New Collections of Ascidians from the Western Pacific and Southeastern

Micronesica 29(2): 133 279, 1996 New Collections of Ascidians from the Western Pacific and Southeastern Asia FRANl;OISE MONNIOT AND CLAUDE MONNIOT Biologie des lnvertebres Marins, M11se11mNational d 'Histoire Nall/re/le, CNRS D 0699 , 55 me B11ffon, 75005 Paris, France e-mail: monniot@cimrs/.11111/mfr Abstract-Recent collections of ascidians from several western Pacific and southeast Asian islands have significantly increased the number of species known from the Inda-West Pacific region. We examined speci mens from Palau, Chuuk, the Philippines, Indonesia, and Papua New Guinea. A large part of them were collected by the Coral Reef Research Foundation, based in Palau. Descriptions and figures are given for 99 species, 34 of which are new. Colonial forms predominate with a peculiar abundance of the Didemnidae family. The geographical distribution is indicated for each species, but the sampling is not sufficient to allow general statements, and presently it is not possible to delimit faunistic provinces in this large region. Introduction The tropical western Pacific Ocean has a large area of shallow waters with numerous islands and reefs, and an extremely diverse coast-line. The diverse or igins of the present day sea floor, the rather uniform temperature, and the high content of nutrients carried in sea water from nearby land masses, are all char acters obviously favorable to the development of a varied fauna. For all inver tebrates , the western Pacific is considered a major source of taxonomic diversity. Studies of scleractinian corals, for example, have shown a decreasing diversity from the western Pacific adjacent to the Inda-Malayan region which is considered to be the center of their evolution, to the central Pacific (Wells 1988). The same pattern is likely for ascidians, as they are most abundant on coral reefs in tropical regions. Previously, ascidians had not been systematically collected in the western Pacific. Many of the described species were the result of sporadic collections from limited areas. The first descriptions of ascidians from this part of the world (Heller 1878, von Drasche 1884, Traustedt 1885) were made from specimens collected by Naval Officers interested in natural history and the specimens were deposited in large European Museums. Most of our knowledge of ascidians of this region is due to the 1899- 1900 Siboga Expedition and the works of Sluiter (1904, 1909). The only two kinds of habitats that were investigated were the reef flat accessible on foot, and bottoms 134 Micronesica 29(2), 1996 below 40 m depth explored with dredges from a ship. Ascidians, however, are common in virtually all shallow marine habitats which shows how limited sam pling was in the early 20th century. Other oceanographic expeditions to the western Pacific from which ascidians were collected were the Challenger Expedition (Herdman 1882, 1886), the Alba tross Cruise (Van Name 1918), but they did not collect extensively. Later, samples from sporadic collections were deposited in several Museums. Those of the Smith sonian Institution were studied by Tokioka (1967). Millar (1975) described some from the Zoological Museum in Copenhagen. Smaller collections from the Ara fura sea (Tokioka 1952), Palau Islands (Tokioka 1950, 1955), and Philippines (Tokioka 1970) have also increased our knowledge. Other short publications in dicate that about 250 ascidian species have been recorded from Indonesia, and only about 100 species from the Philippines . These figures demonstrate how little is known about the western Pacific tunicate fauna. The ascidian fauna is bettter known on each side of this wide tropical region. In Japan, over a period of 50 years, Tokioka, and later, Nishikawa have described more than 300 species. Around Australia, mostly on the Great Barrier Reef, as cidians were extensively collected and described by Kott in 1985, 1990 and 1992, and excluding the didemnids, which are not yet published, this fauna numbers more than 400 species. The ascidian fauna of Australia is estimated to be 500- 600 species. The recent popularity of SCUBA diving and the presence of specialists in the field have increased the number of ascidians collected and identified considerably. For example Kott (1981) described 60 species on the Fiji reef flat and Nishikawa (1984) recorded 62 species, excluding Didemnidae, in Micronesia (Chuuk, Pohn pei, and Majuro). We have recorded about 100 species from French Polynesia (Monniot & Monniot 1987) and 202 species from southern New Caledonia (C. Monniot 1987 to 1991, F. Monniot 1987 to 1994). Nevertheless ascidians remain poorly known in the tropics. Besides the tech nical difficulties of collecting, especially colonial animals, a taxonomic study re quires fully mature specimens, fixation in formalin, dissection and staining before any microscopic observation. The present study includes collections made by the Coral Reef Reseach Foun dation which is based in Palau, Caroline Islands, a few samples collected by col leagues at Scripps Institute of Oceanography, and specimens deposited in the Museum National d'Histoire Naturelle (MNHN) collections. Many type speci mens from several Museums were observed for comparisons; the species described here do not constitute a complete inventory. Very often only one specimen of each species was preserved and no intraspecific variation can be addressed. Often, a species previously collected from an area was not recollected elsewhere. No precise geographic distributions can be given among the different archipelagos and only very general conclusions can be drawn. The present work improves our knowledge of the shallow water fauna of the western Pacific by giving descriptions of many new species, and redescriptions of other poorly known species. This contribution clearly shows the great diversity of the western Pacific coastal fauna of ascidians and the need for future continued work on this group. Monniot & Monniot: New Ascidians 135 Order Aplousobranchia Family Polyclinidae Aplidium controversum new species Fig. 1, Pl. IA Aplidium ca/ifornicum: F. Monniot 1987: 518, fig. 8 c-g, New Caledonia Aplidium multiplicatum: Kott 1992a: 567, fig. 90, Australia Holotype : MNHN: Al Apl B 312 - Palau, Koror State, marine lake, 7°17.81' N; 134°26.82' E, l m . Description: The colonies form cushions or balls, 2 to 3 cm across. The zooids are visible as pink spots through a translucent tunic and are arranged in double 1'';-'", -..'. 0.5 mm 0,5 mm Figure I . Aplid ium control'ersum n. sp.: A, zooid; B, section of th e stomach; C larva. 136 Micronesica 29(2), 1996 lines along cloacal channels that open at the top side of the colony. The general color is pale yellow (Pl. IA). The consistency is soft, but there is no mucus. The zooids reach 15 mm in total length. The thorax, 2 mm long when relaxed, is wide (Fig. IA). The oral siphon has 6 lobes; its basal part encircled by white pigment cells. The cloacal aperture forms a short, narrow tube, dorsally prolon gated in a stout, short, pointed languet (Fig. IA). The latter sometimes has a pair of small lateral swellings. The thoracic muscles are mostly longitudinal. The bran chial sac has IO rows of 15 to 20 stigmata. The rapheal languets are only slightly displaced to the left side. The abdomen is shorter than the thorax. The stomach is plicated in 20 to 24 longitudinal folds (Fig. IB), few of them incomplete. The post-stomach has an annular rod. The intestine begins with an olive-shaped seg ment, followed by a narrow tube joining the rectum between 2 well-marked caeca (Fig. IA). The anus opens at two thirds of the way down the cloaca} cavity. The post-abdomen is very long. The ovary lies some distance from the abdomen, fol lowed by a double row of testis follicles extending down to the heart (Fig. IA). Several larvae are incubated inside the cloaca! cavity. They measure 0.9 mm and have 3 flat adhesive papillae. On each side there is a row of about 30 round epidermal vesicles along the anterior half of the perimeter of the trunk (Fig. IC). The sensory organs are located posteriorly. In some larvae 2 rows of stigmata begin to differentiate. Remarks: This species resembles the specimens identified as Aplidium cali fornicum (Ritter, 1900) from New Caledonia by F. Monniot (1987) and Aplidium multiplicatum Sluiter, 1909 by Kott (1992a) except the synonyms she gave, which have to be verified by reexamining the specimens. However, we consider the Palau colonies are different and represent a new species, the species name reflecting the successive confusion of several authors about this species and its relatives. The external appearance and numerous similar anatomical characters in A. californicum and A. multiplicatum have been noted by ascidian taxonomists for a long time. This caused Hartmeyer (1909 - 1911) and Kott (1963) to synonymize the two species, however insufficient descriptions have successively complicated the question. The type specimen of A. multiplicatum is registered at the Zoologisch Museum of Amsterdam, however the type of A. californicum has not been located. Only newly-collected specimens of the latter species from British Columbia have been studied. We provide a brief redescription of each species for comparison with A. controversum. In A. californicum from British Columbia the colonies form rounded cush ions, yellow or pale orange in color. The zooids are arranged in double rows converging to common cloacal openings at the upper part of the colony. The zooids have 6 oral lobes, 12 tentacles in 2 orders of size. The cloacal aperture forms a short tube and has a triangular short languet on its dorsal rim. The branchial sac has 8 to 11 rows of stigmata, usually 9 or 10. The dorsal rapheal languets are strongly displaced to the left sie1e.The stomach has 14 to 15 deep folds, some of them interrupted or irregular. There is an annular post-stomach and 2 cacea at the beginning of the rectum.

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