The Occurrence in New Zealand of the Enteropneust, Balanoglossus australiensis (Hill)
[Read before the Auckland Institute, May 7, 1949; received by the Editor, September 27, 1919.]
The first New Zealand species of the Enteropneusta, Saccoglossus otagoensis, was recorded by Benham (1899), and Kirk has more recently (1938) contributed a note on the breeding habits and direct development of this form. The species is frequently seen at Cook Strait or in the South Island, but hitherto there has been no enteropneust recorded from the northern part of the North Island. Eariy in 1946, however, the writer collected from the sandflat at Cheltenham, at the mouth of the Auckland Harbour, numerous specimens of a much larger species which—by the presence of wide genital wings, well-developed hepatic sacs, and slit-like gill openings—was assigned to the family Ptychoderidae.
The species, which has since been taken nearby at St. Heliers and Howick, has been found to be identical with the New South Wales Balanoglossus australiensis (see van der Horst, 1927) described as Ptychodera australiense by Hill (1895), who gave a detailed account of its anatomy. A new genus and family is thus added to the New Zealand fauna, and a short diagnosis is given, drawn up from Auckland material.
The total length of a large specimen of Balanoglossus australiensis reaches 20 cm. The proboscis is short and tongue-shaped, 0·7 cm. in length when extended, and half as much in diameter at the base, becoming rounded and acorn-shaped when retracted. The collar is 0·5 cm. long and of equal width, with five distinct epithelial zones, the first forming the frilled anterior half of the collar investing the proboscis neck; the second a narrow circular groove; the third a broad, cushion-like zone slightly darker in colour; the fourth a groove; and the fifth a circular cushion forming the posterior margin of the collar. In the trunk, the branchiogenital region is characteristically expanded into wide dorso-lateral genital wings, passing backward for 3–4 cm. behind the collar, and reaching a maximum width of 0·8 cm. on either side about halfway back, just behind the gill area. The edges of the wings may remain in contact along the dorsal mid-line to form a temporary tube concealing the gills, or they may spread out widely to the sides. The gonads form a series of finely branched digitiform lobules. The gill area may reach to 15 mm. in length, up to 40 pairs of slits opening into deep lateral grooves just median to the insertion of the wings. The skeletal bars are three-pronged, and each slit is deeply divided by an incomplete tongue bar and crossed by synapticula. The alimentary canal in the gill region (Fig. 5) shows the typical condition of the genus in its constriction into distant dorsal branchial and ventral oesophageal portions. The hepatic region is 2·5 cm. long
Fig. 1—The entire animal, X 1 ½. Fig. 2—Sagittal section of proboscis organs, X 18. Fig. 3—Transverse section of proboscis organs, X 27. Fig. 4—Transverse section of proboscis neck, X 27. Fig. 5—Transverse section of branchiogenital region, X 18. Fig. 7—Tornarin larva (?Balanoglossus), off Lyttelton Harbour, X 55.
(Figure by Miss Frances Nurse)
BR.C., branchial cavity: BR.R., branchial region: BR.S., branchial slit; B.SK., body of the proboscis skeleton: C.EP., coelomic epithelium; Colls., collar; D.SP., dorsal septum; D.V., dorsal blood vessel of proboscis; EF.V., efferent blood vessel of proboscis; EP., epithellum; EP.N.S., epidermal nervous system: GEN.W., genital wing; GM, glomerulus; GON., gonad; H.B., hind body; HEP., hepatic sacs: BT., heart vesicle; K.SK., keel of proboscis skeleton: LUM., lumen of stomochord; M.COLL., anterior edge of collar; OES., oesophagus: P.C., pericardium: P.COE., proboscis coelom.: PRE.O., pre oral organ: PROB., proboscis; PR.P., proboscis pore; SCH., stomochord; SKEL., anterior cup. like portion of proboscis skeleton: SKL., proboscis skeleton; V.B., ventral blood vessel; V.SP., ventral septum.
with up to 75 pairs of well-developed sacs, with 6–10 pairs of reduced sacs enclosed by the posterior portions of the genital wings in front, and an equal number of small tubercles behind. The sacs are simple in form, attaining their greatest width about the thirtieth pair. The hind-body is narrow and thin-walled, with impermanent annular rugae, and two longitudinal epidermal stripes, close to the dorsal midline, overlying corresponding ciliated grooves in the intestine. In coloration the proboscis is lemon-yellow and the collar a rather deeper yellowish brown, the genital wings in the male a distinctive bright saffron-yellow, and in the female a less conspicuous creamy-white. The hepatic sacs are anteriorly light brown, passing through deep brownish-green, slate-green to a uniformly lighter green behind. The trunk is whitish or translucent. Hill states the species to be destitute of any odour; however, New Zealand specimens kept alive in the laboratory made themselves detectable by a mild but distinct smell of iodoform.
The proboscis organs are illustrated in Figs. 2, 3, 4. The proboscis cavity is in large part occupied by some 20 radiating masses of longitudinal muscle running distally from the base. The proboscis neck in the specimens sections was traversed dorsally by the fused backward prolongations of two coelomie pockets, opening by a single symmetrical dorsal proboscis pore. Hill states, however (loc. cit.), that the proboscis pore and pockets may show considerable variation. The stomochord lumen is floored posteriorly by flattened cuboidal cells, and roofed by long epithelial cells of grandular character. Further forward the stomochord dips to form a ventral blind sac containing a bicornuate branch of the lumen, while the main lumen continues dorsally as a restricted space surrounded by clear-staining trabeculate chorde tissue. The proboscis skeleton consists of a main body, a ventral keel—Y-shaped in cross-section—and two posteriorly diverging legs. The body forms anteriorly a cup supporting the blind-sac. The pericardium is a medium sac with its ventral wall infolded as a wide tubular bloodfilled space acting as a pulsatile heart. The glomerulus is two-lobed, attached to the anterior and lateral surface of the stomochord with a narrow dorsal isthmus. At the base of the proboscis is a well-developed horseshoe shaped tract of ciliated epithelium almost surrounding the proboscis neck, forming the pre-oral organ, first described in Enteropneusta by Rogers-Brambell and Cole (1939).
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,
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.