Tuatara: Volume 10, Issue 3, September 1962
Pogonophora — Their Mode Of Life And Distribution On New Zealand Coasts
Their Mode Of Life And Distribution On New Zealand Coasts
In an earlier article on the Pogonophora (Tuatara 7 (2), 1958) the main facts about this peculiar and recently established animal group were reported by Fell. Since then our knowledge of pogono phorans has been considerably amplified.
Until recently, it could easily have been supposed that the extant Pogonophora comprise only an insignificent relict of an ancient group, once richly represented. Every year, however, oceanographic expeditions are yielding more and more newly discovered representatives of the Pogonophora, from different parts of the world's oceans, so that it has now become clear that it is actually a flourishing group, though comprising mainly forms from the abyssal sea-floors.
At the present time we have information on more than a hundred species of Pogonophora, of which fifty-eight have already been described and assigned generic and specific names. A particularly large number of Pogonophora have been found in the Pacific Ocean, and latterly also in the Indian Ocean. They have also been discovered in the Atlantic, off the coasts of Europe, Africa and America, off the coasts of Antarctica, and in the Arctic. Not long ago pogonophorans were also found in the Norwegian fiords (Brattstrom and Fouchald, 1961), and even in the Mediterranean Sea.
The Pogonophora typically inhabit the abyssal zone, but many species are also met with in comparatively shallow regions. About Professor A. V. Ivanov is recognised as the world authority on Pogonophora and is the author of the only monograph on the group.page 110
60 per cent of the species are encountered at depths exceeding 3,000 metres, and about 40 per cent in lesser depths. At depths of less than 100 metres not more than twenty species have been reported. Some species are distinguished by a very wide range of vertical distribution; for example, Siboglinum caulleryi, inhabiting the Sea of Okhotsk and the north-western region of the Pacific, has been taken on the Sakhalien coast (north of Japan) at depths of only 20 metres, yet also ranges down into the abyssal zone, and even into parts of the Kurile-Kamchatka Trench, down to a depth of 8,164 metres.
All Pogonophora have a sedentary, tubicolous mode of life. The elongate cylindrical tube, which is secreted about the body, is composed of chitin (Brunet and Carlisle, 1958). Various sedentary animals are found adhering to this tube—forams, sponges, hydroids, alcyonarians, small actinians, serpulids, polyzoans, ascidians, Scalpellum, and even stalked sea-lilies. There are also encountered not infrequently the chitinoid thecae of the seyphistoma of Stephanocyphus, attached to the tubes. The localised disposition of all these epibionts shows that a significant part of the tube of pogonophorans protrudes freely above the surface of the sea-floor, more or less vertically, with the remaining, basal, part of the tube deeply immersed in the mud. However, the delicate, annulated tubes of the species of Siboglinum usually do not carry epibionts, so they are probably almost entirely immersed in mud. It is evident that in associations of pogonophorans the individuals are disposed in close proximity to one another. This inference would seem to be justified by the fact that pogonophorans have separate sexes, and lack pelagic larvae (Ivanov, 1960a).
Not infrequently Pogonophora occur in immense numbers, so they are quite characteristic elements of the bottom biocoenosis. In the north-western part of the Sea of Okhotsk extensive shallow-water expanses of mud-bottom (at depths of 90-200 m.) are occupied by a dense population of Siboglinum caulleryi. In the Bering Sea, at depths of 1.400-5,000 m., Polybrachia annulata occurs, and frequently dominates numerically in the complex biocoenosis, almost all members of which occur attached to the tubes of these pogonophorans. Among the predatory species in these biocoenoses the decapod crustacean Munidopsis feeds upon Polybrachia (Sokolova, 1956).
Figure 1. Siboglinum vinculatum. A, anterior extremity of body of male, in ventral aspect. B, anterior extremity of body of female, in dorsal aspect. C, same in ventral aspect. D, portion of the tentacle. E, two pinnules. F, zone of aggregated papillae on the ventral side. G, cuticular platelets from from the zone of aggregated papillae. H, annular region in ventral aspect. I, same in dorsal aspect. J, portion of an annulus. K, anterior portion of tube. L, posterior portion of tube.
Abbreviations: an, annulus; c, cephalic rostrum; ca, capillary of pinnule; co, dorsal ciliated region; dp, posterior group of denticulations; f, frenulum; go, genital papilla; ms, mesosoma; mfs, metasoma; p, cuticular platelets; pa, papillae; pi, pinnules; ps protosoma; si, furrow between protosoma and mesosoma; s2, furrow between mesosoma and metasoma; s4, post-tentacular furrow; s5, second furrow of mesosoma; sv, ventral furrow; t, tentacle; vl, lateral vessel of head region, translucent through integument.
It seems dubious whether pogonophorans can vacate the tube, for they are not adapted for locomotion outside it. However, they are able to move rapidly within the tube, so as to extrude the anterior extremity of the body from the tube, together with the tentacles, or to withdraw deeply within the tube. In this respect they resemble sedentary tubicolous polychaets, to which they present superficial resemblances, caused by an identical mode of life. The length of the tube is always considerable. It exceeds the length of the animal itself, and thus does not impede movement of this kind. Numerous attachment papillae, with their chitinous platelets (illustrated in the figures herewith), serve for the support of the animal on the internal surface of the tube. A well-developed longitudinal musculature in the body-wall indicates that pogonophorans have a considerable capacity for extension and contraction. Extension of the anterior extremity of the body from the tube is aided by the fine denticu lations on the annular girdles (see figures). Upon stimulation, or danger, the animal instantly vanishes into the depths of the tube, by means of a simple contraction of the longitudinal musculature; and of course, the firm grip exerted by the girdles facilitates this “flight reaction’. Similar inferences are confirmed by the histological data namely, the presence of elongate giant nerve-fibres, these apparently subserving the rapid mediation of impulses to the longitudinal musculature of the contractile part of the trunk region (Ivanov, 1959).
As Fell has already reported in the pages of Tuatara, pogono phorans present us with a remarkable instance of animals totally devoid of an alimentary canal. They assimilate nutritive material by means of the tentacles (or by means of a solitary tentacle).
In order to accumulate food particles in the intertentacular lumen, by means of filtration of the water, it is not absolutely necessary for the animal to extrude the entire tentacular crown; it suffices if the distal portion only is thrust outside the tube. In Siboglinum, which has only a single tentacle, the latter is probably used to select particles from the superficial mud, “exploring’—as it were—the surrounding region, with the aid of its tentacle. Apparently the tentacle can be coiled, in the manner of a corkscrew, so as to invest a quantity of food-particles; after that, it is withdrawn into the tube, where the food is digested. It is possible that all Pogonophora retreat into the tube, from time to time, so as to digest the food accumulated in the tentacular apparatus. In the female, however, once the eggs have been deposited in the upper section of the tube, the animal must of necessity be content to remain in the lower part of the tube throughout all that interval of time during which the embryonic development proceeds.page 113
Figure 2. Siboglinum tenue. A, anterior extremity of female in dorsal aspect. B, the same in ventral aspect. C, the same in right lateral aspect. D, annular region. E, portion of an annulus. F, denticulate platelet seen from side. G, anterior part of tube. H, middle part of tube. I, posterior part of tube.
Abbreviations: ci, glandular cingulum; da, anterior group of denticulations; f, keel of frenulum; gt, tubiparous glands (i.e., the glands which secrete the tube), visible through the integument. Other abbreviations as in Figure 1.
These inferences, nonetheless, must be regarded as tentative, for we still lack observations based on living animals.
From New Zealand coasts four species of Pogonophora have been recorded: Siboglinum vinculatum, S. tenue, S. variabile and S. bogorovi. All these species were collected by G. M. Belyaev, A. I. Savilov and Z. A. Filatova. during the operations of the Russian research vessel Vitiaz, belonging to the Oceanographic Institute of the Academy of Sciences of the U.S.S.R. The Vitiaz worked off New Zealand in 1958, and also visited Wellington at that time.
The genus Siboglinum, to which these species belong, is included in the order Athecanephria (family Siboglinidae), and it is also the most widely distributed genus. Numerous species belonging to it are distributed in all parts of the world's oceans. The most distinctive feature of Siboglinum is the presence in all its species of only a single tentacle—though this, however, reaches a very great length. It is often found to be twisted into a tightly coiled corkscrew-shaped spiral, and it usually bears either one or two rows of delicate pinnules (or villi), though these may be wanting from a number of species. The protosoma is demarcated from the mesosoma by a distinct furrow. In some species there is a more or less complete glandular girdle, situated just posterior to the cuticular frenulum (see figures). This glandular girdle, or cingulum (labelled ci in the figures), sometimes extends in the form of two elongate ventrolateral glandular bands, which may reach so far back as the boundary of the mesosoma. The attachment papillae (labelled pa) on the anterior portion of the metasoma have no cuticular platelets. In Siboglinum the tube, as a rule, is annulated, and greyish, brown or brownish in colour.
Key to the species of Siboglinum found off New Zealand
|1 (6)||Keels of the frenulum confluent or closely contiguous on the ventral surface.|
|2 (3)||Keels of the frenulum confluent on the dorsal surface. No visible glandular cingulum posterior to the frenulum. Two rows of short pinnules (or villi) along the tentacle. On the middle part of the metasoma there are aggregations of irregularly arranged papillae, each bearing a curved platelet. Keels of the frenulum moderately thick. On the middle part of the metasoma are two annular concentrations of denticulate platelets, whose length is 11-13 mu. The tube is thick-walled, with regularly arranged, white rings. Tube up to 15 cm. long, its diameter 0.2 mm. (figure 1).||S. vinculatum Ivanov|
|3 (2)||Keels of the frenulum do not join on the dorsal side. There is an incomplete glandular cingulum posterior to the frenulum. The tentacles lack pinnules.|
Figure 3. Siboglinum variabile. A, anterior extremity of the body in ventral aspect. B, the same in dorsal aspect. C, region of aggregated papillae in ventral aspect. D, annular region, in ventral aspect. E, portion of an annulus. F, denticulate platelet seen obliquely from one side. G, tube, at the beginning of the region where rings occur. H, middle portion of tube. I, posterior portion of tube. J, tube near its posterior extremity.
Abbreviations: o, ovum visible in the oviduct. Other abbreviations as in the preceding figures.
|4(5)||Three annuli of denticulate platelets on the middle part of the metasoma. The two anterior annuli lie considerably anterior to the posterior one. Length of the denticulate platelets 8-10 mu. The keels of the frenulum are disposed in a narrow, brownish, cuticular band which is intersected by darker transverse lines (visible under a microscope). The anterior margin of the mesosoma has no transverse bolster-like thickening. Tube unsegmented, filamentar, with brown rings arranged in consecutive pairs. Tube up to 9 cm. long, diameter 0.1 mm. (figure 2).||S. tenue Ivanov|
|5 (4)||Two adjacent annuli on the middle part of the metasoma, their denticulate platelets each 9-12 mu. long. Keels of the frenulum simple. The anterior margin of the mesosoma has a weakly-developed dermal thickening, in the form of a transverse ring. Tube segmented, mostly with three rings on every segment, the rings regularly arranged, brown, sometimes joined in pairs. Tube up to 7.5 cm. long, diameter 0.2 mm. (figure 3).||S. variabile Ivanov|
|6 (1)||Keels of the frenulum not united on the ventral surface. No pinnules on the tentacle. A transverse furrow lies posterior to the fentacle. An incomplete glandular cingulum lies posterior to the frenulum. On the middle part of the metasoma there are two widely separated annuli, the denticulate platelets of which measure 11-12 mu. Tube brown, with elongate segments, partly spotted or composed of 2-3 secondary rings. Tube up to 20 cm. long, diameter 0.2 mm. (figure 4).||S. bogorovi Ivanov|
The pogonophoran fauna of the waters around the islands of New Zealand is, of course, by no means exhausted merely by enumerating four species of Siboglinum. Other species are probably living off New Zealand, including undescribed forms representative of other genera and families.
With the deepest sincerity we wish New Zealand zoologists “Good luck!’ in the study of these pogonophorans.page 117
Figure 4. Siboglinum bogorovi. A, anterior extremity of female, in dorsal aspect. B, the same in ventral aspect. C, metameric zone of the pre-annular region, in ventral aspect (the continuation of that part of the body illustrated in B). D, region of concentrated papillae, in ventral aspect. E, annular region in ventral aspect. F, the same in dorsal aspect. G, portion of an annulus. H, denticulate platelet seen in oblique lateral aspect. I, portion of the post-annular region. J, anterior membranous region of tube. K, tube fowards the anterior region. I, middle portion of tube. M, posterior portion of tube.
Abbreviations: sc, dorsal glandular shield; v, ventral papilla. Other abbreviations as in preceding figures.
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As this issue goes to press Dr. Elizabeth J. Batham advises that a new pogonophoran has been discovered in material taken from Canyon A, in 260-400 fathoms, E.N.E. of Otago Heads. It has 4-5 alternately pinnulate tentacles, but its precise systematic status has not yet been determined. A formal report is in preparation.—editor