Aplidium crateriferum ( Sluiter, 1909 )

Kott, Patricia, 2008, Ascidiacea (Tunicata) from deep waters of the continental shelf of Western Australia, Journal of Natural History 42 (15 - 16), pp. 1103-1217 : 1151-1153

Aplidium crateriferum ( Sluiter, 1909)

( Figures 7E–G )

Amarancium crateriferum Sluiter 1909, p. 103 .

Aplidium crateriferum: Kott 1992a, p. 536 and synonymy.

Not Aplidium crateriferum: Monniot F. and C. 2001, p. 207.

Distribution

Previously recorded (see Kott 1992a): Western Australia (near Onslow and Exmouth); Queensland (south to central Great Barrier Reef), Philippines. New records: Western Australia CSIRO SS10/05 (Point D’ Entrecasteaux, Stn 18, 100 m, 21.11.05, QM G328436; Albany, Stn 22, 100 m, 22.11.05, QM G328111, G328113, G328117; Jurien Bay, Stn 83, 113 m, 02.12.05, QM G328147, G328151).

Description

Colonies are mushroom, turnip shapes or upright cones or paddles. Often they are sessile but sometimes they have a short, thick, and cylindrical to tapering stalk. The most conspicuous characteristics of this species are the deep pit-like depressions in the surface, about 2 cm apart and up to 2 cm in maximum extent, evenly spaced over the top half of the colony,. These depressions have one or two conspicuous chimneylike, cylindrical common cloacal siphons protruding from near the centre. A large, common cloacal cavity is beneath these surface depressions and some short canals may converge to it, although these are obscured by sand in the newly recorded specimens. One colony (QM G328113) is an irregular, sandy slab narrowing to what looks like a handle on one side and with large dimples along the other side as if a stalked colony had fallen on its side, the dimples being distorted circular depressions with chimney-like common cloacal protrusions. Colonies are up to 15 cm high, including the stalk. Their maximum diameter (to 9 cm) is usually about halfway down large egg-shaped colonies or at the base of the head.

Zooids usually are withdrawn from the surface and their openings to the exterior, either around or in the saucer-like depressions, are obscured by the sand crowded in the surface or embedded deeper in the test. The sand crowded in the outer layer of test forms a hard crust but is less crowded internally where the firm, hard test can be seen to be translucent. Zooids are red in the preserved colonies and their mutilated remains are sometimes evident between the sand grains in the centre of the colony. The red pigment is in spherical cells in the body wall of the zooids and is conspicuous in the base of the colony surrounding the zooids where they are crowded together having withdrawn from the surface. Zooids are robust, with a conspicuous branchial sphincter at the base of the siphon. The muscular atrial lip arises from the body wall anterior to a relatively short atrial siphon. About 20 rows of stigmata are in the branchial sac although the number of stigmata could not be determined. The stomach is small, with five longitudinal folds. Testis follicles usually are in two rather irregular rows in the posterior abdomen although occasionally only a single row of follicles was observed.

Remarks

The newly recorded specimens appear be consistent with those previously recorded in most characters, including the red zooids, the deep pits depressed into the surface test and the tubular common cloacal siphons rising from the base of these depressions. Zooids are also characteristic, narrowing at the anterior end and with a strong muscular atrial lip from the body wall some distance anterior to the atrial siphon. However some variations are reported in the amount of sand embedded in the test and in the number of folds in the stomach wall.

Specimens from the type location (Jolo Light - Philippines) recorded by Millar (1975) appear to have been correctly assigned. However other specimens from the type location ( Van Name 1918) and those from the Palau Is. ( Tokioka 1967) probably are not conspecific. The Australian specimens Kott (1992a) recorded are similar to the type in most characters except for the absence of sand in some of the specimens. As in the present specimens, the majority of those previously recorded have sand crowded in the surface and less crowded internally. At this stage, lacking other distinguishing characters, the sandy specimens and naked ones may reflect intraspecific variation. Also there is some variation in the number of folds reported to be in the stomach wall, Sluiter’s (1909) report of 12 stomach folds and Millar’s (1975) of six or seven could be errors (see Kott 1992a; Millar 1975, Figure 31), inconsistencies in these counts possibly resulting from counting folds on only one side of the stomach or they could be the result of intraspecific variation in a species with the wide geographic range of the present one.

The robust zooids and colonies resemble those of A. clivosum and A. lunacratum which also have conspicuous protuberrant common cloacal apertures and zooids that narrow in front of the large atrial tongue projecting from the body wall well in front of the atrial siphon. Although Kott (1992a) discussed the relationship between A. lunacratum and A. crateriferum , she did not include A. clivosum in that discussion. In A. clivosum the surface depressions are large, wide and saucer-shaped with long canals converging to the protuberant common cloacal apertures, while Aplidium lunacratum has regular, crowded, pit-like depression with a short but wide common cloacal siphon surrounded by a regular circle of zooids. These colonies resemble those of A. crateriferum more closely than A. clivosum , although the systems of A. crateriferum are less regular, more separated from one another and more deeply depressed into the surface than those of A. lunacratum . Zooids of A. lunacratum have only 10–15 rows of stigmata while A. crateriferum has 18–20 rows. The larvae of both these species are exceptionally large, having a trunk over 2 mm long with the anterior end obscured by epidermal vesicles. However they can be distinguished by the single median ampullae that alternate with the adhesive organs in A. lunacratum but not in A. crateriferum .

The general shapes of the colonies of A. crateriferum in the present collection resemble those of A. panis sp. nov. Both species also have atrial tongues separated from the atrial siphon, five stomach folds, similar numbers of rows of stigmata and two rows of male follicles. However, the present species is distinguished by the red colour of its zooids, zooid openings confined to the upper half of the colonies and the characteristic deep circular depressions into which the systems open with conspicuous chimney-like cylindrical common cloacal siphons. The distribution of sand in the colony of A. panis is also distinctive.

The descriptions of specimens from the Philippines assigned to this species by F. and C. Monniot (2001) are equivocal and the specimens may be incorrectly assigned. They are said to have five stomach folds but zooids are reported to be ‘‘arranged in lines’’ and the characteristic chimney-like common cloacal siphons are not reported.

Figures

Figure 7. Synoicum sphinctorum (QM G328068): A, larva. Synoicum vesica sp. nov. (QM G328100): B, colony; C, zooid. Aplidium clivosum (QM G328133): D, colony. Aplidium crateriferum (E1–2 QM G328113; F, G, QM G328111): E1–2, colonies; F, thorax and abdomen; G, posterior abdomen showing male follicles. Scales: A, C, F, G, 0.2mm; B, D, E, 1.0 cm.