FAU Institutional Repository http://purl.fcla.edu/fau/fauir This paper was submitted by the faculty of FAU’s Harbor Branch Oceanographic Institute. Notice: ©1991 John Wiley & Sons, Inc. This manuscript is an author version with the final publication available at http://www.wiley.com/WileyCDA/ and may be cited as: Svane, I., & Young, C. M. (1991). Sensory structures in tadpole larvae of the ascidians Microcosmus exasperatus Heller and Herdmania momus (Savigny). Acta Zoologica, 72(3), 129-135. doi:10.1111/j.1463-6395.1991.tb00939.x ~<{ /( A cra Zoologica (Stockholm) . Vol. 72.No . 3. pp. 129- 135. 1991 000 1- 7272/9 1$3.00 + .00 Printed in G reat Britain Pergamon Press pic © 199\ T he Royal Swed ish Academy of Sciences Sensory Structures in Tadpole Larvae of the Ascidians Microcosmus exasperatus Heller and Herdmania momus (Savigny) Ib Svane ' and Craig M. Young" ' Kristineberg Mar ine Biological Station. Kristineberg 2130. S-450 34 Fiskeb acksk il,Swede n ' Harbo r Branch Oceanog raphic Institutio n. 5600 O ld Dixie Highway. Ft. Pierce . Florida. U.S.A . (Accepted fo r publication 14 A ugust 1990) Abstract Svane, I. & Youl/g. C. M. 199 1. Sensor y str uctures in tad pole larvae of the ascidians Micro­ COS /l IlIS exasperatus Heller and Herdmania momus (Sa vigny) .-Acta Zoologica (Stockho lm) 72: 129-1 35. In this paper we describe the larval mo rphology of two spec ies fro m the ascidian family Pyuridae , .. Microcosmus exasperatus and Herdm ania momus, with spe cial emp hasis o n co mpo nents of the ce rebral vesicle . Larvae have not previously been described fo r any spec ies in the large genus Microcosmus. Besides a difference in size (larvae of H. m omus are about 40'X. larger than those of M. cxasperatuss, larvae of the two species differ prima rily in the num ber and arra ngement of senso ry structures. Bot h spec ies possess a well-developed sta tocyte but o nly H. momu s has an oce llus. T he abse nce of an oce llus in M. exasperatus is uniq ue amo ng pyurid ascidians. An auxiliary vesicle was found situated o n the left side of the ce rebral vesicle in bot h species. However . un like the larvae of H. momu s and ot he r pyuri d spec ies. ther e is no appa rent communica tio n between the auxiliary and ce rebral vesicles of M. exasperatus . Ep ithelial cells in the auxiliary vesicles of bo th spec ies carry mod ified cilia abo ut 2 u rn in diameter ; auxiliary vesicles of H. /110mus also have simple cilia with axo ne mes in a 9 + 0 microtubu le configuration. In H. /l 1O/JIl IS the membran es of the epithe lial cells are highly convoluted and exte nd into the lumen of the auxiliary vesicle . Mo rp hological arrange me nts of auxiliary vesicles and globular cilia rep or ted so far in ascidia n tadpole s are contras ted and discussed . Ib Svane, Kristineberg Marine Biological Station, Kristineberg 2130. .'1-450 34 Fiske biicks kil, Sweden. Introduction parent materi al surrounding a sma ll gra nule of melanin (Grave 1944; Whittaker 1966). In the larvae of Styela Ascidian larval morphology has attracte d the interest of coriacea, Polycarpa spp., Dendrodoa spp., and severa l many workers because of possible infer ences relevant to species of Molgula, a statocyst is present, but no ocellus chordate struc ture , function, and ph ylogeny (BerriIl 1948; (Grave 1926; Berri1l1931; Millar 1971). Finally, members Dilly 1964; Barnes 1971; Cavey & Cloney 1976). Ind eed , of the styelid subfa mily Botryllinae and tadpoles of the the classificati on of tun icat es as chordates is based almost solita ry stye lid Cnemidocarpa jinma rkiensis possess com­ entirely on larval structures (Be rrill 1955; Barrington pound senso ry structures known as phot oliths, which are 1965). Ascidian larvae ofte n carry complex adult struc- presum abl y sensitive to both light and grav ity (Berrill tures which become funct iona l only during rnetamor- 1975; Vorontosova & Malakhov 1984; Torrence & Clo ney phosis; likewise . specialized lar val structures such as 1988). Several species of Pyuridae in the genera Boltenia, oce lli and statocysts are ultim ately lost , leaving no trace Pyura and Halocynthia possess an additio nal struc ture of in the adult (Clo ney 1982). unknown function , the auxiliary vesicle (Svane 1982) or Solitar y ascidians gene ra lly have simple tadpo le larvae 'ne uro hypo physea l cavity' (Clo ney 1959), situated in the with undifferentiated adult tissues and organs. T hose lar- left wall of the cereb ral vesicle. It has been sugges te d val senso ry structures loca ted in the cereb ral vesicle of that this structure may be hom ologou s with the verte brate the trunk dem on strate substa ntial variab ility amo ng Iarnil- sacc us vasculosus (Svane 1982). A ltho ugh the structure ies and genera (reviewe d by Torren ce & Cloney 1988; has not been reported in any othe r ascidia n family, struc­ Svane & Young 1989) . In its most commo n for m, the tures resembling the ciliary compo ne nts of the pyurid cerebra l vesicle includes an oce llus for light reception and auxiliary vesicle have been reported in the stye lid Cnemi­ a statocyst for perception of gravity. Outside the sensory docarpa finmarkien s is. and in seve ra l phlebobranchiate vesicle , the major receptor s are probabl y mechanorecep- species with simple larvae (Voro ntosova & Malakhov tors and che mo rece pto rs located in the three ante rior 1984). papillae , and ciliary senso ry struc tures, possibly proprio- With respect to adult structure, the ascidian family ceptors, assoc iated with the tail epide rmis (To rre nce & Pyuridae contains th e most highl y developed species of Cloney 1982). A typical oce llus consists of three lens solita ry ascidians (Be rrill 1950) . Th e larvae of 11 pyurids cells, a nu mber of sensory ret inal cells, and a unicellul ar have been described previou sly (Tabl e 1). However , no pigment cup. Most larvae in the genus Stye/a , however, larvae in the genus Microcosmus (one of the four lar gest have a red uced ocellus consisting of a thin layer of tran s- gene ra in terms of species number) have been described . 129 130 I. Svane and C. M. Young Table 1. Egg diameter, larval length, sensory structures, and occurrence of an auxiliary vesicle in described larvae of ascidians in the family Pyuridae. Sizes are in um. Egg diameters include the chorion except where specified. Tadpo le lengths are for the cellular portion of the animal only (i.e, excluding the caudal fin) except where indicated in footnotes. (+) Presen t; (-) not present ; ('1) not investigated Egg Larval Oce llus! A uxiliar y Specie s dia meter len gth statocyte vesicle Authorfs) Pyura microcosmus 235 1035 +1+ '1 Millar ( 1954) P. praeputialis 230 1100 +1+ '1 A nderson et al. ( 1976) P. pachydermatina 250 1000 +1+ oJ A nde rso n et al. ( 1976) P. squam ulosa 175 930t +1+ '1 Millar ( 1951) P. stolonifera 28U-31Xl 1040 +1+ '? G riffiths ( 1976) P. tessellata 160 780 +1+ + Sva ne ( 1982) P. haustor 220 1075 +1+ + Young (pe rs. obs.) ; Clon ey ( 1959) Boltenia echinata 180-200 975 +1+ + Svan e (1982. pers. obs. ) B. villosa 200 870 +1+ + Clon ey (1959. 1961); Young (pers. obs .) Halocynthia roretzi 360 1530:j: +1+ '? Harai (1941) H. aurantium 368 1357 +1+ '1 Young (pers. o bs.) H. pyriform is 260 +1+ '? Berrill (1929. 1935) , H. igaboja +1+ + Cloney ( 1959) Herdman ia mom us 280 1650 +1+ + Present study H. pal/ida 190' 1150 +1+ '1 Seb astian (1953) Microcosmu s exasperatus 250 1000 - 1+ + Present study ' Measurement exclusive of cho rion. t Measurement includes cauda l fin. :j: Details of measur em ent not spec ified . In the genus Herdmania (a small genus with circumtrop­ pigment can be distinguished (Fig. I). Th e larval trunk is ical species) the development of onl y on e species, Herd­ about 250 IJ.m long and 125 IJ.m wide and the tail is about mania pallida (Sebastian 1953), has previously been 750 IJ.m long excluding the tail tunic. The larva is colour­ reported. In thi s paper, we describe the larvae of a species less and quite transparent. As in other tadpole larvae, in each of these two genera, emphasizing senso ry struc­ the test layer includes a wide vertical fin which runs along tures in the cerebral vesicle . [The systematic position of the dorsal and ventral side s of the trunk and tail. The fin the genus Herdmania is not clear. Monniot (1965) does contracts and is partially lost during fixation (Figs 2B , not recognize the genus and includes the group in the D). The fin extends about 100 IJ.m above and below the genus Pyura, but subsequent workers (Lowenstam & tail, and the caudal portion ext ends about 200 IJ.m beyond Abbott 1975; Lambert & Lambert 1987) have not fol­ the tail epidermis. The anterior end of the trunk has lowed this scheme.J three conical adhesive papillae arranged in a triangular configuration, two dorsally and one ventrally. The ventral portion of the trunk contains undifferen­ tiated tissue which will ultimately form the pharyngeal structures of the adult. Dorsally, the right side of the Materials and Methods trunk is occupied by the cerebral vesicle . A statocyte containing a pigmented statolith projects from the floor Adult Microcomus exasperatus Heller and Herdman ia momus (Savigny) of the cerebral vesicle (Fig .