Acanthopale

Watson, Charlotte & Faulwetter, Sarah, 2017, Stylet jaws of Chrysopetalidae (Annelida), Journal of Natural History 51 (47 - 48), pp. 2863-2924 : 2870

Genus Acanthopale San Martín, 1986

( Figures 2a–d , 3a–c ; Tables 1, 2)

Type species: Acanthopale perkinsi San Martín, 1986

Material examined

Four specimens Acanthopale perkinsi: RMNH, VER 19921, Barbados, Caribbean , W Atlantic (mCT-00001, mCT-00035, mCT-00096, mCT-00105) .

Distribution

Acanthopale perkinsi dwells in coral reefs of the tropical Western Atlantic . Acanthopale is regarded as a monotypic genus with the distinction of being the only record of a chrysopetalid reefal endemic (CW pers. obs.). The species has so far been recorded from five locations, ranging from off the Everglades , Florida , Gulf of Mexico , to Bonaire, Netherland Antilles in the southern Caribbean Sea between ~ 26°S and 12°N .

Habitat

Documented habitats are primarily coralline rubble associated with calcareous algae in shallower waters, with one collection in muddy sand with shells and sponges at 200 m.

General morphology

Acanthopale perkinsi possesses a unique notochaetal morphology consisting of anterior and posterior fascicles of curved, heavily serrated spines and slender paleae that form very ‘prickly’ fans imbricating down the dorsum ( Figure 2a, b ) ( San Martín 1986). A median paleal fascicle is absent in this taxon and leaves the mid-dorsum partly bare ( Figure 2a, b ). Sensory structures include a prominent prostomium (not fused with anterior segments), two pairs of complex pigmented eyes, an ovoid ciliated caruncle with posterior notch and pigment spots; large, cylindrical palps with distal tip depressions and glandular ventral pads present immediately posterior to the ventral cirri (CW pers. obs.).

Pharynx and jaws

Acanthopale displays a relatively long proboscis and a shorter, undifferentiated pharynx with posterior caeca. The paired jaws occupy most of the anterior buccal cavity and sit close to each other along most of their length, diverging slightly outwards anteriorly and ending in attenuated distal tips ( Figure 2b–d ). Jaws have a mid-margin, sloping, rounded, slightly raised ridge; the mid-jaw section anterior to this ridge appears thinly calcified and almost hyaline. The jaws end posteriorly in a flared, triangular base with the raised longitudinal ridge of the inner margin extending to a proximal spur ( Figure 3a–c ). Jaws appear hollow but with a dense core in the section posterior to the ridge ( Figure 3c , cross-sections). Although faint, it is possible that the ‘granular’ band present immediately posterior to the jaws in the anterior pharynx is composed of calcified material ( Figure 2c ); this area was mentioned by San Martín (1986, p. 309) as a possible ‘glandular’ band.

Figures

Figure 2. Anterior end of Acanthopale perkinsi (mCT-00035), imaged through micro-CT and rendered in 3D. (a) dorsal view; (b) dorsal view with lowered opacity to show position of jaws; (c) dorsal view, virtually dissected to expose pharyngeal structures; (d) lateral view, virtually dissected to expose pharyngeal structures.

Figure 3. Jaws of Acanthopale perkinsi (mCT-00035), imaged through micro-CT. (a) dorsal view; (b) ventral view; (c) dorsal view and cross sections through the jaw along its length.