Paleanotus Schmarda, 1861

Watson, Charlotte & Faulwetter, Sarah, 2017, Stylet jaws of Chrysopetalidae (Annelida), Journal of Natural History 51 (47 - 48), pp. 2863-2924 : 2886-2888

Genus Paleanotus Schmarda, 1861

( Figures 13a–f , 14a, b ; Tables 1, 2)

Type species: Paleanotus chrysolepis Schmarda, 1861

Material examined

Two specimens Paleanotus bellis ( Johnson, 1897) , FMNH 2495, FMNH 2493, Washington, USA, Eastern Pacific (mCT-00097, mCT-00104).

Distribution

Paleanotus comprises temperate and tropical species found globally between ~ 55°N and 52°S.

Habitat

Paleanotus species are found from predominantly shallower waters to ~ 40 m and inhabit crevices of coral and rocky reefs; dead shell middens on sand or mud and among tubiculous polychaete colonies. Species are commonly part of bryozoan, tunicate and algal encrusting accretions on jetty piers and fouling on wooden platforms and hulls of boats ( Watson 2015). There are also many instances of commensal association with invertebrates, e.g. Paleanotus chrysolepis inside the mantle cavity of Mytilus Linnaeus, 1758 (CW pers. obs.); Paleanotus bellis ‘from inside the mantle cavity of Balanus sp. ’ and from ‘branchial cavity of Loxorhynchus grandis ’ (LACM collection data); P. bellis underneath barnacles on pilings at Friday Harbour (McHugh, pers. comm.).

General morphology

Paleanotus species are slender chrysopetalids with larger species attaining up to ~100 segments for ~ 15 mm length and smaller species attaining maturity at <5 mm length ( Watson 2015). The dorsum is completely covered by bright golden to silvery coloured, asymmetrical-shaped main paleae in fans and flattened median fascicles that intersect at mid-dorsum ( Figure 13a ). Sensory structures include a prostomium, fused with the anterior segments, two pairs of complex eyes, moderate sized oval palps, a glandular nuchal fold and well-developed lateral organs ( Watson 2015).

Pharynx and jaws

Paleanotus species possess a relatively short proboscis and a moderately long, partly differentiated pharynx with an anterior constriction and posterior caeca ( Figure 13b–f ). The elongate, slender jaws sit very close to one another but do not interlink along their length. Cross sections illustrate that the posterior halves of the jaws are situated close together, but anteriorly the jaws diverge outwards, revealing broad internal grooves. There is a slight mid-way swelling on the inner margins at the point that the jaws diverge ( Figure 14a, b ). Paleanotus stylets possess brown-coloured distal tips roughened like sandpaper, only visible under a compound microscope ( Watson 2015, figure 6G).

Muscle fibres enhanced with calcium form a discrete ring surrounding the jaws ( Figure 13b–f ). Micro-CT scans, virtually dissected and viewed from the posterior end, illustrate that the ring registers a similar density to that of the jaws ( Figure 13f ). In dorsal top view the calcified section of pharynx is clearly visible as a pair of structures overlying the anterior end of the stylets ( Figure 13b, c, e ). Interestingly, a similar pharyngeal calcification is seen in related taxa (compare figures of Paleanotus , Treptopale , and Hyalopale ).

Figures

Figure 13. Anterior end of Paleanotus bellis ((a) mCT-00097; (b–f) mCT-00104), imaged through micro- CT and rendered in 3D. (a) dorsal view; (b) dorsal view, virtually dissected to expose pharyngeal structures; (c) dorsal view, virtually dissected and rendered with lowered opacity to show position of jaws; (d) dorsal view, virtually dissected to expose pharyngeal structures; (e) lateral view, virtually dissected to expose pharyngeal structures. (f) Body cross section at level of jaws.

Figure 14. Jaws of Paleanotus bellis (mCT-00104), imaged through micro-CT. (a) anterolateral view; (b) dorsal view and cross sections through the jaw along its length.