Cypris Ultrastructure, Metamorphosis and Sex in Seven Families of Parasitic Barnacles (Crustacea: Cirripedia: Rhizocephala)

\cta Zootogica (Stockholm), Vol. 70, No. 4, pp. 229-242. 1989 ITinted in Great Britain

(KH)l-7''7"'/89$3 OO-h 00 Per'gamon Press pic © 1989 The Royal Swedish Academy of Sciences

Cypris Ultrastructure, Metamorphosis and Sex in Seven Families of Parasitic Barnacles (Crustacea: Cirripedia: Rhizocephala) H, Glenner, J, T, H0eg, A, Klysner and B. Brodin Larsen Institute of Cell Biology and Anatomy, The Zoologieal Institutes, Universitetsparken 15, DK-21(K) Copenhagen, Denmark (.Accepted for publication 17 May 1989)

Abstract

Gtenner. H.. Hoeg. J. T.. Ktysner. A. & Larsen. B. B.. 1989. Cypris ultrastructure. metamorphosis and sex in seven families of parasitic barnacles (Crustacea: Cirripedia: Rhizocephala).— Acta zooi. Stockh. 70: 229-242.

Cypris morphology in the Rhizocephala differs both between the sexes of individual species and between the species. The large aesthetasc on the third antennular segment is unique to male cyprids of the Lernaeodiscidae, Peltogasteridae and Sacculinidae (suborder Kentrogonida) and Mycelomorphii vancouvercnsis (suborder Akentrogonida). A fourth segmental aesthetasc. common to both sexes, is much longer in males than in females. A spinous process on the attachment disc is another male-specilic character, but is absent altogether in the Lernaeodiscidae. It is argued that these aesthetascs help locate the settlement targets. Except in Mycetomorpha vancourierensis. aesthetascs have been secondarily lost in cyprids ot the suborder Akentrogonida. and there are no other morphological means for separating the male and female settling stage. In cyprids o( Syton hippolytes (Sylonidae) and of Mycetomorpha vancomerensis and Thompsonia sp. (Akentrogonidae) the long and slender antennules are probably used in penetration without formation of a kentrogon. as already reported for Clistosuccus paguri (Clistosaccidae). Cyprids of Sylon hippolytes and Clistosaccm paguri are almost morphologically identical.

Jens T. Hoeg, Institute of Cell Biology and Anatomy. The Zoological Institutes. Universitetsparken /5, DK-2100 Copenhagen. Denmark.

Introduction

families Sylonidae and Clistosaccidae, are relegated to the suborder Kentrogonida, while the suborder Akentrogonida comprise the Chthamolophilidae and the Akentrogonidae (Spivey 1982). Evidently, however, this classiflcation implies' that one of 'the two suborders is paraphyletic. Moreover, the presence of a kentrogon has only been conflrmed in the Lernaeodiscidae, Peltogasterjjae and Sacculinidae, so usage of the terms "kentrogonid' and "Kentrogonida' should at present be restricted to these three families and all other rhizocephalans considered as members of the Akentrogonida. Substratum location, settlement and metamorphosis are crucial events in the life cycle of all rhizocephalans. Hence, differences in these events would expectedly be reflected in their settlement stage larva, the cypris,'and could yield characters useful for a revised clas'siflcation, j h e present study surveys cypris morphology in representatives from all seven rhizocephalan families and evaluates to which extent antennular structure and sense organs reflect the sex, settlement and metamorphosis of the jarva. The phylogenetic implications of the results are given by H0ee (in press)

The Rhizocephala comprise seven families which differ markedly in their mode of metamorphosis and in their sexual systems (Hoeg & Lutzen 1985). Members of the Peltogasteridae, the Lernaeodiscidae and the Sacculinidae have gonochoristic life cycles. This is reflected early on in the larvae, since male and female cyprids differ both m their choice of substratum for settlement and in the ensuing metamorphosis. Female cyprids settle onto prospective new hosts and metamorphose into the infective kentrogon instar. Male cyprids settle at the mantle aperture of the recently emerged female externa, where they metamorphose into the trichogon instar and are implanted into receptacles as dwarf males (Ichikawa & Yanagimachi 1958; Ritchie & H0eg 1981; H0eg 1987a). Male cyprids are generally larger than females (Yanagimachi 1961; Ritchie & H0eg 1981; H0eg 1984a; Walker 1985), but a clear-cut morphological difference between the sexes is only known in Sacculina carcini, where male and female cyprids differ in the morphology of the antennules and in ultrastructural details related to the metamorphosis. In the remaining four families of the Rhizocephala the larvae are mostly insufflciently known and their sexuality

Materials and Methods

and mode of metamorphosis are still much debated. Bocquet-Vedrine (1961, 1972a) and Spivey (1982) use the presence or absence of the kentrogon instar to divide the

Table l lists the rhizocephalan species from which cypris larvae were investigated. In some species infested hosts were collected in the field

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Rhizocephala into two suborders. The PeltOgaStndae, Lernaeodiscidae and Sacculinidae, and the two monotypic

•'"'^ 'he parasite larvae reared to the cvpris stage in the laboratory as

Jescnbed by Hoeg (19S4/)). However, .n.Wr,,,/W^'v'". Mv«'omorpha vuncotiverensis. Thompsonia sp., Chthamatophitus detagei and 229

230 H. Glenner et al. Table 1. List of species from which cyprid larvae of the Cirripedia Rhizocephala were examined Parasite species

Host speeies

Colleetion site

Pelrolislhes cabrilloi Glasell. 1945

Scripps Institution of Oceanography. California, U.S.A.

Pagurus bernhardus (L.. 1758) Pagurus cuanensis Bell. 1845 A napugurus chiroacanthus (Lilljeborg. 18.55)

Kristineberg Marine Biological Station. West coast of Sweden

Pagurus cuanensis Bell. 1845 Anapagurus chiroacanthus (Lilljeborg. 1S55)

Kristineberg Marine Biological Station. West coast of Sweden

Carcinus maenas (L.. 1758)

Station Biologique de Roscoff. Bretagne. Franee

Pagurus bernhardus (L.. 1758)

Kristineberg Marine Biological Station. West coast of Sweden

Spirontocaris lilljeborgi (Danielssen. 1859)

Oslo Fjord. Norway

Unidentified prawn

San Juan Straits. WA. U.S.A. (NMNH Ace. no. 149132)

Unidentified prawns and hermit crabs

San Juan Straits. WA. U.S.A. (NMNH no. 80483)

Chthamalophilidae Chthamalophilus delagei BocquetVedrine, 1957

Chthamalus stellatus (Poli. 1791)

Station Biologique de Roscoff. Bretagne. France

Boschmaella sp.

Chlhamulus challengeri Hoek. 1883

Japan

Lernaeodiscidae Lernaeodiscus porcellanae (Muller. 1852) Peltogasteridae Peltogaster paguri Rathke. 1842

Pettogasterella sulcata Lilljeborg. 1859 Sacculinidae Sacculina carcini Thompson, 1836 Clistosaceidae Clistosaccus paguri Lilljeborg, 1860 Sylonidae Syion hippolytes M. Sars. 1870 Akentrogonidae Mvcetomorpha vancouverensis Potts. 1912 Thompsonia sp.

Boschmaetta sp. it was possible to collect the cyprids directly from the mantle cavity of parasite externae as the free-living nauplius phase has been abandoned. Most cyprids were fixed in a 2% glutaraldehyde 4% paraformaldehyde mixture or in 1% OsOj (see details in Hoeg 1985ft. 1987a). The specimens of Sylon hippolyles were originally fixed in Bouin s fluid and transferred to 70% ethanol. while the initial fixative of the Thompsonia and Mvcetomorpha vancouverensis specimens, now stored in 70% alcohol, is unknown. Nevertheless, the eyprids of M. vancouverensis rendered surprisingly good SEM micrographs, while those of Thompsonia and S. hippolytes were ill suited for this technique. For SEM the cyprids were postfixed in 1% OsO^. dehydrated in acetone, critical point dried with CO; and examined in a Jeol SEM microscope. Ultrasound cleaning was not employed for fear of losing or damaging setae and sensilla. Cyprids. whole-mounted in lactic acid or glycerol. were also examined with conventional, phase and Nomarski optics and the antennules drawn with a camera lucida.

Results The cypris body The rhizocephalan cyprid is small compared to other cirripedes with a body length ranging from c. 50 to 400 jim (Fig. 1). Table 2 surveys the various cypris morphologies, while Fig. 40 illustrates the antennules. The carapace is surprisingly smooth compared to cyprids of the Cirripedia Thoracica (Walker & Lee 1976; Dineen 1987) (Figs 16, 17). The number of carapace setae differs considerably between species. The setae emerge from depressions in the carapace. Pore-like depressions on the carapace may either be places where carapace setae have broken away leaving empty sockets, or true openings of epidermal glands (Fig. 27). A band of cuticular fringes comparable to those seen by Grygier (1988) in ascothoracid

larvae follows the inside margin of the carapace (Fig. 38). In species hatching as nauplii, the cyprids retain long paired frontal filaments in the anterior mantle cavity and frontal horn glands with paired, oblong openings near the anterioventral margins of the carapace (Table 2; Figs 1, 17, 24). Opposed to this, species hatching as cyprids lack the nauplius eye, frontal filaments and frontal horn glands (Table 2; Figs 27, 28, 33). The antennules The general structure of the antennules is similar in all investigated species (Fig. 40). They are suspended from the roof of the anterior mantle cavity (Fig. 28) and consist of four segments, except in the Chthamalophilidae. The first antennular segment. The first segment consists of two sclerites, which articulate at the posterior, elbowshaped point of the antennule. The proximal sclerite is a broad plate with two anteriorly projecting rods. The tip of the medial rod articulates with its counterpart in the other antennule (asterisks in Fig. 40). The distal sclerite reinforces the posterior (ventral) wall of the first segment and articulates distally with the second segment. The lateral and anterior (dorsal) walls of the first segment consist of very thin cuticle, which is usually not discernible in the light microscope. The second antennular segment. The cylindrical second segment may be encircled by a distal, preformed breakage

Cypris Ultrastructure, Metamorphosis and Sex

231

Figs 1-7. Fig. I. Lernaeodiscus porcellanae. live female cyprid. Evaginated thorax, antennules and frontal filaments protrude from the mantle cavity. Proximal sclcritcs of left and right antennules articulate in mantle cavity roof (arrow). Nomarski optics.—Fig. 2. Mycetomorpha vancouverensis. male cyprid. Nauplius eye absent. Long and slender second antennular segment. Aesthetascs (arrows) obscured from view in the lowermost antennule. Phase contrast.—Fig. i. Peltogasier puguri. Antennules of the male cyprid. Aesthetascs shown by arrows. Phase contrast. Vertical scale bar: 50 \i.m.—Fig. 4. Clislosacciis pagiiri. cyprid. Nauplius eye absent. Two long, terminal setae on fourth antennular segment (arrow). Cement gland seen as dark area in cyprid body.—f;>,'. .''. Syton hippolyies. cyprid. Nauplius eye absent. Note similarity in shape to Ctistosaccus paguri in Fig. 4.—Fig. 6. Ctistosaccus paguri. anterior end of cyprid. Note the proximal and distal sclerites of first antennular segment and long and slender seeond segment. Nomarski optics—f/^v 7. Boschinuetta sp.. anterior end of cyprid. Black bands within second antennular segments are muscles and cuticular tendons. No fourth antennular segment. Phase contrast. 1-4 first-fourth antennular segment: ab abdominal rudiment: eg cement gland: ds distal sclerite of first antennular segment: // frontal filaments: ne nauplius eye: ps proximal sclerite first antennular segment; sa subterminal aesthetasc: th thorax. All scale bars in (im.

232 H. Glenner et al. Table 2. Character distribution in cyprids of the Cirripedia Rhizocephata Ifor species abbreviations, see footnote) Species Character Ontogeny Nauplii Kentrogon in females Triehogon in males Cyprid morphology Carapace setae Nauplius eye Compound eyes Frontal filaments Frontal horn glands las: postaxial seta las: distal breakage zone lias: axial seta lias: aesthetasc 7>as: spinous process 4