Polysyncraton magnilarvum ( Millar, 1962 )

Oliveira, Livia M., Hoeksema, Bert W. & Rocha, Rosana M., 2019, Polysyncraton (Ascidiacea, Didemnidae): a re-examination of some specimens and descriptions of three new species, European Journal of Taxonomy 519, pp. 1-25 : 15-17

Polysyncraton magnilarvum ( Millar, 1962)

Fig. 9

Didemnum (Polysyncraton) magnilarvum Millar, 1962: 165 , fig. 25.

Material examined

MADAGASCAR • 3 slides; South Madagascar, further collecting data unknown; MNHN A2-2466, MNHN A2-2767, MNHN A2-2470.

Emended description

The specimen from Magadascar has a long and trifurcated atrial languet ( Fig. 9a ), while Millar’s material from Mozambique has a short atrial languet ( Millar 1962). The lateral thoracic organs are circular and not protruding, localised in the anterior half of the thorax at the level of the 1 st row of stigmata, close to the endostyle ( Fig. 9b ). The muscular process is longer than the abdomen, up to 1.4 mm in length and inserted in the middle of the esophageal peduncle. The abdomen is positioned perpendicularly to the thorax. The secondary gut loop does not overlay the stomach ( Fig. 9a ). The stoloniferous vessels are small and rounded, and a glandular tissue in the shape of a crescent lays inside the gut loop on the right side. The testis is slightly below the gut loop, divided in 10 to 12 follicles and surrounded by three to five coils of the sperm duct ( Fig. 9 c–d). The larvae are elliptical, gemmiparous and the trunk is 1.4 mm long. A tail with a diameter of 104 µm winds halfway around the trunk. The three adhesive papillae are close to each other, with short peduncles. The sucker of the central adhesive papilla is 133 µm in diameter and the peduncle is 401 µm long. There are 12 to 15 elongated ectodermal ampullae on each side of the larva body, 113 to 333 µm long, depending on the developmental stage of the larva ( Fig. 9e ). The sensorial vesicle (including ocellus and statocyte) is located in the mid-dorsal region of the larval trunk. The ocellus is 57 µm long and 436 µm distant from the anterior region of the tail.

Remarks

This species was first reported from Mozambique by Millar in 1961, but the original description was published later by him in 1962 ( Millar 1962) with the following diagnostic characters: short atrial languet, testis with eight to ten follicles surrounded by 2½ coils of the sperm duct and larva with 15 pairs of ectodermal ampullae. The sample from Madagascar has a larger atrial languet and a larger number of testis follicles and coils of the sperm duct, but the larval characters are the same. Kott (1975) synonymised it with P. aspiculatum Tokioka, 1949 , but later, C. Monniot et al. (2001) confirmed that both species were valid and differentiated P. aspiculatum by its globular spicules, the larvae with a trunk length of 1 mm of trunk length and eight pairs of ectodermal ampullae.

Distribution

Type locality: Mozambique ( Millar 1962). South Madagascar (this study).

Figures

Fig. 9. Polysyncraton magnilarvum (Millar, 1962), stained with hemalum. a. Zooid (arrow pointing at atrial languet). b. Ventral view of the anterior region of the thorax (arrow indicating the lateral thoracic organ). c. Testis follicles (arrow indicating one lobe). d. Abdomen (arrow indicates the sperm duct) (MNHN A2-2466). e. Larva (MNHN A2-2467). Scale bars: a = 0.2 mm; c–e = 0.1 mm.