Phallusia obesa ( Herdman, 1880 )

Monniot, Françoise & Monniot, Claude, 2001, Ascidians from the tropical western Pacific, Zoosystema 23 (2), pp. 201-383 : 307-311

? Phallusia obesa ( Herdman, 1880)

( Figs 83 ; 126A )

Pachylaena obesa Herdman, 1880: 462 . Type locality: Australia, Victoria.

Phallusia obesa – Traustedt 1885: 16.

MATERIAL EXAMINED. — Federated States of Micronesia. Yap, Colonia, main wharf, 9°30.91’N, 138°07.57’E, 10 m, 4. VI.1996 ( MNHN P5 PHA 86).

DESCRIPTION

The specimens are of large size, more than 10 cm in length. Their shape is variable and depends on the disposition on the substrate. One specimen is particularly elongated ( Fig. 126A ), with the cloacal siphon slightly anterior to the mid-length of the body. This ascidian was attached by a large part of its ventral side. The other specimens have the siphons nearer to each other and were attached by the left posterior side.

The tunic is bare with a few tubercles. The siphons are protruding and tubercular. The surface of the tunic is covered with very small papillae, which correspond to the ampullar extremities of the branches of blood sinuses in the tunic. The tunic is up to 1 cm thick and stiff. The grey tunic becomes light brown when preserved in formalin. There are 12 lobes on the oral siphon and eight on the cloacal siphon; they have patches of pigment. Their size is variable. The musculature is weak, in a loose network on the right body side and in just the anterior part of the left side. About 40 short oral tentacles in three to four orders of size are planted on a high crest. The prepharyngeal area is particularly narrow, covered with small papillae. It is necessary to lift the crest with the tentacles to observe the prepharyngeal band. The band has two protruding parallel and unequal sides, with the anterior edge high and thin and the posterior edge thicker. The dorsal tubercle has a U-shaped slit with slightly rolled horns and occupies the whole dorsal curve of the prepharyngeal band ( Fig. 83B ). The neural ganglion is far from the dorsal tubercle, at the base of the cloacal siphon. No accessory opening was found in the specimens of this collection.

The dorsal lamina begins with a double blade down to the neural ganglion and continues as a high blade with a dentate rim.

The branchial sac extends well beneath the gut. The branchial papillae are stout. The square meshes contain six to eight stigmata. There are no parastigmatic vessels and no intermediate papillae. The branchial tissue is only slightly pleated.

The gut is massive, the secondary loop wellmarked, and the rectum is applied against the proximal intestine ( Fig. 83A ). The posterior intestine is only slightly dilated. The anus opens a little anteriorly to the top of the gut loop. It seems cut obliquely with regard to the rectum. Its rim, underlined by an accumulation of blood cells, has low lobes.

The ovary is made of thick tubules grouped in a mass restricted to the primary intestinal loop. The oviduct opens with the sperm duct beside the anus. A poorly developed testis spreads on the intestine; but the sperm duct is full.

REMARKS

We hesitated to identify these specimens as Phallusia obesa . The presence of accessory openings of the neural gland channel, which is the only character separating the genus Phallusia from Ascidia , was not detected. But by other characters such as the thickness and stiffness of the tunic, a weak musculature, the narrow prepharyngeal area, the disposition of the neural ganglion, and the shape of the gut, this species is closely allied to the Phallusia species of the tropical Pacific Ocean.

The absence or presence of accessory openings of the neural gland channel is not a stable character. In Phallusia mammillata (Cuvier, 1815) , Phallusia nigra Savigny, 1816 , and P. julinea Sluiter, 1919 , several authors have noted that these openings appear late during growth. In Phallusia julinea , even adult specimens without accessory openings have been noted by Tokioka (1961) and Kott (1964, 1985). Monniot C. (1987a) described a whole population from New Caledonia without accessory openings. Conversely, some Ascidia species exceptionally may have accessory openings ( Ascidia melanostoma in Monniot C. & Monniot F. 1987).

The distinctions between the Phallusia species of the Pacific Ocean are not clear. P. julinea Sluiter, 1919 is well-characterised by a superficial dilation of the tunic vessels filled with gold yellow granules and a very pronounced widening of the rectum. Phallusia barbarica Kott, 1985 has a tunic partially covered with sand and debris, and its anus lies posterior to the top of the gut loop. Phallusia millari Kott, 1985 has siphons that are notably closer together, an anus with lobes, and a non-dilated intestine. Phallusia arabica Savigny, 1816 and Ph. obesa ( Herdman, 1880) lack distinct identifying characters. For Kott (1985) the disposition of its siphons distinguishes that species. We believe that P. arabica lives hidden in crevices with only its siphons apparent while Ph. obesa lives exposed on the rocky surface. The specimen figured by Herdman (1882) and Hartmeyer & Michaelsen (1928) and the picture in Kott (1985) attest to this. This difference may reflect chemical defences in Ph. obesa , as shown in P. mammillata and P. nigra , which live exposed at the substrate surface.

The samples from Yap look like the photograph in Kott (1985: pl. 1, fig. 6). Ph. obesa has close relations to Ascidia kreagra Sluiter, 1895 , sensu Nishikawa (1986), from the Solomon Islands, as suggested by the tunic, the position of the neural ganglion, and the gut shape. But the size is very different, as the type of A. kreagra measures 23 mm and the largest Nishikawa’s specimen is only 62 mm long including a very long oral siphon.

Phallusia philippinensis Millar, 1975 ( Figs 84 ; 126B )

Phallusia philippinensis Millar, 1975: 275 , fig. 55, Philippines and Banda Sea.

? Phallusia depressiuscula – Van Name 1918: 116, pl. 27, figs 10-13.

Phallusia depressiuscula – Tokioka 1970: 87, fig. 4 (15- 22), Philippines.

MATERIAL EXAMINED. — Philippines. Bohol Sea, Camiguin Island, 9°12.89’N, 124°38.03’E, 18.IV.1997 ( MNHN P5 PHA 87).

Palau. Koror, Malakal Harbour, rock islands near Ngerchaol, on boat hull, 7°20.37’N, 134°22.02’E, 3 m, 14.VIII.1997 ( MNHN P5 PHA 92).

DESCRIPTION

The specimen from the Philippines, 4.2 × 2.2 cm was attached to coarse sediment by half of the left side. The distance between the siphons is 2 cm. The siphons are erect with grooves. The tunic is bare except for some kamptozoans growing on the siphons and in the grooves of the tunic. In life the species is black ( Fig. 126B ), and it becomes dark brown when preserved in formalin. The thick cartilaginous tunic contains a network of whitish vessels. The extremities of these vessels make ampullae filled with clear granules. They protrude slightly at the tunic surface but do not constitute papillae. These ampullae are not ramified as they are in P. julinea . Black granules lie in the tunic between the ampullae.

The body wall is brown. The strong musculature exteriorly forms anastomosed longitudinal bundles, and internally is a continuous layer of circular fibres. The muscles are reduced on the posterior part of the right side, and on the left side they are limited to the region anterior to the gut ( Fig. 84A, C ).

The oral siphon has eight cone-shaped lobes exteriorly prolonged by eight crests. There are no ocelli.

About 55 oral tentacles in four orders have almost joined bases. The prepharyngeal area is entirely covered with papillae. The prepharyngeal band has two blades, the anterior of which is covered with papillae similar to that of the prepharyngeal area ( Fig. 84D ). The dorsal tubercle is small, its slit C-shaped, and lies in a small indentation of the prepharyngeal band. The neural ganglion lies at the base of the cloacal siphon. The channel of the neural gland has numerous accessory apertures along its whole length. The dorsal lamina has two blades as far as the neural ganglion; posteriorly it forms a blade of medium size with teeth corresponding to one per every two transverse vessels. It disappears at the oesophagus entrance, replaced by long papillae corresponding to one per each two vessels. On the right side, starting from the oesophagus entrance extends a row of triangular papillae.

The branchial sac has an equal width on each side. There are large main papillae and small buttons corresponding to intermediate papillae. The branchial tissue is pleated.

The gut is massive ( Fig. 84A, B ) and wrapped in an opaque tissue filled with blood lacunae. It is covered with small papillae. Externally some lines appear on the stomach corresponding to blood lacunae. The posterior intestine is slightly thickened. The gaping anus has a rolled rim. The ovary in packed lobules occupies the top of the gut loop. The testis lies along the intestine, and externally it can be seen only in the secondary gut loop. Eggs were found in the cloacal cavity.

REMARKS

This species is closely allied with P. nigra Savigny, 1816 . It differs in the shape of the siphons, the more translucent tunic and the presence of minute papillae between the main papillae on the branchial vessels.

Figures

FIG. 83. —?Phallusia obesa (Herdman, 1880); A, left side of the body; B, dorsal tubercle. Scale bars: A, 1 cm; B, 2 mm.

FIG. 126. — A,?Phallusia obesa (Herdman, 1880); B, Phallusia philippinensis Millar, 1975; C, Phallusia sp.; D, Botryllus perspicuus (Herdman, 1886); E, Botryllus tyreus (Herdman, 1886); F, Eusynstyela hartmeyeri Michaelsen, 1904.

FIG. 84. — Phallusia philippinensis Millar, 1975; A, left side of the body; B, internal side of the gut loop; C, right side of the body; D, dorsal tubercle. Scale bars: A-C, 1 cm; D, 0.5 mm.