Microcosmus exasperatus Heller, 1878

Monniot, Françoise, 2018, Ascidians collected during the Madibenthos expedition in Martinique 3. Stolidobranchia, Pyuridae and Molgulidae, Zootaxa 4459 (3), pp. 401-430: 406-408

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Microcosmus exasperatus Heller, 1878


Microcosmus exasperatus Heller, 1878 

Figs 6View FIGURE 6, 7View FIGURE 7

Heller, 1878, Jamaica; Van Name: 1921 and synonymy; Monniot C.:1983, Martinique; Rocha et al: 2012a, Brazil.

Stations: AB 149, 452. AM 34. AR 101, 314, 558. (MNHN S2 MIC 204)

The body is fixed by its ventral part, partially covered with epibionts with protruding siphons well apart. The tunic is red and wrinkled externally and red also internally on the siphons. There are dense spinules on the siphons. The body wall is thick with crossed bundles of muscle fibres ( Fig. 6AView FIGURE 6). There is a thin oral velum adhering to the tunic lining which has brown longitudinal lines. The 12-14 largest oral tentacles are bushy, three times ramified. The prepharyngeal band forms a wide and deep V including the dorsal tubercle with rolled horns ( Fig.7AView FIGURE 7). The dorsal lamina has a plain edge. There is an average of 9 branchial folds on each side ( Fig. 6BView FIGURE 6, 7AView FIGURE 7), the most ventral thinner and incomplete disappearing ventrally; a formula of a 3.2cm large specimen is on the right side: E- 1 (12) 3 (15) 3 (17) 4 (17) 4 (23) 3 (23) 4 (24) 4 (22) 3 (20) 2-DL.

There are parastigmatic vessels and irregularly some papillae on the transverse vessels. The second curve of the long digestive loop is wide open ( Fig. 6AView FIGURE 6, 7AView FIGURE 7), the rectum being close to the stomach. The hepatic gland has two parts ( Fig. 7BView FIGURE 7) each with convoluted papillae wearing button like papillae. After the hepatic gland on the ascending limb of the intestine are 1 to 4 endocarps ( Fig. 6AView FIGURE 6, 7BView FIGURE 7). These endocarps were not mentioned in previous descriptions. There are no endocarps on the body wall.

There is one gonad on each side the left one crossing the intestine ( Fig. 6AView FIGURE 6, 7AView FIGURE 7). They contain 3 or 4 well separated lobes linked by a longitudinal gonoduct. The male and female papillae are short and linked. Numerous thread-like papillae cover the entrance of the atrial siphon and the large velum.

From its first record from Jamaica M. exasperatus  was described in detail from several Caribbean locations ( Van Name 1921; 1945) and from Martinique ( Monniot C. 1983). This species is common in the whole western Atlantic ( Rocha et al 2012a) and its distribution is also worldwide, from the Mediterranean Sea ( Ramos et al 2013), the Indian Ocean ( Monniot C. 2002), and from the western Pacific Ocean ( Kott 1985; Monniot C. 1989).