Family PLURELLIDAE

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Introduction

In the family Plurellidae Kott, 1973, parts of the body wall along the dorsal mid-line, both anterior and posterior to the atrial aperture and including the neural complex and the gonads, are embedded in the test. Ovary and testis are separate, the undivided testis being embedded near the posterior end of the body, and the ovaries around the base of the atrial siphon. An arc of the body wall around the ventral border of the gut loop to the left of the mid-ventral line, containing the heart, is also embedded in the test. The duct of the neural gland, embedded in the test between the atrial and branchial apertures, opens into the atrial cavity by numerous simple ciliated pits along its length.

In the genus Plurella Kott, 1973, the male duct divides into distal branches, each expanded into a seminal vesicle to open with the separate short, wide, almost sessile oviducal openings of about six ovarian sacs arranged around the posterior rim of the base of the atrial siphon. Microgastra Kott, 1985 has only one ovarian sac and the vas deferens does not divide distally.

In both colonial Plurella and solitary Microgastra the test is sandy, hard and sometimes brittle, and the very thin body wall generally has few and delicate transverse muscles in a short band down the right side. The body musculature closely resembles and is probably convergent with that of Ascidia scaevola (Sluiter, 1904) which shares the characteristically brittle test of the solitary plurellids, Microgastra spp. Also, the right side of the body is narrower than the left and it has a fold of the branchial sac on the right side of the body resembling that of A. scaevola.

Plurella is known from four species, three tropical (Plurella kottae Monniot. F. & C., 1996, P. monogyna Monniot, F. & C., 2000, and P. testacea Monniot, F. & C., 2000) from the Philippines) and one temperate Australian species (P. elongata Kott, 1973). Microgastra is known from one species, common on sandy substrates from Bowen to Indonesia, Sri Lanka and Japan (Kott 1990).

General References

Kott, P. 1973. Plurellidae, a new phlebobranchiate family of the Ascidiacea. Proceedings of the Linnean Society of London 97(4): 258-261

Kott, P. 1985. The Australian Ascidiacea Pt 1, Phlebobranchia and Stolidobranchia. Memoirs of the Queensland Museum 23: 1-440

Kott, P. 1990. The Australian Ascidiacea, Phlebobranchia and Stolidobranchia, supplement. Memoirs of the Queensland Museum 29(1): 267-298

Monniot, F. & Monniot, C. 1996. New collections of ascidians from the western Pacific and Southeastern Asia. Micronesica 29(2): 133-279

Monniot, F. & Monniot, C. 2000. Ascidiacea: Plurellidae collected in the Pacific Ocean by the cruises MUSORSTOM, KARUBAR and the "Coral Reef Research Foundation". In Crosnier, A. (ed.) Résultats des Campagnes MUSORSTOM, Volume 21. Mémoires du Muséum National d'Histoire Naturelle, Paris, 184. 703-721 pp.

Sluiter, C.P. 1904. Die Tunicaten der Siboga-Expedition. Pt. I, Die socialen und holosomen Ascidien. Siboga-Expéditie Report 56A: 1-126

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