Ralph I. Smith

Salinity variation in interstitial water of sand at Kames Bay, Millport, with reference to the distribution of Nereis diversicolor

The sheltered beach of Kames Bay, Millport, Isle of Cumbrae, Scotland has been the scene of several important studies on intertidal zonation (Stephen, 1929; Elmhirst, 1931; Watkin, 1942). The last paper is most comprehensive and records in detail the zonation of over twenty species of animals. In the course of the present study I have found Watkins account very accurate, but incomplete in respect to salinity variation in the interstitial water of the sands. My attention was initially directed to Kames Bay in a search for a population of Nereis diversicolor O. F. Muller inhabitating an essentially ‘marine’ environment in respect to salinity. The suitability of Kames Bay was suggested by a statement of Watkin (1942, p. 558):

Three nephromixial patterns in polychaete species currently assigned to the genus Pista (Annelida, Terebellidae)

A comparative morphological study of nephromixial systems in three Californian terebellid polchaetes currently assigned to the genus Pista shows that P. fimbriata has all attributes of the generic type, but that P. pacifica and P. elongata differ markedly. The features of typical Pista include (among others): two pairs of usually unequal branchiae, long‐handled anterior uncini (hooks) of crested avicular (bird‐head‐like) from, muddy, unornamented tubes, one pair of anterior excretory nephromixia (ENMX), and two pairs of separate thoracic reproductive nephromixia (RNMX) with genital papillae on segments VI and VII. A review indicates that P. fimbriata shares these typical features with practically all adequately described Pista species. However, P. pacifica and P. elongata possess three pairs of branchiae, long‐handled uncini of distinctive crochet‐like form, and membranous tubes with apertural hoods. Both have two pairs of ENMX, the first supplied by one pair of ciliated renal funnels, the second by two pairs of such funnels. But they differ in their RNMX: P. pacifica has three pairs of complex RNMX, those on each side united by a common duct. P. elongata has 11–13 pairs of simple RNMX united by common ducts. Although these species do not fit into Pista, no genus has been found to accommodate them. Generic placement is complicated by the fact that no instances of intra‐generic nephromixial variation have been reported in the Terebellidae, although inter‐generic variation is well known. If they are congeneric, this would be the first example of intrageneric RNMX variation in Terebellidae. But if assigned to separate genera or subgenera on the basis of their RNMX, their similarity of anterior uncini might be attributable to parallel or convergent adaptation to life in comparable tubes. More evidence, including molecular analysis, is needed for phylogenetic studies of Terebellidae.

The larval nephridia of the brackish‐water polychaete, Nereis diversicolor

The larval nephridia of the brackish‐water polychaete Nereis diversicolor are described for the first time, and have been studied to determine if their times of development and structural characteristics are consistent with a role in the osmotic regulation of the larva. As shown in serial paraffin sections and by interference‐contrast optics, the nephridia of the three‐setiger larva consist of a single pair of very large metanephridia, arising in the 3rd larval setiger, but with their elongated terminal ducts and coiled ciliated tubules pushed forward into the 2nd setiger; their open metanephrostomes and anterior anchoring filaments lie dorsal to the 2nd set of setae. In contrast, the definitive or juvenile metanephridia, arising in the 4th and subsequently formed setigerous segments, have short terminal ducts and coiled ciliated tubules confined to the segments on which their external nephropores open; their nephrostomes are ventrally located and open into the rear of the next anterior segment. These findings are in contrast to the claims of Edouard Meyer (1887), who described two pairs of closed protonephridia in the 2nd and 3rd larval setigers of Perinereis cultrifera. Although it is not excluded that the single larval pair of metanephridia of N. diversicolor may arise as protonephridia, Meyers claim of two pairs of larval protonephridia was an observational error. The larval nephridia of the marine Platynereis dumerilii resemble in form, but are considerably smaller than, those of N. diversicolor. It is concluded that the hypertrophied pair of larval metanephridia of N. diversicolor is an evolutionary adaptation to existence in habitats of low and unpredictably varying salinity. Their development occurs irrespective of the prevailing salinity; hence, it must be genetically determined.

Notes on gamete production in Lanice conchilega (Annelida, Polychaeta, Terebellidae)

Summary Male and female gametogenesis in Lanice conchilega are described and illustrated as seen by light microscopy. There is no evidence for size-selectivity in the uptake of male gametes by the hypertrophied reproductive nephromixia, since undissociated motile sperm platelets as well as spermatozoa appear to be taken up by the genital funnels, and such funnels show no sexual dimorphism. Maturation of the coelomic oocytes is marked by a change in shape and the appearance of a surface reticulum of ridges.

Mixonephridia or nephromixia in terebellid polychaetes? a clarification

Abstract 1. In recent texts confusion exists in the usage of E.S. Goodrichs terms “mixonephridia” and “nephromixia”, in reference to the segmental organs of polychaete annelids. 2. Goodrich (1945) himself applied the term mixonephridia to the segmental organs that had been described in several families of sedentary polychaetes by Meyer (1887). 3. However, it is shown that the ciliated funnels of these organs in the terebellids Lanice conchilega and Eupolymnia nebulosa in fact contain two distinctly different tissues corresponding to the nephrostomial and coelomostomial components of a nephromixium as defined by Goodrich. 4. Examination of Meyers text and figures shows that this author had in 1887 already presented clear evidence, apparently overlooked by Goodrich, that in terebellids the ciliated funnels of the segmental organs have the dual composition typical of nephromixia in the sense of the terminology introduced by Goodrich and widely, if at times inaccurately, used today.