General Anatomy

TUBE:  One of the key characteristic of this family of polycheatae is their habitation of a self-constructed white translucent calcareous tube.  This tube comprises of a mixture or calcium carbonate (calcite dominated in F. implexa) interposed in a mucopolysaccharide matrix.  These structures are simply a singular unbranched tube in which fine growth rings may be visible (Senowbari-Daryan and Link, 2005).  During early trochophore larval settlement tube is initially open ended, however, eventually the “primary tube” oriented end is sealed leaving the posterior tube end open for extending tentacles into water column for feeding.  Tubes often have a smooth interior and though these worms are not physically attached to tube,they do not normally leave them (Vinni et al., 2008).    

HEAD AND TENTACULAR CROWN:  The soft body of F.implexa typically characteristic of all polychaetaes.  The head region possess two well-developed eyes and is separated into two lobes.  Each lobe comprising of four colourless, white or pinkish pinnate tentacles or radiole.  In each lobe one of these dorsal radiole are modified into a yellow soft cup shaped operculum (Richards, 2008; Van Nieuwenhuijzen, 2011).  These operculum acts to seal tube entrance when tentacles are not extended for feeding or respiration and are often used as a distinguishing feature between related species (Glasby, 2000).  At the base of tentaclular crown a collar of chaeta is present; consisting of both  straight capillary chaeta and bent chaetae with a toothed fin and minute serrated blade, notched on the ventral -underside of animal, (Van Nieuwenhuijzen, 2011).

Tentacular basic anatomy 
Photo by Emma Blacklock

THORAX AND ABDOMEN: Body of F.implexa is segmented and possesses parapodia (fleshy paired appendage often used in locomotion) according to primary characteristics of all annelids.  Its reddish orange body is composed of up to 35 chaetae (bristle) bearing segments.  A thoracic membrane spans the length of the thoracic region from the collar of chaeta.  It consists of 6-9 segments all which possess particularly large chaeata compared to those on the abdomen.  Thorax and abdomen are divided by an unsegmented region before.  Each segment has a parapodia attaching to a pair of rasped shaped plates (uncini), (Richards, 2008; Van Nieuwenhuijzen, 2011).  

Anatomical division of a filograna implexa individual

Photo by Emma Blacklock