Polyandrocarpa zorritensis ( Van Name 1931 )

Brunetti, Riccardo & Mastrototaro, Francesco, 2004, The non-indigenous stolidobranch ascidian Polyandrocarpa zorritensis in the Mediterranean: description, larval morphology and pattern of vascular budding, Zootaxa 528 (1), pp. 1-8 : 2-5

publication ID	https://doi.org/10.11646/zootaxa.528.1.1
DOI	https://doi.org/10.5281/zenodo.15749766
persistent identifier	https://treatment.plazi.org/id/36512248-FFB8-FFB5-955C-F93995D08486
treatment provided by	Felipe
scientific name	Polyandrocarpa zorritensis ( Van Name 1931 )
status

Treatment

Polyandrocarpa zorritensis ( Van Name 1931)

is a colonial Styelidae of the subfamily Polyzoinae . See: Stolonica zorritensis Van Name 1931 , 218, Polyandrocarpa zorritensis: Van Name 1945 , 245; Millar 1958, 505; Brunetti 1978 –79, 647; Turon & Perera 1988, 84.

External morphology. The colony is a closely packed group of zooids of various sizes which are joined by basal stolons but otherwise remain independent of one another ( Fig. 2 View FIGURE 2 ). The basal portion of the colony is a tangle of stolons along which there are orange globular bodies (buds) that will become new zooids. Adult zooids are sub cylindrical, yellowgreen in color, with an apical oral siphon and a slightly eccentric atrial siphon. Each aperture is fourlobed with two dark, almost black, bands per lobe. The test is thin and leathery and is packed with branching vessels and spherical terminal ampullae. A number of large cells with granular cytoplasm accumulate on the external surface of the vessels and ampullae ( Fig. 3 View FIGURE 3 , A).

Internal morphology. Welldeveloped zooids, removed from the test, range in hight from 9–10 to 12–13 mm. The body wall has delicate musculature with regularly arranged longitudinal and transverse fibres of the same size. Twenty to 30 simple tentacles of two lengths vary in number with zooid size. The dorsal tubercle has a wavy slitshaped transverse opening. The dorsal lamina is flat with a smooth edge. The branchial sac has four narrow, low folds per side with up to 12 internal longitudinal vessels on the folds and up to two between. Muscle fibres are in the larger transverse vessels. A typical branchial formula is: E0(4)0(7)1(5)1(6)2DL0(6)1(6)2(7)0(4)0E and in more developed zooids E1(7)1(12)2(11)3(12)2DL2(8)2(11)2(7)0(12)0E. Some short lengths of parastigmatic vessel are present ( Fig. 3 View FIGURE 3 , C). The gonads are oval polycarps in a row on each side of the endostyle, 9 to 10 on the right and 6 to 8 on the left ( Fig. 3 View FIGURE 3 , B, D). All ovarian apertures are directed dorsally. The sexually mature zooids have several embryos in the peribranchial cavity, some adhering to the external wall of the branchial sac by a fragile mucous string derived from the external envelope of the embryo. Solitary brooding ascidians are known to retain their embryos in a sticky mucus ( Lambert et al. 1995; Lambert 2004); this may be a similar adaptation. It is not known whether this mucous string is an artefact, or whether embryos are free as a consequence of fixation. The larval trunk, at the developmental stage in which the tail completely surrounds it, is about 530 µm in length (average from ten measurements = 524.5, min.= 458, max.= 600). Three triradially arranged adhesive organs are in a sessile frontal process from which three clusters of ampullae originate at metamorphosis ( Fig. 3 View FIGURE 3 , E). The intestinal canal (gut), on the left of the branchial sac, consists of a short oesophagus, a trapezoid stomach with a folded wall (generally 10–15 folds in addition to the typhlosole). A fingershaped gastric caecum with a spherical tip extends from the external posteroventral corner of the stomach but is obscured by an endocarp located in the intestinal loop ( Fig. 3 View FIGURE 3 , F). The diameter of the intestine gradually decreases from the pyloric end of the stomach to the plain edge anus near the atrial siphon.

Vascular system and Replication. The basic circulatory plan is the same as in all ascidians: subendostylar vessel, perigastric lacunae, dorsal vessel, pericoronal vessel and again subendostyle vessel (for this terminology see Burighel & Brunetti 1971). The heart is large, extending along the posterior third of the branchial sac, surrounding it posteriorly then extending anteriorly as far as the stomach., At the level of the anterior end of the heart, a vessel branches off the subendostyle (or ventral) vessel, extends posteriorly ventral to the heart and enters the basal stolon ( Fig. 4 View FIGURE 4 , A). The stolon branches and forms spherical swellings (buds) into which the stolonic vessel branches, each branch with a terminal ampulla filled with blood cells. New zooids develop inside these buds ( Fig. 4 View FIGURE 4 , B), vascular connection with the parent closes and the ampullae around the buds empty themselves, are reduced in size and become the test vascular system of the new zooids. The latter are completely formed before reaching 2 mm in height and at 3 mm gonads often are present.

Ecology

In both basins the species colonized a significant proportion of the hard substrata present in shallow water down to a depth of 2 m. In particular, extended colonies were found under iron buoys, on mussel breeding piles and on the steel wires connecting them. In November 2003 colonies collected in the two inlets were compared. The number of zooids present in three replicates of an area of 4 cm 2 was calculated and the percentage of small (3–6 mm), medium (6–10 mm) and large (> 10 mm in hight) size were noted. As we can see in Figure 5 View FIGURE 5 , the percentage of large zooids is higher in the surface colonies of the 2 nd inlet. This greater development may be due to the higher water temperatures registered during the previous months ( Fig. 1 View FIGURE 1 ) and probably also to a more euthrophic condition. At the deepest level colonies were present only in the 2 nd inlet. However the percentage of medium and small zooids dramatically increases in comparison to the situation of the surface colonies. This was due to minor development of the bottom animals as confirmed by the observation that the gonads are low in number or absent.