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Chapter 30. To see and not to be seen: The evolutionary problems of the Ostracoda Xestoleberididae

Chapter 30. To see and not to be seen: The evolutionary problems of the Ostracoda Xestoleberididae

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1-A. Schematic principle of light diffraction through a double prism (lens). Redrawn after Gregory,

1966. B. Focusing of the iris8 Redrawn after Gregory, 1966. C.The human eye with the schematic system of

the ocular muscles and ligament. Redrawn after Gregory, 1966. D. The principle of focusing of a correcting

additional lens. Redrawn after Weymouth, 1963. E.Scheme of the eye function, following Leonard0 da Vinci.

Redrawn after Kemp, 1981. F. Structure of the median eye of Cypris puberu (horizontal section). Schematic

drawing from Novikoff, 1908, redrawn after Hartmann, 1967. (Lo-lateral ocellus; Co-central ocellus; cccorneal (lens) cell; pl-pigment layer). G, H. Carapace lenses and median eye in Notodromus monuchu. G : q ;

H:$. Redrawn after Fox, 1966.

Evoluiionary Problems of Xestoleberididae 377

Salvini-Plavenand Mayr (1977) tried to reconstruct the major pathways of the evolution of photoreceptors and eyes.

Three problems concerning vision have fascinated mankind : how we perceive objects, how

images form and how visual experience is further transmitted. These problems mainly represent

the domain of human anatomy, physiology and psychology (for this last domain see Gregory,

1966). Zoologists and ecologists in modem times are faced more and more with similar problems

(e.g. see the discussion on copepod perception, cognition and adaptation in Marcotte, 1983).

Animals are not faced only with the problems of what they see but also with the problem that

other animals see them and can prey on them. Many organisms have developed special shapes and

colour patterns which help them to become better integrated in a three-dimensional environment

that is biologically and physiologically structured. In fact, colour patterns help them pass unobserved by predators. Man has been faced with similar problems and during his cultural evolution

we can see the development of a tremendous diversity of colours and shape patterns, most of which

display a sense of order. We present here a description and interpretation of the ocular structures of

ostracodes and in a later paper the colour patterns of the Xestoleberididae which represent an

aspect of the general problem which has interested mankind for more than two thousand years.



SARS, 1928

General Information

The Xestoleberididae are ostracods which live in marine and brackish waters. Hartmann (1975)

noted that this family is a very diversified cytherid group, represented by seven genera and about

200 species, more than half of which are known only as fossils. Xestoleberidids diversified during

the last hundred m.y. (e.g. during the Cenomanian and Senonian in the Cretaceous and later

on during the Tertiary and Quaternary; for the Mesozoic Xestoleberididae, see Whatley and

Stephens, 1976).

The Xestoleberididae are creeping crustaceans which move slowly on or into the substrate. Most

of the species live in shallow marine environments in the photic habitats of the littoral and sublittoral zones, on sandy substrates or on various algae. Some Xestoleberidids colonise interstitial

habitats in coarse-sandy substrates and a few species have adapted to living at great depths (e.g.

the bathyal zone ranging from 600 m to more than 1300 m in the Mediterranean basin). Other

species are commensals on Crustacean Malacostraca as Aspidoconcha limnoriae which lives fixed

on the wood boring isopod Limnoria lignorum (McKenzie, 1972).

As a group the Xestoleberididae is easy to identify using several morphological characters: the

ocular structures are well developed, the median eye has 3 separate ocelli (Text-figs. 2C, F, G).

A semilunar “imprint” called the “Xestoleberis-spot” (e.g. Text-figs. 2C, D) occurs behind the

lateral ocellus on the valve.

Many Xestoleberididae which live in photic habitats have developed dioptric structures and

“Xestoleberis-spots” on the carapace. They also display various epidermal pigmented patterns

which alow the animal to pass unnoticed by predators (Text-figs. 2C, E, F, G).

Systematics and Material

This chapter deals with the description of Platyleberis n. genus and of Xestoleberis prognata

n. sp. ;for those species sufficiently described, 3 groups of the Xestoleberis are proposed in relation

to their morphological affinities. The chapter also furnishes information on the origin of the Xestoleberididae material utilized. The data on the material used are reported in Table 1.



TEXT-FIG.2-A, B. Xestoleberis delamarei 9. A. Carapace in dorsal view with Xestoleber&spots (s). B. Right

value in external view with Xestoleberis-spot and surroundingmilky area. C. Xestoleberis decipiensv. Carapace

in dorsal view with median eye, X-spot (s) and colour-patterns. D. Xestoleberis disparv. Right valve with transparent lens ( 0 ) and X.-spot (s). E. Xestoleberis communisv. Left valve with X.-spot (s) and colour patterns. F.

Xestoleberisplum? : Carapace in dorsal view with median eye and colour patterns. G. Xestoleberis parva 8 .

Carapace in dorsal view with reduced pigmented areas. (C, E, F, G: Redrawn after Miiller, 1894.)


n. gen.

Etymology.-From greek platys = flat

Type species.-Microxestoleberis profunda Breman 1975 (Pl. 1, A-F; P1. 2. A-D)

Diagnosis.-A genus of the family Xestoleberididae characterised by a small, well-calcified, subrounded or triangular carapace in lateral view, and a completely smooth exterior surface. The size

is generally smaller than 500em in length. The hinge is of a merodont-type (sensu Hartmann, 1966)

with a well-developed and uncrenulated central bar in the left valve and a smooth and elongated

posterior cardinal tooth in the right valve; the anterior tooth is not defined and substituted by a

strong long bar within which the posterior extremity steeply protrudes. It shows the presence of a

PLATE l-Figs. A-F. Platyleberisprofunda. A. LV from outside. Holocene: Alboran Sea Stn. SV-8107. B. Detail

of the hinge of the RV. C. LV from outside. Saba Bank Stn. 108. D. RV in dorsal view. Saba Bank: Stn. 108.

E.LV from outside-Upper Pliocene: Mount S. Nicola, Stn. 53. F.RV from outside. Upper Pliocene: Mount

S. Nicola, Stn. 53. Figs. G. H. Xestoleberis prognuta n. sp. G. RV from outside. Upper Pliocene: Mount S.

Nicola Stn. 53. H. LV from,outside (slightly tilted). Upper Pliocene: Mount S. Nicola Stn. 53.







PTtyleberis n. g.

P. prof& (Breman)

Microxestoleberis Miiller

M.nuna G.W. Miiller



Mnt. S . Nicola-St 53

(Sicily, Italy)

Alboran Sea-SU8107

(W. Mediterranean)

Saba Bank-St 108

(Caribbean Sea)

bathyal(*600800 m)

bathyal(l375 m)


bathyal(720 m)



sublittoral (61Om)

(W. Mediterranean)

Amphioxus sand

Xestoleberis Sars

gr. communis

X. communis G.W. Miiller Banyuls/M

(W. Mediterranean)




Up. Pliocene


deep-sea assemb.

(G.B. leg.)

deep-sea assemb.



deep-sea assemb.






interstitial assemb.

(D.L.D. leg.)




interstitial assemb.

(D.L.D. leg.)

phytal assemb.

(D.L.D. leg.)

littoral (4 m)

Scario (Policastro

bay) (Tyrrhenian

Sea, Italy)

Scario (Policastro bay) littoral,

interstitial (1 m)



(Lower Austria)

Mnt. S. Nicola-St 53

bathyal (HiOO800m)

(Sicily, Italy)

bathyal (not less

El Cuervo

than 600 m)

(Andalusia Spain)

Recent (living,


Mid. Miocene


Up. Pliocene

X.plana G.W. Miiller


sublittoral (6-lOm)

(W. Mediterranean)

Amphioxus sand

Recent (living,


X.dispar G.W. Miiller




Recent (living,


X.parva G.W. Miiller


(Policastro bay)


(Algarve, Portugal)

littoral (4m)




Up. Miocene

littoral (lm)

brackish water









interstitial assemb.







Recent (living,

subfossil ?)




littoral, interstit.

littoral, sandy






interestitial assemb.




interstitial assemb.



X. sp. (aff. X. communis)

X.glubrescens (Reuss)

X.prognata n. sp.



Up. Miocene

phytal, interstitial

assemb. (D.L.D. leg.)

littoral assemb.


deep-sea assemb.

(G.B. leg.)

deep-sea assemb.


in BKRGGREN et al., 1976)t

gr. plam

X.sp. 1 Nascimiento

gr. arcturi

X. arcturi arcturi Triebel

Arcturus lake (Power

Is]., Galapagos)

X.arcturi darwini Gottwl. Academy beach

(Sania Cruz Is].,


X.galapagoensis Gottwl. Tower Id.,


X. delamarei Hartman


X.xenomys Barb.-G.


(Policastro bay)

Gulf of Taranto -St

134E CIonian Sea, It.)


interstitial assemb.

(D.L.D. leg.)


interstitial assemb.

(D.L.D. leg.)

phytal assemb.

(D.L.D. leg.)

littoral assemb.


(G.B. leg.)


Evolutionury Problems of Xestoleberidialae 381



Ornutoleberis Keij

0.morkhoveni Keij

Foveoleberis Malz

F. foveolutu (Brady)

F.ymchenzi Malz

Notoakomus Lilljeborg

N. monuchu Liljbeborg





Balikpapan Bay



littoral (5 m)




Seria (N. Borneo)

littoral (2653m)


S . Maanhan-Pr.

7826 (Taiwan)







littoral assemb.






littoral (1.5 m)



N.persica Guerney



t material not directly examined by G.B. & D.L.D.


well-defined “X.-spot” which does not protrude into the valve interiorly. Platyleberis profunda

(Breman) is the only species so far described which belongs to this new genus.

Occurrence.-Holocens-Recent : bathyal Atlantic Ocean and Mediterranean (Breman, 1975;

Nachite, 1984).

Upper Pliocene: Mount S. Nicola (Sicily): Stn. 53 (Bonaduce leg. and det.). Another undescribed species is known from the Early Oligocene of Southern Moravia (Pokorny, 1981 and pers.




(PI. 3, figs. A, ByC; P1. 1, figs. G, H)

Etymology.-From latin prognatus = descending

Ho1otype.-A right valve (Pl. 3, fig., A). Upper Pliocene: Mount S. Nicola (Sicily) Stn. 53B.O.C. (Bonaduce Ostracode Collection): 795.

Paratypes.-2 valves from the same sample. B.O.C. 796.

Description.-The shape of the valves is very similar to that of X. communis Miiller in lateral

view, with an anteriorly obtusely rounded, postero-ventrally upturned and antero-ventrally gently

concave left value (Pl. 1, fig. H). The right valve appears less elongated (Pl. 1, fig. G). In dorsal

view, the carapace is subacutely rounded anteriorly and very inflated postero-ventrally.

Size.-L = 350-370pm, H = 250-260 pm.

Aj7nitie.s.-Xestoleberisprognata n. sp. differs from X.communis Miiller and X.glabrescensReuss

due to its smaller size (X.communis, L = 600 pm; X. glabrescens, L = 600 pm), more upturned

postero-ventral margin and peculiar posterior inflation that is best seen in dorsal view.

Environment.-This species has been found at the type-locality associated with numerous species

of Krithe, Henryhowella, Buntonia, Cytheropteron testudo etc. and the assemblage appears absolutely

uncontaknated by shallower fauna. The evaluated minimum palaeodepth corresponds to 600800 m.

Remarks.-Benson (1976) and Berggren et al. (1976) cite X.prognatu n. sp. as X. glabrescens

Reuss in an Upper Miocene deep-sea ostracod assemblage from El Cuervo (Span).

THEXestoZeberis GROUPS

The Xestoleberis species taken into consideration have been classified into three groups on the

basis of their morphological features.




COMMUNIS Muller group

(Text-fig. 2 E; P1. 4, fig. A; P1. 5, figs. A, B; P1. 3, figs. D-H)

A XestoIeberis group of species, characterised by more or less rounded valves in lateral view

(especially the LV). The hinge is hemi- and antimerodont with long, crenulate cardinal teeth. The

calcareous lamella shows (e.g. X.communis) opaque patches in some species. The “X.-spot” is commonly divided into two cells. In the littoral species, the “X.-spot” is strongly calcified and protrudes on to the inner side of the calcareous lamella. The ocular dioptric structure is generally

plano-convex and sometimes appears delineated by a shallow groove. The anterior part of the

selvage in the left valve is widely rounded and does not reach the outer margin.

The second antenna does not show a dimorphic distal claw “Gm”. The hemipenis includes a

thin conical vas deferens and an ejaculatory tube of intermediate length that is commonly S-shaped.

The sclerotized sleeve of the ejaculatory tube is large. (See Miiller, 1894, P1. 25, fig. 32; and Athersuch, 1976, Text-fig. 8).

Species.-X. communis Miiller, 1894; X.rara Miiller, 1894; X.ventricosa Miiller, 1894; X.glabrescens Reuss, 1850, etc.


(Text-fig. 2 D, F, G; P1.4, figs. E-G; P1. 2, figs. E, F; P1. 3, figs. I, J)

A XestoIeberis group of species which ranges between 400 and 700 pm in size and which is characterized by generally elongated valves with a gently concave ventral margin. The “X.-spot” is

from weakly to well-deveoped but always without a protrusion and consists of only one cell.

When present the lenses are plano-concave. The distal part of the central hinge-bar is denticulate.

The second antenna does not show a dimorphic distal claw “Gm”. The hemipenis (Text-fig. 3 E)

includes a large membraneous vas deferens and a long ejaculatory tube that is largely coiled and

conically shaped.

Species.-Xestoleberis plana Miiller, 1894; X. dispar Muller, 1894; X.plauta Athersuch, 1976;

X.fuscomaculata Muller, 1894; X. parva Miiller, 1894; X . perula Athersuch, 1976; X. pellucida

Muller, 1894; X. sp. Nascimiento.


ARCTURI Triebel group

(Text-fig. 2 A, B; Text-fig. 3 A-D; P1. 4, figs. H, I ; P1. 5, figs. E-J; P1. 2, figs. G-K)

A Xestoleberis group of species characterised by elongated valves with a gently arched dorsal

margin. The hinge is of hemimerodont-type with slightly crenulate cardinal teeth. The central

hinge-bar appears thin, poorly-developed and smooth. The selvage extends anteriorly to the proximity of the outer margin. The “X.-spot” is weakly developed even in surface literal dwellers. The

size of the carapace is generally less than 400 pm.

The second antenna (Text-fig. 3 A, B) shows a dimorphic distal claw “Gm”: The male claw is

strongly pectinate as compared to that of the female.

The hemipenis (Text-fig. 3 C, D) includes a large membranaceous vas deferens and a short ejaculatory tube, that is ;ell sclerotized and commonly L-shaped. The distal lobe “a” of the hemipenis is elongated.

PLATE2-Figs. A-D. Plutyleberis profundu. A. RV from inside. Alboran Sea. Stn. SU-8107. B. LV from inside.

Upper Pliocene: Mount S. Nicola Stn. 53. C. &spot of LVfrom inside of the same specimen of B. D. “X.-spot”

of RV from inside. Saba Bank (Caribbean Sea) Stn. 108. Figs. E. F. Xestoleberis dispur. E. LV from inside.

Banyuls/Mer. F. &spot and ocular lens. Same specimen of E. Figs. G-K.Xestoleberis delumurei. G . RV from

from inside. Banyuls/Mer. K. X.-spot and ocular area

inside. Banyuls/Mer. H, I. X.-spots of RV (I) and LV (H)

of LV from inside. Scario; J. Microxestoleberis nunu. LV from inside with eye-spot. Argeles. (s = X.-spot,

o = lens, dm = dorsa muscle scars).




3-A-D. Xestoleberis delmarei (Banyuls/Mer): A. General view of second antenna 3.B. Detail of

the second antenna 9.C, D. Details of the hemipenis (GM, Gm-distal claws of the antenna; a, b-distal lobes

of the hemipenis; VD-vas deferens; ET-ejaculatory tube; shclerotized sleeve). E.XestoleberispIuna (Argeles):

Hemipenis in general vifw.

PLATE>Figs. A-C. Xestoleberis prognutu n. sp. A. RV from inside with X.-spot. Upper Pliocene: Mount S.

Nisola Stn. 53. B. LV from inside with X.-spot. Mount S. Nicola Stn. 53. C. Detail of the X.-spot area of the LV

from inside. Figs. D, E. Xestoleberis communis. D. LV from inside with X.-spot. Banyuls/Mer. E. X.-spot and

ocular lens of the RV from inride. Figs. F-H. Xestoleberis sp. gr. communis (Scario). F. R V from inside with X.spot and ocular lens. G. Detail of the X.-spot and ocular lens of RV from inside. H. Detail of X.-spot with

remnants of tissues in the LV from inside. Figs. I, J. Xestoleberis purvu r;! (Scario). I. R V from inside. J. Details

of X.-spot. Fig. K.Xestoleberis sp. 1. Detail of the X.-spot and of the ocular lens of the R V from inside.

Upper Miocene Cacela (Algarve), Portugal. Fig. L. Notodromus persicu 3.RV from inside with detail of the

ocular lens. Neue Siedlersee (Austria). (s = X.-spot, o = lens).



Species.-X. arcturi Triebel, 1956; X. galapagoensis Gottwald, 1983; X . delamarei Hartmann,

1953; X. costata Hartmann, 1953; X. ? xenomys Barbeito-Gonzalez, 1971.


G.W. Muller, 1894

(PI. 4, figs. C-E; P1. 2, fig. J)

A Xestoleberidid group characterised by its elongated valves and small shape (less than 400,um).

The hinge is adont and consists in a thin uncrenulated central bar in the left valve. The anterior

marginal area appears large and with a reduced number of simple marginal pore-canals. The inner

calcareous lamella is well developed.

The second antenna shows a dimorphic claw “Gm”. The male claw is strongly sclerotized and

pectinate as compared with that of the female which appears as a thin seta (see Muller, 1894, P1.

39, figs. 45, 46).

Species.-Microxestoleberis nana Muller, 1894.


The Median Eye

Most of the Xestoleberididae have a median, nauplius, eye formed by three ocelli (two lateral

and a median one). Their main structure follows the model described by Nowikoff (1908) (see data

in Hartmann, 1967; Andersson and Nilsson, 1981 and here Text-fig. 1 F). Basically, an ocellus is

formed by a pair of corneal (lens) cells, several retinal cells, a refractive tapetum and a dark pigmented cup. The axons of the retinal cells form an efferent nerve.

Species such as Xestoleberis parva (Text-fig. 2 G) have three ocelli grouped together but most

of the Xestoleberididae species have lateral ocelli that are widely separated from the median one

(e.g. Xestoleberis decipiens, Text-fig. 2 C ; X.plana, Text-fig. 2 F).

Theoretically, with one median and two widely spaced laterally oriented ocelli the Xestoleberidids are able to see simultaneously a larger area than species with compact median eyes.

The Ocular Structures of the Carapace, Introductory Notes

We have already mentioned that many Xestoleberididae species display a lens on the carapace

in front of the lateral eye, which is more or less well-defined as compared with the surrounding

area. This lens is located within the procuticle of the outer calcified lamella and, consequently, the

light rays are difracted when crossing the more dense medium and concentrated on the retinal

cells. Theoretically, an ostracod biconvex lens such as one can find in some Xestoleberididae (e.g.

species of the genus Foveoleberis, see further details) can be compared to a double prism (see PI. 3,

figs. F, G). The lens is surrounded by a clear ring which may play the role of a diaphragm. Theoretically, this helps once again to focus the light rays within the lateral ocellus. Also, at low magnification, the lenses of many Xestolberididae are visible as a translucent spot surrounded by an opaque milky calcitic area (e.g. Text-fig. 2 D). We believe that the crystals within the lens area are

more tightly packed and have a position parallel to the surface of the valve, as compared with the

surrounding area where the crystals should be more loosely packed and inner micro-voids

should form. A similar situation can be observed in valves corroded by chemical and microbial


&Fig. A. Xestoleberis communis. Left valve from inside (Banyuls/Mer). Fig. B. Platyleberis profunda.

Right valve from inside. Upper Pliocene. Mount S. Nicola. Sample 53 (Sicily). Figs. C-E. Microxestoleberis

nana 9. C. LV from inside. D. RV from inside. E. LV from outside (Argeles). Figs. F, G. Xestoleberis

dispar 9. F. RV from outside. G. Carapace in dorsal view (Banyuls/Mer). Fig. H. Xestoleberis xenomys

8 . Carapace in dorsal view. Gulf of Taranto (Stn. 134 E). Fig. I. Xestoleberis delamarei 3.Carapace in

dorsal view (Banyuls/Mer). (a = X.-spot).

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Chapter 30. To see and not to be seen: The evolutionary problems of the Ostracoda Xestoleberididae

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