The integument of Parathalestris harpactoides (Claus, 1863) is studied by scanning and transmission electron microscopy. The general structure of the ...
Hydrobiologia 2921293 : 137-142, 1994 . F D. Ferrari & B . P Bradley (eds), Ecology and Morphology of Copepods . ©1994. Kluwer Academic Publishers. Printed in Belgium
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The integumental ultrastructure of Parathalestris harpactoides (Claus, 1863) (copepoda, harpacticoida) Jose Bresciani l & Hans-U . Dahms 2 1 Department of Ecology and Molecular Biology, Zoology Section, Royal Veterinary and Agricultural University, Bulowsvej 13, DK, 1870 Frederiksberg C, Denmark 2 Fachbereich 7 (Biologie), Arbeitsgruppe Zoomorphologie, Universitaet Oldenburg, Postfach 2503, D-2900 Oldenburg, Germany
Key words: Ultrastructure, morphology, integument, copepoda, crustacea
Abstract The integument of Parathalestris harpactoides (Claus, 1863) is studied by scanning and transmission electron microscopy. The general structure of the integument conforms to the common pattern known from Copepoda . Emphasis is given to the structural variation of the cuticle in different regions of the body . The cuticle measures about 6 sm in most parts of the body, and shows a laminate appearance . The epicuticle is about 60 nm thick. Numerous pore canals containing muscular tonofilaments penetrate the procuticular layer of the integument . A peculiar feature is the presence of a `honeycombed' layer in the outermost zone of the cuticle of some parts of the body . The epidermal layer, muscle insertions and integumental pores are of common type . The cuticle of some specimens, both males and females, is covered with microorganisms .
Introduction Studies of the integumental ultrastructure among copepods are reviewed by Bresciani (1986) and Boxshall (1992) . These papers mention six harpacticoid species for which the cuticle has been studied at the ultrastructural level : Cletocamptus retrogressus by Gharagozlou-van Ginneken & Bouligand (1973), Tisbe holothuriae by Garagozlou-van Ginneken (1974), Porcellidium fimbriatum and P viride by Gharagozlou-van Ginneken & Bouligand (1975), Alteutha depressa by Gharagozlou-van Ginneken (1976), and Diarthrodes nobilis by Hicks & Grahame (1979) . In addition, we mention the studies of Dahms (1993) on Paraamphiascella fulvofasciata and of Gharagozlou-van Ginneken (1977, 1979) on the labral glands of Porcellidium fimbriatum and P. viride, and the glands associated with the lateral parts of the male genital somite in Tigriopus brevicornis . Despite the fact that only a few species have been investigated, some interesting morphological features have been described : the tubular microvilli and cuticular channels in the Peltidiidae and Porcellidiidae and
the cuticular vents associated with food uptake in the algal dwelling harpacticoid Diarthrodes nobilis. The present study extends our knowledge of copepod integuments in general and discusses some functional aspects in particular .
Material and methods Male and female specimens of Parathalestris harpactoides were separated from stock cultures . The single ovigerous female originally used to etablish the stock culture was collected from sediment bound small macroalgae from the NW intertidal of Helgoland (North Sea) on 5th May 1986 (cf . Dahms, 1990) . No attempt was made to eradicate small contaminants . Fixation for transmission electron microscopy (TEM) was made in 3% glutaraldehyde in filtered sea water for 2 h ; postfixation in 1 % osmiun tetroxide for 1 h at 4 °C and blockstained for 2 h at room temperature in 5% aqueous uranyl acetate ; embedding in Epon after dehydration . The preparation for scanning electron microscopy (SEM) was done as described
138 by Dahms & Bresciani (1993) for another harpacticoid species . The sections were cut with a diamond knife on a Reichert Jung ULTRACUT E ultramicrotome, stained with uranyl acetate and lead citrate and examined with a Jeol 1200 Ex at 60 kV.
Results The integument of Parathalestris harpactoides is generally similar to the common copepod type of integument. The epidermal cells are very flat and their nuclei usually oval in shape . They show a well developed endoplasmatic reticulum, mitochondria with several cristae, Golgi bodies, vacuoles, and lateral border cells in a complicated spatial arrangement . No microvilli are found at the apical surface of the cells . The cuticle measures about 6 pm in most parts of the body . An exception is the cuticle of the arthrodial membranes (Figs 3 A, B) measuring barely 1 µm . The classical division of the procuticle into two strata, pl and p2, with a more electron dense pl layer, and their laminate appearance (about 55 striations) is observable in many parts of the body (Figs 2 D, G ; 3 B, C) . In oblique sections, the characteristic bow-shaped structure is clearly seen . In the soft cuticle of the joints and the appendages, the integument is tiny and flexible . A sharp transitional zone is present (Fig . 3B) where the laminar structure of the cuticle is clearly visible . Here, the laminae show a wave-like loose structure, contrary to the ordinate and stratified structure occurring in most other parts of the cuticle . In certain zones, patches of electron dense material (ecdycial droplets?) penetrate the cuticle (Fig . 3C) and are arranged in either a compact or disperse fashion . The cuticular morphology of the spines, setae and hairs (Figs 3 D, E) is difficult to interpret . In general, the common architecture of the cuticle seems to be maintained . The epicuticle is about 60 nm thick, subdivided in the common e 1 to e4 layers, and is covered by a surface coat . Muscles attached to the integument by microtubular filaments, traverse the epidermal cells, penetrate the procuticle (Fig. 2G), and terminate shortly under the epicuticular layer. There they form, together with the distal ends of the muscle filaments and striations of the p1 layer, a lattice-like structure of about 300 to 400 nm thickness (Fig . 2D, E, F ; 3C) . In tangential sections (Fig . 2F) the morphology of the filaments is represented as a central lucent core surrounded by an
electron dense zone . The filaments are spaced to a distance of 100 to 400 nm and the average diameter is 32 urn . Integumental vents are distributed over various parts of the cuticle, especially on the legs and ventral and dorsal parts of the cephalothorax (Figs 2A, B) . Among the specimens examined by SEM, some had their body surface covered with bacteria and filamentous algae (Figs 1 A-D) . There are individuals completely covered and others with sporadic occurrence of microorganisms on the legs, the dorsal shield or the oral area . The degree of coverage seems not to be correlated with age or sex . The microorganisms adhered firmly to the cuticle (Fig . 1D), and were surrounded by a sheath of thin filaments (Fig . 2C) .
Discussion The integumental architecture of Parathalestris harpactoides is similar to the corresponding structures of the harpacticoids Canthocamptus retrogressus described in detail by Gharagozlou-van Ginneken & Bouligand (1973), Tube holothuriae (Gharagozlou-van Ginneken, 1974), Tigriopus brevicornis (Gharagozlou-van Ginneken, 1979), and surprisingly, also to the cyclopoid Paranthessius anemoniae (Briggs, 1978), a commensal on Snakelocks anemone with a cuticle similar to the freeliving harpacticoids . The peculiar `honeycomb' layer of P harpactoides was described for Paranthessius anemoniae . Briggs (1978) made the hypothesis that this zone is probably , an adaptation to reduce the weigth of the cuticle without loss in strength' . This statement is hard to accept in the light of our present knowledge . We call attention, however, to the fact that this structure is present also in the cuticle of 7igriopus brevicornis, as shown by Gharagozlou-van Ginneken (1979, his Fig . 5), without any comments in the text . Features of the muscle attachment to the cuticle are similar to those described by Bouligand (1966) . The significance of various microbiota and agglutination of organic material to the surface of marine copepods is still a matter of discussion . These may have unknown positive or negative effects for the carrier, and may be correlated with age or the physical state, as it is the case with some bottom living copepods . Adhesive microbiota can be used as nutritive components as is demonstrated by Hicks & Grahame (1979) for the harpacticoid Diarthrodes nobilis, belonging to the same family Thalestridae as does Parathalestris
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Fig. 1 . Parathalestris harpactoides . A . SEM-micrograph . Lateral habitus of the female. Scale bar = 100 µm. B. SEM-micrograph. Ventral aspect of the cephalothorax of a specimen free of epicuticular microorganisms . Scale bar = 50 gm . C. SEM-micrograh . Same area as in B, but of a specimen densely covered with microorganisms, particularly at the labrum (l) and the antenna (a). Scale bar = 10 µm . D . SEM-micrograph . Microorganisms clinging to the cuticular surface of the antenna, note the circular rims at the attachment point to the cuticle (more details of these are shown in Fig . 2C) . Scale bar = 1 lam.
harpactoides . In D . nobilis the cuticular vents of the cephalothorax and legs produce mucus which acts s a mucus-trap for microorganisms and particulate a organic matter. If this mechanism holds also for P
harpactoides, the vents present here (Fig . 2A, B) may have a similar function .
1 40
Fig . 2 . Parathalestris harpactoides . A . SEM-micrograph of the frontal portion of the head in ventral view, showing the rostrum and the antennular bases . The arrows indicate the opening of several cuticular vents . Scale bar = 10 µm. B . SEM-micrograph of a portion of the inner lateral rim of the cephalothorax showing a cuticular vent (circle) . Scale bar = 10 µm . C . TEM-micrograph of a longitudinal section of a microorganism attached to the surface of the cuticle, surrounded by a sheath of filaments . Scale bar = 0 .5 µm . D . TEM-micrograph. Longitudinal section through the caudolateral part of the cephalothorax (the arrow points towards the frontal part) . Note the 'honeycomb' region of the external wall (*) of the cephalothorax, this structure is not present at the internal wall (**) . Scale bar = 2 µm . E . TEM-micrograph . Transverse section in flexible area, showing the 'honeycomb' structure and surface coat (p = procuticle, ep = epicuticle) . Scale bar = 200 µm. F. TEM-micrograph . Oblique section through the dorsal cuticle showing the 'honeycomb' zone. Scale bar = 0 .2 µm . G . TEM-micrograph . Transversal section showing muscle attachment to the cuticle by systems of tonofibrils penetrating into the procuticle . Scale bar = 1 µm .
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Parathalestris harpactoides. A . SEM-micrograph . Sagittal section through two dorsal adjacent abdominal somites (2 and 3) (d) . Note the arthrodial membrane (white arrow) and the laminar structure of the cuticle . Scale bar = 10 µm, B . TEM-micrograph . Transversal section of a region similar to that shown in Fig . 3A (a= arthrodial membrane, t = transitional zone, lc = laminar cuticle) . Scale bar = 2 µm. C . TEM-micrograph. Transverse section showing a patch of electron dense material penetrating the procuticle (p1, p2 = procuticular layers) . Scale bar = 1 µm. D. TEM-micrograph . Transverse section of small hairs on one thoracic appendage . Scale bar = 1 µm . E. TEM-micrograph . Longitudinal section . High magnification of a pinnate seta . Scale bar = 0.5 µm . Fig. 3.
Acknowledgements
tion of this papers was supported by a grant to JB from the Royal Veterinary and Agricultural University, DenWe extend our thanks to Mrs Bodil Weng Jorgensen mark. HUD acknowledges a research grant from the for her excellent technical assistance . The presentaDeutsche Forschungsgemeinschaft .
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