Chrysopetalum Ehlers, 1864

Watson, Charlotte & Faulwetter, Sarah, 2017, Stylet jaws of Chrysopetalidae (Annelida), Journal of Natural History 51 (47 - 48), pp. 2863-2924 : 2878-2881

Genus Chrysopetalum Ehlers, 1864

( Figures 8a–d , 9a–c ; Tables 1, 2)

Type species: Chrysopetalum debile ( Grube, 1855) Material examined

Three specimens Chrysopetalum sp. 14: NTM W.7463, Madang, New Guinea, SW Pacific (mCT-00006, mCT-00042, mCT-00098); 2 specimens Chrysopetalum debile: NTM W .25562, Crete, Mediterranean Sea (mCT-00043, mCT-00103).

Distribution

Chrysopetalum is the most speciose genus within the paleate subfamily Chrysopetalinae and possesses the largest temperate and tropical geographical range across all world oceans, 64°N to 52°S.

Habitat

Chrysopetalum species possess a body form that is flexible and mobile amongst the epifauna and are found in diverse crevicular habitats among hard substrates, e.g. aggregations of polychaete tubes, barnacles, hydroids, bryozoans, calcareous and noncalcareous algae, sunken mammal bones and rocky and coral rubble, in depth ranges intertidal to ~ 1000 m (Watson and Chatzigeorgiou, Forthcoming). Additional collecting data includes: among Phyllochaetopterus socialis Claparède, 1870 tube communities at low water mark ( Gibbs 1971); inside Eunice Cuvier, 1817 tubes in muddy tidal pools (CW pers. obs.); and habitat ‘mid-tide zone under basalt boulders embedded in sand, feeding on serpulids and terebellids’ (collection data, LACM).

General morphology

Chrysopetalum species have an elongate, relatively slender body shape with asymmetric or symmetric-shaped notochaetal main paleae, with raised tubercules, forming ‘prickly’ or flattened, bright golden or silver coloured fans that imbricate down the dorsum ( Figure 8a, b ). Sensory structures include a prominent prostomium (not fused with anterior segments), two pairs of complex pigmented eyes, ciliated rounded caruncle with pigment spots, large cylindrical palps with distal tip depressions ( Racovitza 1896; Watson 2001) and red pigment spots in live individuals (CW pers. obs.). Chrysopetalum debile is described as possessing complex musculature and well-developed intersegmental and interramal ciliate bands ( Tzetlin et al. 2002). Glandular ventral pads (pigmented in life) are present immediately posterior to the ventral cirri (Watson and Chatzigeorgiou, Forthcoming).

Pharynx and jaws

Chrysopetalum species display a relatively long proboscis and a broad undifferentiated pharynx with posterior caeca. The jaws are very robust, strongly calcified and occupy most of the anterior buccal cavity ( Figure 8b–d ). Stylets sit close to each other along most of their length, diverging slightly outwards anteriorly and ending in pointed and often serrated distal tips (visible under microscope). Chrysopetalum jaws possess a mid-way, diagonally sloping, rounded projection that extends from the outer to inner margin; an inner margin with a raised longitudinal ridge extending to a proximal spur and a unique basal, broad, blunt-ended, flared ‘foot’ ( Figure 9a–c ). A partly calcified muscle is present in the anterior proboscis, faintly encircling the jaws but particularly evident in the anterior pharynx, immediately posterior to the basal plates of the jaws ( Figure 8c ).

Figures

Figure 8. Anterior end of Chrysopetalum debile (mCT-00103) imaged through micro-CT and rendered in 3D. (a) dorsal view; (b) dorsal view, semi-transparent rendering to show position of jaws; (c) dorsal view, virtually dissected to expose pharyngeal structures; (d) Chrysopetalum sp.14 (mCT-00042), lateral view, virtually dissected to expose pharyngeal structures.

Figure 9. Jaws of Chrysopetalum sp.14 (mCT-00042), imaged through micro-CT. (a) ventral view; (b) dorsolateral view; (c) dorsal view and cross sections through the jaw along its length.