ARCHIANNELIDA The Archiannelida or Haplo drili are a small group of simply organized marine, aquatic and terrestrial worms, which have been affiliated by various authors with the Rotifera, the Turbellaria and the Annelida. The most re cent opinion is that they are modified and often degenerate Annelids allied to the Polychaeta. The view taken of the group as a whole must depend upon the number of forms the student elects to include in it. For ex ample E. Reisinger in his survey of the group published in 1925 claims as Archiannelids the gen era Aeolosorna and Pleurophleps usually attributed to the Oligo chaeta ; similarly he includes in that group as the family Cteno drilidae the genera Zeppelinia, Ctenodrilus and Raphidrilus, which P. Fauvel treats as a sub-division of the Polychaete family Cirra tulidae, and again Fauvel regards as a true Polychaete Histriob della, which Reisinger put among the Archiannelida.
The older view that the Archiannelida are primitive forms is no longer generally held : many of the features regarded by the older authors as primitive are due to the persistence into adult life of larval characters or to degeneration, the outcome of a para sitic habit of life. Moreover these putatively primitive features are in most cases equally found in well characterized Polychaetes. Thus the fusion of the nervous system with the epidermis, the presence of bands of cilia, a very simple vascular system, even the absence of chaetae have their counterpart in the Polychaeta. A definition of the group as a whole is rendered impracticable by its heterogeneous nature, and the families are best treated sepa rately.
Fauvel recognizes four families: I. The Dinophilidae; II. The Parergodrilidae; III. The Polygordiidae; IV. The Nerillidae.
The Dinophilidae are small marine Archiannelida without either appendages or chaetae, with bands of cilia and with a short caudal region provided with adhesive glands : there is an unarmed exsertile pro boscis ; the sexes are separate and often a marked sexual dimorphism exists. They have been affiliated with both the Rotifera and the Turbellaria: E. Perrier who created for them the class Trichotoma, re garded them as intermediate between the Turbellaria and the Nemertea. They are probably Annelids which have retained their larval characters. The reproductive processes of Dinophilus gyrociliatus are of great interest and have been much studied.
The Parergodrilidae are terrestrial Archiannelids living in humus and in damp leaves : only one species, Payergodrilus heideri, is known. They are distinctly seg mented, without appendages or bands of cilia, with segmental dorsal glands, with two rows of chaetae of an Oligichaetous type, with a cerebral ganglion, an unseg mented unpaired nerve-cord in direct con tact with the epidermis, a well developed digestive system and several pairs of nephridia. They are hermaphrodite; and they use their exsertile proboscis and chaetae for climbing.
The Polygordiidae are relatively large marine, rarely fresh water, vermiform Archiannelids, more or less cylindrical in shape, usually with a ventral ciliated groove and segmental bands of cilia; with two tentacles and with a pygidium provided with adhesive glands. Polygordius, distinguished from Protodrilus by the absence of the ventral ciliated groove and of distinct lobes to the pygidium, has a very markable development which has given rise to an immense amount of discussion. Protodrilus has hollow tentacles connected with an ampulla at their base, both ter c e l l u l a r and intracellular nephridia and large salivary glands. It is hermaphrodite and there are also complementary males ; the development of the sperm is very unusual. In cirrus the male has in each sexual segment two seminal vesicles and two exsertile penes. dius and one species of drilus are provided with chaetae.
The Nerillidae are distinctly segmented freshwater and marine Archiannelids with pa.ips and often with tentacles; with para podia carrying two bundles of chaetae, between which there is often a cirrus. Troglochaetus is a freshwater worm found in caves. Nerilla and Nerillidium are both marine forms. Nerilla has many points of resemblance to Protodrilus and Saccocirrus. Nerillidium is an intermediate form between Troglochaetus and Nerilla.
(1922) ; E. Reisinger, "Ein landbewohnender Archiannelide. (Zugleich ein Beitrag zur Systematik der Archianneliden") ; Zs. Morphol. Oekol. Tiere, Bd. III. (1925) ; P. Fauvel, "Archianntilides" in "Polychetes sedentaires," etc., Faune de France XVI. (1927), containing a large bibl. incorporated with the general Polychaete bibl. ; the extensive specific synonymies make it easy to pick out the works dealing with the Archiannelida. (C. C. A. M.)