARTMANN-SCHRBDER



Hadacypridina (monotypic), Azygozypridini with Azygozypridina (8) and Zsocypridina (monotypic),

and Gigantocypridiniwith Gigantocypris (7).

The Cylindroleberididae and Philomedidae, rich in species in littoral waters, are less important

in the deep-sea. The Rutidermatidae are represented only by a single species. Among the Philomedidae Igene is a true deep-sea genus.



Anteil der Unterordnungen an den



-Tiefseegattungen



TEXT-FIG.1-Diagram of the suborders of

the deep-sea genera



Anteil der Unterordnungen an den

TefseeaFten



TEXT-FIG.

2-Diagram of the suborders of

the deep-sea species.



The Halocypridina are more difficult to judge since their species are nearly completely pelagic

and many undertake vertical migrations thus occurring in water bodies of different depths. There

are no deep-sea taxa of genera or higher taxonomic level.

Among the Archiconchoeciinae Archiconchoecia contains 14 deep-sea species, and among the

Halocypridinae, Bathyconchoeciu, with 10 deep-sea species, has the majority of its species in this

environment. The entire family Thaumatocyprididae exists, though not exclusively, but with the

majority of its species in deeper waters. Danielopolina also occurs in marine caves.

The same is nearly true for the Cladocopina. The family Polycopidae, rich in species, populates

with many of its species the deep-sea bottom. In littoral biotopes this family lives in interstitial systems, both in the sublittoral and eulittoral regions. It is not possible to determine if this family

invaded the interstitial systems of the littoral zone from the deep sea or vice versa.

Species of Platycopa are also found in the deep sea, but the number of species here remains small.

The Podocopa present a confusing picture in that most families of this subclass have representatives in the deep sea. Sometimes it is difficult to decide if their occurrence is autochthonous or

if their shells have been transported to this biotope passively. In the tables, these species have been

marked “questionable”. Although this subclass is the richest in species, the number of exclusively

deep-sea taxa is also small.



701



T m



&DEEP-SEA

GENERA

AND NUMBER

OF THE SPECIES

OF MYODOCOPA-MYODOCOPIDA-MYODOCOPIN

A.



(“ma with exclusively deep-sea distribution are italicized)

ylF

i’



Cypridiniahe:



Tribes Cypridini:

Bathyvargula 2

Cypridina 2

Doloria 1

Haakcypridina I (only in deep-sea)

Macrocypridina 2

Metavargda 3

Paradoloria 2

Vargula 4



Dibes Azygozypridini (only in deep-sea):

Azygocypridina 8

Isocypridina I

Tribes Gigantocypridini (only in deep-sea) :

Gigantocypris 7



Family Cylindroleberididae (prevailing in littoral

regions) :



Subfamily Cylindroleberidinae:

Archasterope 1

Bathyleberis 2

Diasterope 1

Empoulsenia 2

Parasterope 3

Skogsbergiella 3

Synasterope 6



Subfamily Cyclasteropinae :

Cycloleberis 1

Asteropterygion 1

Family Philomedidae (prevailing in littoral regions) :



Subfamily Pseudophilomedinae:

Angulorostrum 2

Harbansus 1

Paramekodon 2

Subfamily Philomedinae :

Anarthron 1

lgene 2 (only in deep-sea)

Philomedes 11

Scleroconcha 3

Tetragonodon 2

Family Sarsiellidae:

Parasarsiella 1

Sarsiella 1

Spinacopia 7

Streptoleberis 1

Family Rutidermatidae (nearly exclusive to littoral regions):

Alternochelata 1



TABLE2-DEEP.SEA GENERA

AND NUMBER

OF SPECIES OF MYODOCOPA-HALOCYPRIDIDA-HALOCYPRIDINA

AND &ADOCOPIDA-CLADOCOPINA.

Family Halocyprididae:



Subfamily Archiconchoeciinae:

Archiconchoecia 14 (many in deep sea)

Subfamily Halocypridinae:

Bathyconchoecia 10 (many in deep sea)

Fellia 3

Halocypris 2

Subfamily Conchoeciinae :

Alacia 6

Boroecia 3

Conchoecetta 2

Conchoecia 20

Conchoecilla 3

Conchoecissa 5

Discoconchoecia 3

Gaussica 2

Loroecia 2

Metaconchoecia 8

Mikroconchoecia 4

Mollicia 5



Obtusoecia 1

Orthoconchoecia 4

Paraconchoecia 18

Paramollicia 5

Porroecia 1

Pseudoconchoecia 1

Spinoecia 2

Family Thaumatocyprididae (prevailing in deep sea) :

Danielopolina 1 (also found in caves!)

Thaumatoconcha 11

Thaumatocypris 1

Family Polycopidae:

Archipolycope 9 (many in deep sea)

Metapolycope 4

Polycope 29

Polycopsis 4

Pontopolycope 2

Pseudopolycope 2 (all in deep sea)



702 G. HARTMANN

AND G. HARTMANN-SCHRODER



Among the Bairdioidea, only the family Bythocyprididae is frequent at depth. Bythocypris contains 15 species in this environment, this being a large part of its species spectrum. Zabythocypris,

with 12 species known to date, exclusively inhabits the deep sea.

Very important for deep-sea ostracods is the genus Argilloecia of the Cypridoidea. The number

of its deep-sea species is constantly rising with the progress of deep-sea research. Seventeen species

have been found in the deep, and among ostracods sampled by the research vessels Polarstern

and Walther Herwig in Antartica, more have been found by the authors.

Among the Cytheroidea, generally rich in species, only occasionally have species been reported

from deeper waters. This is, for example, true for the families Leptocytheridae and Cytherideidae

which are very rich in littoral species. The Paradoxostomatidae, as forms which live mainly on

algae and suck their sap, are not inhabitants of lightless depths. There are some exceptions among

semi- and full-parasitic species. The Krithidae have, with the genus Krithe, a unit which includes

11, the Cytheruridae with Cytheropteron a unit with 16 deep-sea species. Most of the exclusivly

deep-sea inhabiting genera contain however, only a few species or are monotypic:

Abyssocythere-5 species, Poseidonamicur--4 species, Abyssocythereis-monotypic, Pelecocytheremonotypic, and Vitjasiella-monotypic.

as well as the new genus Profmdocythere with 3 species recently noted by the present author

(1985).



Moreover, Table 3 shows that most of the remaining genera have at most 8, usually 1-5, deep

sea representatives.

Summing up, there is no doubt that many ostracod taxa inhabit the deep sea environment, but

it must also be pointed out that the number of exclusivelydeep-sea living taxa is astonishingly small.



btidermatidae



Anteil der Familien an den Tiefseearten der Mg(ocbapida



TEXT-FIG.

3-Diagram of the families of

the deep-sea species of Myodocopida.



QCytheridae

Q Leptocytheridae

0 Eucytheridae

0 Cytherideidae



6) Cytherettidae

@ Micmcytheridae



Anteil der Familien an den Tefseearten

der Cytheroidea



TEXT-FIG.

4. Diagram of the families of

the deep-sea species of Cytheroidea.



Deep-sea Ostracoda, Taxonomy, Distribution and Morphology 703

TABLE 3a-DEEP-sEA



GENERA

AND NUMBER

OF SPECIES OF PLATYCOPA AND POWCOPA.



Fmly Cytherellidae:

Cytherella 10

? Cytherelloidea 1 (uncertain)

Family Slpirridae:

Saipanetta 1



Family Bythocyprididae:

Bythocypris 15 (many in deep sea)

Orlovibairdia 1

Zabythocypris 12 fall in deep sea)

Superfamily Cypridoidea:

Family Macrocyprididae:

Macrocypris 8



Superfamily Bairdioidea:

Family Bairdiidae:



Subfamily Bairdiinae (prevailing in littoral regions) :

Bairdia 10

Bairdoppilata 4

Neonesidea 1

Paranesidea 3

Rerobairdia

Subfamily Pusselinae (prevailling in littoral regions) :

Anchistrocheles 2



Family Pontocyprididae:

ArgilIoecia 17 (many in deep sea)

Australoecia 3

Pontocypria 1

Pontocypris 6

hopontocypris 1

Family Candodidae (prevailing in littoral regions) :

? Aglaiocypris 1 (uncertain)

? Paracypris 2 (uncertain)



DISTRIBUTION

OF DEEP-SEA

OSTRACODA

Because of the great spatial, wide geographical, temporal and ecological continuity of the deepsea environment, zoogeographers agree that many, if not most, deep-sea animal species have a wide



distribution. Is this also true of deepsea ostracods?

Analyzing the distribution of the 520 deep-sea species and subspecies it is not possible to confirm

this general statement as applying to ostracods. On the contrary, most of the species appear to have

only small vertical and horizontal ranges! This is possibly due to the lack of knowledge of deep-sea

ostracods. However to postulate a wide distribution of deep-sea ostracods simply because this is

true for other animal groups is not permissible.

Among the Myodocopina species of the checklist, only two species are found to be widely or

circumtropically distributed. All others have a small range.

The pelagic Halocypridina naturally have a wider distribution. Twenty-three of the deep sea

species have a circumtropical distribution, while 15 occur worldwide. However, the wide geographical distribution is mostly combined with a wide vertical distribution, that is, 18 of the 23 circumtropical species are also found in epipelagic communities, with the same being true for 12 of the

18 worldwide species.

Not a single species of the Cladocopina is recorded as having a wide distribution!

The Platycopa appear to be widely distributed with several species having been recorded from

widely separate localities. It is however remarkable that only these three species appear to have a

wide range, which clearly do not represent a single species. The Bairdioidea of the Podocopa show

a similar picture. A wide distribution is also reported for species described by Brady (1880). The

systematic status of these species, however, is not clear.

Among the Cytheroidea the following species are evidently widely distributed:

Krithe bartonensis, Krithe producta, Echinocythereis spp., and Bradleya dictyon.



704 G. HARTMANN

AND G. HARTMANN-SCHRBDER



TABLE

3 b D E E P - S E A GENERA

AND NUMBER

OF SPECIES OF PODOCoPA (SUPERFAMILY

Family Cytheridae:

? Cythere 2

Paijenborchella 1

Family Leptocytheridae:

Leptocythere 1

Family Eucytheridae:

Eucythere 1

Family Cytherideidae:

Cytheridea 1

Family Krithidae:

Krithe 11 (many in deep sea)

Parakrithella 1

Family. Trachyleberididae:

Bosquetina 2

Buntonia 1

Quasibuntonia 2

“Cythereis” 13

Abyssocythere 5 (all in deep sea)

Acanthocythereis 1

Henryhowella 1

Robertsonites 1

Trachyleberis 1

Arnbocythere 2

Hiltermannicythere 1

Pterygocythereis2

Bathycythere 1 (deep sea of questionable)

Echinocythereis 4

Basslerites 1

Family Hemicytheridae:

Agrenocythere 5

Cletocythereis 1

Tenedocythere 1

Thaerocythere 1

Bradleya 2

Poseidonamicus 4 (all in deep sea)

Caudites 1



mEROIDEA).



? Orionina 1 (questionable)

? Aurila 1 (2) (questionable)

? Mutilus 1 (questionable)



Family Cytherettidae:

Abyssocythereis I (monotypic)

Pelecocythere I (monotypic)

Family Microcytheridae :

Microcythere 1

Family Loxoconchidae:

Loxoconcha 5 ( 3 uncertain)

? Phlyctocythere 1 (questionable)

Family Cytheruridae:

? Cythenua 3 (questionable)

? Hemicytherura 2 (questionable)

? Semicytherura 4 (questionable)

Cytheropteron 16 (many in deep sea)

Pedicythere 2

Family Xestoleberididae:

Microxestoleberis 2

? Ornatoleberis 1 (questionable)

Xestoleberis 8 (some questionable)

Family Bythocytheridae:

Bythocythere 2 ( I questionable)

Monoceratina 2

Vitjasiella I (monotypic)

Bythoceratina 2

Pseudocythere 2

Family Paradoxostomatidae:

Acetabulastoma 1

Cytherois 2

? Paracytherois 4 (3 questionable)

? Paradoxostoma 4 (all questioable)

? Sclerochilus 1 (questioable)

Incertae sedis:

? Saida 1 (677 m)



The majority of species of this group have, based on present knowledge, a small range.

Examples of wide distribution are also found among the Cyprioidea with these species:

Macrocypris similis, Argilloecia pusilla, and Aglaiocypris meridionalis.



Most species of this superfamily also have a small overall range.

Summing up the findings it must again be emphasized, that on the basis of present knowledge,

only a few species show a wide distribution that has been proved. Among these, pelagic species

with a broad vertical distribution predominate.



Deep-sea Ostracoda, Taxonomy, Distribution and Morphology 705



THEMORPHOLOGICAL

CHARACTERS

OF DEEP-SEA

OSTRACODA

Morphological characters, influenced by the environment, are known from ostracod shells as

well as from the soft parts. This has been studied especially in brackish water species, several characters of which respond to different environmental factors. It is to be expected that characters of

deep-sea ostracods will show reactions to their deep-water environment.

A study of the literature on deep-sea ostracods and their morphological characters demonstrates,

however, that general statements are as difficult to make as for taxonomy and distribution. Nevertheless, different authors (Benson, 1971, 1972; Poulsen, 1965) have drawn attention to characters

obviously influenced by the deep-sea environment. It is difficult however, to generalize these findings.

A morphological change easy to correlate with depths is shown by the ostracod eye, by that of

the nauplius as well as the lateral eyes.

For example, the lateral eyes of the Myodocopina reduce the number of ommatids with increasing depths (Poulsen, 1965 for the Cylindroleberididae). In deeper water the lateral eyes are

often completely reduced. This is true for nearly all real deep-sea forms, such as Huhcypridinu,

the Azygocypridini, Gigantocypridini, Igene, Buthyleberis, and Spinacopia.

The nauplius or median eye is often also reduced in deep-sea ostracods. This trend is, however,

not uniform. Well known, although not yet studied morphologically in detail, is the median eye of

Giguntocypris, which is transformed into a paired large reflector eye, surely a specialisation for the

deep sea. Kornicker (1969) also found a large median eye by reduced lateral eyes in Spinucopiu

(Sarsiellidae).

The Podocopa generally reduce the median eye when living in greater depths while lateral eyes

have never been found in this group. Frequently, the valves form eye spots or transparent zones in

their outer lamella above the median eyes. These spots disappear in the deep-sea environment

(Poseidonamicus,Benson, 1972; Xestoleberis, Bonaduce and others).

In spite of this trend, a reduction of eyes cannot alone be regarded as a deep-sea character.

Halocypridina, Cladocopida, Platycopida Darwinuloidea and Cytherettinae among the Cytheroidea do not possess lateral or median eyes. Other ostracods, such as cave-dwelling forms or

species living in interstitial environmenta also reduce their eyes. Another character frequently

observed in deep-sea animals is the prolongation of extremities, i.e. antennae, legs and their

bristles. Indeed, many deep-sea ostracods possess long antennae and walking or swimming legs, and

often, especially in Cytheroidea, terminal claws on the walking legs which are extremely long

(Zubythocypris, Pelecocythere, Vitjusiella for example). Other real deep-sea species, however, d o

not show these adaptations. Abyssocythereis and Poseidonamicus can be named as examples.

Moreover, it should not be forgotten that ostracods living in coral debris, on algae, or on soft

substrates also show the same transformation of extremities.

The frontal organ of ostracods (better known as the organ of Bellonci) is reported to have a

different form in deep-sea individuals of species with a wide vertical rang (Igene, Kornicker, 1975).

It is, however, not clear, if this transformation is a deep-sea adaptation or not.

Morphological changes of the ostracod shell concern the thickness of their walls as well as their

total length. Corresponding to the growing hydrostatic pressure and the inability of animals to

build up strong calciferous skeletons in greater depths (4000 meter lysokline), deep-sea ostracods

have thinner valves in deeper waters. This is true for both Myodocopa and Podocopa (Huducypridinu, Buthyvurgulu, several Podocopa). Benson (1972) mentioned the loss of marginal spines on the

valves of deep-sea ostracods, regularly equipped with these features. A reduction in the number of

marginal bristles is reported by Poulsen for Huducypridinu. Benson and Peypouquet (1983) believe



AND G. HARTMANN-SCHR~DER

706 G. HARTMANN



that the variation of the marginal zone of Krithe is related to the changing hydrochemical and

hydrophysical conditions in deeper waters.

Kornicker (1969) observed larger valves in deep-sea individuals of Spinacopia (Sarsiellidae).

While Benson (197 1) reported similar conditions for Abyssocythere and Poseidonamicus.

Finally, different authors believe that the ventral flattening of the ostracod shell and the develop

ment of wings, observed in several Cytheroidea (for example, Trachyleberididae, Cytheruridae,

Pelecocythere) are a deep-sea character.

When the above-mentioned morphological characters, i.e. thickness of shell walls, size ventrally flattened shells, wings, etc., are analyzed, it is found that none of these characters may be

called typical for the deep-sea environment. The calcification of ostracod shells depends on many

factors. Weakly calcified shells are also frequent in brackish water and in species living on algae

(such as Xestoleberis and Paradoxostoma species). The same is true for the ornamentation and

size of the valves. Thus Kiihl (1980) found in Leptocythere that different sizes and ornamentation

could be correlated with the time of year. As flattened ventral surfaces and wings are frequently

observed in ostracods living on soft substrates (Cytheruridae), the development of wings in deep

sea ostracods may be related with soft substrates - also widespread in the deep.

Summing up, it must be stated that, similar to the statements given for taxonomy and distribution of deep-sea ostracods, there are no morphological characters exclusively present in deep-sea

forms. Numerical methods (computer programs) should be applied to solve these problems.



SUMMARY

1. The deep-sea is populated by numerous taxa also present in littoral regions. Only a few taxa of



higher systematic categories are exclusively deep-sea taxa.

2. The distribution of deep-sea ostracods is poorly known. A wide distribution is observed espe-



cially in pelagic species which also have a large vertical distribution.

3. There are no morphological characters which are exclusive to deep-sea Ostracoda.



REFERENCES

1971. A new Cenozoic deep-sea genus Abyssocythere (Crust. Ostracoda; Trachyleberididae), with

description of five new species. Smiths. Contr. Puleobiol., 7 , 1-25.

1972. The Bradleyu problem, with descriptions of two new psychrospheric Ostracoda genera, Agrenocythere

and Poseidonamicus (Ostracoda: Crustacea). Ibid., 12, 1-136.

-and PEYPOUQUET, J.-P. 1983. The Upper and Mid-Bathyal Cenozoic Ostracode Faunas of the Rio Grande

Rise found on Leg 72 Deep Sea Drilling Project. In BARKER, P.F. et ul., DSDP, 72, 805-918.

BRADY, G.S. 1880. Report of the Ostracoda dredged by the H.M.S. Challenger during the years 1873-1876. -Reports

on the voyage of H.M.S. Challenger, Zoology, 1, 1-184, London.

HARTMANN, G. 1985. Ostracoden aus der Tiefsee des Indischen Ozeans und der Iberischen See, sowie von ostatlantischen sublitoralen Plateaus und Kuppen. (Mit besonderer Beriicksichtigung der Tiefsee und einer Tabelle

der bislang bekannten rezenten Tiefseeostracoden.) Ergebnisse der Meteorreisen 1 (1964/65), 3 (1966), 8 (1967)

und 9 (1967). In Senck. maritima, Wilhelmshaven (in German).

KORNICKER, L.S. 1969. Morphology, Ontogeny. and Intraspecific variation of Spinucopju, a new Genus of Myodocopid Ostracoda (Sarsiellidae). Smiths. Contr. Zool., 8, 1-50.

1975. Antarctic Ostracoda (Myodocopina) part 1 and 2. Ibid., 163, 1-420.

KOHL. CHR., 1980. Die Variabilitiit von Leptocythere psummophifuGUILLAUME, 1976: Schalenabmessungen und

Schalenstrukturen (Crust. Ostr. : Cythereidae). Verhundl.Nut. Ver. Hamburg (N.F.), 23, 275-301 (in German).

POULSEN, E.M. 1962. Ostracoda-Myodocopa. part I: Cypridiniformes-Cypridinidae. Dana Rep., 57, 5-41 3.

1965. Ostracoda-Myodocopa, part 11: Rutidermatidae, Sarsiellidae, Cylindroleberididae. Ibid., 65, 1-483.



BENSON. R.H.



-



-



-



Deep-sea Osiracoda, Taxonomy, Disiribuiion and MorphoIogy 707



DISCUSSION

Adamczak: What about the carapace thickness in the deep-sea forms?

Hartmann: Generally it is accepted that deep-sea ostracods have thinner valves. However,

as thin valves also occur in other biotopes such as the phytal and interstitial waters, it is not possible to generalize this statement. Intraspecific research has to be done on species which occur at

different depths.

Maddocks: I believe you are aware of this already, but let me report for the record that nearly

all subsequent reports of Macrocypris similis and other Challenger species are misidentifications, as

are at least 50% of sightings of Macrocypris minna.

Hartmann: I am afraid that “accidents” like this one will happen often in the future. That is.

what makes work so difficult.

Sohn: Can you suggest to palaeonotologists criteria in Ostracoda for the recognition of deep-sea

habitats? (I agree with your conclusions, but woud like to see your published statement for use by

palaeontologists).

Hartmann: I am afraid that I cannot help you. Most of the characters which change with depth

in Myodocopa are those of soft parts (the eye, etc.). Intraspecific work should be done to prove

characters in fossil species paying attention at the same time to the entire fauna discovered in the

sample in question.



This Page Intentionally Left Blank



The Anatomy of the Ostracod Pelecocgthere purii sp. nov. and

some Features connected with the Abyssal Mode of Life in this

and some other Deep Water Forms

JOHN W.NEALE

University of Hull, England



ABSTRACT

The new species Pelecocythere purii is distinguished from P. sylvesterbradleyi and its anatomy

compared with that of the shallow water type species of Cytheropteron. Some modifications, probably connected with its life in deep waters, are noted and attention is drawn to some features of

other abyssal ostracods.



INTRODUCTION

In recent years, considerable ostracod faunas have been obtained from the abyssal regions of the

North Atlantic. Many of the forms are new and show considerable modifications to their anatomy

compared with the more commonly encountered shallow water species. Some of the smaller species

belonging in genera such as Rockallia, ‘‘Pedicythere” and a new genus externally similar to Cytherura are only rarely encountered. Others are common and belong dominantly in the genera

Polycope, Cytherella, Bairdoppilata, Krithe, Bythocypris, Pelecocythere and Pseudocythere amongst

others. In dealing with the anatomy of a large new species of Pelecocythere it became apparent that

there were considerable differences from the somewhat similar, but shallow water, type species of

Cytheropteron which might be considered in connection with its habitat. The new species is described below and its anatomy discussed in relation to other forms.



TAXONOMY

Family CYTHERURIDAE

G. W. Miiller, 1894

Subfamily CYTHEROPTERINAE

Hanai, 1957

Genus PELECOCYTHERFJ

Athersuch, 1979

PELECOCYTHERE

PURII sp. nov.

(Pl. 1, figs. 1-4, text-figs. 1-3)

Derivation of name.-In honour of Dr. Harbans Puri who was instrumental in organising the

First International Ostracod Symposium at Naples in 1963.

Diagnosis.-A Pelecocythere species of elliptical shape in side view, with a short blunt caudal

709



710 J. W. NEALE



process in the right valve and ending in a short posteroventral point in the left. Surface finely pitted

and showing incipient reticulation, but with a smooth alar rim and lateral surfacejust above the rim.

Pars incisivu of mandible deep-bodied with relatively slender, toothed termination. Hemipenes with

fairly blunt distal termination and oval in shape.

Ho1otype.-A male specimen 0 s 302a (left and right valves), 302b (dissection) deposited in the

Museum National d'Histoire Naturelle, Paris.

Other Material.-This is a commonly encountered species between depths of 4,000 and 5,000

metres in the Eastern North Atlantic. Nine typical examples have been deposited in the MNHN,

Paris, Nos. 0 s 303a, b - 31 la, b.

Type Locality.-INCAL CP12: 46"00.5'N, 10" 18. 3'W at a depth of 4,796 m.

Dimensions of figured specimens.MNHN 0 s 302a Holotype



8RV



MNHN 0 s 303a



PRV

W V



$LV



Length

1545 p m

1580 p m

1555 pm

1580 pm



Height

840 p m

960 p m



930 pm

1040 pm



Description.-Carapace large, alate, broadly elliptical in side view with the greatest height at

about mid-length. Dorsal margin of left valve evenly rounded, dorsal margin in right valve straight,

Surface appears smooth under ordinary optical examination; the SEM shows it to be finely

pitted with incipient reticulation, but smooth where it approaches the alar rim. Alar rim smooth with

four fine, anastomosing, longitudinal ribs on its ventral surface. Short blunt caudal process. A

flange is present anteriorly, ventrally and posteriorly where it ends in a small posteroventral point

(Pl. 1, fig. 4). The posterior part of this flange is apparent in lateral view (Pl. 1, figs. 1,3) Hinge antimerodont in the right valve with five, well-developed teeth anteriorly and six or seven posteriorly,

joined by a finely locellate groove of uniform width which may even become a little constricted at

its extremities. Left valve complementary with straight accommodation groove to receive the

dorsal margin of the right valve. Normal pore canals single, simple and sparse. Marginal pore

canals straight and simple about five anteroventrally and three or four posteroventrally. Internally

some ten or eleven orifices appear at the alar margin. These lead into the ala where they give rise to

two pairs of porecanals, one pair opening on the dorsal surface of the ala, the other on the ventral

surface. Just below the dorsal margin in the left valve the outer surface of the shell is perforated by

six pores which end in pore conuli. The carapace shows clear dimorphism, the males being lower in

proportion to their length than the females (Pl. 1, figs. 1, 3).



Appendages

Antennule robust, consisting of six segments. First two segments relatively long, protopodite

with a fringe of strong bristles dorso-distally, second segment with pilose tufts proximo- and

dorso-distally and ventrally together with an annulate ventro-distal seta. Third, fourth and fifth

segments almost equidimensional. Third segment with one slightly curved, sword-like seta dorsodistally, fourth with two of different lengths and fifth with two in similar position. The fourth and

fifth segments also have one rather finer seta latero-distally in the former and ventro-distally in the

latter case. Both fourth and fifth segments are finely pilose dorsally. Distal segment more slender

PLATE1-Pelecocyrherepwii sp. nov. Stereographic paired photographs. All x44. Figs. 1,2,4. Holotype, Male,

MNHN 302a. INCAL CP12: 46°00.5", 10°18.3'W. Depth 4,796m. 1. Left valve in lateral view. 2. Right

valve in lateral view. 4. Oblique ventral view of inside of right valve. Fig. 3. Female, left valve. MNHN 0 s

303a. INCAL CP13: 46'02. l'N, lO"14.8'W. Depth 4,800m.



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Chapter 50. Deep sea Ostracoda, taxonomy, distribution and morphology

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