Molluscan 'Witches' at Slaughden

102

MOLLUSCAN

" WITCHES "

AT SLAUGHDEN.

MOLLUSCAN " W I T C H E S " AT SLAUGHDEN. BY

CHESTER

G.

DOUGHTY,

B.A.

A F R I E N D of mine who is a Member of our Society, when collecting Crustacea with the help of a water-net in the saltmarshes at Slaughden about two miles southward of Aldeburgh last year, discovered in the brackish ditch on the seaward side of the Aide River wall a number of animals quite unknown to him, which his net was too short-handled to reach. " Of course, you will know them quite well," he said ; but, when he described them, I had to confess that I had not the slightest notion of even to what order of Invertebrata they belonged. The description follows: " Each specimen was about five inches long and black, though appearing greyish by the light refracted through the water ; it consisted , as far as one could see from the bank, of an elongate-ovate body with a distinct neck and a subcircular head ; the whole appeared shell-less, bare and fleshy, having a sort of fin on each side that looked like nothing so much as arms akimbo; from these arms hung some loose extension of the epidermis, suggesting a cloak, though how such a ' cloak ' was attached to the body was not piain. The animals, propelling themselves in a jerking manner by forcibly throwing the elbows with their dependent cloaks backwards, bobbed along the surface with the tide in a heavy and ungainly way for three or four (timed) minutes, evidently having difficulty in retaining their vertical Position ; then they would seem to tire, and sink to the bottom of the ditch which was only some two feet deep. After lying on the mud for about a minute, up they would struggle to the surface again, and resume their tedious j ourney."

At first he fancied they might be young Cephalopods or cuttlefish ; but the total absence of tentacles ruled these out, quite apart from the unlikelihood of the locality. Then my friend suggested some form of Jelly-fish, but the creatures seemed too unsymmetrical. Next he thought he had identified them as the Pteropod molluscan Clio borealis, Brugiere, or some species of that genus, judging by the rather rough figure (after Gray) in Gosse's Manual of Marine Zoology which, except for the cloak, seemed to agree with the Slaughden animals very well; though he later learned that only one kind, Clio pyramidata, Browne, had occurred and that no more than once in Britian, viz. in the Shetlands, where but one specimen was found to contain the animal and then in a collapsed condition ; also the total length was less than one inch (to which record Mr. Brockton Tomlin adds the Irish coast as a locality). There the question of the identity of these " Witches," as my friend aptly calls them, had to rest during the winter, throughout which they continued so

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" WITCHES "

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pretty a problem that another of our Members suggested analogy between the Slaughden ditches and the canals of Mars, with an equally puzzling fauna!

We paid a visit to the spot on lOth April last, and, with no small satisfaction, I saw the implement of attack was a beetle water-net that this time measured a good twelve feet in length, with the handle in two joints.* The creatures, as described, seemed so altogether uncanny that one wondered whether they might not bite, sting, spit or exude poisonous secretions : hence care in manipulation became indicated.

The locality, by the way, has the probably unique distinction of being at one and the same time a Royal Air Force experimental Bombing Ground and a Bird Sanctuary. Judging by the little heaps of thrown-up marsh earth that have been converted into brick-dust, the bombs dropped must be pretty ' hot stuff' ; and the mud in the dykes has numerous pink splotches, as though it had been sprinkled with carbolic powder, presumably resulting from bombs. Still, a subsequent visit showed that at least one Redshank (Totanus calidris, L.) had hatched out safely.

Soon after our arrival, I noticed two Witches looping along in a very graceful manner and quickly had them in the net ; as all seemed quiet there, I ventured to peer in and saw two extremely placid and inert lumps of jelly, enveloping two partially visible and very shining shells : " Some species of Bulla, of course ! " I said to my friend. They proved to be Acera bullata, Müller, on being referred to Dr. Gwyn Jeffreys' British Conchology.

This work, published in 1867, gives the Orwell Riverf as a locality upon the authority of Clarke, presumably the famous malacologist, and Walton-on-Naze on the faith of W. B. King; there the Bulla is described as flitting about, like a Pteropod, by means of its ample and flexible foot-lobes. Certainly I must differ from my friend in seeing nothing ungainly about the motion, for it was distinctly graceful. Later we noticed one swimming against the tide ; and, although irrelevant, perhaps I may be allowed to interpose that it is a most curious sight to observe Nereid worms about six inches long, in the summer (presumably the breeding season of Nereis diversicolor, Müll.— cf. Trans. Norf. Nat. Soc. vii, 65 ; ix, 456 ; and x, 164), swimming strongly against a heavy tide on the surface of our river at Gorleston. * T h i s net is historic.

I t was customarily used b y DR. JOHN A. POWER, the famous B r i t i s h coleopterist, whose collection forms t h e basis of our national one in t h e B r i t i s h Museum.

A t his death, it was purchased b y Mr. W . H. T u c k , who bequeathed it t o t h e present owner, along with Power's walking-stick. f T h i s locality has since been confirmed b y t h e R e v d . Carleton Greene, Dr. S o r b y (Vict. Hist.), and in 1908 b y Mr. Mayfield.—ED.

MOLLUSCAN

" WITCHES "

AT

SLAUGHDEN.

We saw and captured many Witches that day, but they were only half the size computed by my friend ; and, comparing those we obtained with the ones illustrated by Jeffreys, our shells can have been merely half-grown, and when mature the animal may easily be the size previously described, viz. about five inches long. Some twenty-five years ago I took swimming in Martlesham Creek two molluscs, which I had never been able to identify in the interim. Now they prove to belong to the present species and, as far as I remember, were swimming horizontally and not vertically. It is practically impossible not to notice the creatures when in motion, but the ditches round the riverwall at Martlesham have always appeared to me absolutely devoid of life.

According to Professor Loven, the egg-case may be compared to a rope twisted in different ways ; and these pale yellow masses we found at Slaughden to be plentiful, by fishing among the water-weeds of the ditch and the adjacent brackish pools.

Düring May we again visited the spot in the hope of securing maturer specimens, but without success.

Upon this occasion hardly any Witches were in motion, but we dredged them, together with numerous dead shells of the same species, from the bottom of the dyke. Acera bullata, seems to be commonest upon the south coast of England ; and, unlike several of its near alhes which prey on small shelled molluscs, its food is stated to consist of ' soft organisms.' Quite possibly ours had resorted to the present Situation for spawning purposes and would laterpassto the river-mudflats, as the ditch in question, to judge by its current, communicated somewhere lower down with the River Aide.

M O R T A L I T Y I N Nonagria MOTHS.—The comparative mortality of pupse of the Bulrush and Reed Wainscot moths, Nonagria typhce, Esp. and N. cannce, Och., is well displayed by the fact that, of seventeen N. cannce that were collected in the Norfolk Broads, all were healthy excepting two, whence parasites emerged singly in September 1930.

Of an equal number of N. tvplice from Norfolk and Suffolk, eight failed to emerge : four produced parasites by October 1930, though that of Oehna ochracea (Gortyna fla.va.go, SV.), does not emerge tili the ensuing June.

The parasites [Melanichneumon saturatorius, Linn.—ED.] of N. cannce are distinguished by a white dot on the thorax and abdomen ; otherwise they are superficially similar to those of 0. ochracea [iCcelichneumon impressor, Zett.—ED.] : large black Ichneumons, with red legs.—E. P . W I L T S H I R E .