INTRODUCTION
The genus Eudistoma is common in tropical regions of the world (Kott, Reference Kott1990). In the Caribbean nine species are known (Rocha et al., Reference Rocha, Moreno and Faria2005) and in Brazil six species are registered (Millar, Reference Millar1977; Lotufo, Reference Lotufo2002; Lotufo & Silva, Reference Lotufo, Silva, Cascon and Lotufo2006), but only E. carolinense Van Name, 1945 has been recorded in southern latitudes (Rocha & Moreno, Reference Rocha and Moreno2000), probably introduced in this region (Rocha & Kremer, Reference Rocha and Kremer2005). There is also a Eudistoma sp. listed in Rodrigues et al. (1998) but it is a different species forming very small encrusting colonies. Here we describe a new species found both on the coasts of São Paulo and Santa Catarina, on islands close to the coast in shallow waters (10–15 m). In both cases, ascidians have been surveyed in a broader region, including other islands nearby, but the species was collected only in specific sites, indicating specific habitat requirements.
MATERIALS AND METHODS
The species was collected by SCUBA diving at depths of down to 15 m. Samples were anesthetized with menthol crystals and fixed in 10% neutralized formalin. Dissection followed routine procedures. The holotype and paratypes were deposited in the collection of Museu de Zoologia (MZUSP), University of São Paulo.
SYSTEMATICS
TYPE MATERIAL
Holotype: one colony, Lighthouse (Arvoredo Island, Marine Biological Reserve of Arvoredo, Santa Catarina; coordinates: 27°17′50′′S 48°21′40′′W; depth: 10–12 m) [MZUSP 17371]. Collected by R.M. Rocha, October 2002.
Paratypes: zooids mounted on two permanent slides (south side of Deserta Island, Marine Biological Reserve of Arvoredo, Santa Catarina; coordinates: 27°16′40′′S 48°22′40′′W; depth: 10–12 m), [MZUSP 17372]. Collected by R.M. Rocha, 27 November 1999; one colony and two permanent slides (Oratório Bay, Alcatrazes Island, São Paulo; coordinates: 24º06′S 45º42′W; depth: 15 m) [MZUSP 17373]. Collected by R.M. Rocha, 02 May 2002.
DIAGNOSIS
The colony is formed by numerous clavate lobes connected by the base. The main diagnostic characters are the shape of the colony and the larvae with distinctive small projections at the base of the ectodermal ampullae. Other characteristics are: zooid 5–7 mm long with abdomen 3.5 times the length of the thorax, not organized in systems, up to 20 longitudinal and 23 transverse muscle bands on the thorax, decreasing number of stigmata from the first (21–24 per side) to the third row (13–19 per side), 16 oral tentacles of two sizes arranged in one circle, 8–13 testis follicles, 2–4 embryos developing in a wide atrial cavity, larva 0.5 mm long with long ampullae and tail winding 3/4 of the way around the trunk.
DESCRIPTION OF THE COLONY
The colonies are found hanging from vertical surfaces or ledges. At Arvoredo Marine Reserve they are formed by clavate lobes 2.5 cm long and with maximum diameter of 1.5 cm (Figure 1A). Alive they are cream coloured, almost the same colour when preserved in formalin, sometimes more whitish when preserved. The colony from Alcatrazes Island are a little shorter, maximum 2 cm high, and up to five lobes arise from the same common base. This colony was found hanging from a ledge where very few others were seen.
Eudistoma clavatum sp. nov. (A) Colony from Ilha Deserta, Reserva do Arvoredo, SC (MZUSP 17372), insert with a detail of one transparent head showing the clavate shape and zooids; (B, C) zooid. Scale bars: A, 1 cm, B, 1 mm.
The tunic is soft and transparent, without any sand on the surface, but might have a small amount of sand inside the peduncle. The peduncle is 1 cm long and usually has bryozoans and other organisms encrusting its surface.
DESCRIPTION OF THE ZOOID
The zooids are uniformly spread around the whole extension of the head, without forming any systems. The abdomens converge to the centre of the head and reach the peduncle.
The zooids from Arvoredo Marine Reserve samples are about 7 mm long when well relaxed (Figure 1B,C) but the thorax is only 1.5 mm long (Figure 2A,B). In the colonies from Alcatrazes Island the most extended zooids were shorter (5 mm long). They are colourless and transparent, although the stomach and ascending rectum are yellow. Both oral and atrial siphons are tubular and short, with a fringe of six round lobes. The atrial cavity is usually wide, giving the thorax a rounded shape. In the holotype there are 12 longitudinal muscle bands on each side of the thorax, which join into two strong ventral bands along the abdomen that extend to the posterior extremity, where they form two small projections. Eighteen to 22 transverse muscles are also conspicuous on the thorax, at the level of the three rows of stigmata. Although shorter, the zooids from Alcatrazes Island have up to 20 longitudinal muscle bands on the right side of the thorax, 16 on the left and 23 transverse bands per side. Oral tentacles occur in one circle of 16 tentacles, of two sizes in both sites. The prepharyngeal groove is simple and the dorsal tubercle is very small. In one zooid of the holotype, the first row of stigmata had 24 and the third 19 stigmata per side, but another zooid had, 21, 14 and 13 (Figure 2A,B). The abdomen is long, almost 3.5 times the thorax and the stomach lies at the posterior end. There is a belt of very thin circular muscle fibres around the anterior region of the abdomen, just beneath the thorax. The stomach is globular and sometimes has a longitudinal depression (typhlosole) turned to the ascending rectum. The duodenum is as long as the stomach, the post stomach is tubular and there is a rectal caecum bilobed, but not very conspicuous, at the proximal end of the rectum. This proximal region of the rectum is large and covers the stomach when ascending to the anus, which is bilobed, ending between the second and third rows of stigmata. The pyloric tubules were not visible. There is one long stoloniferous vessel which can ramify in some zooids. The end of the abdomen extends a little further beyond the intestinal loop.
Eudistoma clavatum sp. nov. (A, B) Thorax; (C, D) larva. Scale bars: A, 1 mm; C, 0.1 mm.
The testis is inside the intestinal loop more anterior than the ovary. There are 13 round or pyriform follicles (Figure 1B,C), but in one zooid from Alcatrazes the testis has only eight round follicles. The ovary of the type specimen has seven oocytes simultaneously, one of them larger than the others and up to two embryos developing in the atrial cavity, while in Alcatrazes, there were up to four embryos in the atrial cavity.
DESCRIPTION OF THE LARVA
The larva is oval, 0.5 mm long. The three adhesive papillae are long with thin peduncles and lie in the median-anterior line (Figure 2C,D). The four pairs of ectodermal ampullae are very long, finger-like and present a projection in each base. The dorsal pair can be subdivided. Both ocellus and statocyte are present. The young larvae have many vesicles on the body wall. The tail is wound 3/4 of the way around the trunk.
ETYMOLOGY
L. clava = club, cudgel. The species was named because of its club shaped form.
DISCUSSION
There are six known Eudistoma species for the Brazilian coast, four of them with lobed colonies: E. vannamei Millar, Reference Millar1977, E. saldanhai Millar, Reference Millar1977, E. carolinense Van Name, 1945, E. repens Millar, Reference Millar1977. None have projections at the base of the larval ectodermal ampullae, one of the most striking diagnostic characteristics of Eudistoma clavatum. Only Eudistoma carolinense has also been observed in southern latitudes, but the aspect of the colony is very different, the tunic is completely impregnated by sand and there are only 5–6 longitudinal thoracic muscle bands per side (Monniot, Reference Monniot1983; Rocha & Moreno, Reference Rocha and Moreno2000). Eudistoma vannamei and E. saldanhai have larger larvae (1.4 mm and 0.7 mm, respectively) than E. clavatum, while E. repens has a smaller one 0.38 mm (Millar, Reference Millar1977).
From the Caribbean there are E. olivaceum (Van Name, 1902) with a different colony structure, longer zooids (15 mm) and a larger number of testicular follicles (20) (Monniot, Reference Monniot1983); E. capsulatum (Van Name, 1902) with dark pigment on the thorax, oral tentacles in three circles and 30–40 testis follicles. Still in the Atlantic, Eudistoma platense Van Name, 1945 has many larvae in the atrial cavity, only 12 stigmata per side in each row and 30 or more testis follicles.
There are other stalked Eudistoma comparable to our specimens. The two species that are more similar to E. clavatum are E. laysani (Sluiter, 1900) and E. tumidum Kott, Reference Kott1990. Both are Pacific species (Millar, Reference Millar1975; Kott, Reference Kott1990; Monniot & Monniot, Reference Monniot and Monniot2001). Eudistoma laysani has the same number of longitudinal muscle bands (8–16 per side), similar number of stigmata decreasing from the first to the third row. On the other hand, oral tentacles form four concentric circles, the transverse muscle bands are restricted to the central region of the thorax, abdominal regions are located in the stalk, larval ampullae are without basal projections and the tail is short (Millar, Reference Millar1975; Kott, Reference Kott1990). Eudistoma tumidum has 20 bands of longitudinal muscles per side, 20 stigmata in the first row and larva with projections at the base of the ampullae (Kott, Reference Kott1990) but differs from E. clavatum by the shorter lobes of the colony, zooids forming circular systems, oral tentacles in three circles and more transverse muscle bands—30 (Kott, Reference Kott1990). Another species with projections at the base of the larval ampullae is E. occultum Monniot, 2001 from South Africa, but these are filiform projections very different from the ones in E. clavatum (Monniot et al., Reference Monniot, Monniot, Griffiths and Schleyer2001).
Eudistoma ritteri Van Name, 1945 has zooids of similar structure to E. clavatum, but oral tentacles lay in three circles and there are only 14 stigmata per half-row. Eudistoma elongatum (Herdman, 1886) has very long stalked heads (up to 60 cm), zooids not arranged in systems, the larva has a shorter tail and long ectodermal ampullae without projections (Kott, Reference Kott1957, Reference Kott1990). Eudistoma parvum (Oka, 1927) has shorter heads (up to 1 cm), fewer stigmata in each row, also in constant numbers across rows, and larval ectodermal ampullae without projections (Tokioka, Reference Tokioka1954; Kott, Reference Kott1957). Eudistoma caeruleum (Sluiter, 1898) has dark blue colonies, with small and dark zooids not forming systems, with oral tentacles in two circles and more stigmata per row (35 in the first and 28 in the others) (Monniot et al., Reference Monniot, Monniot, Griffiths and Schleyer2001). Eudistoma album Monniot, Reference Monniot1988 has the surface of the colony not smooth because of the prominent siphons, zooids have more oral tentacles in many circles and larval ectodermal ampullae do not have projections (Monniot, Reference Monniot1988).
In conclusion, there is no other described species similar to the material here described, and this new species seems to be endemic to subtropical waters on the Brazilian coast. Although there are some differences between colonies of different sites, the structures of the colony and of the zooids are very similar and justify their description as a single species. The species has a restricted spatial distribution in locations, Deserta Island inside the Arvoredo Marine Reverse being the location of major abundance.
ACKNOWLEDGEMENTS
We would like to thank Dr Roberto Berlinck for dive support, Dr James J. Roper for the English text correction, and CNPq for IC scholarship to N.Y.K.B. and a research grant to R.M.R. This is contribution no. 1709 of the Zoology Department, Universidade Federal do Paraná.
