Phallusia nigra Savigny, 1816

Monniot, Françoise, 2018, Ascidians collected during the Madibenthos expedition in Martinique: 1 - Phlebobranchia, Zootaxa 4387 (3), pp. 451-472 : 465

Phallusia nigra Savigny, 1816

Fig. 12

Stations: AM 06; AM 26; AR 101; AR 453. (MNHN PHA 126)

Phallusia nigra: Monniot C. 1983 Guadeloupe; Bonnet & Rocha: 2011, Brazil; Vandepas et al: 2015 and synonymy.

Collected between 1 and 6 m depth, all specimens have a black smooth and shining tunic without epibionts. The largest of six ascidians is 8cm long. The atrial siphon is at 1/3 of the body length and directed anteriorly. The oral aperture has 11 to 12 lobes. Extracted from the tunic the body wall contains a variable amount of black pigment cells ( Fig.12A ), more abundant at the siphons. The oral tentacles are in 3 sizes and variable in number. The narrow prepharyngeal area has small papillae. The prepharyngeal groove has two plain rims. The dorsal tubercle opens in a simple U or with sides slightly rolled inward. The neural ganglion is located close to the atrial aperture and covered by the neural gland. The neural gland duct parts in small branches along the dorsal line which open in a double series of urn-shape holes ( Fig 12B ). The dorsal lamina begins with two blades to become a rolled lamina with strong ribs on the left side ending in papillae. The dorsal lamina overpasses the oesophagus on a great length. Below the oesophagus entrance, on the right side, large papillae in a row prolong the transverse branchial vessels. The branchial tissue is thick and contains black pigment cells. The branchial papillae are spoon-like with a basal bump. There are no intermediate papillae.

The body musculature has a constant design in all specimens ( Fig.12C,D ). On the right side the longitudinal fibres issued from the oral siphon run downwards and become slender at the body end; they are crossed by oblique fibres starting from the atrial siphon which spread in a fan in the half posterior right side of the body ( Fig. 12 C,D ). On the left side the longitudinal fibres of the oral siphon reach the gut level. On the right parallel transverse muscles form a band along the ventral line, they become progressively thinner and increase again in thickness when they reach the dorsal side ( Fig.12C–D ). On the left of the dorsal line a bundle of longitudinal fibres issued from the atrial siphon spread toward the intestine and reaches the space of the secondary gut loop ( Fig.12C–D ).

The digestive tract occupies half of the left body side ( Fig.12C–D ). The oesophagus is narrow well marked from the olive shaped stomach. The primary gut loop is long and narrow, the secondary loop is slightly open. The intestine is not inflated. The anus has 2 lips, the internal one deeply indented. The ovary in a single mass lies in the primary gut loop. The testis vesicles are spread above both intestinal limbs.

Numerous pyloric vesicles cover the whole gut.

Remarks. Phallusia nigra is a very common species recorded from the tropical and subtropical Atlantic Ocean in shallow waters. It is spectacular with its tunic totally black naked and shining.

Figures

FIGURE12. Phallusia nigra: A, left side of the bodywithout tunic not stained (scale bar = 1cm); B, neural area stained; C, D, dissections stained with hemalum.