Pseudopotamilla aspersa ( Krøyer, 1856 )

Knight-Jones, Phyllis, Darbyshire, Teresa, Petersen, Mary E. & Tovar-Hernández, María Ana, 2017, What is Pseudopotamilla reniformis (Sabellidae)? Comparisons of populations from Britain, Iceland and Canada with comments on Eudistylia and Schizobranchia, Zootaxa 4254 (2), pp. 201-220: 208-210

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Pseudopotamilla aspersa ( Krøyer, 1856 )


Pseudopotamilla aspersa ( Krøyer, 1856)  reinstated

( Fig. 4View FIGURE 4)

Sabella aspersa Krøyer, 1856: 19  –20.

Material examined. Type material: Type ( ZMUCAbout ZMUC POL 00423View Materials), Greenland, by default as two other syntypes are missing. In the description, other data in brackets comes from unpublished drawings and notes of one of Krøyer’s missing syntypes ( RLC, New Royal collection, 322).

Diagnosis. Collar with low, rounded lappets dorsally; dorsal collar margin convex; peristomium slightly exposed laterally; lateral margins of collar V-shaped; handles of companion chaetae twice length of handles of adjacent uncini.

Description. Body length (without radiolar crown) about 31 (48) mm and 2 mm wide ( Fig. 4View FIGURE 4 A). Crown damaged, but Krøyer’s unpublished figures of a lost syntype shows crown length equal to length of 8 thoracic segments and Fig. 4View FIGURE 4 M (copy of Krøyer’s figure) shows a detached crown with one or two single compound eyes per radiole, except dorsal-most. Dorsal lip with bifid appearance, but difficult to see ( Figs 4View FIGURE 4 B–D). Body (damaged posteriorly) with about 60 (90) abdominal segments and 10 thoracic ones. First thoracic segment about twice length of following ones ( Fig. 4View FIGURE 4 B). Dorsal collar margins convex with rounded, low lappets extending above junction of crown and thorax. Oblique lateral collar margins sloping posteriorly, forming each side a wide V–shaped notch showing peristomium ( Fig. 4View FIGURE 4 B). Highest ventral collar margin distant from midline incision in front of small ventral sacs ( Fig. 4View FIGURE 4 B–D). Anterior margin of first ventral shield indented medially, following thoracic shields rectangular, some with indistinct transverse grooves ( Fig. 4View FIGURE 4 D). Thoracic tori with gap between ventral ends and lateral margins of shields ( Fig. 4View FIGURE 4 B). Thoracic tori with about nine avicular uncini each with numerous teeth on crest covering third of main fang, and handle not much longer than length from breast to crest, but adjacent companion chaetae with handle at least twice as long ( Figs 4View FIGURE 4 J–L). First thoracic fascicle with two rows of broadly hooded chaetae, hood a little wider than handle. Superior notochaetae of other thoracic fascicles narrowly hooded (about 5), most longer than inferior ones that are paleate (about 17) with a distal mucro ( Fig. 4View FIGURE 4 F–G). All abdominal chaetae elongate broadly hooded, each with hood twice width of handle ( Fig. 4View FIGURE 4 N, P). Abdominal uncini smaller than those of thorax (shorter handles, Figs 4View FIGURE 4 K–L). Pygidium bilobed. Tube “leathery, tenacious, rather pale or yellowish, covered with sand or bare” ( Krøyer 1856).

Colour. “Yellow or orange with the lateral margins of the first four to ten segments purple” “purple spots on paler radioles (with a single eyespot or two.)” ( Krøyer, 1856). Preserved type pale.

Remarks. The type is one of three specimens of Sabella aspersa  listed in Krøyer’s catalogue of sabellids (RLC). Some of his material was passed on to the Zoological Museum of the University of Copenhagen. Only one specimen remains in the ZMUC collection, which can be regarded as type. Excellent drawings exist (RLC) of a lost syntype and Krøyer shows the unusually long handles of the companion chaetae compared with those of the adjacent uncini ( Fig. 4View FIGURE 4 K–L), the main diagnostic character of the species.

Krøyer mysteriously mentioned “Buccal cirri very minute almost rudimentary, but more numerous than usual (5–6 each side)”. There should be only four, if one counts the enlarged pinnule attached to each dorsal lip (e. g. Fig. 1View FIGURE 1 F). The other ‘cirri’ may have been digitiform regeneration of radioles after damage similar to the protuberances in Fig. 4View FIGURE 4 D, where the left side of the crown has been shed. Krøyer also noted that the faecal groove continues longitudinally across the thoracic ventral shields of one of his specimens. This is not uncommon, and represents a thorax once regenerated from abdominal segments after predation (or scissiparity). He notes that the species is rare so probably not found together in a clump, often an indication of scissiparity.

Malmgren (1867 as Potamilla  ) and McIntosh (1923 as Potamilla  ) wrongly synonymised P. aspersa  with P. reniformis  , but they probably did not see Krøyer’s material and unpublished drawings.

The collar of P. aspersa  differs from P. reniformis  in being low ventrally; in having low, rounded dorsal lappets slightly exposing the peristomium; and dorso-lateral margins with deeper notches. The most consistent difference between P. reniformis  and P. aspersa  is that the latter differs in having each companion chaeta with a handle about twice as long as that of its adjacent uncinus (measured from the breast).

Habitat. Krøyer does not note the habitat of Pseudopotamilla aspersa  . Pseudopotamilla reniformis  , commonly found on the shore, is also found in Greenland, so niche separation may indicate that P. aspersa  is found in deeper water.

Distribution. Greenland.


Zoological Museum, University of Copenhagen














Pseudopotamilla aspersa ( Krøyer, 1856 )

Knight-Jones, Phyllis, Darbyshire, Teresa, Petersen, Mary E. & Tovar-Hernández, María Ana 2017


Sabella aspersa Krøyer, 1856 : 19

Kroyer 1856: 19