Polychaeta

“ Among the Oligochaeta the sexually mature worm is distinguished from the immature worm by the clitellum and by the development of genital setae. Among the Polychaeta the sexual worm is often more marked from the asexual form, so much so that these latter have been placed in different species or even genera. The alteration in form does not only affect structures used in generation; but the form of the parapodia, &c., alter. There are even dimorphic forms among the Syllids where the sexes are, as in many Polychaets, separate. ”

“ There are no renal organs with a wide intercellular lumen, such as occur in the Polychaeta, nor is there ever any permanent association between nephridia and ducts connected with the evacuation of the generative products, such as occur in Alciope, Saccocirrus, &c. In these points the Oligochaeta agree with the Hirudinea. They also agree in the general structure of the nephridia. It has been ascertained that the nephridia of Oligochaeta are preceded in the embryo by a pair of delicate and sinuous tubes, also found in the Hirudinea and Polychaeta, which are larval excretory organs. ”

“ I. Nephridia.—Excretory organs which are undisputed nephridia are practically universal among the Oligochaeta, Hirudinea and Archiannelida, and occur in many Polychaeta. Their total absence has been asserted definitely only in Paranais littoralis. Usually these organs are present to the number of a single pair per somite, and are commonly present in the majority of the segments of the body, failing often among the Oligochaeta in a varying number of the anterior segments. They are considerably reduced in number in certain Polychaeta. ”

“ Oligochaeta.—As contrasted with the other subdivisions of the Chaetopoda, the Oligochaeta may be thus defined. Setae very rarely absent (genus Achaeta) and as a rule not so large or so numerous in each segment as in the Polychaeta, and different in shape. Eyes rarely present and then rudimentary. Prostomium generally small, sometimes prolonged, but never bearing tentacles or processes. Appendages of body reduced to branchiae, present only in four species, and to the ventral copulatory appendages of Alma and Criodrilus. ”

“ Setae.—The setae of the Polychaeta are disposed in two bundles in many genera, but in only one bundle in such forms as have no notopodium (e.g. Syllis) . In some genera the setae are in vertical rows, and in certain Capitellidae these rows so nearly meet that an arrangement occurs reminiscent of the continuous circle of setae in the perichaetous Oligochaeta. The setae vary much in form and are often longer and stronger than in the Oligochaetes. Jointed setae and very short hooks or “uncini” (see fig. 3) are among the most remarkable forms. ”

“ The eggs and spermatozoa in the Polychaeta are discharged into the sea either by rupture of the body-wall or through the nephridia; the male and female elements unite, and the resulting fertilised eggs undergo development, either floating separately in the water, or embedded in jelly, or attached to the body or to the tube of the worm. ”

“ They are divisible into the Haplodrili (q.v.) or Archiannelida, the Polychaeta containing the marine worms, the Oligochaeta or terrestrial and fresh-water annelids (see EARTHWORM) , the Hirudinea or leeches (see Leech) , and a small group of parasitic worms, the Myzostomida (q.v.) .
The distinctive characters of the class Chaetopoda as a whole are partly embodied in the name. They possess (save for certain Archiannelida, most Hirudinea, and other very rare exceptions) setae or chaetae implanted in epidermal pits. ”

“ They contrast with those of the Oligochaeta and Hirudinea by reason of their frequently close association with the gonads, the same organ sometimes serving the two functions of excretion and conveyance of the ova and spermatozoa out of the body. On the hypothesis that such a form as Dinophilus (see Haplodrili) has preserved the characters of the primitive Chaetopod more nearly than any existing Polychaet or Oligochaet, it is clear that the nephridia in the Oligochaeta have preserved the original features of those organs more nearly than most Polychaeta. ”

“ The Oligochaeta contrast with the Polychaeta in the general presence of outgrowths of the septa in the genital segments, which are either close to, or actually involve, the gonads, and into which may also open the funnels of the gonad ducts. These sacs contain the developing sperm cells or eggs, and are with very few exceptions universal in the group. The testes are more commonly thus involved than are the ovaries. It is indeed only among the Eudrilidae that the enclosure of the ovaries in septal sacs is at all general. ”

“ Cobangia, the anus is anterior and ventral. A gizzard is present in a few forms. The buccal cavity is sometimes armed with jaws. The oesophagus is provided often with caeca which in Syllids and Hesionidae have been found to contain air, and possibly therefore perform the function of the fish’s air-bladder. In other Polychaetes one or more pairs of similar outgrowths are glandular. The intestine is provided with numerous branched caeca in Aphrodite.
Reproduction.—As is the case with the Oligochaeta, the Polychaeta furnish examples of species which multiply asexually by budding. ”

“ The Class Chætognatha is represented by one genus and species, Amiskwia sagittiformis. The Class Chætopoda by six genera of the sub-class Polychæta as follows: Miskoia, Aysheaia, Canadia, Worthenella, Pollingeria, Wiwaxia, and Selkirkia; and the Class Gephyrea by four genera: Ottoia, Banffia, Pikaia, and Oesia.
The list of families, genera, and species may be found in the table of contents.
Relations to living annelids.—The discovery of this remarkable group of annelids in the Burgess shale [4] member of the Stephen formation opens up a new point of view on the development of the Annulata. ”

“ Their shape and size varies greatly and is often of use in classification. The setae are organs of locomotion, though their large size and occasionally jagged edges in some of the Polychaeta suggest an aggressive function. ”

“ Polyzoa are very abundant in the Cainozoic beds of Australia, New Zealand, and elsewhere (Fig. 25) . In the Mesozoic series, on the other hand, they are not so well represented; but in Europe and North America they play an important part in forming the Cretaceous and some Jurassic strata by the abundance of their remains.
WORMS (VERMES) .—The hard, calcareous tubes of Sea-worms, the Polychaeta (“many bristles”) are often found in fossiliferous deposits, and sometimes form large masses, due to their gregarious habits of life ”

“ Several forms of cells float freely in the fluid of the coelom. In another sense also the coelom is not a closed cavity, for it communicates in several ways with the external medium. Thus, among the Oligochaeta there are often a series of dorsal pores, or a single head pore, present also among the Polychaeta (in Ammochares) . In these and other Chaetopods the coelom is also put into indirect relations with the outside world by the nephridia and by the gonad ducts. ”

“ From this great and unnatural group, which has survived as "Vermes" even in some quite modern text-books, we can separate off those forms which show a plain segmentation or division of the body internally as well as externally into a series of more or less similar rings, as a Class Chaetopoda. This Class, consisting of the Orders mentioned on p. 241, includes the worms which form the subject of the present chapter—the Oligochaeta, as they were originally called by Grube, on account of the fewness of their chaetae as compared with the number possessed by the majority of the Polychaeta. ”

“ Among many Oligochaeta the dorsal blood-vessel is partly or entirely a double tube, which is a retention of a character shown by F. Vezhdovský to exist in the embryo of certain forms. The blood in the Chaetopoda consists of a plasma in which float a few corpuscles. The plasma is coloured red by haemoglobin: it is sometimes (in Sabella and a few other Polychaeta) green, which tint is due to another respiratory pigment. The plasma may be pink (Magelona) or yellow (Aphrodite) in which cases the colour is owing to another pigment. In Aeolosoma it is usually colourless. ”

“ Coelomoducis.—In this category are included (by Goodrich and Lankester) the gonad ducts of the Oligochaeta, certain funnels without any aperture to the exterior that have been detected in Nereis, &c., funnels with wide and short ducts attached to nephridia in other Polychaeta, gonad ducts in the Capitellidae, the gonad ducts of the leeches. In all these cases we have a duct which has a usually wide, always intercellular, lumen, generally, if not always, ciliated, which opens directly into the coelom on the one hand and on to the exterior of the body on the other. ”

“ These Annelids, unlike their allies the marine Polychaeta, and even their allies on two other sides, the leeches and flatworms, have no complexly organised eyes or other sense organs. They have in fact no organs to which a definite sense can be attached on histological grounds. There is nothing comparable to an eye or to the auditory sacs of other low worms. There are only particular cells of the epidermis, often associated into small groups, and those again into larger associations of rows of such groups of cells. ”

“ Marine flora and fauna of the northeastern United States. Annelida: Oligochaeta. By David G. Cook and Ralph O. Brinkhurst. May 1973, iii + 23 p., 82 figs. For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.
375. New Polychaeta from Beaufort, with a key to all species recorded from North Carolina. By John H. Day. July 1973, xiii + 140 p., 18 figs., 1 table. For sale by the Superintendent of Documents, U.S. Government Printing Office. Washington, D.C. 20402.
376. Bottom-water temperatures on the continental shelf. Nova Scotia to New Jersey. ”

“ There can be little doubt that many {301}Polychaetes are very "plastic," and can adapt themselves to changed conditions of life with considerable ease; for Nereis diversicolor, Arenicola marina, and others live equally well in water of very different densities, and with a different food supply. The great variety in the "habitats," and presumably therefore in their food supply, etc., exhibited by many Polychaetes, as well as the great variation observable in some species of Polynoina, and the close affinity of the species and genera of this sub-family, lead us to the same conclusion. ”

“ By the constant movement of these "fans," which have nearly the same diameter as the tube, a current of water is constantly washed over the animal. The fans represent the notopodia; the neuropodia are bilobed rounded knobs. The region C consists in the adult of about thirty segments, all alike, and less modified than the preceding. The animal is the most truly tubicolous of the Polychaetes, and is much modified on this account. No locomotor chaetae are present, though the great wings and notopodial processes of region C contains chitinous bristles, which, however, do not project ”

“ The amphinomid polychaete Hermodice carunculata (Annelida, Amphinomidae) is a cosmopolitan and ecologically important omnivore inhabiting coral reefs and other habitats throughout the Atlantic Ocean, including the Gulf of Mexico and the Caribbean Sea, as well as the Mediterranean and Red seas [1] . It is known to prey on a diverse suite of reef organisms such as zoanthids [2] , [3] , scleractinian corals [4] - [5] , milleporid hydrocorals [6] , [7] , anemones [8] and gorgonians [6] . ”

“ This family is one which it is exceedingly difficult to define and to split up into different genera. It shades almost imperceptibly into the Perichaetidae on the one hand, and is very hard to differentiate from the Acanthodrilidae on the other. A Cryptodrilid, like any member of the genus Cryptodrilus, with complete circles of chaetae would be a Perichaetid; and as there are species of Perichaeta in which the anterior segments have only a few chaetae in each segment, it is perhaps wrong to separate the two families at all. ”

“ Polychaetes nearly all the Eunicidae secrete a parchment-like tube, and some Polynoids form mud tubes. Among the "sedentary worms" there are forms which merely burrow; while Myxicola readily leaves its gelatinous tube and swims freely; Pectinaria carries its house with it as it moves about, and Polycirrus, a Terebellid, does not form any tube at all.
Owing to their sedentary habits, quite a representative collection of genera may be made, especially at a spring tide, at any seaside place which is provided with a sandy shore, and with rocks and seaweed. ”

“ Some few even among coral-polyps live individual lives, but the greater number follow the community-system. This must always be looked upon as an inferior way of existence.
The most usual way in which polyps increase is by “budding”—not unlike the growth of a plant by buds. A small lump appears on one side of the parent, which increases fast in size, develops a mouth and tentacles, and by-and-by gives birth itself to other buds. The increase of numbers is enormous. One polyp may produce in a short time thousands or even tens of thousands of descendants. ”

“ Apart from the chaetae, there is no peculiarity in the organisation of the family Perichaetidae that is not also met with in the Cryptodrilidae. Even the highly characteristic intestinal caeca so distinctive of the genus Perichaeta itself, as contrasted with Megascolex and the other genera, occur, though more numerously, in the African Millsonia, where there are forty or fifty pairs of them. ”