Protoholozoa pedunculata Kott, 1969

Monniot, Françoise & Tatián, Marcos, 2020, Questions on the taxonomic status of species of Protoholozoa Kott 1969 (Ascidiacea Aplousobranchia, Holozoidae) with a description of a new genus, Zootaxa 4718 (2), pp. 261-268 : 262-263

Protoholozoa pedunculata Kott, 1969

( Figures 1–4 )

The examined colonies from the Poker 4 survey, have a soft vitreous tunic expanded in a cone above a thin peduncle ( Fig. 1A,B ). The zooids are parallel to each other with the siphons opening independently at the surface of the head on small protuberances ( Fig. 1C,D ). The thorax and abdomen have almost the same size ( Fig. 2A,B ). A long vascular post-abdominal process extends far into the colony peduncle. The rim of the oral aperture is slightly lobed with a weak sphincter. The atrial aperture is round and more or less dentate ( Fig. 3A ) at the base of the thorax. We counted up to 18 oral tentacles of two orders of size on a rod ( Fig. 3A ). The pre pharyngeal band is flat and dorsally curved to surround a button-like dorsal tubercle ( Fig. 3A ). The neural ganglion is close to the dorsal tubercle. About ten muscular fibres on each side, well-spaced, run obliquely on the thorax ( Fig. 3A,B ). There is no branchial sac. Inside the atrial cavity on each side there are two free transverse bridles attached to the endostyle at one extremity and joined dorsally to a vertical dorsal band ( Fig. 3A,B ), erect internally in two triangular papillae. These transverse bridles are linked to the medial side of the body wall by two thin strands of tissue.

The abdomen is in direct prolongation of the thorax ( Fig. 2A,B ). The digestive loop is not twisted and has a rather long oesophagus followed by a round stomach with six longitudinal folds ( Fig. 2A,B ). The anus opens at the base of the thorax with two lobes. The massive gonad lies in the gut loop with numerous testis follicles and a central ovary ( Fig. 2B ). The sperm duct follows the rectum and opens close to the anus. A very long vascular process prolongs the abdomen.

Several buds are present in the tunic at the abdominal layer ( Fig. 1D ) and posteriorly in the colony.

One to four larvae are incubated inside the thoracic cavity at different stages of development ( Figs. 2C,D ; 3C ; 4A,B ). There is no brood pouch. The fully mature larvae measure 2.5mm for the trunk ( Fig. 4A,B ); they have an otolith but no ocellus. The tail is wound in ¾ of a turn. The three adhesive anterior papillae are placed in a median front line. Between them are two pairs of epithelial ampullae and another ampulla lies on each side of the adhesive papillae ( Fig. 4A,B ), for a total of 6 ampullae.

The same larval shape is present (but was not described) in specimens from South Orkney Islands ( Monniot & Monniot 1983) ( Fig. 4C ) and in specimens from the Scotia Arc ( Fig. 4D ), and confirms the species identity of the Atlantic and Indian colonies.

Figures

FIGURE 1. Protoholozoa pedunculata: A,B, both sides of a colony from the Indian Ocean; C,D, zooids seen in transparency through the tunic. Scale bars = 1 cm.

FIGURE 2. Protoholozoa pedunculata: A,B, two zooids of a colony from the Indian Ocean; C,D, larvae incubated inside the thorax. Scale bars = 2 mm.

FIGURE 3. Protoholozoa pedunculata: A,B, the thorax of two zooids opened along the endostyle and stained with hemalum; C, zooid with incubated embryos in the thorax. Scale bars = 2 mm.

FIGURE 4. Protoholozoa pedunculata: A,B, two tadpoles of a colony from the Indian Ocean, scale bar = 1 mm. C, tadpole, specimen from South Orkney Islands (USNM), scale bar = 0.5 mm. D, tadpole, specimen from the Scotia Arc (MZUC) scale bar = 0.6 mm.