This order is represented by the marine Saccocirrus papillocercus from the bays of Sebastopol and Marseilles. It has a small prostomium, a large peristomium, a segmented body, which terminates in two processes armed with adhesive papillae. The two prostomial tentacles contain each a tube with muscular walls, which terminates in the peristome in a saccule. The two tubes are connected by a cross branch. Each somite is provided with a pair of latero-dorsal bundles of setae contained in a sheath, capable of protrusion and retraction. Oblique dorso-ventral muscles are well developed, and cut off two lateral coelomic chambers from a median chamber. Transverse septa are present. The nervous system is wholly contained in the hypodermis. It consists of a supra-oesophageal ganglion, oesophageal commissures, and two ventral cords, the latter being connected by a single transverse commissure in the peristome. Ganglionic (hypodermic) cells cover the supra-oesophageal ganglion above and below, the ventral cords only on their external surface. Two pigmented eye-spots are contained in the supra-oesophageal ganglia, and there is a pair of large ciliated cephalic grooves. The mouth is ventral, the anus dorsal and terminal.
The digestive tract consists of an oesophagus with an intestine constricted where it traverses the septa. Both are ciliated throughout. A dorsal vessel has been observed. A pair of nephridia are present in each somite, and traverse the septa, as in all Oligochaeta. Their external apertures are near the setigerous tubes. The sexes are separate. The testes and ovaries are small cellular masses affixed to the posterior faces of the septa in the intestinal region. Their cells are detached and ripen in the coelome. The sexual products are conveyed outwards by the nephridia. The nephridial apertures in the sexual somites of the male are papilliform, and probably copulatory. The sexual somites of the female contain a pair of vesicles, which are filled with spermatozoa; their ciliated ducts open latero-ventrally.
Marion and Bobretzky, Annelides du Golfe de Naples, A. Sc. N. (6), ii. 1875, p. 69. Nervous system, Fraipont, Archives de Biol. v. 1884. Larva, see Claparede and Metschnikoff, Z. W. Z. xix. 1869, p. 175 ('an undetermined Spionid larva'). Developnent, Repiachoff, Z. A. iv. 1881.
The classification of the Chaetopoda is as follows I. Polychaeta: marine, with the setae implanted in parapodia, there being many setae in a bundle; antennae and palpi usually present on the prostomium; cirri and branchiae on the somites of the body. The sexes, as a rule, separate; development accompanied by a metamorphosis.
(a) Errantia: free and carnivorous. Prostomium large and more or less independent; usually furnished with eyes and well-developed antennae; body seldom divided into regions; parapodia large; pharynx generally protrusible. Aphroditidae, Eunicidae, Nereidae, Syllidae, etc.
(b) Tubicola s. Sedentaria: vegetable feeders; tubicolous; the tube sometimes fixed. Prostomium small; body frequently divided into regions; parapodia small; pharynx short, sometimes eversible, but never armed with teeth. Capitel-lidae, Arenicolidae (= Telethusidae), Chaetopteridae, Chlorhaemidae, Terebellidae, Serpulidae, etc.
II. Oligochaeta. No antennae, parapodia, cirri, or branchiae; setae sometimes absent; hermaphrodite; sexual organs restricted to a limited number of somites; special sexual ducts present; ova laid in a cocoon; no metamorphosis in development; aquatic; limicolous or terrestrial1. Aphanoneura (= Aeolosomidae), Naidomorpha, Chaetogastridae, Discodrilidae (= Branchiobdellay, Enchytraeidae, Tubificidae, etc., Lumbricidae, etc.
III. Chaetopoda ectopcyasitica, ante, p. 609.
IV. Archi-Chaetopoda, ante, pp. 609-10.
For lit. of Oligochaeta, see pp. 200, 208, 212; add. Stole, 'Naidomorpha,' Z. A. ix. 1886; Benham, 'Studies,' etc., Q. J. M. xxvii. (I), 1886.
Polychaeta, Ehlers, Borstenwiirmer, Leipzig, 1863-68; Claparede, Annelides Chetopodes du Golfe de Naples, Geneva, 1868; Supplement, 1870; Id. Recherches sur la Structure des Annelides Sedentaires, 1873 (or in Mdmoires de la Society de Physique de Geneve, vols, xix., xx., xxii.); Marion and Bobretzky, Anndlides du Golfe de Marseilles, A. Sc. N. (6), ii. 1875; Marenzeller, Adriatic Annelids, SB. Akad. Wien, lxix. 1874, lxxii. 1875, lxxxix. 1884, all Abth. 1; Mcintosh, Annelids of Challenger Exped., Challenger Reports, xii. 1885; Langerhans, Wurmfauna von Madeira, Z. W. Z. xxxii. 1879; xxxiii. 1880; xxxiv. 1881; xl. 1884.
De Quatrefages, Histoire Nat. des Annele's, 2 vols, with atlas, Paris, 1865.
Polynoe clava, Bourne (A. G.), Tr. Lf S. ii. pt. 7, 1883; P. cirrata, Kallenbach (Kieler dissert.), Jena, 1883. Oligognathus Boneffiae, Spengel, Mitth. Zool. Stat.
1 The Oligochaeta were formerly divided into the Terricola and the Limicola. The Terricola were distinguished by the presence of a sub-neural blood-vessel, a capillary network surrounding the nephridia, a typhlosole, the presence of nephridia in the same somites as the sexual ducts. But the discovery of new forms and the fact that in the Limicola the nephridia of the genital somites atrophy when the genital ducts develope, have broken down the division. See the account of Lumbricus, pp. 196-212.
2 Branchiobdella, which is usually classed among Hirudinea, is placed by Vejdovsky among Oligochaeta. There is one species, B. varians (Voigt), with several local varieties. It is small (3-12 mm.), parasitic on Astacus, but not in England. Of the eight middle somites, seven are formed of two rings, one large, one small. There is a posterior sucker formed by the modification of post-anal somites. The coelome is roomy and divided by transverse septa. Large cutaneous glands open on the head and sucker, and secrete a sticky adhesive substance. The sub-oesophageal ganglion corresponds to four embryonic ganglia, and there is concentration of ganglia again at the posterior extremity of the cord. There is a pair of large stomatogastric ganglia as in Oligochaeta. The ganglion cells form prominent masses as in Leeches. There are tactile setae on the head. The buccal cavity is armed with two opposing chitinoid teeth, one dorsal, one ventral. Glands open into it. The anus is dorsal. Chloragogen cells (p. 202) are present. There is a dorsal and ventral blood-vessel connected by seven transverse anastomoses, five anterior, two posterior, and an intestinal sinus. The blood-system is closed, the blood colourless in young, yellow or red in adult, specimens.