Amphicteis midas can be up to 30 mm long. It is a southern species known from the English Channel. It has not yet been found in Norwegian waters. 

Type locality

Ilfracombe, Devon, United Kingdom, 0 m.

Key characters

Measurements: Up to 30 mm long.

Number of thoracic chaetigers, excluding paleae: 17

Number of thoracic uncinigers: 14

Number of abdominal uncinigers: 15

Prostomium: With longitudinal ridges and transverse nuchal grooves; two oval patches of eyespots.

Mouth tentacles: Smooth.

Branchiae: Four pairs of branchiae in two groups separated by a distance equal to one branchial base diameter; the four branchiae in each group arranged in rhomboid pattern.

Paleae: Long and stout with curved tips; light yellow in colour; 5–10 chaetae on each side.

Special features: All abdominal segments with rudimentary notopodia.

Pygidium: With two long lateral cirri.

Tube: Layer of organic secretion incrusted with silt and sand, and with shell and plant fragments attached.

Distribution

No confirmed records in Norwegian waters

Look-alikes

Amphicteis midas is similar to Amphicteis ninonae in having stout paleae with curved tips. It can be differentiated from A. ninonae by the colour of the paleae, light yellow compared to dark brown in A. ninonae, and number of paleal chaeta, usually less than 10 compared to usually more than 10 in A. ninonae. Amphicteis midas has a southern (English Channel), shallow (20 m) distribution while A. ninonae is distributed from the Norwegian Sea and into the Arctic Ocean in deeper waters. 

Sources

Gosse PH (1855). Notes on some new or little known marine animals. Annals and Magazine of Natural History, (Series 2) 16:27-35, 305-312 (annelids 31-35, 308-312). http://biodiversitylibrary.org/page/2263862

Hartley JP (1985). The re-establishment of Amphicteis midas (Gosse, 1855) and redescription of the type material of A. gunneri (M. Sars, 1835) (Polychaeta: Ampharetidae). Sarsia 70:4, 309-315

Parapar J, Helgason GV, Jirkov I, Moreira J (2011). Taxonomy and distribution of the genus Amphicteis (Polychaeta: Ampharetidae) collected by the BIOICE project in Icelandic waters. Journal of Natural History 45(23-24): 1477-1499. https://doi.org/10.1080/00222933.2011.558640