OCEANOGRAPHY and MARINE BIOLOGY: AN ANNUAL REVIEW (Volume 44) - Chapter 5 ppsx

Epidermal glandular structures, subepithelial glands, glands in the notum tissue and glands in the visceral cavity are distinguished see Table 1.. Glandular structures confined to the epi

Oceanography and Marine Biology: An Annual Review, 2006, 44, 197-276

© R N Gibson, R J A Atkinson, and J D M Gordon, Editors

Taylor & Francis

DEFENSIVE GLANDULAR STRUCTURES

IN OPISTHOBRANCH MOLLUSCS — FROM HISTOLOGY TO ECOLOGY HEIKE WÄGELE1, MANUEL BALLESTEROS2& CONXITA AVILA3

1Rheinische Friedrich-Wilhelms-Universität, Institut für Evolutionsbiologie, An der Immenburg 1, 53121 Bonn,

Germany and Zoologisches Forschungsmuseum Koenig, Adenauer Allee 160, 53113 Bonn, Germany

E-mail: hwaegele@evolution.uni-bonn.de

2Facultat de Biologia, Universitat de Barcelona,

Av Diagonal 645, 08028 Barcelona, Catalunya, Spain

E-mail: mballesteros@ub.edu

3CEAB-CSIC, c/Accés a la Cala Sant Francesc 14,

17300 Blanes, Girona, Catalunya, Spain

E-mail: conxita@ceab.csic.es

Abstract Opisthobranch molluscs are an extremely interesting group of animals, displaying a wide diversity in shape, colour and life strategies Chemical ecology of this group is particularly appealing since most species have a reduced or absent shell and have developed chemical defences

to avoid predation New results on defensive glandular structures as well as a compilation of literature data in sea slugs (Opisthobranchia, Gastropoda, Mollusca) are presented in this review Investigation of these structures is based on detailed analyses of the histology of many representative species of all major taxa of the Opisthobranchia The results are correlated with previous and new findings of secondary metabolites in these animals and are set in a phylogenetic context Addition- ally, information on food sources is given Also, an hypothetical scenario relating chemical ecology

to histology is proposed This information will help future analyses to investigate defensive devices

on a much more accurate basis and allow a better understanding of evolutionary processes, which are observed independently in many opisthobranch clades.

Introduction

Defensive strategies are manifold in Opisthobranchia and comprise cryptic appearance (Edmunds

1987, Wägele & Klussmann-Kolb 2005), formation of spicules (Cattaneo-Vietti et al 1993, 1995), uptake of nematocysts from cnidarian prey (most recent literature: Gosliner 1994a, Martin &

Walther 2002, 2003, Wägele 2004), incorporation of toxic metabolites from the prey, or even de novo synthesis of chemicals Several reviews have covered the last topic of chemical ecology in

molluscs (Karuso 1987, Cimino & Sodano 1989, Faulkner 1988, 1992, 2000, 2001, Pawlik 1993, Avila 1995, 2006, Cimino & Ghiselin 1998, Cimino et al 2000, Stachowicz 2001, Amsler et al 2001) Furthermore, some reviews have dealt with natural products from particular groups, such

as porostome nudibranchs (Gavagnin et al 2001), dorids and sacoglossans (Cimino et al 1999, Cimino & Ghiselin 1998, 1999), or gastropods in general (Cimino & Ghiselin 2001), incorporating

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an evolutionary perspective in their analysis In opisthobranchs, Faulkner & Ghiselin (1983) cussed the importance of the acquisition of defensive chemicals during slug evolution, thus allowing the reduction of the shell (see also Wägele & Klussmann-Kolb 2005) This may have many ecological implications, such as the advantage of searching for new food sources, the exploitation

dis-of new habitats, and the development dis-of mantle glands or structures, among others Cimino & Ghiselin (1999) went even further in claiming that chemical defence is the driving force of opisthobranch evolution.

Chemical defence is the main topic in molluscan chemical ecology, although it is by no means

the only one The importance of correctly demonstrating in situ activity against co-occurring

predators has been a subject of repeated debate (Faulkner 1992, Avila 1995) However, many compounds are still assumed to have a defensive role without the supporting evidence of reliable

ecological experiments Ecological activity of the compounds has been evaluated in situ, against

co-occurring predators for only a few species (Thompson 1960, Avila & Paul 1997, Johnson & Willows 1999, Marín et al 1999, Avila et al 2000, Becerro et al 2001, Gosliner 2001, Iken et al.

2002, Rogers et al 2002, Penney 2004) The methodological difficulties in carrying out in situ

experiments or using co-occuring predators are probably responsible for the scarce information available To overcome these problems, some studies used predators that do not occur in the same habitat (e.g., Mollo et al 2005) On the other hand, there is also some literature that deals with parasites on opisthobranchs (Edmunds 1964; Arnaud 1978; Carefoot 1987; Huys 2001; Schrödl

2002, 2003; see also Rudman 2000a) but nothing is known about possible defensive strategies against these parasites.

Since the review of the natural products of opisthobranch molluscs published 10 years ago (Avila 1995), many other articles have appeared that deal with opisthobranchs and which describe new interesting aspects of their chemistry (see Faulkner 2002 and previous reports; Blunt et al 2005) Unfortunately, they cannot all be reviewed here The geographic variation of natural products

in Asteronotus cespitosus (Fahey & Garson 2002) and in Cadlina luteomarginata (Kubanek et al.

2000) has provided new insights into the field Kubanek et al (2000) suggested that in some

nudibranchs, de novo biosynthesis may be modulated by habitat-specific external factors, thus

working only when dietary compounds are not available The authors suggested this represents an intermediate stage in the evolution of nudibranch chemical defences, between the probably primitive

chemical sequestration from diet and the more evolved processes of de novo biosynthesis The fact

that some nudibranchs may only biosynthesise when dietary compounds are not available is an

open question that needs to be tested in other species Among nudibranchs, only C luteomarginata and Dendrodoris grandiflora seem to possess both dietary sequestered compounds and biosynthetic

chemicals (Cimino et al 1985a, Avila et al 1991a, Kubanek et al 2000) Regarding the origin of these compounds, the number of biosynthetic compounds, compared with those obtained from the diet, continues to increase (Garson 1993, Cimino & Sodano 1994, Avila 1995, Faulkner 2002) The

sesquiterpene aldehydes of the nudibranch Acanthodoris nanaimoensis are another example of

de novo biosynthesis (Graziani & Andersen, 1996) Further studies on biosynthesis include Fontana

et al (1999a, 2003) and Jansen & de Groot (2004), and others reviewed by Garson (2001) and Cimino et al (2004).

Dietary chemicals are selected by a still unknown mechanism Faulkner (1992) proposed two different mechanisms by which the selection of chemicals could be achieved, but this was never

studied in detail The sea hare Stylocheilus striatus accumulates very different metabolites when

offered artificial diets (Pennings & Paul 1993) Fontana et al (1994b) showed that in the laboratory

a chromodoridid species was able to accumulate in the mantle glands compounds from a sponge that is not usually its prey in the field These experiments would support the idea that the initial role of accumulation structures was that of excretion or autoprotection from the dietary chemicals and evolved later into a defensive mechanism.

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DEFENSIVE GLANDULAR STRUCTURES IN OPISTHOBRANCH MOLLUSCS

199

The available information on location and structure of the possible storage organs for chemical defences is scarce and mainly based on literature from the nineteenth to the early twentieth centuries (e.g., Blochmann 1883, Vayssière 1885, Perrier & Fischer 1911) The older literature was reviewed

by Hoffmann (1939) More recent studies including histological structures are found, for example,

in Edmunds (1966a,b), Thompson & Colman (1984), Thompson (1986), Gosliner (1994a), Wägele (1997), Kolb (1998), Brodie (2005) and Wägele & Klussmann-Kolb (2005) The couple Evelyn and Ernst Marcus, to whom we owe many thorough descriptions of opisthobranchs, very often included histological investigations when describing species, but only in very few cases do these cover defensive glands (also called repugnatorial glands) and then only in a rather sketchy way (e.g., Marcus & Marcus 1955; Marcus 1957, 1958, 1959) The same holds true for many descriptions from the Danish opisthobranch scientist Rudolph Bergh, which are not included here for the same reason.

Recent and more extensive investigations on defensive glands are mainly confined to the mantle dermal formations (MDFs) in the doridoidean family Chromodorididae (García-Gomez et al 1990, 1991; Cimino et al 1993a; Avila & Paul 1997) and the glands of sea hares (Johnson & Willows 1999) Few investigations deal with epithelial structures or other glandular structures (e.g., Marín

et al 1991, Avila & Durfort 1996, Wägele 1997, Wägele & Klussmann-Kolb 2005) MDFs are suspected to store biochemicals from sponges, the food items of chromodorids They are discussed

as important key characters in the evolution of this particular family (Gosliner & Johnson 1994, Gosliner 2001, Wägele 2004) but, in fact, it is now known that other groups of opisthobranchs that

do not forage on sponges also possess MDFs (see Wägele 1997, 2004 and this study) Finding

MDFs in a bryozoan-consuming nudibranch (Limacia clavigera) (Wägele 1997) and in an consuming sacoglossan (Plakobranchus ocellatus (see Wägele 2004)) renders invalid all the pre-

algae-vious assumptions of the mantle glands as an exclusive characteristic of the Chromodorididae Until now, very few attempts have been made to relate knowledge on defensive chemicals to

glandular structures known from histology (e.g., Marín et al 1991 for Tethys fimbria, Marín et al.

1999 for Cephalaspidea) Avila (1993), Fontana et al (1994b) and Avila & Durfort (1996) showed

a preliminary relationship between some defensive glands and natural products for several species

of nudibranchs Actually, all the assumptions on location of chemicals are based on dissection and separation of body parts (e.g., MDFs, mantle border, etc.), and not on cytology or cytochemistry.

This is the case in most of the located compounds, such as furanosesquiterpenes of Hypselodoris and Ceratosoma species, diterpenes of Chromodoris species, sesterterpenes of Glossodoris species,

or sesquiterpenes of Dendrodorididae This study tries to fill the gap in the knowledge of the relationship between glandular structures and defensive compounds by summarising histological studies on defensive glands or structures within Opisthobranchia and by tabulating published results

on their secondary metabolites Furthermore, the development of defensive glands, which are

supposed to accumulate dietary chemicals in juvenile specimens of Hypselodoris species, was

studied in order to ascertain their ontogeny.

Material and methods

To analyse the maximum information available on the defensive glands at histological, ecological and chemical levels, several species were selected from each group Selection was based mainly

on the availability of biological material for carrying out rigorous histological studies and also on existing data on ecology and chemistry for the species However, this proved to be very difficult because very often data are incomplete For example, data may be available on the chemistry but not on the histology and ecology of a species, and vice versa Considerable effort has been made

to include as many species as possible in the review so that it offers all the information available

© 2006 by Taylor & Francis Group, LLC

For analysis of the chemical composition of some structures (especially the mantle dermal formations), specimens of six species were embedded in Paraplast and sectioned (thickness of sections 5–6 μm) Different staining techniques were applied including two trichrome stains (Poinceau-Acidfuchsin-Azophloxin after Goldner, and Azocarmine-Aniline-Orange G after Heiden- hain) and a special staining technique for connective tissue (after Pasini) All methods are described

in Böck (1989) Except where noted otherwise, staining records in the text and tables usually refer

to Toluidine blue.

Hypselodoris villafranca specimens for the ontogenetic studies were collected in Blanes and

Tossa (Catalonia, Spain) in August 2003 Sizes of the juveniles ranged from 3–6 mm length Some adults (15 mm) were also collected and studied to compare with the juveniles of the same popu- lations They were fixed as described above.

Results

Description of glands

Nearly all opisthobranch and pulmonate species investigated have more glands than just the repugnatorial or defensive glands and the foot in particular is highly glandular These latter struc- tures, and others which are more likely involved in crawling (e.g., the tubular foot gland in pulmonates and some cephalaspideans), are not listed here, only those which might be of defensive value.

The glandular structures can usually be assigned to certain types, some of which are already well known, others are newly described here Defensive glandular structures are located in different areas of the animals They can be located in the epidermis and are therefore part of the outer epidermis They can lie subepidermally in the notum as single glandular structures or form distinct organs Some lie in the notum, usually forming rather large organs In a few cases, large glands are present in the visceral cavity Table 1 and Figure 1 to Figure 9 give an overview of the types Table 2 lists all the species investigated during the study and lists some types of glands found in particular species The food and the chemical structure of the known secondary metabolites from the slug are also provided (Table 2) The glands are described and listed with regard to their location

in the organism Epidermal glandular structures, subepithelial glands, glands in the notum tissue and glands in the visceral cavity are distinguished (see Table 1).

Glandular structures confined to the epidermis (Table 1, Table 2 Column 9)

Single glandular cells (Table 1) Single glandular cells are mainly located in the notum epithelium

and are widely spread The contents of the vacuoles of the cells mainly stain dark violet, indicating acid mucopolysaccharides Although morphological and histological complexity is rather low in these

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DEFENSIVE GLANDULAR STRUCTURES IN OPISTHOBRANCH MOLLUSCS

201

kinds of cells, a typical appearance of single glandular cells was noticed in many representatives of the Dendronotoidea ( Figure 1A, Marionia blainvillea; see also Table 2 Column 9) Here the cuplike glandular cells are characterised by a huge vacuole, staining homogenously dark violet, indicating acid mucopolysaccharides In other taxa, the contents of the vacuoles may be granular or even homogenous

(Figure 1B, Dendrodoris nigra, arrow) This indicates the presence of different substances in the glandular cells In Roboastra gracilis the glandular epithelium is characterised by numerous extremely tall violet-stained mucous cells with a granular appearance (continued on page 227)

Table 1 Overview of the different types of glandular structures arranged according to location, composition and staining properties

Gland type

Staining propertiesViolet staining —

indicating acid mucopolysacharides

Bluish staining indicating neutral mucopolysaccharides

Nonstaining — indicating acidic or other substances

Single gland cells in

epidermis

Cup cells (e.g., in many Dendronotoidea)(Figure 1A,B)

Cells with a huge vacuole, contents staining homogeneously(Dendrodorididae) (Figure 1B)

Spongy glands (Figure 1C)

Single glands

forming a layer

Hypobranchial gland (Figure 1D)

Subepithelial glands Single glandular cells of

moderate size usually opening to the outside (Figure 4B at bottom)

Bohadsch gland or opaline gland (Figure 2D,E)

‘Cellules spéciales’

(Figure 1F,G)

Blochmann’s glands:

some Cephalaspidea (Figure 2A,B) and Anaspidea (here known as ink gland or purple gland) (Figure 2C)

Subepithelial acid glands (Pleurobranchoidea)(Figure 2G)

(Doriopsilla, Melibe, etc.)

(Figure 6B–D, Figure 9A–F)

Agglomeration of glandular

cells (Thecacera, Cadlina)

(Figure 4B,C)

MDFs (Chromodorididae) (Figure 5A–F, Figure 6E–G, Figure 7A–F)

Plocamopherus)

(Figure 4D–F)

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Natural products (references)

Previous histology (references)

Unknown Perrier & Fischer

1911, Hoffmann

1939, Wägele & Klussmann-Kolb 2005

Pupa solidula

Linneus, 1758

Web site Seaslugforum)

Hydatinidae Hydatina physis

Linneus, 1758

Web site Seaslugforum)

Thompson 1998)

Klussmann-Kolb 2005

Klussmann-Kolb 2005,

Chia 1989, own studies)

OC (Spinella et al 1998, Alvarez et al 1998, Izzo

et al 2000) **

Haminoea cymbalum

(Quoy & Gaimard, 1833)

Web site Seaslugforum)

SQ (Poiner et al 1989, Fontana et al 2001) **

Thompson 1998)

MO (Spinella et al

1992b, 1992c, 1993, Marín et al 1999) **

Bullidae Bulla vernicosa

Gould, 1859

Web site Seaslugforum)

(Bulla striata:

discoidal glands above gill, open into mantle cavity)Smaragdinellidae Phanerophthalmus

Unknown

Natural products (references)

Previous histology (references)

Smaragdinella cf calyculata

(Broderip & Sowerby 1829)

Cylichnidae Scaphander lignarius

Lineus, 1758

gland

Foraminifera, Annelida, Crustacea, Mollusca, Echinodermata,(Rudman Web site Seaslugforum)

OC, IA? (Guiart 1901, Cimino et al 1987a, 1989b) ***

Perrier & Fischer

1911, Hoffmann 1939

Gosliner, 1989

& Klussmann 2003Runcinidae Runcina adriatica

Thompson, 1980

*Hoffmann 1939,

Ovies 1983

Caulerpa, Halimeda

(Jensen 1993)

PP (Ireland et al., 1979, Ireland & Faulkner 1981, Ksebati 1985, Ksebati &

Schmitz,1985, Gavagnin

et al 1996, 1997a, 2000

(some as Tridachia crispata)) **

Green algae (Jensen

1993, Gavagnin et al

1994, Trowbridge, 2004)

PP (Gavagnin et al 1992, 1994c) **

Thompson 1960,Wägele 1997

Kawaguti et al

1966, Wägele & Klussmann-Kolb 2005

Thuridilla hopei

(Verany, 1853)

contents of subepider-mal glands

Derbesia tenuissima

Green algae (Gavagnin et al

Natural products (references)

Previous histology (references)

Perrier & Fischer 1911,

Klussmann-Kolb 2004

Akeridae Akera soluta

(Gmelin, 1791)

Web site Seaslugforum)

Unknown ** *Perrier & Fischer

1911, *Hoffmann

1939, *Morton 1972

Aplysiidae Aplysia parvula

Guilding in Mörch, 1863)

0 0 + ? 0 0 Opaline gland Green and red algae,

Delisea pulchra, Laurencia filiformis, Portieria hornemannii

MT DT SQ (Willan 1979, Fenical et al 1979, Miyamoto et al 1995, de Nys et al 1996, Yamada

& Kigoshi 1997, Higuchi et al 1998, Rogers et al 2000a,b, Ginsburg & Paul 2001, Jongaramruong et al

2002)

*Marcus & Marcus 1955,

Klussmann-Kolb 2004

(Carefoot 1967, Quiđố et al 1989, Faulkner 1992)

MT DT SQ TS NC OC (Minale & Riccio 1976, Castedo et al 1983, Jiménez et al 1986, Quiđố et al 1989, Ortega et al 1997, Butzke et al 2002, Findlay & Li 2002)

Blochmann 1883, Mazzarelli 1893, Hoffmann 1939, Merton 1920, Eales 1921, Wägele 1997, Wägele & Willan 2000,

Klussmann-Kolb 2004

Bursatella leachii

Blainville, 1817

0 + 0 0 0 0 Opaline gland Cyanobacteria

(Rudman Web site Seaslugforum)

Dolabrifera dolabrifera

(Cuvier, 1817)

Hoffmann 1939, Wägele &

Klussmann-Kolb 2005

Natural products (references)

Previous histology (references)

1905, Hoffmann 1939

Clione limacina

(Phipps, 1774)

glandularcells

Thecosomata TS TT (Baalsrud 1950,

Fisher et al 1956, McClintock & Janssen

1990, Yoshida et al

1995, Bryan et al 1995, McClintock & Baker

1997 (some as C.

antarctica), Kattner

et al 1998)

Hoffmann 1939, Wägele &

Klussmann-Kolb 2005

1993, Ebel et al 1999, Thoms et al 2003)

Wägele &

Klussmann-Kolb 2005,

*Mazzarelli 1897,

*MacFarland 1966Umbraculidae Umbraculum umbraculum

Klussmann-Kolb 2005

Willan & Bertsch, 1987

gland

IA (Avila, unpublished data)

Wägele 1997, Wägele & Willan 2000

*Thompson 1960,

*1969,Thompson &

Porifera ?Anthozoa (Rudman Web site Seaslugforum)

IA ( Franc 1968, Thompson, 1969, 1970, Edmunds & Thompson

1972, Marbach &

Tsurnamal 1973, Thompson & Colman 1984)

Marbach &

Tsurnamal 1973, Thompson &

Colman 1984, Wägele &

Klussmann-Kolb 2005

Berthellina edwardsii

(Vayssière, 1896)

glandSubepithelialacid gland

2000)

SQ (Iken et al 1998, Avila et al 2000)

Natural products (references)

Previous histology (references)Doridoidea

Onchidorididae Acanthodoris pilosa

Abildgaard in Müller 1789

Nybakken Web site)

Thompson 1960, Wägele 1997

Onchidoris bilamellata

(Linné, 1767)

Bryozoa (McDonald &

Nybakken Web site)

TS IA? (Herdmann &

Clubb 1892, Edmunds

1968, Voogt 1970, 1972,

1973, Potts 1970, 1981, Thompson 1960)

Potts 1981, Thompson 1988, Wägele 1997,

* Thompson 1960,

*Edmunds 1968Goniodorididae Ancula gibbosa

& Nybakken Web site)

Bryozoa (McDonald &

Nybakken Web site)

Corambidae Corambe lucea

Bergh, 1869

Nybakken Web site)

Schrödl & Wägele 2001,

*Fischer 1892,

*MacFarland & O’Donoghue1929Gymnodorididae Gymnodoris striata

(Eliot, 1908)

opisthobranchs(McDonald &

Nybakken Web site)

Unknown

Polyceridae Polycera quadrilineata

(Müller, 1776)

Nybakken Web site)

Wägele 1997

Polycerella emertoni

Verrill, 1880

Nybakken Web site)

Probably other polycerids (Pola et al

Bryozoa (McDonald &

Nybakken Web site)

Klussmann-Kolb 2005

Triophidae Crimora papillata

Alder & Hancock, 1862

Nybakken Web site)

Nybakken Web site)

Natural products (references)

Previous histology (references)

Plocamopherus ceylonicus

(Kelaart, 1858)

gland

2 types of MDF-like structures

Bryozoa (McDonald &

Nybakken Web site)

Porifera (McDonald &

Nybakken Web site, Carmely et al 1989)

Nybakken Web site)

TS TT DG (Cimino et al

1993b, Zubía et al 1993, Soriente et al 1993, Armstrong et al 2000 (see also Avila 1995))

Potts 1981

Austrodoris kerguelenensis (Bergh,

1884)

Cynachira barbata,

Porifera(Wägele 1989a, Iken et al 2002)

DG (Davies-Coleman &

Faulkner 1991, Avila

1995, Gavagnin et al

1995, 1999a, 1999b, 2003a, 2003b, Iken et al

2002)

Doris verrucosa Linné,

& Durfort 1996

Jorunna tomentosa

(Cuvier, 1804)

Nybakken Web site)

Porifera(McDonald &

Nybakken Web site, Castiello et al 1978,

1980, Cimino et al

1980b, 1982, Cattaneo-Vietti et al

1993, 2001 Avila

1993, 1995, 1996, Gemballa &

Schermutzki 2004)

AC TS (Voogt 1973, Castiello et al 1978,

1980 Cimino et al

1980b, 1981, 1982, 1985a, 1989c, 1990c Avila 1992, 1993)

Avila 1993, Avila

& Durfort 1996, Wägele 1997

Platydoris argo

(Linneus, 1767)

Bryozoa (McDonald &

Nybakken Web site, Megina et al 2002)

TS (Avila 1992, 1993)

Natural products (references)

Previous histology (references)

Rostanga pulchra

MacFarland, 1905

pennata,

Porifera (McDonald &

Nybakken Web site, Ong & Penney, 2001)

TT (Coulom 1966, Anderson 1971, 1973)

*Foale & Willan 1987

Chromodorididae Cadlina marginata

Porifera (McDonald &

Nybakken Web site, Thompson et al 1982, Hellou et al 1982, Tischler & Andersen 1989)

SQ DT ST (Hellou et al

1981, 1982, Thompson

et al 1982, Walker 1982, Gustafson et al 1985, Gustafson & Andersen

1985, Tischler &

Andersen 1989, Tischler 1990, Faulkner

et al 1990, Tischler et al

1991, Burgoyne et al

1993, Dumdei 1994, Fontana et al 1995, Dumdei et al 1997a, Kubanek et al 1997,

2000, Kubanek 1998 (but see also Avila 1995))

*Marcus 1955

(Cadlina rumia)

Nybakken Web site, Barbour 1979)

Ortea and Pérez, 1983

& Durfort 1996,

*Marcus 1955

(Glossodoris) neona) Chromodoris krohni

(Verany, 1846)

Nybakken Web site)

DT (Avila et al 1990b, Avila 1992, 1993, 1995)

Chromodoris luteorosea

(Rapp, 1827)

Nybakken Web site)

DT (Avila et al 1990b, Cimino et al 1990a, Gavagnin et al 1992, Puliti et al 1992, Avila

1992, 1993, 1995)

Chromodoris purpurea

(Laurillard, 1831)

Nybakken Web site)

DT (Avila et al 1990b, Avila 1992, 1993, 1995)

(O’Donoghue, 1925)

Glossodoris atromarginata

(Cuvier, 1804)

Nybakken Web site)

DT (Fontana et al 1997, 1999b)

ST (Rogers & Paul 1991, Avila & Paul 1997)

Avila & Paul 1997

Glossodoris rufomarginata

(Bergh, 1890)

Nybakken Web site)

ST (Gavagnin et al 2004)

Natural products (references)

Previous histology (references)

Nybakken Web site)

Unknown

Hypselodoris cantabrica

Bouchet & Ortea, 1980

Porifera (McDonald &

Nybakken Web site, Bouchet & Ortea 1980, Fontana et al 1993)

SQ (Avila 1992, 1993, Fontana et al 1993)

García-Gómez

et al 1990, Avila 1993, Avila & Durfort 1996

Hypselodoris fontandraui

(Pruvot-Fol, 1951)

Porifera (Avila 1993, McDonald &

Nybakken Web site)

SQ (Avila 1993) García-Gómez

et al 1990, Wägele 1997

(Verany, 1846)

Porifera (McDonald &

Nybakken Web site, Cimino et al 1973,

1974, 1982, 1993a, Avila 1993)

ST (Cimino et al 1982, 1993a, Avila 1992, 1993)

Avila 1993, Avila

& Durfort 1996

(Avila 1993, Cimino &

Sodano 1989, Avila

et al 1990b, 1991b, Fontana et al 1994a,b)

SQ (Cimino et al 1982, Cimino & Sodano 1989, Avila 1992, 1993, Avila

et al 1990b, 1991b, Fontana et al 1994a, b

(as H webbi) Hypselodoris tricolor

(Cantraine, 1835)

Porifera (McDonald &

Nybakken Web site, Avila 1993, Fontana

et al 1993)

SQ (Cimino et al 1982, Avila 1992, 1993, Fontana et al 1993, 1994b)

García-Gómez

et al 1991, Wägele 1997, Wägele & Willan 2000

Hypselodoris villafranca

(Risso, 1818)

Porifera (McDonald &

Nybakken Web site, Cimino & Sodano

1989, Avila 1993, Avila et al 1990b, 1991b)

SQ (Cimino et al 1980b,

1982, Avila 1992, 1993, Cimino & Sodano 1989, Avila et al 1990b, 1991b, Fontana et al 1993)

(Garrett, 1873)

Nybakken Web site)

Klussmann-Kolb 2005

Natural products (references)

Previous histology (references)Dendrodorididae Dendrodoris grandiflora

(Rapp, 1827)

Fasciospongia cavernosa (= Microciona toxystila), Spongia officinalis, Porifera

(McDonald &

Nybakken Web site, Cimino et al 1975, 1980b, 1982, 1985a, 1986a, 1990b)

SQ ST MO OC (Cimino

et al 1980b, 1982, 1985a, 1986a, 1988b, 1990b, Avila 1992, 1993, Avila et al 1991a, Fontana et al 1999a, 2000)

*Brodie 2005

Dendrodoris limbata

(Cuvier, 1804)

Nybakken Web site)

SQ (Cimino et al 1981,

1982, 1983, 1985b, 1986a, 1988b, Avila

Nybakken Web site)

SQ (Okuda et al 1983) Wägele 1997,

Phyllidiidae Phyllidia flava

Aradas, 1847

Porifera (Cimino et al

1982, unpublished data of HW)

SQ (Cimino et al 1982,

1986a (as P pulitzeri)

(but see also Avila 1995)) **

(Karuso 1987, Fusetani

et al 1991, Kassühlke

et al 1991, Dumdei

et al 1997b, Wright 2003)

SQ, DT (Karuso 1987, Kassühlke et al 1991, Fusetani et al 1991,

1992, Okino et al 1996, Hirota et al 1998, Dumdei et al 1997b, Simpson et al 1997, Garson et al 2000, Wright 2003, Manzo

et al 2004)DEXIARCHIA

Doridoxidae (1) Doridoxa ingolfiana

Nybakken Web site)

Klussmann-Kolb 2005

Bergh, 1884

grouped and sunken into notum

Nybakken Web site)

Nybakken Web site)

NC (Kennedy & Vevers 1953)

Natural products (references)

Previous histology (references)

(Ascanius, 1774)

in epidermis

Hydrozoa,Octocorallia,Hexacorallia, Bryozoa (McDonald &

Nybakken Web site)

Hancockiidae Hancockia uncinata

Phylliroidae Phylliroe bucephala

Peron & Lesueur, 1810

Appendicularia(McDonald &

Nybakken Web site)

Crustacea larvae (McDonald &

Nybakken Web site)

MT TS (Ayer & Andersen

Nybakken Web site, Guerriero et al 1987,

1988, 1990)

DT (Guerriero et al 1987,

1988, 1990)

Kolb 1998, *Bergh 1866

Baba, 1949

Charcotiidae Charcotia granulosa

Natural products (references)

Previous histology (references)

Pseudotritonia antarctica

(Odhner, 1934)

(as Telarma antarctica) Pseudotritonia

Nybakken Web site)

Unknown

Janolus cristatus

(Delle Chiaje, 1841)

Nybakken Web site)

NC (Sodano & Spinella

1986, Cimino et al

1986a, Giordano et al

2000)

Trinchese 1881, Hoffmann 1939

Janolus mokohinau

Miller & Willan, 1986

Nybakken Web site)

UnknownMadrellidae Madrella ferruginosa

Alder & Hancock, 1864

Nybakken Web site)

Nybakken Web site)

Flabellina

species),

*Marcus du Reymond 1970

Nybakken Web site)

Unknown

Calmidae Calma glaucoides

(Alder & Hancock, 1854)

Hoffmann 1939, Streble 1968

Natural products (references)

Previous histology (references)Facelinidae Cratena peregrina

Octocorallia(Avila et al 1998, Slattery et al 1998, McDonald &

Nybakken Web site)

DT (Avila et al 1998, Slattery et al 1998)

Wägele 1997, Avila et al 1998

Phyllodesmium jakobsenae

Burghardt & Wägele, 2004

(Burghardt & Wägele 2004)

Unknown

(Vicente, 1975)

& Nybakken Web site)

UnknownGlaucidae Glaucus atlanticus

Forster, 1777

Siphonophora(McDonald &

Nybakken Web site)

Unknown

Eubranchidae Eubranchus exiguus

(Alder & Hancock, 1848)

& Nybakken Web site)

Edmunds 1966aTergipedidae Cuthona caerulea

(Montagu, 1804)

& Brown 1984, McDonald &

Nybakken Web site)

Onchidiidae Onchidella celtica

(Cuvier, 1817)

Diatoms, detritus, bacteria(Stanisic 1998)

OC ** (Young et al 1986, Abramson et al 1989)

Young et al 1986, Weiss & Wägele 1998

*Marcus du Reymond 1971Siphonariidae Siphonaria javanica

Natural products (references)

Previous histology (references)HETERO-

de Keyzer 1998)

Notes: All species listed have been re-investigated by histological means, except for the members of the Chromodorididae, where only a few species have been investigated For a

compilation of all available data on presence or absence of MDFs in Chromodorididae see Table 3 A question mark indicates lack of data, due to inappropriate histological slides orbecause of lack of literature data Column 7: * indicates that only one or two MFDs were found Column 8: * indicates that only one to four MDF-like structures were observed.Column 9: indicates special glandular structures, which are typical of only a small group Column 10: indicates the food preference Very often, only the general groups of prey areknown Whenever possible, details of genera or species are given Column 11: summarises known natural products The category of the substance is given, instead of the names ofthe products, as follows: AC acetylenes, DG diacylglycerols, IA inorganic acids, MO compounds with mixed origin, MT monoterpenes, DT diterpenes, SQ sesquiterpenes, STsesterterpenes, TS triterpenes and steroids, TT tetraterpenes, NC nitrogenated compounds, OC other compounds, PG prostaglandins and eicosanoids, PP polyproprionates ** indicates

that other species of the same genus have been chemically studied *** Philine alata, Scaphander lignarius and Umbraculum umbraculum do not produce an acid secretion (Avila,

unpublished data) Column 12: References including previous histological investigations and pictures on probably defensive glandular structures *indicates that other species of thesame genus are described

DEFENSIVE GLANDULAR STRUCTURES IN OPISTHOBRANCH MOLLUSCS

227

In a few species, cells are present which have a large vacuole with homogenously staining light

blue contents (Figure 1B, Dendrodoris nigra, asterisk).

Spongy glands at mantle rim (Table 1, Table 2 Column 4) This gland is also called

“Mantelrand-drüsen” (Hoffmann 1939), or “glande semi-lunaire” (Pelseneer 1888, 1894) Several members of the Opisthobranchia, belonging to many different groups, show these spongelike vacuolated cells The cells are very large, with a tiny nucleus The single large vacuole does not stain (Figure 1C,

Acteon tornatilis) The cells are actually epithelial cells but, due to their size, they can come to lie

subepthelial in comparison with the other epithelial cells Due to invagination of the epidermis, the glandular cells lie in saclike depressions In many species, these glands are located near to the mantle edge and can be clearly identified by their kind of pores, which are formed by the invagi- nation of the epidermis This glandular epithelium is restricted to the mantle rim in members of

Figure 1 Histological sections of opisthobranch epidermal and subepithelial glands (A) Marionia blainvillea

epidermis (B) Dendrodoris nigra epidermis; Arrow: single glands with acid mucopolysaccharides, asterisk: homogenously light blue stained glandular cell (C) Acteon tornatilis spongy glands, note the invagination of the epithelium (D) Chelidonura ornata, hypobranchial gland (arrow) and spongy tissue (asterisk) (E) Thu- ridilla hopei subepithelial glands with crystalline structures (F) Chelidonura pallida glandular stripe, note the duct of one of the cells (arrow) (G) Akera soluta glandular stripe, note the small duct (arrow) Scale bars in μm.

© 2006 by Taylor & Francis Group, LLC

and a huge nonstaining vacuole ( Figure 1D, Chelidonura ornata, asterisk) In these cases, however,

no openings through the epidermis could be observed Therefore, this type of cell is not considered

to be homologous with the spongy glandular epithelium shown in Figure 1C.

Hypobranchial gland (Table 1, Table 2 Column 3) This gland consists of elongate epidermal cells

which stain light violet to red They form a compact layer, with tiny supporting cells interspersed

(Figure 1D, Chelidonura inornata, arrow) In some cephalaspidean species, this gland is voluminous and secretes copious amounts of mucus (e.g., in Haminoea callidegenita) Sometimes, this glandular

layer is reduced to few cells interspersed with ordinary epithelial cells When the locality and staining properties of these few cells are identical to the typical hypobranchial gland in other opisthobranchs, these glandular cells are considered to be a hypobranchial gland This gland is mainly found in species which still have a mantle cavity (e.g., many Cephalaspidea).

Subepithelial glands (Table 1)

Subepithelial single glands producing acid mucopolysaccharides (staining violet to red) (Table 1)

The single cells have a drop-like structure with their duct-like part running between the epidermal cells and opening to the outside The cells stain violet These glands are widespread in many Opisthobranchia and probably are one of the major glandular structures ( Figure 4B, Thecacera pennigera) Some species (e.g Elysia crispata) are completely covered by this type of gland In Thuridilla hopei, the contents of the cells resemble small globular crystals (Figure 1E) This is

rather unusual and was observed only in this species.

Opaline gland (gland of Bohadsch, grape-shaped gland) (Table 1, Table 2 Column 9) The opaline

gland lies beneath the ventral floor of the mantle cavity The cells are considerably larger than the normal subepithelial cells and open to the outside with a small pore each They also have a large nucleus ( Figure 2D arrow, Bursatella leachii) In a few aplysiids only, the single glandular cells

open into a common duct, which leads to the outside The opaline gland is considered to be present only in Anaspidea Similar glands have been detected in members of the Gymnosomata (Figure

2E arrow, Clione limacina) They are also considered to be opaline glands.

Supepithelial single gland cells staining bluish (cellules spéciales, glandular stripe) (Table 1, Table

2 Column 6 as glandular stripe) The contents of these cells stain bluish, the nucleus is of moderate

size (Figure 1F, G) Sometimes a duct leading to the outside can be observed (Figure 1F, G arrows) These supepithelial glandular cells are widespread in some taxa (e.g., Anaspidea, Cladobranchia) but are missing in others (e.g., Doridoidea) In gill-bearing opisthobranchs, like cephalaspids and anaspids, the position of the glandular cells is related to the gill The glands are usually found in the hyponotum, the ventral side of the notum covering and protecting the gill In gill-less species (mainly the Cladobranchia) the glandular cells are arranged into a longitudinal stripe starting behind the genital papilla on the right side and running to the end of the lateral mantle side In some

species (e.g., Dirona) the glands are also located in a stripe on the left side In some cerata-bearing animals, the glandular cells can be found at the base of the cerata (Doto, Eubranchus).

Blochmann’s glands and ink gland (purple gland) (Table 1, Table 2 Column 5) Blochmann’s gland

is a large single glandular cell lying subepithelially and characterised by a big nucleus The contents hardly stain The single gland has a duct composed of small cuboidal cells leading to the outside The glandular cell is surrounded by muscle fibres This glandular type is only present in some

members of the Cephalaspidea (e.g., Figure 2A, Haminoea antillarum, Figure 2B, Bulla vernicosa)

and Anaspidea In Anaspidea this gland is called the ink gland and is composed of many Blochmann’s

© 2006 by Taylor & Francis Group, LLC

DEFENSIVE GLANDULAR STRUCTURES IN OPISTHOBRANCH MOLLUSCS

229

glands lying close together in the dorsal mantle cavity and opening above the gill (Figure 2C,

Aplysia parvula) The ink gland exudes whitish or purple secretions The ink gland is considered

to be only present in Anaspidea, but it is difficult to differentiate between the ink gland in the Anaspidea and the presence of the Blochmann’s glands in several members of the Cephalaspidea.

Subepithelial acid glands (Table 1, Table 2 Column 6) Huge subepithelial acid glands are present

in some members of the Pleurobranchoidea (Berthellina) These structures can have a diameter of

~500 μm The glands are composed of very few cells and lead to the outside (Figure 2G) Their contents do not stain, or only small pale patches are present.

Figure 2 Histological sections of opisthobranch subepithelial glands (A) Haminoea antillarum Blochmann’s

gland with duct composed of cuboidal small cells (B) Bulla vernicosa Blochmann’s gland (C) Aplysia parvula ink gland (composed of Blochmann’s glands) (D) Bursatella leachii opaline gland (gland of Bohadsch), note the large nucleus (arrow) (E) Clione limacina opaline glands (gland of Bohadsch), note the large nucleus (arrow) (F) Cadlina laevis compound glands lying in notum with outleading duct (G) Berthellina edwardsii

acid glands in notum with opening to the outside Scale bars in μm

© 2006 by Taylor & Francis Group, LLC

Other subepithelial glands composed of several cells These compound glands have larger vacuoles with granular and bluish stained contents They have been observed in several species, e.g., Cadlina luteomarginata and C laevis ( Figure 2F) In the latter species, the glands are sunk deeply in the notum, and could also be assigned to the notum glands (see below).

Glandular organs lying in the notum (Table 1, Table 2 Column 9)

Dorsal mantle gland This gland is present in members of the Tylodinoidea Although the position

is similar in the two investigated species, Tylodina perversa and Umbraculum umbraculum, the

morphology and histology are different In both species, the gland is located in the dorsal notum

tissue and it opens to the outside above the mouth area U umbraculum ( Figure 3A) has a highly branched system of many tubules Glandular tissue is only present in the finer tubules (Figure 3A, arrows) These connect to bigger tubules, which are surrounded by flat to cuboidal cells with no glandular vacuoles (Figure 3A, asterisks) The whole gland opens above the mouth in the mantle

rim via one or two openings Tylodina perversa (Figure 3B, C) has huge glandular follicles which

stain grainy and in a greyish colour (asterisks) They seem to fuse in the anterior part of the mantle rim and form a large reservoir of secretion Part of the gland has bigger cells with uniform violet contents (arrows) These areas are more confined to the dorsal part of the mantle and form several distinct ducts which open separately to the outside.

Interpalleal gland The interpalleal gland in the genus Scaphander is roundish in its general

appear-ance (Figure 3D) It is composed of many tiny tubules These run together into a common duct, which opens in the outer part of the dorsal mantle cavity (Figure 3D and E, arrows) The cells lining the tubules are small, with a large vacuole Their rather transparent contents stain light bluish.

Marginal sacs of Arminidae These glandular and saclike structures are very conspicuous and

arranged in the mantle rim of the animals The glands are large (up to 1 mm), globular and composed

of many cells which more or less stretch from the margin to the middle of the globes The single vacuole contains a homogenously dark violet-stained substance Nuclei are not visible in mature marginal sacs The sacs are surrounded by a thin layer of muscular tissue ( Figure 4A, Dermato- branchus semistriatus) These glandular structures only occur in members of the Arminidae and

their staining properties are listed in Table 4 (see page 245).

Agglomeration of glandular cells in ceratal processes or tubercles Thecacera pennigera (Figure 4B) and Cadlina luteomarginata (Figure 4C) have glandular tissues, which are characterised

by nonstaining vacuolated cells These glands, which can easily be overlooked, are probably not

homologous In Thecacera pennigera the glands are arranged like a flower and were only observed

in the ceratal processes next to the gill In Cadlina luteomarginata the glandular tissue is located

in the apical parts of the tubercles.

Mantle dermal formations (MDF types) (Table 1, Table 2 Column 7, Table 3 and Table 4) Basically,

MDFs are globular structures of usually >300 μm and are composed of many cells, each with a single large vacuole Very often, especially within the Chromodorididae, these vacuoles do not stain with toluidine blue The whole organ can be surrounded by a thin or rather thick layer of muscles (Table 3) MDFs are widely distributed in members of the doridoidean family Chromodorididae, but are also observed in members of other opisthobranch taxa (Table 2 Column 7) Whereas some

of these taxa have MDFs rather regularly arranged (Chromodorididae, Limacia clavigera, branchus ocellatus), some seem to have only a few irregularly arranged MDFs (Newnesia antarctica, Elysia ornata, Haminoea orteai) Their appearance can vary to a great extent even within the same

Plako-genus At least three different types can be distinguished.

Type 1 ( Figure 5A, B) is characterised by the presence of a duct which leads to the outside It

is present in Cadlina luteomarginata, which has a specialised duct (Figure 5B) and in Chromodoris

© 2006 by Taylor & Francis Group, LLC

DEFENSIVE GLANDULAR STRUCTURES IN OPISTHOBRANCH MOLLUSCS

231

tumulifera ( Figure 5A), where the MDF is located beneath the epidermis and the vacuoles reach the outside.

Type 2 (Figure 5C–F, Figure 6A) is characterised by a muscular clot which connects the MDF

to the outside (see Table 3, e.g., Hypselodoris orsinii, Limacia clavigera) The clot is composed

of muscle fibres which are arranged parallel to the epidermis and the MDF (Figure 5C, D, F).

Figure 3 Histological sections of opisthobranch glands lying in the notum (A) Umbraculum umbraculum

cross section of anterior part of body with dorsal mantle glands To the left more fine tubules with dark violetstaining glandular cells are visible (arrows), whereas to the right, ducts with a wide lumen are more common

(asterisks) (B) Tylodina citrina cross section through frontal part with the dorsal mantle separated from the

underlaying body wall Dorsal mantle glands with glandular ducts leading separately to the outside (arrow);

greyish part of gland, which is connected to the glandular ducts marked with an asterisk (C) Detail of Tylodina citrina dorsal mantle glands Connection between greyish staining part (asterisk) to the violet staining part (arrow) (D) Scaphander lignarius interpalleal gland with main collecting duct, which leads to the outside (arrow) at the ventral part of dorsal notum (E) Scaphander lignarius detail of interpalleal glands Arrows

indicate small ducts leading into main duct Scale bars in μm

© 2006 by Taylor & Francis Group, LLC

Newnesia antarctica also has MDFs in its mantle, although these are not regularly arranged along

a rim, but are rather clumped together Nevertheless, these MDFs also show a muscular clot, with fibres arranged parallel to the epidermis ( Figure 6A).

Type 3 (Figure 6G, Figure 7A–F) seems to be independent of the outer epithelium and most

of the MDFs investigated here were of this type The density of the vacuoles may differ greatly,

as does the muscle layer surrounding the MDF in the species investigated For example, the density

Figure 4 Histological sections of opisthobranch glands lying in the notum (A) Dermatobranchus semistriatus

marginal sac Note the orientation of the cell vacuoles to the centre of the globe (B) Thecacera pennigera

glandular agglomerations in ceratal processes next to gills (arrows) At bottom of picture, subepithelial glands

staining dark violet visible (C) Cadlina luteomarginata glandular agglomerations in the apical parts of tubercles (D) Bathyberthella antarctica acid glands Note the tubular structure (E) Plocamopherus ceylonicus acid glands in visceral cavity Note the tubular structure and similar size as in Bathyberthella antarctica (F) Plocamopherus ceylonicus acid glands in visceral cavity Scale bars in μm.

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DEFENSIVE GLANDULAR STRUCTURES IN OPISTHOBRANCH MOLLUSCS

233

of vacuoles is very low in Glossodoris atromarginata ( Figure 7D) and Plakobranchus ocellatus

(Figure 7F) and there is nearly no muscle layer around their MDFs Between the vacuolated cells,

connective tissue is present In contrast, the vacuoles are packed very densely in Hypselodoris tricolor ( Figure 6G) and Risbecia tryoni (Figure 7C) and the muscle layer surrounding the MDF

is very thick (40 μm, see Table 3) The MDF of Chromodoris westraliensis (Figure 7A) is peculiar

because it does not show a muscular layer but a homogenously stained layer of unknown contents.

The MDFs in C westraliensis were the only ones with a flattened appearance Vacuolated cells are

rather sparse and arranged along the periphery These cells are connected with the surrounding

layer (Figure 7A, asterisk) MDFs in Laila cockerelli (Figure 7B) are rare and located in the

cerata-like structures of the notum rim Only two were recognised in the specimen investigated The distribution of the MDFs in the organism is also variable between species and the difference

in distribution in adult specimens of several species is shown in Figure 8 The main areas covered

in most species are the mantle border, or especially near gills and rhinophores However, Limacia clavigera has MDFs in all processes except those next to the gills.

Histochemical analysis showed some differences in the MDFs of five chromodorid species investigated ( Table 4) Even applying different staining techniques, the contents of the vacuoles

never stained, whereas the surrounding layers of Chromodoris westraliensis, Hypselodoris tricolor and Limacia clavigera stain similarly as connective tissue (green in trichrome after Goldner and

blue in trichrome Azan after Heidenhain), but not as muscles (which in both methods stain red) Unfortunately no information is available for the muscular clot.

Table 2 contains additional information on the presence of MDFs taken from the literature combined with data obtained by the authors, although information on the size and description of MDFs is lacking for most species Also, for these species no information on the presence of ducts leading to the outside, or on muscular clots was available and so the presence of these structure is only noted with a + Similarly, for those species possessing MDFs, data on the presence and thickness of a muscular layer, and the presence or absence of a muscular clot, for example, are lacking (Table 3), because notes on MDFs are frequently not accompanied by any description or morphometrical data As far as it is known, all the available data on presence/absence or descriptive details of MDFs are included in Table 2 and Table 3.

MDF-like structures (Table 1, Table 2, Column 8) (Figure 6B, D, Figure 9A–F) There are several other glands similar to the MDFs but they differ in the number of cells, size and/or staining

properties The structures observed in Doriopsilla gemela (Figure 6B) are quite similar to true

MDFs in having a muscular layer surrounding the vacuole cells but the number of the cells is small, and the contents of the vacuole usually stains bluish or sometimes violet The homogeneity of the contents also varies It can be granular or homogenous The diameters of the structures are ~100 μm

and a duct leading to the outside can be observed Melibe leonina also shows globular structures

containing vacuole cells which stain bluish or do not stain at all These structures lack a muscular

layer and a duct leading to the outside (Figure 9D) In addition to these MDF-like structures, Melibe

also possesses agglomerations of cells with a large nonstaining vacuole (Figure 6C) The size of these agglomerations comes close to that of real MDFs The cells are loosely connected by connective tissue in an almost tissue-free notum This unusual type of gland is listed with the MDF- like structures.

Several species show larger globular structures sometimes even surrounded by muscle fibres

and therefore resembling MDFs, but their general appearance differs Plocamopherus ceylonicus

even shows two different types, one with a duct leading to the outside and filled with small, rodlike structures (Figure 9A, arrow), and one type without a duct and composed of several globular subunits (Figure 9B) These subunits are composed of vacuoles of different sizes, the smaller ones filled with homogenously dark bluish stained contents, the larger being lighter in colour These

© 2006 by Taylor & Francis Group, LLC

Table 3 Details of MDFs, when known, from literature or own studies See notes on page 240.

Maximumsize(includinglayer), μm

Thickness

of muscle layer, μm Opening

Muscularstructureconnecting MDF

(Ortea & Pérez, 1983)

García-Gómez

et al 1991, Avila 1993, Avila & Durfort 1996

Ortea & Valdés, 1996

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DEFENSIVE GLANDULAR STRUCTURES IN OPISTHOBRANCH MOLLUSCS

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Table 3 (continued) Details of MDFs, when known, from literature or own studies

Maximumsize(includinglayer), μm

Thickness

of muscle layer, μm Opening

Muscularstructureconnecting MDF

Chromodoris naiki Valdés,

Mollo & Ortea, 1999

© 2006 by Taylor & Francis Group, LLC

Table 3 (continued) Details of MDFs, when known, from literature or own studies

Maximumsize(includinglayer), μm

Thickness

of muscle layer, μm Opening

Muscularstructureconnecting MDF