Rhopalaea crassa (Herdman, 1880)

KOTT, PATRICIA, 2003, New syntheses and new species in the Australian Ascidiacea, Journal of Natural History 37 (13), pp. 1611-1653 : 1613-1615

Rhopalaea crassa (Herdman, 1880)

(figure 1a, b)

Ecteinascidia crassa Herdman, 1880: 723 .

Rhopalaea crassa: Kott, 1990a: 26 and synonymy (not Ecteinascidia fusca , Rhopalopsis fusca ); not Rhopalaea crassa: Monniot, 1997b: 558 .

Rhopalaea perlucida Monniot, 1997b: 560 .

Distribution. After Kott, 1990a: Indo-West Pacific ( Japan, Indonesia, Philippines) and the South China Sea to Sri Lanka and Madagascar.

Remarks. Kott’s (1990a) account of R. crassa is based on the examination of 40 or more specimen lots (each of up to six specimens) including the types of junior synonyms Rhopalopis defecta Sluiter, 1904 and Ecteinascidia solida Herdman, 1906 . She found the species to vary in morphology with age, regeneration and contraction. Particularly affected by age were the shape of the body, consistency of the test, appearance of the apertures, while contraction affected the number and disposition of thoracic muscles. Specimens were colourless or some shade of yellow, pink, blue or greenish blue. Muscles are never present on the abdomen. The branchial and atrial apertures are each surrounded by a very delicate rim of thin body wall, which is gathered into a frill when the strong siphonal muscle at the base of each short siphon is contracted. This transparent rim has six sharp indentations dividing it into six delicate, irregular and usually folded lobes. In preserved specimens, a sinus containing yellowish or yellowish brown blood surrounds the base of the sphincter. The blood sometimes continues in six lines, each extending up the siphon to a spindle-shaped or spherical mass between the branchial lobes; or the yellow masses are isolated from the ring sinus. The branchial and atrial lobes often are obscure and siphons withdrawn into the test in contracted zooids.

Monniot (1997b: 561) states that Kott’s synthesis of R. crassa (with an Indo- West Pacific range shared by many species), as a species in which the consistency of the thoracic test varies with age, is based on a quotation ‘en italien de Salfi (1928), traduite en anglais et faussement interpretée’. In fact the quotation from Salfi is not a translation. It is Salfi’s (1928: 370) English summary of his conclusions based on observations of R. neapolitana . It is quoted by Kott (1990a: 25) in support of her (similar) conclusions. These observations do not support Monniot’s (1997b) proposal that R. crassa always has a tough thoracic test that distinguishes it from R. perlucida with a soft transparent thoracic test. In Rhopalaea perlucida Monniot, 1997b , as in R. crassa , the abdomen, embedded in resilient test, is fixed in crevices while the thorax, with delicate, transparent test and yellow markings around the apertures is free above the coralline substratum. Individuals resemble the photographed specimen of R. crassa (see Kott, 1990a: plate 1c and QM G10150, figure 4e). Thoracic muscles are disposed as in R. crassa and, as is characteristic of contracted specimens, they are pulled into wider bands and the branches are obscured. The position of the anus varies with contraction, and its reported position in R. perlucida opposite the 50th row of stigmata, i.e. about half-way down the branchial sac, is not inconsistent with R. crassa (see Kott, 1990a: plate 1b, c). Branchial and atrial lobes reported in Monniot (1997b: figure 1F) resemble those of R. crassa although the eight (rather than six) reported for R. perlucida possibly results from a misinterpretation of these delicate frilled structures. Further, the implication that the abdomen increases in length as a result of successive regenerations of the thorax (see Monniot, 1997b: figure 1E) cannot be sustained merely by the presence of four irregular constrictions in the abdominal test—which always is irregular, affected by the substratum in which it is embedded. There is no evidence from Monniot (1997b) that R. perlucida is other than a junior synonym of R. crassa .

Rhopalaea crassa: Monniot, 1997b , with two muscle bands on the abdomen is not correctly assigned. These specimens resemble Rhopalaea tenuis (Sluiter, 1904) previously recorded from Torres Strait and the Arafura Sea. The fewer longitudinal thoracic muscles and internal longitudinal vessels in R. tenuis than in R. crassa: Monniot, 1997b may result from contraction or age of the specimens but at this stage the identity of R. crassa: Monniot, 1997b is in doubt. Monniot (1997b) implies that the recurved branchial siphon (Kott, 1990a: figure 5a) is characteristic of R. tenuis , but this is observed only in some specimens (see Kott, 1990a).

Rhopalea piru Monniot and Monniot, 1987 and R. circula Monniot and Monniot, 2001 are also West Pacific species with a pair of longitudinal abdominal muscles. Both differ from R. tenuis and R. crassa: Monniot, 1997b principally in being colonial, R. circula individuals being attached to a network of basal stolons and R. piru possibly budding from the oesophageal region.

Rhopalea fusca (Herdman, 1880) , which Kott (1990a) thought to be a synonym of R. crassa , also is said to be colonial, with individuals attached to a common basal stalk. However, newly examined specimens from the Philippines (QM GH393), that otherwise conform with R. fusca: Monniot and Monniot, 2001 , have irregular processes from the basal and abdominal test tightly associated with those of adjacent zooids although actual organic continuity was not detected.

Although Monniot and Monniot (2001) suggest that poor condition of type specimens has resulted in unacceptable synonymy, it is possible that the lack of studies to determine morphological variations with age/size and contraction may have resulted in unrealistically restricted definitions of species parameters.