Botrylloides magnicoecus ( Hartmeyer, 1912 )

Monniot, Françoise, 2016, Ascidians (Tunicata) of the French Guiana Expedition, Zootaxa 4114 (3), pp. 201-245 : 221-222

Botrylloides magnicoecus ( Hartmeyer, 1912)

Figure: 16.

Stations. SR1; SS7; SS9.

The encrusting colonies show elongated systems of zooids dark brown or somewhat reddish in formalin. The zooid oral siphon has low lobes. The atrial aperture is wide with a long upper languet ( Fig. 16 A). The branchial sac has 8 to 10 stigmatal rows and a spot of pigmented cells is at the ventral extremity of each row. The gut is almost entirely located under the branchial sac ( Fig. 16 A,B). The stomach has 8 straight folds, not enlarged at their extremity which constitutes a clear difference from Botrylloides nigrum . The pyloric caecum is as long as the stomach itself, curved, sometimes with the tip enlarged into an ampulla. ( Fig. 16 C). The gut loop corresponds to the drawings in Monniot C. (1972 Fig 1 ) and Monniot C. (1983b Fig. 1 D,E). The gonads have a lobed testis and a single oocyte. Precocious buds were found in many zooids.

Many characters correspond to the redescription of the type by Brunetti (2010): colony structure, number of tentacles, number of stigmatal rows which are complete and the pigmented extremity of each row and the gut. Unfortunately the gonads were absent in Hartmeyer’s type. Brunetti (2010) estimated that specimens from Bermuda ( Monniot C. 1972), Guadeloupe ( Monniot C. 1983b) and South Africa ( Monniot C. et al. 2001) represent different species; this may be right but the type species revised was an immature single colony and the variability is not known therefore maintain provisionally our identifications. Other records from the Indian and Pacific Oceans likely do not correspond to B. magnicoecus .

Botryllus pumilus n. sp. Figure: 17.

Ethymology. pumilus = dwarf.

Station. CP4357 (Type MNHN S1 BOT.B 230).

Eight colonies, the largest only 5mm in diameter were living free on the bottom. They are covered with sand, less dense at one pole where the oral siphons open, and with a short thread-like tunic expansion at the opposite side. Each colony is a single system of zooids with a central common opening. All zooids have gonads but at different stages of development in a single colony ( Fig. 17 A,B). The body wall is colourless in formalin. The oral siphon is short. The atrial siphon has a thick languet or a tubular aperture ( Fig. 17 E). The tentacles are in 2 sizes on a ring. The branchial sac has 12 to 13 rows of oval stigmata and 3 longitudinal parallel vessels on each side ( Fig. 17 A,B) all reaching the base of the branchial sac. The dorsal lamina is long increasing in height posteriorly. The gut loop is horizontal and partly under the branchial sac. The stomach has 9 longitudinal folds and a tubular caecum ending in an ampulla ( Fig. 17 D). The rectum runs vertically. There is one gonad on each side. On the left side the testis in several round vesicles is located anterior to the gut loop; the right one is symmetrical. The ovary when present contains 1 to 3 large oocytes anterior to the testis. The testis is reduced when tadpoles are present in the atrial cavity ( Fig. 17 B). One bud is appended on each side of the body wall.

These Botryllus colonies are similar to a part of the specimens from Natal erroneously mixed in the collection labelled B. mortenseni in Monniot et al (2001 Fig 40c).The type of B. mortenseni ( Millar 1966) is a colony in large sheet which better correspond to the large colony collected from Cape Point. Monniot et al. (2001) have wrongly associated in a same species small sandy colonies from Isipingo more similar to the new species that may belong to B. pumilus n. sp. but are geographically well distant.

Figures

FIGURE 1. Aplidium lepareurae n. sp. A: colonies; B, stained zooids; C, branchial sac; D, gut cross section; E, siphons. Scale bars: A = 1 cm; B = 2 mm; C = 0.5 mm.

FIGURE 16. Botrylloides magnicoecus stained with hemalum: A, zooid, scale bar = 0.5 mm, B, gut loop; C, stomach caecum.

FIGURE 17. Botryllus pumilus n. sp. stained with hemalum. A, B, two stages of bodies ventrally opened, scale bar = 1 mm; C, internal side of the gut loop; D, stomach caecum, scale bar = 0.3 mm; E, zooid.