On a Collection of Nemerteans from Singapore
Authors: Punnett R. C. 
Published: April 2021

ABSTRACT
The Nemerteans described below were collected by Mr. F. P. Bedford and Mr. W. F. Lanchester during a year’s stay in and near Singapore. They comprise ten species, nine of which have not hitherto been described. All belong to the order Heteronemertini, whilst eight out of the ten come into the family of the Lineidæ. It is worthy of note that no specimens of Drepanophorus were found, seeing that in collections from adjacent seas, previously described by Bürger (1) and myself (7), they form a marked constituent of the Nemertean fauna. It will be noticed that I have assigned all the Lineidæ here described to the genus Cerebratulus. This I have done not because I am convinced that they approximate more closely in every case to the forms already placed in that genus, but because of the difficulties of distinguishing, in preserved specimens only, the three genera, Lineus, Cerebratulus, and Micrura. This difficulty was dealt with in Hubrecht’s case (5) by recognising in the family only the single genus Cerebratulus. As, however, the family already contains more than eighty species, with the probability of large additions in the near future, it seems expedient to adhere to the present arrangement of genera, in spite of its unsatisfactory character, until the accumulation of anatomical data be sufficient to warrant revision. The caudal appendage forms the chief distinction between the genus Lineus on the one hand and Cerebratulus and Micrnra on the other (the small genera Borlasia and Langia being sufficiently well marked to be left out of account here). Though its presence shows its possessor to be either a Cerebratulus or a Micrura, its absence does not necessarily establish the specimen in question as a Linens, unless a large amount of material is forthcoming, since it is a delicate structure which may easily be broken off. In his monograph Burger (3) attempts to place these genera on a firmer basis by taking into account certain anatomical features, such as the sidefolds usually characteristic of Cerebratulus, the presence or absence of a diagonal muscle layer, and of neurochord, cells. Based mainly on a study of the Neapolitan forms, the attempt is for them fairly successful. For exotic forms, however, it is less so. Thus C. nataus, which closely resembles many of the Mediterranean forms in its general form, its well-marked side-folds, and its swimming habits, differs markedly from them in the absence of neurochord cells and of a diagonal muscle layer. Again, C, brunneus agrees with the genus Micrura in the absence of sidefolds and a diagonal muscle layer, whilst its comparatively large size and stoutness of build incline one to associate it rather with the genus Cerebratulus. The small and slender C. erythrus, again, with its absence of a diagonal muscle layer, might be relegated to the genus Micrura, were it not for the presence of small side-folds and of neurochord cells. Other instances might be taken, but the above are enough to show that Bürger’s system is not altogether satisfactory. However, before we can hope to improve upon it more anatomical evidence must be forthcoming, And, indeed, on many-important points much yet remains to be made out in the species inhabiting our own shores. Especially is this the case with the excretory system, its range, topography, and the position and number of its ducts. We are only acquainted with these details in two of the thirty odd species of Cerebratnlus, and in six or seven cases in nearly the same number of species of Lineus. The figures at the end of this paper will give some idea of the diversities shown by this system, even in members of the same genus. Other features which may prove of taxonomic value, and to which I venture to draw attention in the following list, are: The presence or absence of a frontal organ.The presence or absence of a cephalic vascular loop.The extent of the rhynchocœlom.The minute structure of the cutis.Structure of the cerebral organ.