Contributions to Zoolog)’, 68 (3) 143-160 (1999)

SPB Academic Publishing hv, The Hague

Scanning electron microscopy of acrothoracican cypris larvae (Crustacea,

Thecostraca, Cirripedia, , Lithoglyptidae)

¹, ¹ Gregory+A. Kolbasov Jens+T. Høeg² & Alexei+S. Elfimov

1 Department of 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, , cypris , 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 and the . 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 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 (Newman, 1982; Grygier Newman, Lattice organs

Mantle and mantle cavity 150 1985). In spite of these studies the position of the 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 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, 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. 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) size is necessarily minute.

has elon- The cypris headshield, or carapace, an

gated, spindle-shaped form with an anterior rounded Carapace end end and a narrower and truncated posterior (Figs.

1B,C, 2A). The dorsal margin is slightly curved. There is no dorsal hinge line or posterior slit on

the also the At lower its surface The ventral margins of carapace are slightly carapace. magnifications curved in the anterior half, whereas in the poste- appears slightly wrinkled with small longitudinal rior halfthey are somewhat concave. The length : and transversal ridges (Fig. 2A,B), but some of these

fixa- height ratio of the carapace is ca. 3 : 1. In lateral ornaments may be artifacts produced during

At view the shape of the cypris resembles those of tion or preparation for SEM. higher magnifica- other cirripedes. However, the cyprids of both tion the carapace surface appears smooth (Fig. 3 A-D)

Lithoglyptes studied here and those of Trypetesa and without the cellular hexagonal patterning that

characterizes ascothoracid larvae lampas studied by Jensen et al. (1994) deviate from some (Ito &

facetotectan other cirripede cyprids in having a very narrow Grygier, 1990), cypris-y (Schram,

The and some thoracican The carapace compared to the length (Fig. 2A,B). 1970), cyprids. carapace functional significance of this shape is not clear. also lacks large pores (except the frontolateral

In it relate to of settle- and the wheel of Elfimov Trypetesa may peculiarities pores), papillae, organs shells Unlike of ment within the narrow confines of gastropod (1995). cyprids Cryptophialus (unpub-

inhabited by hermit crabs. lished data), there are no long setae but only minute

(0.7 pm) setae sparsely distributed over the entire

carapace (Fig. 3A,C,D). These carapace setae are

General morphology single (Fig. 3A) or double (Fig. 3C,D) and are lo-

cated in 1 wide shallow, pm depressions. Single

The general morphology of Lithoglyptes cyprids setae occur most frequently on the anterior and lateral

surfaces the A agrees with that found in other cirripedes. The of carapace. longitudinal row of

four-segmented antennules are located in the ante- double setae extends from the anterior end along

the rior mantle cavity, which occupies the anterior one the dorsomedial line of carapace (Fig. 3C,D).

third “valves” have of the cyprid Godg. The cement glands lie at The carapace deep longitudinal and

end the basis of the first antennulary segments. They transverse furrows at the anterior (Figs. 2D,

have al- a loboform shape and a brown colour (in 3C).

cohol), darker than the rest of the body. The paired

associated with frontal compound eyes, filaments,

lie in Frontolateral front of the cement glands (Fig. IB,C). The pores

situated the dorsal nauplius eye is near margin, one

third of the length from the anterior end. Retractor Lithoglyptes cypris larvae lack the frontolateral horns

muscles of the antennules and thorax extend through found in a few thoracican species, but sport a pair

the anterior of and middle parts of the cypris body conspicuous frontolateral pores near the 146 G.A. Kolbasov, J.T. Haeg & A.S. Elfitnov — Acrothoracican cypris larvae

Fig. I. A, Lithoglyptes mitis, adult female, lateral view, with a cypris (bottom arrow) and an unidentified (top arrow) inside the mantle cavity, lateral view; B,C, L. habei cyprid, lateral view from light microscopy; D, terminal part of antennule showing attachment disc on 3rd segment (3) with dense carpet of cuticular villi (see Fig. 5D); E, Setation on fourth antennulary segment,

five terminal minute C Setation of in among setae (TS) only seta identified (See Fig. 6D); F, (arrowheads) terminal (2nd) segment

of thoracopodal exopod, isolated basal seta, three subterminal and two terminal setae closely grouped; G, Setation (arrowheads)

of three Terminal end of furcal with terminal (3rd) segment thoracopodal endopod, terminal setae; H, ramus two setae (arrowheads)

CE CG of inside mantle FR furcal LOl-5 lattice (See Fig, 7G). compound eye, cement gland, CT, rows ctenes cavity, ramus, organs

M NE PAS RS radial 1-5, extrinsic antennulary muscles, nauplius eye, OC, oral cone, postaxial sensillum, PS2 postaxial seta 2, setae,

SC proximal sclerite of 1st antennulary segment, SK skirt encircling attachment disc, SSI-4 subterminal setae 1-4, TE telson, TH thorax, TUP thoracopods, TS terminal setae, 1-4 antennulary segments. Scale bars in pm. Contributions to Zoology, 68 (3) - 1999 147

2. L. with extended arrowheads show Fig. Cyprids (A,D Lithoglyptes mills ; B,C habei). A, antennule, ventrolateralview, entrance to

mantle cavity; B, with both antennules and thoracopods extended, lateral view; C, settled male cyprid removed from female mantle

cavity, female tissue remains around antennules(arrowhead); D, anterior end with extended antennule, ventrolateralview, arrowheads

THP denote anterior furrows. AN antennule, FP frontolateral pore, PS2 postaxial seta 2, thoracopods, 2-3 antennulary segments.

Scale bars in pm.

80 dian keel L03 and but anteroventral margin of the carapace ca. pm or crest (in L04), are never

from the The encircled cuticular anterior end (Figs. 2D, 3B,E). pores by a ridge. This means that the

1.3 LOs of have are elongate (3 by 4 pm) and surrounded by a pm Lithoglyptes the same morphology

in a found al. high cuticular ridge without any sculpture. They {‘keel trough’) as by Jensen et (1994)

are the exits for the frontolateral glands that char- in cyprids of T. lampas. The elongate depression

acterize cirripede cyprids. of the LOs has a latticed bottom due to minute

perforations in the epicuticle, but a TEM investi-

of similar in the T. gation organs acrothoracican

revealed that lack in the under- Lattice organs lampas they pores

lying procuticle (Hoeg et al., 1998).

The carapace has five pairs of lattice organs (LO) Terminal pore: A conspicuous terminal pore (TP) in both Lithoglyptes habei and L. mitis. They have lies at the posterior end of LOl and L03-5, but

the of the differs in same position and the same morphology L02 having this pore sited at the anterior

individual the five LO found in end organs as pairs (Fig. 4A-D).

Trypetesa lampas by Jensen et al. (1994). Position and shape: The first (LOl) and second

Individual All individual lattice of lattice lie close morphology: or- (L02) pairs organs (10 pm) to-

are 7-18 and 0.8-1 wide ca. 200 from the anterior end and 5-13 gans shallow, pm long pm gether, pm pm

from depressions (Fig. 4). They may have a weak me- the dorsal midline (Fig. 4A,B). LOl is straight 148 G.A. Kolbasov, J.T. Haeg & A.S. Elfimov- Acrothoracican cypris larvae

Fig. 3. Cyprids (A-B Lithoglyptes mitis, C-E L. habei). A, anterior end, oblique lateral view, setae arrowed; B, anterior end, ventral view front view of and showing entrance to mantle cavity with antennule (AN), at upper left, C, anteriorend, dorsal carapace, furrows

with raised double seta (arrowed); D, dorsal margin of carapace, double setae arrowed; E, frontolateral pore (of frontolateral gland)

AN FP frontolateral Scale bars in rim. antennule, pore. pm. Contributions to Zoology, 68 (3) - 1999 149

4. lattice numbered C L. left lattice 1 and Pig. Cyprid carapace, organs (A,B,D,E Lithoglyptes mitis cyprid; habei). A, side, organs 2

anterior end is terminal in 1 but anterior in left (small arrowheads), left, pore (TP) posterior lattice organ lattice organ 2; B, side, lattice

terminal anterior end is lattice 3 and both with organ 2, pore (TP) anteriorly sited, left; C, posterior end, right side, organs 4, posteriorly

sited terminal end is lattice left sited terminal anterior end is pore (TP), anterior right; D, organ 5, side, posteriorly pore (TP), left; E,

and anterior end is left. bars posterior end, showing relative position of lattice organs 3, 4 5, Scale in pm. 150 G.A. Kolbasov, J.T. Haeg & A.S. Elfimov - Acrothoracican cypris larvae

5. C L. anterior left of removed of mantle Fig. Cyprids (A,B,D Lithoglyptes habei; milis). A, end, side carapace to expose inner side with rows ofcuticular ctenes (CT, arrowheads) and semiparallel rods of proximal sclerite (SC) of the first antennulary segment; B, detail ofA, cuticle ofmantle cavity with ctenes (CT, arrowheads); C, anterior end, right side of carapace and right antennule removed

(breakage at *) exposing left antennule with anteriorly projecting proximal sclerite (SC), white arrowheads show cuticular fold close to ventral mantlemargin; D, distal part of antennule (segments 2-4). AD attachment disc,AM arthrodial membrane (between segment

2 and 3), CT ctenes, PS2 postaxial seta 2, RS radial setae (arrowheads), SS1 -4 subterminal setae (on segment 4), TS terminal setae (on

SC sclerite of 2-4 Scale bars in segment 4), proximal antennulary segment 1, antennulary segments. pm.

and 7 L02 is and Mantle and mantle (tin long. longer (18 pm) very cavity slightly curved. The three posterior pairs (L03-5) are located ca. 300 pm behind the anterior pairs The inner surface of the mantle has a longitudinal and close the fold from are (100 pm) to posteriormost end of 18 pm distant the ventralmost edge (Fig. the cypris (Fig. 4E). L03 and L04 are separated 5C, white arrowheads). In the anterior mantle cav- by only 4 pm and lie approximately in line with ity the cuticle also has five longitudinal rows of

LOI and L02 from the dorsal cuticular to the ventral (4-5 pm midline). ctenes running parallel edge

LOS lie level with L04 but distant of the These about are more carapace. rows are separated by

(16-18 from the pm) midline (Fig. 4E). L03 and 11 pm and their 3-4 pm high ctenes consist of

L04 and are 8-10 pm long straight or only slightly unfused fringes (Figs. 1C, 5 A,B). We were not able curved. LOS is 7 in only pm long. to verify whether similar ctene rows occur the Contributions to Zoology, 68 (3) - 1999 151

Fig. 6. Cyprid antennule(A,C Lithoglyptes mitis; B,D L. habei). A, attachment disc (AD) of segment 3 with dense carpet of cuticular

villi and skirt black and of encircling (SK), arrowheads point to insertion (left) apex (right) postaxial sensillum (PAS); B, dorsal

(preaxial) side of segment 3 showing insertion of segment 4 and diminutivepostaxial seta 3 (PS3); C, segment 3, right lateral view of

of terminal minute right antennule; D, distal end segment 4, four subterminal setae (SSI-4), among five setae (TS) only seta C named,

other clockwise: first thin seta with distended base and distal second thin thick TS (see text) are long seta, taper, long, seta, cylindrical

seta. AD attachment disc, (C) terminal seta C, PAS postaxial sensillum, PS2 postaxial seta 2, PS3 minute postaxial seta 3, SK

cuticular skirt encircling attachment disc, SSI-4 subterminal setae (on segment 4), TS terminal setae (on segment 4), 3-4 antennulary

Scale bars in segments. pm.

posterior part of the mantle cavity. (Terminology without setae. As in all cirripedes this segment has

on ctenes and fringes adapted from Grygier (1987b) a conical or triangular shape and consists of two

and Klepal & Nemeschkal (1995).) sclerites (see detailed description in Hoeg, 1985

and Glenner, in press). The proximal sclerite forms

the base of the cone and carries two anteriorly pro-

1st antennulary segment jecting rods (SC in Fig. 5C). The distal sclerite

connects with the cylindrical second segment at the

As in all other the antennules of the The be cirripede cyprids apex cone. segment can completely

of mantle consist four segments (Figs. IB, 2D, 5C,D, 6). withdrawn inside the cavity, but projects

The first segment (Figs. 1C, 5C) is largest, about outside during exploratory walking and in attach-

80 pm long and 40 pm wide, flattened laterally and ment (Figs. 1C, 2C). 152 G.A. Kolbasov, J.T. Hoeg & A.S. EIJimov — Acrothoracican cypris larvae

7. end ofthorax and left removed Fig. Cyprid, posterior (L. habei). A, posterior part abdomen,part of side carapace (arrowheads); B, thorax, dorsal view; C, thorax, dorsolateral view, terminal segments ofexopod (EX) and endopod(EN) ofleft thoracopod 3, arrowheads

of three thoracic and indicate single basal seta and five terminal setae in exopod; D, detail A, showing last segments (TH 4-6)

5 and from thoracic 5 due directed basalmost limb thoracopods 6, thoracopod 6 may appear to originate segment (TH5) to anteriorly part (BA), thoracopod 6 with three-segmented endopod (1-3, white arrowheads) and two-segmented exopod (1-2, black arrowheads),

2" are serrated shows (I", exopod segments of thoracopod5), exopod segments 1 with single long and seta (SES arrowheads), arrow terminal offurcal is natatory setae onexopod segment 2; E, proximal-middlepart ramus, lateral view, distal end down;F, posteriormost Contributions to Zoology, 68 (3) - 1999 153

4th 2nd antennulary segment antennulary segment

The second is 75 The fourth measures 5 cylindrical segment ca. pm long, cylindrical segment jam by

4 the with a straight ventral (postaxial) and curved dor- pm and inserts laterally on third segment (Figs. sal (preaxial) margin (Fig. 5C). Its width decreases 5D, 6A-D). As in thoracican cyprids (Clare & Nott,

from at the the carries four subterminal and five 35-40 pm proximal ly to only 12-13 pm 1994), segment articulation to the third segment. A conspicuous terminal setae (Figs. IE, 6D). Our terminology of postaxial seta 2, number 13 in the classification of these setae follows the scheme of Gibson & Nott

Nott & Foster (1969), inserts ventrodistally (Figs. (1971) and also used by Clare & Nott (1994),

Glenner& 1D, 5D) as in the groundpattern for cirripede cyprids Hoeg (1995) and Walossek et al. (1996).

(Glenner et ah, 1989; Moyse et ah, 1995). There All setae ofthe fourth segment, except the diminu-

second have are no other segmental setae, but a small tive seta C, an apical pore.

ctene (7-10 fringes) adorns its lateral surface closer The four subterminal setae (setae 1-4) are situ-

the to the basal margin than to distal one. ated close together. They are morphologically iden-

tical, approximately equal in length (9 pm), and

resemble those in thoracican barnacles (SSI-4 in

3rd antennulary segment Fig. 6D).

The of the five terminal homologies setae are

The hoof-shaped third segment measures ca. 30 by discussed below. They differ in regards to length,

15 All pm (Figs. ID, 5D, 6A,C). surfaces except width, and morphology, but not to the extent seen

the attachment disc lack setae. A well-developed in the Thoracica (Gibson & Nott, 1971; Clare &

skirt of thin cuticle (sensu Moyse et ah, 1995) Nott, 1994; Glenner & Hoeg, 1995). In particular,

encircles the attachment disc, which is morphologi- all terminal setae in Lithoglyptes are unsetulated,

cally ventral (Figs. 5D, 6A,C) and is covered by a whereas in thoracicans two terminal setae (A & B)

dense carpet of cuticular villi (Figs. ID, 6A). We have long setules. In Lithoglyptes, two setae are

failed 8-9 and of form. to detect an axial sense organ (sensillum), pm long, narrow, simple One seta

the in but in other cyprids it is often obscured by (C) is vestigial, just as the Thoracica. The long-

but cuticular villi (Moyse et ah, 1995). A well-developed est seta (13 pm) has a distended basal half, tapers

sensillum inserts the rather at around 2/3 rds of the towards postaxial (PAS) at postaxial abruptly way

margin of the segment (Figs. ID, 6A) between the the tip; its surface shows a faint circular or spiral

skirt and the carpet of villi. Two setae situated at pattern that indicates a reinforcement structure in

the of the attachment disc otherwise thin cuticle. distal, preaxial margin an very Finally, one c. 9 pm

(Figs. ID, 5D) represent two of the radial sensilla long, cylindrical and isodiametrical seta has a width

of thoracican cyprids, but there could well be ad- in between the two thin setae and the thick seta

ditional radial sensilla hidden in the carpet of villi. and terminates very abruptly.

An indistinct structure inserts on the lateral sur-

face near the base of the fourth segment (Fig. 6B). Thorax and thoracopods

We interpret it as a rudimentary postaxial seta 3,

in and 120 forms the third which thoracican some rhizocephalan cyprids The ca. pm long thorax posterior

inserts at this place but is a very conspicuous sen- of the cypris body (Figs. 1A,B, 7). As in other

sillum (Nott & Foster, 1969; Moyse et ah, 1995). cirripedes it consists of six segments each bearing

a pair of biramous and natatory thoracopods. In

thorax (TH), abdomen (AB), and telson (TE), ventral view, furrows indicate four putative abdominal segments (arrows), telson with

ventral distal end of furcal lateral and left furcal deep cleft (CL); G, ramus, view; H, abdomen, telson proximal part of ramus, left

lateral view, single setae (SE) on dorsal margin and setae br fringes (arrowhead) on ventral margin of telson are duplicated on

side. abdomen BA basis of CA CL cleft in CT EN EX (unseen) right AB, (but see text), thoracopod, carapace, telson, ctene, endopod,

FR furcal SES serrated seta TE TH thorax numbered in exopod, ramus, SE, seta, (on exopod segment 1), telson, (segments D),

Scale bars in l-3(white) endopodal segments, l-2(black) exopodal segments. pm. 154 G./i. Kolbasov, J.T. Hf-ieg & A.S. Elfimov - Acrothoracican cypris larvae

rhizocephalan cypris larvae Walossek et al. (1996) Hindbody and furcal rami

medioventral inserted found an unpaired process between the sixth thoracic segment and the abdomi- The hindbody consists of a short, cylindrical (6 x

with four furrows on nal rudiment, and they speculated that it might be 10 pm) abdomen, transverse

has the ventral that indicate the of a rudimentary penis. The acrothoracican cypris side, may presence

four and a x 13 telson no such process (Fig. 7D,H). segments, longer (18 pm)

We could not observe all details in each of the (Fig. 7A,D,F).

bears six individual pairs of thoracopods. Small differ- The lateral surface of the telson a row (ctene)

such between the first and second of five elongate denticles 7H). In addition there ences, as occur (Fig.

therefore have is minute seta on each side pair in the Thoracica may gone a single, dorsodistally small of undetected (Glcnner & Hoeg, 1995). The thoraco- of the telson and a group setae or fringes

the ventrodistal The pods in cyprids of Lithoglyptes resemble those laterally on margin (Fig. 7H). described using light microscopy from cyprids of ventral surface of the telson has a deep and distinct

Trypetesa nassaroides (Turquier, 1967). The thora- medial cleft (Fig. 7F). have copods consist of a protopod carrying a two-seg- The furcal rami in cyprids of Lithoglyptes

a 44 7A,E,G). mentcd exopod and a three-segmented endopod (Fig. only single pm long segment (Fig.

the 7C,D). In lateral view, pseudo-quadrangular scler- However, partially cleaved telson can easily be

the mistaken the basal of ites (Fig. 7D) cover the insertion and proximal as segments “two-segmented

rami”. bears part of the thoracopods, so we could not with cer- The lateral surface of a caudal ramus

nine tainty identify a coxa. The thoracopods bend strongly a ctene of fringes and some sparsely spaced backwards between the first ramal smaller while it termi- in the joint seg- fringes (Fig. 7E), distally

A comb of ment and the basis before they insert on the thorax nates in two long setae (Fig. 1H). cu-

(Fig. 7D,F). ticular villi surrounds the furcal setae on the dorsal

the The first exopod segment carries a single, stout margin, but are almost vestigial along ventral seta inserted laterodistally beneath a triangular margin (Fig. 1H, 7G). projection and extending beyond the second seg- ment (SES in Fig. 7D). It carries a basal row of

small spines and a single row of 8-10 much larger Discussion

second spines on the surface facing the segment.

the SEM of all Extensive bending can occur between first and This paper is the first based description

second exopodal segments. The second segment external features in acrothoracican cypris larvae.

Jensen and al. have bears five terminal simple setae and a single iso- et al. (1994) Moyse et (1995)

lated simple seta inserted near the base (Figs. IF, previously used SEM to describe individual organs

7C,D). in cyprids of Weltneria spinosa (lattice organs) and

The endopod is shorter than the exopod. The Trypetesa lampas (lattice organs, attachment or-

In position of segments in preserved cyprids show that gans). addition, Turquier (1967) gave a good

of of T. extensive bending can occur between segments two light microscopical account cyprids

nassaroides. and three. We never saw any flexure between seg-

The of in all ments one and two in the fixed specimens and sur- cyprids Lithoglyptes agree impor-

data for mise that in the live larva little or no movement tant aspects with the scattered available

We confirm occurs between them at all (Fig. 7D). The setation the other acrothoracican species. can

simi- of the endopod is difficult to observe due to obscu- that acrothoracican cyprids show numerous

ration by the exopods, but the second segment seems larities with cyprids of the remaining two cirripede

to while also in the carry one simple seta on the laterodistal margin, orders many respects resembling

the while third segment (Figs. 1G, 7C) carries three cypris-like ascothoracid larvae of the Ascothoracida.

If simple, terminal setae. correct, this setation cor- We will first discuss the individual morphological

responds exactly to that described by Turquier (1967) features concerned before we summarize their phy-

for the endopod of Trypetesa nassaroides cyprids. logenetic significance. Contributions to Zoology, 68 (3) - 1999 155

but sited in L03-5. Lattice organs L02 a posteriorly pore Jensen

et al. (1994) therefore suggested that the taxon

Lattice organs were first described by Elfimov Acrothoracica exhibits an intermediate character

and known in sited in (1986). They are chemoreceptors only state having an anteriorly pore L02 only.

from within the Thecostraca, where five pairs adorn There is nothing in our data to question that con-

the carapace of facetotectan cypris-y larvae and clusion. But Grygier & Ohtsuka (1995) found an cirripede cypris larvae (Jensen, 1993; Jensen et al., anterior position of the terminal pore in LOl and

1994; Hoeg et al., 1998; Hosfeld et al., 1998). Many L03 of Synagoga millipalus indicating that differ- ascothoracidans have fever lattice organs (Grygier, ent ascothoracidan species vary with respect to the

but with of We need pers. comm.), based on comparison the position the terminal pore. therefore a

and the fixed number in both the third group to clarify the plesiomorphic position

consider such ofthe terminal within the Thecostraca. This Cirripedia we cases as apomorphic pores

deviations from a thecostracan ground pattern with highlights the importance of a detailed SEM in-

the five pairs. Lattice organs (LO) vary between vestigation of the cypris-y larvae of the Facetotecta

thecostracan taxa both in their general morphol- (Hosfeld et al., 1998).

and in the the terminal ogy position of large pore, which can be sited either anteriorly or posteriorly in the individual Mantle cavity organ (Jensen et al., 1994).

Lithoglyptes habei, L. mitis, Trypetesa lampas, and of Parallel of cuticular Weltneria spinosa have lattice organs near longitudinal rows ctenes line

and the inner lamellae of the in identical morphology (“keel in a trough” type) carapace both acro- in anterior in L02 thoracican all of them the terminal pore is cyprids (present study), rhizocephalan but posterior in LOl and L03-5. This stereotyped cyprids (Walossek et al., 1996), thoracican cyprids

of the lattice within the and ascothoracid larvae morphology organs (Hoeg, unpublished)

Acrothoracica makes them well suited for discuss- (Grygier, 1987b; Ito & Grygier, 1990). This indi-

ing large scale thecostracan phylogeny. The Acro- cates that such rows represent a ground pattern thoracica “keel in feature of the Thecostraca. have lattice organs ofthe a trough" (apomorphic?) We sug-

combs morphology, but all the numerous thoracican and gest that they function as for cleaning the rhizocephalan species studied by Jensen et al. (1994) antennules.

had lattice of the field an organs “pore type”, i.e.,

oval or elongate area perforated by numerous small

in Antenmiles pores. This variation lattice organ morphology

found be among the Cirripedia can polarized by

with the Ascothoracida and 1 and 2 have a similar outgroup comparison Segments morphology very

the Facetotecta. Both have lattice that seen in other outgroups organs to cirripede cyprids. Segment 3

of the “in resembles the keel a trough” type (Jensen et al., 1994; one Moyse et al. (1995) described

Hosfeld et which indicates that this from lampas but with the differences al., 1998), Trypetesa ,

morphology is plesiomorphic within the Theco- noted below. In all cirripede cyprids, the radial setae

straca. The apomorphic “pore field” type shared are partially or wholly obscured by the microvilli

of the and by cypris larvae Rhizocephala the carpeting the attachment disc, so an exact count

Thoracica TEM indicates that these two taxa are sister requires sections in a plane tangential to the

groups, a conclusion also supported by molecular disc. This has only been done in Semibalanus

data (Spears et al., 1994). balanoides, where Nott & Foster (1969) found 8

The variation in the position of the large termi- radial setae. It is quite normal that two of the ra- nal pore is more problematic. It is posterior in all dial setae distally on the attachment disc are longer

five the pairs (LOl-5) in ascothoracidan Ulophysema than the remaining ones (Moyse et al., 1995), as

in oeresundense, whereas the Thoracica and Rhizo- also seen here Lithoglyptes, where they are the

in cephala have an anteriorly sited pore LOl and only ones visible at all. As in our study, Moyse et 156 G.A. Kolbasov, J.T. Hoeg cfe A.S. Elfimov — Acrothoracican cypris larvae

failed detect in tions both in al. (1995) to the axial sense organ exploratory walking prior to settle-

Trypetesa lampas using SEM only but revealed its ment and in permanent cementation. Important

axial could are: first presence with TEM. An sense organ apomorphies a triangular or cone-shaped

therefore also be present in our species. segment consisting of two sclerites set at an angle

In T. lampas Moyse et al. (1995) specifically to each other (see Hoeg, 1985; Glenner, in press); mentioned the absence of a postaxial seta 3 (ps3), a long, cylindrical second segment; a small third

in both the and the attachment which Thoracica Rhizocephala is a segment with organ and a cylindri- conspicuous structure that inserts near the base of cal fourth segment bearing, in the ground pattern,

is the third and fourth the 4th segment. In Lithoglyptes cyprids the rudi- 4+5 sensory setae. It seg-

knob found the insertion of that mentary adjacent to ments vary most extensively among cirripedes.

4 If This segment could represent a highly reduced ps3. is hardly surprising, since these two segments

so, this indicates that the absence or extreme re- are in direct contact with the many different types duction of ps3 is an apomorphy for the Acrotho- of substrata used in settlement by cyprids of the racica. different species. In acrothoracican cyprids, the most

pronounced difference on the 3rd segment is the

absence or at least extreme reduction of postaxial

Antennulary segment 4 seta 3 (ps3). In thoracican cyprids, this seta is a

in long and conspicuous simple seta, while

This segment has the same number and position of rhizocephalan male cyprids it has the form of a long

in The setae as thoracican cyprids. homology of aesthetasc (Walker, 1985; Moyse et ah, 1995). the four subterminal setae with the similarly shaped Otherwise, the third segment of acrothoracican and positioned ones in thoracican cyprids is straight- cyprids has a fairly conventional morphology. forward. There is also little doubt that the five ter- The fourth segment carries four subterminal and

in minal setae correspond to the five terminal ones in five terminal setae both the Acrothoracica and the Thoracica. One terminal seta is short the Thoracica & and this (C) very (Clare Nott, 1994), repre- in both the Thoracicaand Acrothoracica and clearly sents the cirriped ground pattern. Only the Rhizo-

both The four have fewer this and this homologous in groups. remaining cephala setae on segment,

in much longer terminal setae differ morphology is probably an apomorphic condition (Hoeg & between the two orders, so we hesitate to suggest Rybakov, 1996). However, the Acrothoracica do

The in Litho- deviate in setulation of the terminal any seta-by-seta homologies. seta lacking on any glyptes with a distended basal part and tapered apex setae, whereas the Thoracica have two setulose setae. could well correspond to seta D in thoracicans (and Grygier (1987a) made a pioneering attempt in ho- rhizocephalans). In both acrothoracicans and tho- mologizing segments and setae in antennules of racicans this seta exhibits a distinct pattern on its i ascothoracids, facetotectan cypris-y, and cirripede surface and Clare & Nott (1994) suggested that it cyprids. Further conclusions must await SEM studies is an aesthetasc. of facetotectan antennules.

Apomorphies in antennulary morphology Thoracopods

The unique structure and morphology of the cypris Few studies have focused on the cypris thoracopods, antennule involve several putative apomorphies despite their importance in the rapid swimming bouts which agrees with the claim that the Acrothoracica, during the pelagic phase of the larva. Cyprids of

Thoracica and Rhizocephala form a monophyletic Lithoglyptes and Trypetesa have a three-segmented taxon Cirripcdia. In all three orders, the antennule endopod and a two-segmented exopod just as in

of consists four segments with surprisingly similar the ground pattern for ascothoracid larvae (Turquier,

and shape function. This probably reflects func- 1967, present paper). As discussed in detail by tional the & constraints posed on antennule that func- Grygier (1987b) and commented on by Glenner Contributions to Zoology, 68 (3) - 1999 157

and Hoeg (1995), this signifies that such a segmenta- Tagmosis hindbody tion scheme characterized not only the cypris-like larva of the urthecostracan but also the true cypris According to Grygier (1983, 1987a) and Grygier

the Thecostraca of the urcirripede. Our observation on Lithoglyptes & Ohtsuka (1995) both and the also confirms Grygier’s (1987b) character matrix in general have a 5-7-4 tagmosis in that the fusion in cirripedes occurred between scheme in the ground pattern. In cyprids of

the of short abdominal endopodal segments 1 and 2. The Facetotecta have Lithoglyptes presence four, a three-segmented endopod in the ground pattern, segments and an elongate telson with unsegmented but Schram (1970) and Grygier (1987b) found that furcal rami dovetails with this pattern. The ap- some facetotectans have evolved a two-segmented parently 4-segmented abdomen is plesiomorphic state by fusion between endopodal segments 2 and compared to all other cirripedes (larval or adult).

3. Obviously, the two-segmented endopods found We found no trace of a 7th thoracomere, which in

facetotectans do the unless in some cirripeds and not repre- the thecostracan ground plan carries penis,

of the here des- sent homologous states and again demonstrates how it forms part annulated region we simple counting of limb articles can lead to erro- ignate as abdomen. Unpublished SEM micrographs

in that Thora- neous conclusions as elegantly elaborated Huys reveal cyprids of some lepadomorphan

& Boxshall (1991). cica can have a three-segmented abdomen.

between A less cleaved The apparent lack of flexure endopod more or deeply telson bearing

in caudal rami constitutes segments one and two Lithoglyptes cyprids in- unsegmented a ground pat-

in It in dicates that it was these two segments that fused tern feature cirripede cypris larvae. occurs

into one in the evolution of the Thoracica (and the Acrothoracica (this study), the Rhizocephala

in and in Rhizocephala?). In the Thoracica, a faint suture (Walossek et ah, 1996) apparently also

the first segment of the endopod recalls the plesio- cyprids of lepadid Thoracica (Grygier, 1987b). In morphic three-segmented condition(Glenner et ah, contrast, Walker & Lee (1976) and Glenner& Hoeg

1995). (1995) used SEM to claim that balanomorphan

cyprids (Balanus amphitrite, Semibalanus bala-

All and have “caudalrami” inserted cirripede cyprids carry a single stout noides) two-segmented

the end of the and serrated seta on the first exopod segment ofall eight directly on posteriormost thorax

thoracopods (Glenner & Hoeg, 1995; Walossek et no visible abdomenor telson. We believe that also

rami in- ah, 1996 Fig. 14B). These setae are always shorter balanomorph cyprids have unsegmented

serted than the natatory ones on the second segment, and on a telson, but that the cleft has become

telson they undoubtedly serve in grooming both the nata- so deep that the can easily be mistaken for

tory setae and the limb bases. However, they are “basal ramal segments”. A similar error probably

if lead to describe rarely ever as large and strongly armed as in the Turquier (1967) two-segmented

acrothoracican cyprids studied here. Nothing com- “furcal rami” in cyprids of the acrothoracican Trype-

parable to these grooming setae exists in ascotho- tesa nassaroides. Support for our claim could come

racid or cypris-y larvae, so they represent another from serial sections revealing that the purported of the the “first ramal are united a slim medial many apomorphies characterizing cirripede segments” by

cyprid. connection. The urthecostracan undoubtedly had

The the 2nd caudal since find this single seta inserting on endopod unsegmented rami, we con-

segment is also present in ascothoracid larvae, dition in both the Ascothoracida, the Facetotecta,

cypris-y, and in thoracican cypris larvae. But aside and the outgroup Copepoda (Grygier, 1987b).

from SEM TEM studies this, it is premature to speculate on the ground Obviously, and of the hindbody

pattern of thoracopodal natatory setae in the in additional thoracican cyprids may provide Thecostraca. characters useful for a phylogenetic analysis. 158 G.A. Kolbasov, J.T. Haeg & A.S. Elfimov - Acrothoracican cypris larvae

Conclusion Acknowledgements

JTH and GAK their gratitude to H. Glenner, J. Olesen The data from SEM analysis presented here again express and T. Schiotte for help with SEM preparation and operation. highlight the value of larval characters in elucidat- Grants no. 11-9652 and no. 9701589 from the Danish Natural ing thecostracan and cirripede phylogeny (Grygier Science Research Council enabled JTH to finance GAK visits

1987a& Jensen ct b, 1994, 1995; al„ 1994; Elfimov, to Denmark and are gratefully acknowledged, GAK thanks the

1995; Moyse et al., 1995; Hoeg et al., 1998). The Russian Foundation for Basic Research (grant N 97-04-49803)

for supporting his work in Moscow State University. GAK also cypris larvae of the Acrothoracica exhibit similari- acknowledges Dr. D.L. Ivanov (the chief ofthe mollusc collection ties both with the Ascothoracida and the Facetotecta, of the Zoological Museum of Moscow State University) and and with the two orders. Al- remaining cirripede R.V. Egorov for an opportunity to examine the collections of

though we await a full-fledged phylogenetic analysis, the Zoological Museum and help in the species determination

of mollusc shells. ASE and GAK are finally indebted to G.N. as in Glenner et al. (1995), we will here assume Davidovich and LA. Bogdanov of the Laboratory of Electron that the similarities with ascothoracid larvae and Microscopy ofthe Biological Faculty ofMoscow State University facetotectan cypris-y represent symplesiomorphies. for help with SEM investigations,

They include: the “keel in a trough” shape of the

endo- lattice organ; three-segmented thoracopodal References pods; a five-segmented hindbody.

These plcsiomorphies do not alter the fact that

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