A connecting link between the Annelida and the Echiuroidea (Gephyrea armata)

Abstract

During the course of a hydrobiological survey of Monterey Bay, California, a series of pelagic organisms was taken a t a depth of approximately 350 M., which appears to be a link connecting the Echiuroidea (Gephyrea armata) on the one hand and the polychaetes on the other. The range in body length is from 5 mm. to 27 mm.; and in an extended condition the anterior end of the body with its palps and cirri, bears a close resemblance to a nereid. The supra-oesophageal gknglia and the ventral nerve cord, with eleven pairs of ganglia, are also strikingly annelidan in character.On the other hand, the spacious coelom, communicating with the exterior by a pair of anterior nephridia, allies it with the gephyreans. The same is likewise true of the gonad, which arises from the eoelomic epithelium surrounding the genital vessel. The various systems are described in detail, and their resemblances to those of other annelids are indicated. This new species, Poeobius meseres, is made the representative of a new family, the Poeobiidae, which, provisionally at least, is included in the Echiuroidea.

Polychaete systematics: Past and present

“…poeobiids. Heath 1930;Robbins 1965). Onychophora and Arthropoda are also segmented (Brusca & Brusca 1990).…”

“…Ilyphagus, see Hartman 1969: 293) or covered with a mucus-sheath {Flabelligera). Recognition of the pelagic, achaetous Poeobiidae may make Flabelligeridae paraphyletic; many features known from the poeobiids match features present in flabelligerids (Heath 1930;Robbins 1965).…”

“…Mackie (1990) recognized 14 different kinds of simple chaetae including a variety of feathered chaetae. POEOBIIDAE Heath, 1930 Main references : Heath 1930;Robbins 1965. Evidence for monophyly: Two septa in an otherwise unsegmented body without parapodia or chaetae.…”

Multiple origins of pelagicism within Flabelligeridae (Annelida)

“…For example, oral tentacles were not reported in the original description of the specimens (Buzhinskaya, 1977) and were not found by other researchers examining specimens from the same location (Salazar-Vallejo and Zhadan, 2007). The ''nephridia" between the segments are actually gonopores and are known from other flabelligerids and acrocirrids, typically referred to as segmental organs, and most easily seen as small papillae projecting into the gelatinous sheath (Heath, 1930;Robbins, 1965;Hobson and Banse, 1981) or between segments in the case of acrocirrids (Banse, 1969). additionally used the relative position of the first chaetiger, the relative size of the second chaetiger, and their pelagic habit to distinguish flotids from flabelligerids.…”

“…There are a few non-phyllodocid pelagic polychaetes, notably, Poeobius meseres Heath, 1930, and Chaetopterus pugaporcinus Osborn et al, 2007. Recently, Burnette et al (2005) placed P. meseres firmly within Flabelligeridae.…”