Contributions to Zoolog)’, 68 (3) 143-160 (1999) SPB Academic Publishing hv, The Hague Scanning electron microscopy of acrothoracican cypris larvae (Crustacea, Thecostraca, Cirripedia, Acrothoracica, Lithoglyptidae) ¹, ¹ Gregory+A. Kolbasov Jens+T. Høeg² & Alexei+S. Elfimov 1 Department of Invertebrate Zoology, Biological Faculty, Moscow State University, Moscow 119899, 2 Russia; Corresponding author. Department of Zoomorphology, Zoological Institute, University of Copenhagen, Universitetsparken 15, DK-2100, Copenhagen, Denmark, e-mail: [email protected] words lattice Key : Cirripedia, Acrothoracica, Ascothoracida, cypris larva, morphology, organ. SEM, phylogenetic relationships, larval characters Abstract Antennulary segments 151 Thorax and thoracopods 153 and furcal rami 154 used to full Hindbody Scanning electron microscopy was provide a Discussion 154 morphological description ofcypris morphologyin the acrothora- 155 Lattice organs cican species Lithoglyptes milis and L. habei (Lithoglyptidae). Mantle cavity 155 antennules, Special attention was givento lattice organs, thorax, Antennules 155 thoracopods, abdomen, and furcal rami. Cypris larvae ofthe Antennulary segment 4 156 Acrothoracica share some putative plesiomorphic features with Apomorphies in antennulary morphology 156 the cypris-like ascothoracid larvae of the non-cirripede taxon Thoracopods 156 Ascothoracida. The most notable are traces of abdominal Tagmosis and hindbody 157 and lattice without fields. segmentation carapace organs pore Conclusion 158 Acrothoracican cyprids also share numerous synapomorphies Acknowledgements 158 with those of the Thoracica and the Rhizocephala. This list References 158 with first includes a four-segmentedantennule a triangular seg- ment of two sclerites set at an angle to each other, a cylindrical attach- second segment, a small third segment functioning asan ment fourth organ, and a cylindrical segment bearinghomologous Introduction Further of sensory setae. apomorphies are a pair frontolateral horn glandsexiting anteroventrally on the headshield (carapace), The Cirripedia consist of the orders Acrothoracica, a pair of multicellular cement glands exiting on the attachment and the Thoracica, Rhizocephala (Hoeg, 1992; Hoeg, organs, a single stout, serrated and non-natatory seta on Both the Thoracica and the Acrothoracica thoracopodal exopods and a highly reduced abdomen with at 1995). best traces of segmentation. These synapomorphies in cypris use thoracic limbs (cirri) for setose feeding, but a taxon Cirripedia comprising morphology support monophyletic the Acrothoracica deviate in inhabiting burrows and the Acrothoracica, Thoracica, and Rhizocephala but excluding lacking an armament of mineralized shell plates. the Ascothoracida. This cryptic mode of life has resulted in numerous modifications to their morphology. The Acrothoracica have long been important in Contents discussing both the evolution and phylogeny of the Cirripedia and of the Thecostraca in Introduction 143 general et Material and methods 144 (Glenner al., 1995; Newman, 1971, 1974, 1987; Results 144 Spears et al., 1994; Turquier, 1972). An origin from Size and shape ofthe cyprids 145 or, more precisely, a sistergroup relationship with General morphology 145 various cirripede taxa has been suggested, such as Carapace 145 the Iblidae (Tomlinson, 1969) and the Frontolateral 145 scalpellid pores & 147 Lithotrya (Newman, 1982; Grygier Newman, Lattice organs Mantle and mantle cavity 150 1985). In spite of these studies the position of the Downloaded from Brill.com10/09/2021 08:04:42AM via free access 144 G.A. Kolbasov, J.T. Hoeg & A.S. Elfimov — Acrothoracican cypris larvae Acrothoracica within the Thecostraca remains un- Material and methods clear. The lack of mineralized shell plates and whether this is primary or due to secondary loss Most acrothoracican species brood their larva until the cypris stage is reached (Tomlinson, 1969). It is therefore possible to impedes comparison with the characters used in samplemature cypris larvae from the mantle cavities offemales estimating the phylogeny of thoracican barnacles found in museum collections. Acrothoracican males are always (Glenner et ah, 1995, Newman, 1996). Spears et dwarf forms attached to the females (Gotelli & Spivey, 1992; ah used molecular data in an effort to (1994) clarify Kolbasov, 1996). cirripede phylogeny and their results suggested We examined the collections ofmollusc shells stored in the between the Zoological Museum ofMoscow State University and found more an affinity Acrothoracica and the than 300 specimens containing Acrothoracica. Many of them Ascothoracida, which challenged even the basic hosted either habei or L. mitis and some contained Lithoglyptes , monophyly of the Cirripedia. Despite the wide cypris larvae. Recently settled cypris stages ofdwarf males (Fig. morphological differences adult Thecostraca, and females also among 2C) were isolated. of each All was in 70% alcohol. We most representatives group possess pelagic material preserved investigated larvae L. nauplius and cypris-like larvae. The similarity and five Lithoglyptes habei cypris and five mitis cypris larvae with SEM and also mounted for we some light microscopy unproblematic homology of these larvae includ- after KOH treatment. All larvae for SEM investigation were ing numerous details apparent under the scanning post-fixed with 2% 0s0 for 2 hrs, dehydratedin acetone, and 4 electron microscope make them eminently suited critical point dried in CO Dried specimens were sputter-coated r for the within resolving phylogenetic relationships with gold and examined at 15 kv accelerating voltage (with a in the Thecostraca (Grygier, 1987a, b; Walossek et JEOL JSM-840 SEM Copenhagen and a HITACHI S405A SEM in After of external Moscow). investigation carapace ah, 1996). Jensen et ah (1994) used SEM on cypris features one“valve” of some larvae was removed to reveal the larvae to study the recently discovered lattice or- body. gans in the carapace. They found putative plesio- The material studied came from the following localities. morphic similarities between Ascothoracida and Lithoglyptes habei: Gulf ofAden, 13°59’5”N,48“24’7”E,depth Acrothoracica and putative synapomorphies be- 3 m, coral reef, I female with 1 cypris inside, in Turbo argiro- Seychelles, Silhouette 1.,4"36’5, 56°48’E, subtidal zone, tween Acrothoracica and the remaining two stomum; 6 females and I free cypris in Mancinella mancinella; South cirripede orders. Moyse et ah (1995) employed SEM China Sea, Vietnam 12°N, 109"E: depth 1.5 m, 3 females (1 on cypris attachment organs in a wide selection of with a cypris inside) in Mancinella mancinella; depth 2 m, 2 These two studies focussed on females and 1 free in 2-4 5 cirripede cyprids. cypris Coralliophila deformis; m, but few selected and all works females with a in a organs, previous (1 cypris inside) Drupa morum. Lithoglyptes mitis: Maldives: Feartu I., 3°48’N, 73°05’E, on acrothoracican cyprids used only light micros- intertidal females zone, coral reef, 8 (1 with a cypris inside); copy (Kuhnert, 1934; Tomlinson, 1969; Turquier, Genego I., 3°49’N, 73°06’E intertidal and subtidal zones, coral 1967, 1970, 1971, 1985; Wells & Tomlinson, 1966). reef, 2 females and 1 cypris with stretched antennules in Trochus For acrothoracican cyprids we therefore lack the pyramis, 17 females (2 with a cypris inside) in Mancinellaalauina, level of detail now available from the two other t 8 females (1 with a cypris inside) in Latirolagenasmaragdula, 3 female with in Morula cirripede orders (e.g., Elfimov, 1995; Glenner et specimens (1 a cypris inside) cavernosa , 2 females (1 with a cypris inside) in Hipponix ah, 1989; Glenner & Hoeg, 1995; Hoeg, 1985; sp. Jensen et ah, 1994; Moyse et ah, 1995; Walker, 1985; Walker et ah, 1987). An ultrastructural study Results of the entire morphology ofan acrothoracican cyprid is necessary for gathering the suite of larval char- could detect We not any morphological differences acters that Glenner et ah (1995) advocated for fu- between cypris larvae ofLithoglyptes habei and L. ture studies of cirripede phylogeny. Here we try to mitis. We have therefore not distinguished between in accomplish this part by a study of cypris mor- the two species in the following description, but phology in two species of the acrothoracican fam- the species name is provided for all figures. ily Lithoglyptidae. Downloaded from Brill.com10/09/2021 08:04:42AM via free access 145 Contributions to Zoology, 68 (3) - 1999 of Size and shape of the cyprids and attach to the dorsomedial side the carapace, of the but a complete description cypris muscula- contained will in In our material the adult females never ture require section series as Walley (1969) oral more than a single cypris, while Tomlinson (1969) and Hoeg (1985). The undifferentiated (buc- within the often found two brooded larvae in the same female. cal) cone and the thorax lie posterior located in the lower halfof the The thorax carries six of The brooded cypris larvae are carapace. pairs the and body part of female usually towards the biramous limbs armed with long natatory setae. The dorsal margin of mantle cavity. They measure ca. abdomen is rudimentary but carries a distinct tel- with of furcal rami The 580-600 pm in length, which equals approximately son a pair (Figs. IB, 7). 40% of the length of the brooding female. The size thorax and the antennules can be partially extended ofthe cypris relative to the femalemeans that brood outside the mantle cavity (Fig. 2B,D)