Contributions to Zoology, 70 (4) 229-242 (2002)

SPB Academic Publishing bv, The Hague

The colleteric glands in Sacculinidae (Crustacea, Cirripedia, ): an ultrastructural study of ovisac secretion

Sven Lange

Department of Cell Biology and Anatomy, Zoological Institute, University of Copenhagen, Universitets- parken 15, DK-2100 Copenhagen Ø, Denmark. Present address: Institutefor Biodiversity and Ecosystem

Dynamics (IBED), PO box 94766,1090 GT Amsterdam, The Netherlands

Keywords:: Cirripedia, Rhizocephala, Sacculina carcini, Thoracica, colleteric gland, ovisac, Carcinus

maenas

Abstract Ovisacs and oviposition in S. carcini 235

Colleteric glands and ovisac secretion in H. dollfusi 238

Discussion 238 Ovisac secretion by the paired colleteric glands of Sacculina Functional morphology of colleteric glands in carcini and Heterosaccus dollfusi (Rhizocephala, Sacculinida) S. carcini and H. dollfusi 238 was documented and studied at the ultrastructural level. and masses Oviposition formation of branched egg Preparatory to oviposition, the epithelium of each colleteric in S. carcini- 239 The gland secretes one branched, elastic, transparent ovisac. Ovisacs in other Rhizocephala 239 ovisac wall consists of a reticulated inner zone, secreted first, Morphological comparison between Sacculinidae and a dense outer zone. After secretion, the ovisac detaches and Thoracica 240 from most of the secretory epithelium but remains anchored 241 proximally in the gland until oviposition ends. The exterior Acknowledgements Abbreviations 241 ovisac surface is predominantly smooth and impervious. References 241 Proximally, however, the surface is irregular and perforated.

the the During oviposition eggs enter paired ovisacs, forcing

the ovisacs throughthe ovipores into the maternal mantle cavity.

Simultaneously the ovisac volume increases approximately Introduction 100 The like times. resulting paired egg masses, branched the

and ventilated in the mantle ovisacs, are brooded cavity. Ovisacs

that with the The are aberrant cirripedians that prevent developing embryos are lost prematurely Rhizocephala

ventilation Within two current. days the egg masses solidify parasitise other , mainly Decapoda. They

and attach to retinacula in the mantle cavity cuticle. The ovisacs, have lost the typical cirripedian feeding structures

now probably obsolete, are no longer discernible. The literature and instead absorb nourishment by means of a on colleteric glandmorphology implies that ovisacs are secreted branched root system, which penetrates by all Sacculinidaeand perhapsother Rhizocephalawith colleteric profusely & in both the the host’s interior The glands. Similarities secretory process andmorphology (Bresciani Hoeg, 2001).

between the colleteric ofSacculinidae suggest homology glands part of the parasite engaged in reproduction is and the oviducal glands of Thoracica (Cirripedia) and bet- usually attached externally to the host abdomen.

ween their products. This so-called externa is of simple architecture. It

includes a visceral mass containing a voluminous

and ovary typically two sperm-producing recep- Contents tacles. A mantle surrounds the visceral mass. Be-

tween these structures lies a mantle cavity, which Introduction 229

functions as a brood chamber and communicates Materials and methods 230

with the ambient sea mantle Results 230 by a opening (Hoeg

& Anatomy of the externae of S. carcini and Liitzen, 1985).

230 H. dollfusi Most recent studies on rhizocephalan reproduc- Anatomy of the colleteric glands in S. carcini 230 tion have focused on the sperm-producing tissue Ultrastructure of the gland cells in S. carcini 231 (reviewed by Hoeg 1991; Hoeg & Liitzen 1995), Ovisac secretion in S. carcini 232

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used. Most while the function of the female part of the repro- Only mature, reproducing parasites were were dissected and the colleteric glands fixed immediately after ductive organs remains insufficiently understood. collection.Samples forTEM were fixed in modified trialdehyde addition to the In ovary, most species possess paired (Lake 1973), postfixed in osmium tetroxide for 1 to 2 hours, secretory oviducts, conventionally called colleteric embedded in Epon, ultrathin-sectioned and contrasted in uranyl Gland varies and has glands. design considerably acetate and lead citrate. Ultra sections were made on a LKB

constitute of the been well-studied, as they one ultramicrotome and examined in a JEOL electron microscope

fixed in Bouin few anatomical landmarks of importance for iden- (JLM-100 SX). Other glands were fixative, embedded in paraffin and sectioned for light microscopy. In tification and separation of species. Being flat or order to observe the oviposition and to obtain colleteric glands in shallow secretory epithelial pads some groups, during and immediately after this event a technique developed in other the glands are represented by simple sacs. by Delage (1884) was successfully applied (Fig. 1A). In two families (Clistosaccidae, Sacculinidae) the hosting S. carcini were strapped to a coarse nylon net by 0.5

glands possess richly branchedsecretory blind-sacs mm metal wire. The host was placed with its dorsal side against

to immobilise (Hoeg & Liitzen 1985). the nylon net with special care taken chelipeds and legs to prevent the host from damagingits parasite. Finally Rhizocephala usually produce several broods in the abdomen was strapped down exposing the parasite to in succession (Hoeg & Liitzen 1985). A study of Sac- situ observation under dissection microscope while keeping the culina carcini Thompson, 1836 showed that the water. host and parasite in sea Since oviposition usually occurs colleteric gland epithelium undergoes a secretory 48-72 hours after nauplii-release,host could be strapped cycle, synchronously with the oocyte development, down well before oviposition. Ca. 48 hours after releasea window

mantle ofthe in preparation to oviposition (Delage 1884). Delage (5x5 mm) was cut through the parasite enabling of ofthe colleteric and directobservation one two glands ovipores. concluded that each colleteric gland secretes an Hosts suffered no loss of appetite and the individual parasites ovisac that the when into envelops eggs they pass survived vivisection for more than 24 hours. Egg masses were the conclusion that has been mantle cavity, a ques- preserved at various times during and after oviposition (Figs. tioned authors from his time to the by many own 1B, C, D). Empty ovisacs were examined with interference con- present. trast optics (Nomarski).

Comparative anatomy makes it obvious that the colleteric glands can best be compared to the ovi- ducal glands of the non-parasitic Cirripedia. Recent Results ultrastructural studies have shown that the ovisacs

produced by these glands are important during I. Anatomy of the externae of S. carcini and H.

oviposition and fertilisation (Walley 1965; Klepal dollfusi et al. 1977; Walker 1977, 1980). It was decided in

this to the structure muscular mantle new perspective reinvestigate The bag-like externa consists of a of the colleteric and their secretion. S. carcini glands surrounding a visceral mass (Fig. 1). The visceral was chosen in order to check Delage’s results to- contains voluminous and mass one ovary paired wards modern and because this technique oviducts with colleteric glands situated superficially

the text-book in represents typical Rhizocephala. the lateral surfaces, one on each side (orienta-

tion in Paired explained legend to Fig. 1). recep-

tacles normally housing dwarf males and paired

Materials and methods ovipores all open into the mantle cavity, delim-

ited by the mantle. The mantle cavity, which may

S. carcini parasitising the common shore Carcinus maenas contain of branched communi- a pair egg masses, (L., 1758) were collected in August and September 1993 from cates with the sea through the mantle opening. eel-traps in the western part of Limfjorden, Denmark at 4 to 5

from mussels in m, or as by-catch commercial vessels fishing II. Anatomy of the colleteric glands in S. carcini the same area. Additional sacculinised crabs were collected in

Gullmarsfjorden, Sweden, from ell-traps in August-October 1995 and and observed in water. of another kept running sea Specimens Seen from the outside the colleteric gland occu- sacculinid, Heterosaccus dollfusi Boschma, 1960 infesting the pies an oval- or heart-shaped 2x3 mm area dis- swimming crab Charybdis longicollis Leene, 1938 were collected tinguished from the surrounding ovary by a lighter with a beam-trawl in the Mediterranean off Palmahim, Israel,

and clearer appearance in live as well as in pre- at 35 m in May 1994.

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I. from The ofthe C. the Fig. Experimental set-up (modified Delage, 1884). immobilisation host, maenas, exposes sac-like parasite,

orientation of S. carcini. 1A-D; Steps in the oviposition (explained in text). The conventional the sacculinid externa: The stalk and the

The the visceral mass with mantle opening occur posteriorly and anteriorly respectively. mesentery connecting the mantle, marks the

left side. However, this orientation lacks firm dorsal region. Consequently, the externae are seen from the anatomical evidence (see

Hoeg& Liitzen 1985). Drawn by Beth Beyerholm.

is minute served material. The ovipore a opening while rough endoplasmatic reticulum (RER) oc-

in the mid-anterior perimeter of the gland area. curs more apically together with Golgi complexes.

Each consists of three a Electron dense 0.2 gland parts (Fig. 2); (i) secretory vesicles, pm wide,

proximal funnel-formed part separated by a con- and mitochondria are usually found near the api-

cal striction from, (ii) a spherical atrium opening by membrane. Cell junctions include belt desmo-

of the into the mantle and way cup-shaped ovipore cavity somes, septate junctions hemidesmosomes.

and (iii) six to eight repeatedly branching blind Microtubuli, chiefly running parallel to the long-

tubes issuing from the atrium. The branched tubes axis of the cells, are most prominent in the cells of

the constitute the most prominent part of the colleteric atrium and the funnel.

The is surrounded The size and of the cells gland (Fig. 3). gland everywhere shape vary consider-

by connective tissue. Diffuse bundles of muscles ably according to their position within the gland.

encircle the of the tubes later- In the tubes the cells periphery glandular peripheral are 6-9 pm high, visceral 5-10 wide and widest ally. Transversal muscles cross the mass, pm at the base. Cells in the

but are all together absent from the glandular re- wider part of the tubes and the atrium are colum-

4-5 wide and reach gion. nar, pm a height of 30 pm. A

maximum of 50-60 is reached height pm near the

III. in S. carcini constriction Ultrastructure of the gland cells and followed by a gradual decrease

in the funnel 15 to pm near the ovary. The cell

forms the inner surface of' tends be lower A secretory epithelium height to at the end of each secre-

the gland. The secretory cells have ellipsoid nu- tory cycle.

clei normally situated near the basal membranes

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IV. Ovisac secretion in S. carcini

The secretory cycle corresponding to the repro-

ductive cycle (at 16°C, 15-17 days of duration) is

here divided into five consecutive stages. Stage 1

represents the situation 1-2 days after oviposition.

Stage 2 and 3 are intermediate, but their exact ages

in the secretory cycle are unknown. Stage 4 oc-

curs ca. 14 days later, shortly before the next ovi-

position and stage 5 immediately after oviposition.

All parts of the colleteric gland participate in

secreting the ovisac. Using the size and morphol-

of the cells and their ogy secretory products as

criteria, the colleteric gland may be divided into

four regions (Regions A, B, C and D; see legend

to Fig. 4). Representing these four regions, four

cells from each stage are shown in Fig. 4.

st 1 Stage (Fig. 4)

The apical surfaces of the cells are convex and

with The microvilli equipped microvilli. are 2-3

in A and reach 6 pm long region pm in regions B,

C and D. Mitochondria and RER are both rela-

and the latter is found the tively sparse throughout

cells. There is cell. usually one Golgi complex per

Every cell contains secondary lysosomes and few

secretory vesicles. Discharged contents of the

vesicles refound as electron dense 0.1 -0.3 pm gran-

ules the microvilli among (Fig. 5), mark the ini-

tiation of ovisac secretion.

nd 2 Stage (Fig. 4)

In all regions all cells have numerous microvilli,

and the cells in regions C and D each have a 7.5

pm long apical extension. Compared to stage 1,

the RER is now organised in relatively tight as-

semblies. Also more mitochondriaand Golgi com-

to found and the plexes (up 4 per cell) are (Fig. 8),

number of secretory vesicles has increased to 5-

Figs. 2 & 3. S. carcini. Anatomy ofthe colleteric gland. 15 per section in regions A and D, and 15-30 in 2. Section ofthe colleteric glandalong the long-axis ofthe externa region B and C. An electron dense unit has been show ovipore, atrium, funnelformedpart ofoviduct and branching secreted the of each cell. All units on apex gland gland tubes. The gland contains one completed ovisac only

are of a reticulated structure with hollow bases, attached in the funnel (arrows). 3. Section parallel to the mantle cavity cuticle. The gland tubes constitute most ofthe colleteric which accommodate the convex apices of the cells. gland. The principal sites of secretion seem to be the apical

extensions and the main apical cell surfaces, but

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in the secretion Fig. 4. S. carcini. Schematic representation ofcells from five stages ovisac (Stage 1-5), Each stage is illustrated by four cells respectively from the: A) ultimate glandulartubes; B) broadest glandular tubes; C) constriction between atrium and funnel and D) attachment area in the funnel. Drawn by Beth Bcyerholm.

not the microvilli since secretory vesicles were ingly merge into one continuous structure, the never observed within the microvilli. However, future ovisac. The porosity of the secretion re-

microvilli the C and is during secretion the always occupy gions D unchanged. Thenumberof secretory

most basal cavities of the reticulation and the mi- vesicles in regions A and B has decreased notice- crovilli for the formation whereas their numberin D may actually be responsible ably, regions C and has

30-50 of the numerous cavities in the reticulated part of increased to per section (Fig. 10). the ovisac. (Fig. 8, 19). Because the units of each

rlh cell touch another at the the 4 only one very base, Stage (Fig. 4)

future ovisac wall shows a serrate outline in section.

The units The condensation of material are 5-10 pm high in region A, reach 20 secretory in the basal

in and 30 in and of the ovisac has increased further. pm region B, pm region C D. In part As a re-

D the decreases towards an electron dense 1-2 thick region height gradually sult, pm non-porous

The the ovary. widths of the secreted units are zone now lines the ovisac externally in regions A

4 but reach also the generally pm 5-8 pm in region A. and B (Fig. 11). Now dense, outer zone in

reaches thickness of region C a 5 pm. However,

3 rd in Stage (Fig. 4) this zone is not impervious as regions A and B,

but penetrated by irregular 0.5-1.5 pm wide holes

A In and B more dense secretion has beefi There be one hole regions (Fig. 12). appears to per cell added in units less distribution basally, resulting porous bases and of a corresponding to that of the

(Fig. 9). Consequently, individual units increas- apical extensions seen in stages 2 and 3. Presum-

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th ably the apical extensions imprint the holes in 5 Stage (Fig. 4) region C, holes that persists after detachment of the ovisac. The thickness of the ovisac wall cor- After oviposition the ovisac is no longer present responds to the heights attained by the secreted in region A, B and C. The glandular lumen may units in 2. cells with flat stage appear collapsed having apical sur-

4 marks the cessation of secretion in faces with 2-4 Stage re- (Fig. 16) or appear open pm long gions A, B and C, since in these parts of the gland microvilli emerging from the cell surfaces (Fig. the ovisac has completely detached from the glan- 17). The cells contain low amounts of most cellu- dular epithelium (Figs. 2, 11, 12). The cells con- lar elements including secondary lysosomes. Sec- tain few secondary lysosomes and comparatively ondary lysosomes bear witness of an on-going

and 5 low amounts of other organelles secretory intracellular digestion and reparation in stage as

vesicles. The apical cell membranes have flattened, well as in stage 1 and 4.

lost their microvilli and occasionally ruptured. Part of the ovisac remains attached in region D

Cellular debris including membrane fragments, after the ovipostion (Fig. 18). This remnant is shed

RER, mitochondriaand even nuclei frequently occur before secretion starts anew liberating the entire

in the space between the epithelium and the de- epithelial surface, including the attachment area,

in tached ovisac, sometimes together with a fibrous to form microvilli preparation of the secretion

material of unknown function The of ovisac. The old ovisac (Fig. 13). pres- a new remnant gradually

cell the ence of cellular debris demonstrates that some decays in the oviduct funnel during next secre-

damage accompany the ovisac detachment. tory cycle (Fig. 30) and probably ends up as frag-

in In region D the secreted units have reticulated ments the new ovisac with the next batch of

dense bases. These have fused that to one lining eggs. again is continuous with the ovisac of the regions

A, B and C. The lining of region D remains in V. Ovisacs and oviposition in S. carcini

close contact with the secretory cells (Fig. 14) and

now serves as the only area of attachment for the The transparent and colourless empty ovisac forms

2 entire ovisac (Fig. 2). In region D, the cells are a ca. mm wide branched bush (Fig. 22). The

rich in mitochondriaand especially microtubuli and external surface of the empty ovisac is decorated

form fern with their surfaces or spruce-like structures 4-8 pm wide polygons (Figs. 23, 24). Each

(Fig. 15) that project into the secreted lining. polygon obviously corresponds to one secreted unit

produced by one cell within the colleteric gland

(Fig. 19).

Figs. 5-17. Ovisac secretion, TEM. Figs. 5 & 8-17; S. carcini. Figs. 6 & 7; H. dollfusi.

Fig. 5. Secreted material deposited between the microvilli (stage 1).

of 1 and from Fig. 6. Secreted materialinitially formsunits on the central part ofthe apical cell surfaces (Stage intermediary stages 2

S. carcini).

Same intermediate atrium secrete slender units. Fig. 7. stage as in Fig. 6. Cells in the

Fig. 8. Near the constriction, the columnar cells have slender apical extensions (stage 2).

Fig. 9. The secreted units have acquired dense bases (stage 3).

Fig. 10. Numerous secretory vesicles within the apical part of cells in the atrium (stage 3). reticulated Fig. II. Gland tube with complete ovisac. The ovisac wall consists ofan inner zone of units and an impervious outer zone.

Apical membranes are flat (stage 4).

the constriction the detached that and sometimes traverse the outer cell membranes Fig. 12. At ovisac has holes enter zone. Apical are

flat (stage 4). Note that the shape and size of the holes are similar to the apical extensions in Figs. 8 and 10.

Fig. 13. Fibrous material between ovisac and epithelium (stage 4).

Fig. 14. Ovisac attached to epithelium in the funnel (stage 4).

Fig. 15. Apically fern shaped cells from the attachment area (stage 4).

Fig. 16. After oviposition some cells have flat apical membranes (stage 5).

Fig. 17. Same gland as Fig 16; Some cells have reformed microvilli (stage 5).

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Figs. 18-21. TEM.

remnant Fig. 18. S. carcini. Ovisac in attachment area after oviposition (stage 5).

Fig. I9. S. carcini. Section parallel to the glandular surface; secreted units with polygonal outlining.

Fig. 20. H. dollfusi. Ovisac wall secreted in the gland tubes.

Fig. 21. H. dollfusi. Ovisac wall secreted near the constriction.

The mantle cavity always molts (indicated in from the ovipore. Occasionally one ovisac is filled

Fig. 1 A) one or two days before oviposition. Vig- before eggs start entering the second. Oviposition

orous repeated contractions in the visceral mass lasts ca. 5 minutes.

precede and probably cause the extrusion of the After oviposition the egg mass occupies a vol- branches of the ovisacs through the correspond- ume of approximately 10 x 20 x 2 mm within the

Minutes later mantle and the diameter of each branch has ing ovipores (Fig. IB). eggs pour cavity

into the basal of each ovisac increased to limes. This increase in volume part (Figs. 1C, 22); up ten

2 later as more eggs arrive, the eggs are forced into by ca. orders of magnitude clearly demonstrates

the ultimate branches (Fig. ID). Hereby the ovisac the elastic properties of the ovisac. During this

is strongly distended yet it maintains the branched stretching of the ovisac the reticulated units on the

As result each interior wall and the thickness structure. a egg mass surropnded disappear (Fig. 25)

forms branched of the ovisac wall is reduced 0.15 by an ovisac, a bush, originating to pm (Fig. 26).

Figs. 22-30. S. carcini. The ovisac.

22. One ovisac. The the distended Fig. branching basal part (seen to left) by eggs.

Fig. 23. Tips of ovisac branches.

Fig. 24. Polygonal ovisac surface. Nomarski technique.

Fig. 25. Section of ovisac during oviposition. In the empty part of the ovisac, reticulated units of the inner zone are clearly seen.

Another of the distended has lost part ovisac, by eggs, such structures.

26. Section of after shows in the undivided of the Fig. egg mass, immediately oviposition two adjacent eggs compartment ovisac,

TEM.

27. Section of 48 hours after in Fig. egg mass oviposition. Adjacent eggs appear separated; each egg clearly enclosed a compartment formed its own by tertiary membrane. The ovisac is no longer discernible. TEM.

Fig. 28. Egg masses attached to retinacula in the mantle cavity cuticle.

29. Detail from 28. Retinaculum surrounded membrane of attached Fig. Fig. partly by tertiary egg. ovisac Fig. 31). The remnant from the attachment area lies detached in the gland lumina and a new secretory cycle has been entered.

The apically pointed shape ofthe cells in the epithelium is typical ofactively secreting cells.

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the formed surrounded that the initial secretion forms the In newly egg masses, by eventually tops ovisacs, individual eggs can be readily separated of the mature units, and, thus, that the innermost

and of the wall is secreted first. and removed from the neighbouring eggs. LM part

At of each TEM observations showed that the ovisac wall was the end a secretory cycle colleteric

48 contains ovisac attached within no longer visible ca. hours after oviposition. gland one to an area

the funnel. As in S. theovisac of H. At this stage each egg lies in its own compartment carcini dollfusi delimited by tertiary membranes (Fig. 27). Eggs consists of reticulated secreted units, connected in

removed dense ovisac in are no longer easily from the egg mass a outer zone. The wall the gland

is thick with perhaps because the tertiary membranes cohere tubes 15-30 pm an impervious 2 pm

thick dense zone Near the con- strongly. The egg masses are kept firmly in posi- outer (Fig. 20). tion within the mantle cavity by attachment to striction between the atrium and the funnel, the

40 thick 5-7 thick numerous spiny retinacula (Fig. 28) emerging ev- wall is pm including a pm dense erywhere from the interior mantle cuticle. Attach- outer zone with an irregular surface (Fig. 21). Holes

ment is accomplished when the tertiary membranes in the dense outer zone were observed, but they

in the of the surround did not traverse the ovisac wall. peripheral parts egg masses the tips of the retinacula (Fig. 29).

VI. Colleteric glands and ovisac secretion in H. Discussion dollfusi

I. Functional morphology of colleteric glands in

The V-shaped colleteric gland of H. dollfusi occu- S. carcini and H. dollfusi

3 4 the pies a x mm area centrally in lateral sur-

face of the visceral mass. In addition to a funnel Using TEM and light microscopy, the secretion of and an atrium with an ovipore each gland consists ovisacs was documented in Sacculina carcini and of the ramification of two, a dorsal and a ventral, Heterosaccus dollfusi. The obtained stages of surrounds glandular tube systems. Connective tissue colleteric glands illustrate a secretory cycle lead-

of a secretory epithelium and fills the gap between ing to the fonnation an ovisac (Figs. 5-18). Stages the arms of the V-shaped gland. The heights of 2 and 5 ofS. carcini and the intermediary stage of

cells in the to the secretory arc 10-30 pm tubes, up H. dollfusi are newly discovered, while the stages

30 in the atrium and exceed 50 in the pm may pm I, 3 and 4 of S. carcini in the present study corre-

funnel. spond to stages described by Delage (1884). ofthe colleteric An ultrastructural investigation The present findings thus confirm the report of

H. glands from a dozen dollfusi revealed a secre- Delage (1884) that the colleteric glands secrete

S. and tory cycle comparable to that of carcini a branched ovisacs, each eventually forming an

the same functional the secretory epithelium exhibiting uninterrupted bag surrounding eggs. Delage’s

In intermediate between works and regions. a stage obviously view differed from that of earlier was

stages 1 and 2 in S. carcini, secreted material cov- not accepted by later authors. Leuckart (1859), who

ers the central apical cell surface (Fig. 6) or apical discovered the colleteric glands (in Sacculina inflata

the extensions (Fig. 7), but not peripheral apical Leuckart, 1859), proposed that the gland cells were

membrane. the close resemblance for the secretion of material cell Considering responsible a liquid

and in S. of the secretory events products carcini that cemented the eggs together. This kind of

it that the and H. dollfusi seems reasonable inter- material had already been reported in Peltogaster

is mediary stage found in the latter also passed paguri Rathke, 1842 (see Rathke 1842). The ce- during the secretory cycle in S. carcini. The shape ment-secretion theory gained support from Lillje-

the of the secretion covering apical extensions in borg (1861) who discovered colleteric glands in

be the intermediary stage (Fig. 7), can recognised two stages in S. carcini and by Kossmann (1872)

in in C the ultimate tops of secreted units regions who studied the anatomy of indo-pacific Sac-

demonstrates and D in H. dollfusi (Fig. 21). This culinidae. It was further advocated by Smith (1906

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Fig. 31. S. carcini. Ovisac extrusion according to Delage (1884). After ovisac detachment(1) the ultimate tips ofthe ovisac branches

fold themselves and slide towards the back upon the atrium along secretory epithelium (2). The ovisac branches concentrate in the atrium Ovisac branches forced (3). are through the ovipore (4) shortly before oviposition. Drawn by Beth Beyerholm.

studying the sacculinid Drepanorchis neglecta remains on the inside of the extruded ovisac (Fig.

and Ramult The ovisac (Fraisse, 1877)) by (1935, describing 25). branches seem to be transferred

in S. oviposition carcini). Both favoured the ce- into the atrium before oviposition. Fig. 31 illus- ment-secretion theory and refused to accept the trates how this is accomplished, according to Delage ovisac theory of Delage. Believing the glandular (1884).

to be a cement Smith masses older than 48 hours of product liquid (1906, p. 26) Egg consists eggs claimed that each branch of the egg masses corre- in individual compartments produced by tertiary

sponded “to a diverticulum of the ovary”, a state- membranes. It seems obvious that the substance

based ment not on anatomical evidence. Smith believed cement the formerly to eggs together is failed how each batch of the fused obviously to explain eggs nothing but tertiary membranes of

is able form branched as Such to complex egg masses, neighbouring eggs. structures have been

it the life of sacculinids. observed other happens repeatedly through in many Rhizocephala whether the On the branched ovisacs contrary, prefabricated glands are simple (Peltogastridae) or branched

molded on the branched ducts of the colleteric (Clistosaccidae) (Rathke 1842; Liitzen 1981). Fused

offer a to the formation of glands simple explanation tertiary membranes are also present in species of branched egg masses. Thompsoniidae and Polysaccidae, both lacking

colleteric glands, proving the independent origin II. and formation Oviposition of branched egg of the cementing structure (Liitzen & Jespersen

masses in S. carcini 1992; Liitzen & Takahashi 1996). The tertiary

membranes mechanically support and sustain the

The molt of the mantle structure of the the pre-ovipository cavity pro- egg masses once surrounding vides the forthcoming batch of eggs with a brood- ovisac, if present, has vanished.

ing chamber with a reduced infection risk by ex-

fouled unfertilised and dead Ovisacs pelling cuticle, eggs III. in other Rhizocephala

cuticular embryos. Simultaneously, plugs are re-

moved from the ovipores the molt and it The data on sacculinid by sup* existing morphology sug- the mantle with plies cavity new retinacula (Smith gests that branched ovisacs are produced in all The reticulated inner 1906). part of the ovisac Sacculinidae: (i) All known species of Sacculinidae

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branchedcolleteric & Liitzen units each possess glands (Hoeg (L. 1767), numerous polygon-shaped so-called ‘chiti- with central make the ovisac. Further- 1996). (ii) Ovisacs, reported as a pore, up

nous linings’ within the colleteric glands have been more the ovisac wall also consists of two zones in

described in of Sacculina the flocculent inner zone and dense many species (see Thoracica; a a

Boschma 1937), Heterosaccus Smith 1906 (see outer zone. Ovisac detachment is also accompa-

Boschma 1950), Drepanorchis Boschma 1927 (see nied by a partial degradation of the oviducal gland

Boschma 1960) and Loxothylacus Boschma 1928 cells (Walker 1980). All these anatomical and func-

(see Boschma 1955) representing the four of the tional similarities between the oviducal gland of

Fi- the Thoracica and the colleteric of the six genera of Sacculinidae richest in species. gland

those Sacculinidae that these nally, (iii) branched egg masses resembling strongly suggest glands are

in of S. carcini and H. dollfusi are also formed homologous.

Drepanorchis (see Smith 1906) and Loxothylacus

(see Reinhard 1950). 2. Oviposition and fertilisation

Ovisacs have not been noticed in rhizocephalan

families other than Sacculinidae. However, the short After detachment, the ovisac of S. balanoides re- duration (apparently less than48 hours) of the ovisac mains anchored to a limited proximal part of the combined with their extreme delicacy in S. carcini, oviduct until the oviposition comes to a hold. could explain the failure to discover them in other Arriving oocytes distend each ovisac through the

families. secretion in similar to into the mantle A many respects ovipores cavity, greatly reducing the ovisac in the colleteric gland of Sacculinidae the ovisac wall thickness of the resulting egg mass

is produced in the glands of Peltogaster paguri (Walley 1965). In S. carcini, the ovisac must also

(Peltogasteridae) (unpublished). Secretion also stay attached during oviposition to allow the

in the occurs branched colleteric glands of Clisto- funnelling of eggs into the elastic ovisac.

1860 In in the saccus paguri Lilljeborg and Sylon hippolytes Thoracica, spermatozoans are deposited

mantle and the M. Sars 1870 (both Clistosaccidae) (see Boschma cavity subsequently pass through

Clistosaccidae ovisac wall of the and fertilise the 1928). Interestingly, egg masses are by way pores

the existence inside the ovisac branched, indicating of a mechanism oocytes (Walker 1977; Klepal et responsible for shaping the egg masses. It is there- al. 1977). Fertilisation has not been observed in

in fore possible that ovisacs are produced in most, if Sacculinidae. The irregular holes the ovisac of

with colleteric S. in similar to the not all, rhizocephalans glands. carcini, produced a manner pores

in the thoracican ovisac, may fulfill the same role.

IV. Morphological comparison between Since the spermatozoans of S. carcini are ca. 0.5

in diameter the holes Sacculinidae and Thoracica pm (Pochon-Masson 1971),

wide to allow are sufficiently passage.

The non-parasitic Thoracica is considered the sistergroup of Rhizocephala (Jensen et al. 1994; 3. Function of the ovisacs

Spears et al. 1994). The thoracican oviducts are paired and include distal oviducal glands (Walker The ovisacs of S. balanoides provide the initial

1992). control over the newly laid eggs allowing the eggs

to make contact and cohere (Walley 1965) and form

solidified al. At this I. Oviducal gland morphology egg masses (Walley et 1971).

the solid masses in Thoracica either stage egg are

The oviducal glands in Thoracica secrete ovisacs attached to special structures, so-called ovigerous in that S. H. be lost the mantle many ways similar to of carcini and frena, or simply to large to through

The dollfusi although much simpler in shape. The opening (Walker 1992). now unneededovisacs

The estimated of the thoracican ovisacs are also colourless, transparent deteriorate. duration ovisac

in 10 and elastic (Nussbaum 1890; Walley 1965; Walker a rangeof Thoracica is at least days (Walley

1980). In the thoracican Semibalanus balanoides 1965; Barnes & Barnes 1977) and thereby consid-

Downloaded from Brill.com10/09/2021 04:32:24PM via free access Contributions to 70 - 2002 Zoology, (4) 241

erabiy longer than the two days observed in S. References

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