Microcosmus exasperatus, HELLER, 1878

Monniot, Claude, 2002, Stolidobranch ascidians from the tropical western Indian Ocean, Zoological Journal of the Linnean Society 135 (1), pp. 65-120 : 105-106

MICROCOSMUS EXASPERATUS HELLER, 1878 ( Fig. 31 )

Microcosmus exasperatus: Kott, 1985: 348 – Australia, and synonymy; Monniot C., 1983: 1035 – Guadeloupe, 1989: 479, fig. 2, pl. 1 A – New Caledonia.

Microcosmus pupa ( Savigny, 1816) : Monniot, 1973: 58 part, fig. 4A – specimen from Eilat.

Material

Suez, coll. R. PH. Dollfus, 1928.

Gulf of Aden.

Madagascar: Nosy-Be, 27 m, coll. P. Laboute, 1992.

Mozambique: Ibo Island, coll. C. Monniot, 1995.

Yemen: Socotra Island, coll. C. Monniot, 1997.

Description

The body shape varies with the substrate. The moreor-less red tunic may be naked or with epibionts; it is always wrinkled. The tunic is not thick but resistant, and has a nacreous lining. The siphons are short.

Despite its strong musculature, the body wall is thin and reveals the internal organs. The muscles form large bundles that issue from the siphons, and regularly cross each other.

The ramified tentacles arise at the base of a large velum. The dorsal tubercle is U-shaped with the anterior horns slightly rolled inwards; it lies in a dorsal V of the prepharyngeal band.

There are eight-to-nine high branchial folds on each side of a smooth edged dorsal lamina. The stigmata are cut by parastigmatic vessels.

The gut makes a closed primary loop ( Fig. 31A–D ) leading to a dorsally curved intestine that adheres to the dorsal lamina. The anus is smooth-edged.

One gonad lies on each side ( Fig. 31A–D ), made of three or four massive lobes linked only by the gonoducts. The left gonad crosses the intestine ( Fig. 31A–D ). Male and female papillae are short and close together and protrude from the body wall.

There are no endocarps on the internal layer of the body wall itself, but sometimes one or two of them lie on the ventral side of the stomach.

Filiform papillae cover a wide field around the base of the cloacal siphon.

Remarks

Microcosmus exasperatus is cosmopolitan in warm waters. It differs from Microcosmus pupa ( Savigny, 1816) by the absence in the former of endocarps and the shape of its gonads, made of lobes in a line.

MICROCOSMUS MADAGASCARIENSIS MICHAELSEN, 1918 ( Figs 27D , 32 )

Microcosmus madagascariensis, Michaelsen, 1918: 20 – Madagascar, Nosy-Be; Vasseur, 1969, – Madagascar, Tulear.

Not Microcosmus agglutinans Hartmeyer, 1919: 26

Not Microcosmus madagascariensis: Hartmeyer & Michaelsen, 1928: 398 ; Kott, 1985: 35.

Material

Madagascar, Nosy-Be, coll. R. Plante, 1967.

Description

The single specimen is 16 mm in diameter. The tunic is encrusted with coarse sediment and projects some long, hair-like extensions also encrusted with sand. The short siphons diverge at 90°. The siphonal spinules are very sharp spines issued from a wide base ( Fig. 27D ).

The body wall is rendered opaque by a dense musculature regularly distributed over the whole body. The oral velum is covered with button-like papillae.

Several orders of oral tentacles alternate; the largest tentacles have three orders of branching. The C-shaped dorsal tubercle opens to the left in the middle of a deep V of the prepharyngeal band ( Fig. 32D ). The peritubercular area is papillate. The dorsal lamina is smooth.

The branchial sac has seven high folds on each side, overlapping each other. The formula is:

Figures

Figure 27. Siphonal spinules: A, Pyura gangelion; B, Pyura scortea; C, Pyura tongae; D, Microcosmus madagascariensis; E, Microcosmus pupa. Scale bars: A,C,D,E = 100 mm, B = 20 mm.

Figure 31. Microcosmus exasperatus: A, specimen from Madagascar ventrally opened. B,C,D, specimen from Aden. Scale bars: A = 1cm, B,C,D = 5 mm.

Figure 32. Microcosmus madagascariensis: A, body ventrally opened. B,C, external view of the left and right sides. D, dorsal tubercle area. E, detail of hepatic papillae. Scale bars: A,B,C = 1cm, D = 2mm, E = 0.5 mm