Acanthochitona fascicularis (Linnaeus, 1767)

Avila, Sergio P. & Sigwart, Julia, 2013, New records for the shallow-water chiton fauna (Mollusca, Polyplacophora) of the Azores (NE Atlantic), ZooKeys 312, pp. 23-38 : 30-31

Acanthochitona fascicularis (Linnaeus, 1767) Fig. 9

Acanthochites communis Risso, 1826 =

Chiton fascicularis var. major Philippi, 1836 =

Chiton fascicularis var. rubra Issel, 1870 =

Acanthochites discrepans var. minorflava Monterosato, 1878 nomen nudum =

Acanthochites hamatus Rochebrune, 1882 =

Anisochiton discrepans var. elongata Dautzenberg, 1893 =

Anisochiton discrepans var. marmorata Dautzenberg, 1893 =

Anisochiton discrepans var. nigrolineata Dautzenberg, 1893 =

Acanthochites discrepans var. albina Dautzenberg and Durouchoux, 1900 =

Anisochiton discrepans var. viridis Pallary, 1902 =

Acanthochites discrepans var. violaceolimbata Dautzenberg and Durouchoux, 1906 =

Acanthochiton discrepans var. angustivalva Bergenhayn, 1931 =

Acanthochiton heterochaetus Bergenhayn, 1931 =

Acanthochiton communis var. barashi Leloup, 1969 =

Acanthochitona bonairensis Kaas, 1972 =

Chiton echinotus de Blainville, 1825?

Acanthochites carinatus Risso, 1826?

Chiton crinitus Pennant, 1777 sensu Sowerby, G.B. II, 1840!

Chiton discrepans Brown, 1827 sensu Sowerby, G.B. II, 1840!

Records for the area.

MacAndrew (1856), Dautzenberg (1927), Morton (1967), Van Belle (1984), Kaas (1985, 1991), Ávila and Albergaria (2002).

Distribution and biotope.

Found in the North Atlantic from Ireland and Britain, south to Portuguese shores ( Nobre 1931), Azores, Madeira, Selvagens ( Albuquerque et al. 2009), Canary Islands and throughout the Mediterranean Sea ( Kaas 1985, 1991). From the intertidal zone down to 50 m depth ( Van Belle 1984).

Material examined.

Faial (10-23 m depth: DBUA 410, 1 spm; DBUA 433, 1 spm; DBUA 801, 1 spm), Flores (intertidal zone down to 20 m depth: DBUA 240, 2 spm; DBUA 569, 1 spm; DBUA 574, 1 spm; DBUA 577, 2 spm; DBUA 725, 1 spm; DBUA 799, 1 spm), Formigas (6-15 m depth: DBUA 332, 1 spm; DBUA 355, 1 valve), Pico (intertidal zone down to 15 m depth: DBUA 486, 1 spm; DBUA 667, 5 spm; DBUA 671, 1 spm; DBUA 800, 1 spm; DBUA 857/DOP/ML 0050, 1 spm; DBUA 858/DOP/ML0051, 1 spm; DBUA 1047, 1 spm), São Miguel (intertidal zone down to 20 m depth: DBUA 176, 1 spm; DBUA 637, 1 spm; DBUA 683, 1 spm; DBUA 700, 2 spm; DBUA 708/F, 1 spm; DBUA 719, 1 valve; DBUA 721, 1 spm; DBUA 730, 3 spm; DBUA 731, 1 spm; DBUA 732, 2 spm; DBUA 733, 1 spm; DBUA 748, 2 spm; DBUA 751, 1 spm; DBUA 752, 2 spm; DBUA 767, 1 spm; DBUA 794, 2 spm; DBUA 1056, 3 spm).

Fossil record.

No fossil representatives are known from the Azores.

Description (abridged).

Rather large, up to 24 × 15 mm (DBUA 667). Overall colour is variable (black, blue, olive, orange, cream). Valves typically olive-green with reddish blotches; the wide jugal area is usually lighter (cream or beige) with dark longitudinal streaks. Visible portion of the valves is trapezoidal, little or no beak. The central area with faint longitudinal grooves; lateral areas covered with closely-spaced, small round granules in quincunx and forming radiating rows. Girdle broad and densely covered with short spicules, with 18 large tufts of spines arranged around the head and at the sutures. One specimen from the Azores had a girdle that appeared cyan blue in life. There is a distinct marginal fringe of small tapered spicules.

Remarks.

This is the largest chiton in the Azores, commonly found under stones buried in pebbles or in sand, in shallow water, sometimes in groups of two or three specimens. Acanthochitona fascicularis is particularly variable in colour.