A monograph of the free and semi-parasitic Copepoda of the British islands.

Abstract

In preparing this monograph it was not part of my plan to enter at all into the consideration of the physiology or internal anatomy of the Oopepoda, but, in compliance with the wishes of some of my friends, expressed while the first volume was passing through the press, I have put together, in the form of a preface to this third volume, a condensed account of some of the more important observations which have hitherto been made on this part of the subject. It will be at once apparent that what I have attempted is nothing more than a general outline, in the production of which I have been greatly indebted to the works of Glaus, Gegenbaur, and Huxley. Had I included the truly parasitic species, in whose anatomy, physiology, and general habits of life so many points of the highest interest occur, I should have been travelling beyond VOL. III. A 2 BRITISH COPEPODA. the professed limits of my work, and have extended this preface beyond reasonable bounds,-on which account those species are noticed in the most cursory manner, and only in elucidation of the proper subject of the memoir. The non-parasitic Copepoda may be described as Entomostraca, having an elongated body of variable form, but generally cylindrical, without a bivalved shell, and showing more or less completely a division of the body into numerous rings, or somites. There are two pairs of antennse, three pairs of prehensile and masticatory, or suctional, mouth organs, and five pairs of feet, adapted chiefly for swimming. The females are mostly fertilized by means of spermatophores ; the ova are usually carried in external ovisacs ; when first hatched the larvse have only three pairs of limbs, and go through several metamorphoses before attaining the mature form. The parasitic species, at one end of the series approach very nearly in structure and general appearance to the non-parasitic ; at the other end they are extremely different, exhibiting, especially in the males, many most remarkable examples of retrograde development, so that without the study of their metamorphoses it would be quite impossible to recognise them as Copepoda, or even as Crustacea of any kind. Yet even in these degraded forms-at any rate in the females--natatory limbs in a very much atrophied condition are almost constantly found. General eorm. -The animal is usually somewhat pear-shaped, rounded in front and tapering towards the GENEEAL ANATOMY. 3 hinder extremity, convex on the dorsal and flattened on the ventral surface. The degree of dorsal convexity, however, is variable, the most common form of the body being sub-cylindrical, but in many cases-notably amongst the Poecilostoma, Siphonostoma, and in some genera of the Harpacticidge (Zaus, Peltidium, Por-ceUidmm, Idya, ScuteUidium) -the animal is markedly flattened, constituting a type of structure almost as widely distinct from the normal Copepoda as are the Isopoda from the Amphipoda, amongst the sessile-eyed Crustacea.But in the genera of Harpacticidge here referred to, the flattened form does not coincide with any deep-seated ...

Two copepod species largely confused: Asterocheres echinicola (Norman, 1868) and A. violaceus (Claus, 1889). Taxonomical implications

“…Except for the length of the caudal ramus, which in A. violaceus is only one and a half times longer than wide and not twice as long as wide, the information that he provided was closer to A. violaceus than to A. echinicola. The confusion came later, when Brady considered the type specimens lent by Norman to be identical with Cyclopicera lata (Brady, 1880). It is very possible that Norman had mixed these two species since those Asterocheres collected later by him and labeled as A. echinicola had the diagnostic characteristics that currently deWned A. echinicola.…”

“…Cyclopicera lata Brady 1872Brady , 1880 Asterocheres echinicola Giesbrecht, 1899 Ascomyzon parvum Sars, 1915 (Figures 3, 4, 5, 10) Material examined Two females (NHM 1911.11.8.47267-268; in alcohol) collected in Firth of Forth (Scotland) by Norman; eight females (NHM) 1911.11.8.47269-273; in alcohol) collected in Firth of Forth (Scotland) by Norman; 5 females (NHM 1911.11.8. 47262-266;in alcohol) …”

“…Four years later, Brady described the species Cyclopicera lata which were living among algae in UK (Brady 1872). However, later on, the same author (Brady 1880) after a re-examination of type-specimens of Ascomyzon echinicola and studying more specimens of Cyclopicera lata collected from dredged material from Ireland, realized that these two species were conspeciWc. Brady's confusing suggestion of favouring the name of Cyclopicera lata to Ascomyzon echinicola in spite of the priority of the latter was followed by Thompson (1889Thompson ( , 1893 and Scott (1893Scott ( , 1898Scott ( , 1900).…”

“…He reported 16 specimens associated with the sponge Halichondria panicea (Pallas) collected from Norfolk in 1959 and compared them with A. echinicola (as Ascomyzon parvum Sars) and A. latus (Brady, 1880). Hamond claimed that there were two diVerent forms among the Norfolk specimens: the latus-like and the echinicola-like with intermediate states.…”

The biology of a commensal copepod,Ascidicola roseaThorell, in the ascidianCorella parallelogramma(Müller)

“…Thus Sars (1921) described the penultimate abdominal segment as 'having the ventral part of the hind edge remarkably thickened and densely clothed with small pricks'-a feature which was also noticed by Brady (1878). These 'small pricks' are in fact tiny sharply pointed spines, and since the region in which they occur is pressed closely against the mucus cord there can be little doubt that they aid in maintaining a firm grip, functioning, in fact, rather like a crampon (Fig.…”