1911-12.] Structure and Affinities of Branchiomaldcme vincenti. 69 
Systematic Position and Affinities of Branchiomaldane. 
According to Langerhans, Branchiomaldane exhibits unmistakable 
relationship with the Maldanidm, but he placed it in the family Thelethusse 
(Arenicolidse) on account of the presence of gills on a number of the 
posterior segments. Branchiomaldane presents, however, few features of 
resemblance to Maldanids ; their only common characters * are the tubi- 
colous mode of life, the possession of a non-ganglionated nerve cord, and 
the absence of statocysts. The parapodia and chsetse of Branchiomaldane 
exhibit a general similarity to those of certain Maldanids, but they are in 
still closer agreement with those of Arenicola. That the differences 
between Branchiomaldane and the Maldanids are much more striking 
than the resemblances is realised on considering the following features of 
the Maldanidse — the prostomium and paired nuchal organs, the elongate 
non-annulate segments, often with bands of bright colour, the specialised 
pygidium, the simple alimentary canal without caeca, the absence of gills, 
and the dioecious character of each individual. 
It is clear from a consideration of the anatomy of B. vincenti that this 
worm is more closely related to Arenicola than to any other Polychaete, 
and that it must be included in the family Arenicolidae ; but the writer is 
of opinion that the coalescence of the genera Branchiomaldane and 
Arenicola, recommended by Professor Fauvel, is not advisable. Professor 
Fauvel has pointed out that Branchiomaldane presents several points of 
resemblance to a young A. ecaudata, and he regards the former as furnish- 
ing a new case of “ neotenie ” f in Annelids. It may be noted in this con- 
nection that, as these worms live under practically identical conditions, 
some of the similarities may be due to convergence. Further, some of 
the resemblances, cited by Professor Fauvel in support of his argument, 
are not so close as they were believed to be ; for instance, the gills of 
B. vincenti were stated to resemble those of a young A. ecaudata, and the 
nephridia of Branchiomaldane to have the same form as those of Arenicola, 
and to lie in the same segments as in A. grubii ( = branchialis Aud. et 
Edw.) and claparedii ( =pusilla Quatrefages). But the branchial segments 
of B. vincenti are bi-annulate, whereas in Arenicola they are five-ringed ; 
the gills of the former are borne on the annulus behind the chmtigerous 
* An extension of a nephridium through two or more segments occurs occasionally 
also in the Maldanids, e.g., in Proclymene mulleri , in which the nephridia of the eighth 
segment extend backwards into the tenth. See Arwidsson, I., Zool. Jahrb. Alt. Syst., Suppl. 
Bd. ix. (1907), p. 132. But little is known of the nephridia of Maldanidse. 
t A term used by Kollman to designate the abnormal persistence of larval characters in 
an adult. 
