Paleanotus silus, Watson, Charlotte, 2015

Watson, Charlotte, 2015, Seven new species of Paleanotus (Annelida: Chrysopetalidae) described from Lizard Island, Great Barrier Reef, and coral reefs of northern Australia and the Indo-Pacific: two cryptic species pairs revealed between western Pacific Ocean and the eastern Indian Ocean, Zootaxa 4019 (1), pp. 707-732 : 722-724

Paleanotus silus n. sp.

( Figs 1 G; 6A −L)

Type material. Holotype: NTM W.9309, Eastern Indian Ocean, WA, Ashmore Reef, west side, outer reef, Stn. RH 87-22, rubble, 6 m, coll. L. Vail, Apr 1987, (1NE, mid-body section 40 segments, L: 3.5 mm, W: 0.55 mm, ovigerous female).

Other material examined. NTM W. 23731, Arafura Sea, NT, Darwin, East Point, coral head, 0.1 m, coll. C. Watson, Feb 2011, (1, 16NE, male with sperm & oil globules, W: 0.5 mm); NTM W.23711, Kimberley, Adele Island, Stn. K09/10, 33º18, 115º39, 3.5 m, coll. WAM & Woodside Kimberley Survey, Oct 2009, (1NE, mid-body section 9 segments, W: 0.4 mm); NTM W.24187, Andaman Sea, Thailand, Similan Island, dead Acropora corals, 5 m, coll. A. Nateewathana, Feb 1981, (2: 1, 44E, L: 3.7 mm, W: 0.4 mm; 1, 115 NE, mid-body section, L: 10 mm, W: 0.4 mm).

Description (based on holotype and other material where noted). Long, very slender body with small parapodia becoming bead-like when full of gametes; short notochaetal paleae held in tight dense fans, coloured pale gold to transparent (observed in all material examined).

Prostomium with two lateral antenae, median antenna elongate with slight club shaped tip, two pairs large red eyes, two ovoid palps. Discrete nuchal fold not seen but highly glandular area present posterior to prostomium. Segment 1 very compressed laterally with one pair of dorsal and slender ventral tentacular cirri. Notopodium of segment 2 with dorsal cirri same shape, length as tentacular cirri plus fascicle of short, slender paleae with 6–7 ribs. Neuropodium of segment 2 with spinigerous neurochaetal fascicle, ventral cirri absent. Ventral cirri present from segment 3 onwards. Mouth opening ventrally appears as small tuck; stylets slender with brown tips ( Fig. 6 G).

Notochaetae of mid-body notopodium composed of (2) 3–4 pointed lateral paleae with slender, fine serrate margins, with 4−6 (7 ribs); broad, symmetrical 1–2 sub-unit 1 paleae with 7−8(9) ribs ( Fig. 6 A). Main number up to 11, with very shallow, tiny snub-nosed apices; serrate convex margin to apex, tiny hoods may be present. Ribs number 13–15 (16); majority with full length, fine b.l. pattern (e.g., out of 16 ribs, 12 b.l.). Apices of main paleae less asymmetric ( Figs 1 G, 6C). Median paleae number 3, similar length to main paleae with 8, 9, 10 (11) ribs; 1 raised rib plus 1–3 b.l. Median paleae slender, almost symmetrical in shape, medial-most slimmest ( Fig. 6 B), others slightly broader ( Fig. 6 C, F). Dorsal cirri 2/3 length of main paleae.

Neurochaetae of mid-body neuropodium number about 20 with all shafts and compound articles very slender: 2 superior long falcigers plus 1 slightly shorter ( Fig. 6 H, I); mid-group falcigers number about 10; inferior group falcigers about 5. Ventral cirri subulate, comparatively slender ( Fig. 6 D, H–L). Small pygidium with two short anal cirri.

Remarks. Paleanotus silus n. sp. (eastern Indian Ocean), has similar body proportions in common with its sister species P. silopsis n. sp. (western Pacific Ocean). The two species have a relatively narrow body width compared to the length, plus the largest number of segments and potential length compared to all other Paleanotus species treated herein. For example, the only entire specimen of silus possesses 44 segments, length 3.7 mm, width 0.4 mm; another long mid-body section of 115 segments has a length of approximately 10 mm, width 0.4 mm.

Further characters shared by P. s i l us n. sp. and P. silopsis n. sp. include: short neuropodia tucked in under notopodia; main paleae with the majority of their ribs finely raised in the ‘broken line’ pattern and median paleae near symmetrical in shape in comparison to the asymmetrical median seen in other Paleanotus species.

Paleanotus silus n. sp., in comparison to P. silopsis n. sp., possesses more slender median paleae with less number of ribs (10–11vs 12–14: cf Figs 6 B & 7B) and slightly fewer number of main paleae ribs (13–15 vs 14–17). P. s i l u s n. sp. main paleae have a longer serration brow pattern and the shallowest, tiny snub-nosed apices of all species; P. silopsis n. sp. has a finer brow serration and also very small apices ( Fig. 1 G cf 1H). Ventral cirri of P. silus n. sp. appear basally slender ( Fig. 6 D) and broader in P. silopsis n. sp.

All specimens (except the tiny fragment from the Kimberley) are mature with females possessing large eggs (100 µm diameter) and males, large rounded sperm and oil globules. Segments full of gametes often appear beadlike ( Fig. 6 D, E). Falcigerous neurochaetae are very slender with slim articles and minimal serration ( Fig. 6 H–L). Morphological characters in P. s i l u s n. sp. material from all eastern Indian Ocean and Arafura Sea localities agrees, especially the slim median paleae eg. similarity between Ashmore Reef and Andaman Sea specimens (respectively Fig. 6 B & F).

Etymology. The species name silus is from the Latin and refers to the very small ‘pug-nosed’ shape of the apex of the main paleae.

Habitat / Distribution. Paleanotus silus n. sp. is present along the eastern Indian Ocean rim (northern Australia to Andaman Sea, Thailand) and found from coral rubble in 0.1− 6 m.

Figures

FIGURE 6. Paleanotus silus n. sp. A – D: NTM W. 9309: Ashmore Reef, WA. A. Ovigerous female, detail of lateral paleae, subunit 1 palea; B. Micropic of median palea; C. Detail of medial main and median paleae; D. Mid-body segment (neurochaetae omitted); E. Male with sperm and oil globules, micropic of mid-body segment, NTM W. 23731: Darwin, NT; F. Median paleae group, NTM W. 24187: Thailand; G – L: NTM W. 23731: Darwin, NT. G. Anterior end, ventral view; H – L: Neurochaetal types. Abbreviations: roman numerals I – IV = anterior segments 1 – 4; l. a. = lateral antenna, m. a. = median antenna, me = median paleae, mm = medial main paleae, p = palp, s = stylet, su 1 = sub-unit 1 palea. Scale bars: A, C = 30 µm, D, F = 100 µm, E = 250 µm, G = 70 µm, H – L = 10 µm.

FIGURE 1. A. Paleanotus generalized notochaetal fan; B. Main paleae sculptural detail. C – I: Comparative micropics of main palea in Paleanotus new species. C. Paleanotus inornatus n. sp., NTM W. 23684; D. P. adornatus n. sp., NTM. W. 23660; E. P. acquifolia n. sp., NTM W. 23440; F. P. latifolia n. sp., NTM. W. 23710; G. P. silus n. sp., NTM. W. 23731; H. P. silopsis n. sp., NTM W. 23186; I. P. chrysos n. sp., NTM. W. 25641. Abbreviations: b. l = ‘ broken line’sculpture, c = cilia, gl = gland, h. s = horizontal striae, la = lateral paleae, ma = main paleae, me = median paleae, r. r = raised rib, su 1 = sub-unit 1 palea.