Micropodarke dubia (Hessle, 1925)
|Synonyms: Micropodarke amemiyai, M. trilobata|
|Micropodarke dubia, 14 mm long, found in 5m subtidal sediment clinging to a Zostera marina eelgrass rhizome.|
|(Photo by: Dave Cowles, March 2014 )|
Description: Members of family Hesionidae have segments at least as wide as they are long, and without dorsal elytra, paleae, or other setae. They have two prostomial anteroventral palps and peristomial tentacular cirri. Enlarged ventral cirri on the first several segments is a synapomorphy for this family. Micropodarke dubia has palps with 2 segments of approximately equal length (photo). Some of its setae are compound. It has 2 (not 3) prostomial antennae (photo) and two pairs of eyes (photo). The pharynx (photo) has no jaws nor teeth. The species has 6 pairs of tentacular cirri, 4 of which are on the peristomium (photo). There are large lobes at the bases of the parapodia. The pygidium has two cirri (photo). This individual is colored creamy white ventrally and has brown speckles dorsally.
How to Distinguish from Similar Species:Kefersteinia cirrata and Podarkeopsis brevipalpa have 8 pairs of tentacular cirri. Ophiodromus pugettensis has 3 prostomial antennae (two anteroventral and one between them and slightly dorsal).
Geographical Range: SE Alaska to central California, + Yellow Sea and Japan in the western Pacific.
Depth Range: Low intertidal to 40 m.
Habitat: Fine sand
Biology/Natural History: I found
this individual crawling through the sediment attached to the rhizome of
some subtidal Zostera marina
eelgrass. The family description on the Tree of Life (tolweb.org)
says that the few species studied from the family seem to be predators.
However, this species has no jaws nor teeth in its pharynx, and its gut
was stuffed full of sediment when I found it. The sediment was gradually
voided over several hours as I studied it.
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Pleijel, Fredrik and Greg Rouse, 2005. A revision of Micropodarke (Psamathini, Hesionidae, Polychaeta). Journal of Natural History 39:17 pp 1313-1326
Tree of Life Project (family Hesionidae)
General Notes and Observations: Locations, abundances, unusual behaviors:
Although this animal was anesthetized, it never did stop a slight but continual writhing motion, which made it difficult to photograph with the microscope camera (which requires a slow shutter speed).
Right side view of the head. The long tentacular cirri are visible projecting to the right. The shorter prostomial palps project to the left.
Dorsal view of the head. Note the 4 dorsal eyes and the two 2-segmented prostomial palps with the two segments of similar length. The two prostomial antennae can also be partly seen anteriorly.
This ventral view of the head shows the open mouth in the peristomium. The pharynx is inside the mouth. This species has no teeth on its pharynx, although this would not be visible unless the animal everted its pharynx. The two prostomial antennae can also be seen. The larger, 2-segmented palps are extending from the prostomium directly toward the viewer.
This view of the head (top right) and pygidium (left) shows that the pygidium has two long projecting cirri.
Salish Sea Invertebrates web site provided courtesy of Walla