Zittel, Handbuch d. Palaeontologic (Palaeozoologie), i. 1876-80, p. 562.
Ehlers, Zeitschr. f. wiss. Zool. xviii. 1868, p. 241.
The Chaetopteridae may have to be placed elsewhere in the system, as they are peculiarly modified, and present features recalling the Cryptocephala, from which it is possible they have descended.
Meyer (Mt. Zool. Stat. Neapel, vii. 1887, p. 669, note) suggests that the tentacular filaments of Cirratulids are really prostomial, but have shifted back on to the peristomium, or even farther.
It is probable that the genital ducts of Sternaspis and Chlorhaemids are modified nephridia.