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Biology
At Cheltenham, Balanoglossus australiensis forms long, U-shaped burrows, 8–10 inches deep, in fine, relatively well-aerated low tidal sand. Wave attack is subdued, and a surface mantle of organic detritus and diatoms is able to accumulate, forming the food supply of an association of deposit feeders of which the principal other members are the lamellibranch Macomona liliana, the holothurian Trochodota dendyi, and the ophiuroid Amphiura australe. Balanoglossus is easily the most abundant form present, two or three specimens being generally turned up with every spadeful of sand. Burrowing is performed by thrusting into the substratum with the pointed, turgescent proboscis, which is finally protruded from one opening of the completed tube to ingest surface detritus. There is no apparent attempt at sorting,
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and large masses of sand grains pass through the gut; ingestion does not, however, take place below the surface during burrowing. The tube walls are thinly mucus-lined, mainly by the integumentary glands of the collar and proboscis, and the animal moves freely backwards and forwards, leaving a clear space dorsally for the branchial water current, and periodically protruding the hind-body for the discharge of sand castings like those of Arenicola.
The present abundance of this species at Cheltenham, together with the absence of any previous records from New Zealand, might suggest that it may fairly recently have established itself, or increased its numbers, in the local fauna. Balanoglossus has a lengthy tornaria larval stage and could well have been carried to these shores by the Tasman current in common with a small Recent molluscan element from Australian seas. Plankton sampling at Auckland has not to the writer's knowledge revealed any specimens of a tornaria, but in the collection of the Biology Department of the Canterbury University College is a well-developed tornaria collected in March, 1946, about two miles off the entrance to Lyttelton Harbour, on which Miss Frances Nurse has been kind enough to supply the drawing reproduced as Fig. 6, together with the following note: “The mounted specimen is 0·7 mm. long and 0·45 mm. in diameter. It appears to be at the stage described by Stiasny as ‘T. mulleri’ (Zool. Anz., Vol. 52, p. 493, 1913). The ciliated bands have been thrown into folds and the telotroch is well-developed. The larva resembles Stiasny's figures 4 and 5 of T. mulleri, which is the larva of Balanoglossus clavigerus, now known as Ptychodera clavigera.”
References To Literature
1. Benham, W. B., 1899. Balanoglossus otagoensis n.sp. Quart. J. Micr. Sci., xlii, 497–504, pl. 45.
2. Brambell, F. W. Rogers, and Cole, H. A., 1939. The Preoral Ciliary Organ of the Enteropneusta. Proc. Zool. Soc. Lond., Ser. B.109, 181–193.
3. Hill, J. P., 1895. On a New Species of Enteropneusta (Ptychodera australiense) from the Coast of New South Wales. Proc. Linn. Soc. N.S.W., 10, 1–42.
4. Horst, C. J. van der, 1927. Bronn's Klossen und Ordnungen des Tierreichs, Bd. 4, Abt. 4, Buch 2, Tiel 2.
5. Kirk, H. B., 1938. Notes on the Breeding Habits and the Early Development of Dolichoglossus otagoensis Benham. Trans. Roy. Soc. N.Z., 68, 49.