Aplidium petrense Michaelsen, 1919

Monniot, Françoise, 2009, Some ascidians from Indonesian marine lakes (Raja Ampat Islands, West Papua), Zootaxa 2106, pp. 13-40 : 22

Aplidium petrense Michaelsen, 1919

( Figure 8 )

Aplidium petrense Michaelsen, 1919: 92 figs 5–7, Zanzibar; Millar, 1956: 915 Mozambique; Millar, 1962: 337; Vasseur, 1970:209 fig. 1 Madagascar.

Material. Indonesia. West Papua, Gam Island, Danau Nine Gam marine lake, 00°26.970’S – 130°29.149’E, 0.5m, 01/XII/2007, coll. L.J. Bell and L.E. Martin, DNG 0 0 4 ( MNHN A1 APL B 506).

The numerous colonies are distributed as black buttons ( Fig. 8 A) on all kinds of substrates: rock, wood, Halimeda leaves… Each colony is soft, about 1cm tall and and 5 to 10mm wide at the top when inflated, the base narrowed in a thick peduncle. The tunic is dark but translucent. The oral aperture has a black pigmented circle. The zooids are arranged around a central common cloacal aperture in a simple hole at the top of the colony. The zooids, 5mm in length, have 6 pointed oral lobes. The atrial languet has 3 long thin lobes starting from the dorsal rim of the aperture. Twelve oral tentacles are arranged in 2 orders of size. All zooids have 6 stigmata rows ( Fig. 8 C). On one side the first row Counts 17 stigmata, the second row 15 stigmata. The stigmata are elongated, their size decreases toward the dorsal and ventral lines. The short dorsal languets are displaced on the left side. The stomach ( Fig. 8 E) occupies the middle of the abdomen, its wall with 20 to 27 folds. The post-stomach is enlarged in a ring. The rectum begins with caecum. The post abdomen is as long as the abdomen at full maturity and contains an anterior ovary followed by 2 irregular rows of testis vesicles.

A single larva ( Fig. 8 D) is incubated in the peribranchial cavity where it makes a protruding dilatation but not a pedunculate pouch. Thirteen adhesive papillae in a line were counted in a larva of 1.1mm, encircled by a row of numerous round vesicles. The tail is wound in ¾ of a turn around the trunk.

This species was only previously known from Zanzibar, Mozambique and Madagascar, it is recorded here from the Pacific Ocean for the first time. The original description ( Michaelsen, 1919) gives 5 rows of branchial stigmata instead of 6 here, all other characters being similar. Later authors from the same region mention a variable number of stigmata rows: 5 to 7 for Millar (1956), 6 rows for Vasseur (1970). We have examined specimens collected by P. Laboute in Nosy Be ( Madagascar) ( MNHN A1 APL B 342), the shape and color of the colonies are the same ( Fig. 8 B), and all the zooids have 6 stigmatal rows; all other characters are the same. The larvae have never been described. As many ascidians are common to the western Pacific and Indian oceans, the identification of the material from Raja Ampat is assigned to A. petrense .

Aplidium multipapillatum Millar 1975 has also a large larva 0.7 to 0.8mm for the trunk and 4 to 6 adhesive papillae but elongated vesicles alternating with the papillae; it has 12 stigmatal rows and 2 to 35 stomach folds, a structure figured by Millar (1975 Fig.35 c,d,e). An examination of the type has confirmed these characters. A. multipapillatum is also present in New Caledonia ( Monniot F. 1987) and is obviously different from A. petrense .

Figures

FIGURE 8. Aplidium petrense: A, colonies from Raja Ampat; B, colonies from Madagascar; C, branchial sac; D, larva; E, zooid. Scale bars: C, D = 0.5 mm; E = 2 mm; C, D, E stained with hemalum.