Lygdamis nasutus, Capa, María, Faroni-Perez, Larisse & Hutchings, Pat, 2015

Capa, María, Faroni-Perez, Larisse & Hutchings, Pat, 2015, Sabellariidae from Lizard Island, Great Barrier Reef, including a new species of Lygdamis and notes on external morphology of the median organ, Zootaxa 4019 (1), pp. 184-206 : 188-198

Lygdamis nasutus n. sp.

( Figs 2–7 )

Type material. Holotype: AM W.47372, Lizard Island, North Point, off Mermaid Cove, 14°39'S, 145°27'E, coral rubble, 20 m. Paratypes: AM W.44467, MI QLD 2424, partially mounted on a SEM stub; AM W.47750, MI QLD 2435.

Comparative material examined. Holotype of Lygdamis giardi ( McIntosh, 1885) BMNH 1885.12.1.6, New South Wales, off Port Jackson, 33°51'S, 151°22'E, 64 m, 3 Jun 1874.

Description. Colour pattern. Live specimens with bright pigmentation pattern on epithelium of operculum, consisting of white opercular lobes with 3–4 orange transverse bands on outer and inner side of opercular lobes ( Fig. 2 A–D) and 7–9 short brown and white transversal bands on ventral side of lobes, flanking the tentacular filaments ( Fig. 2 B). Median organ deep orange at base, becoming paler towards tip, dark ring around the tip with a white pigmented flattened top. Base of opercular lobes, around insertion of median organ, strongly pigmented in black. First two chaetigers with white pigment. Rest of body unpigmented except for red-brown branchiae ( Fig. 2 A, E). Preserved specimens lack white pigmentation (including the top of the median organ, distally dark on preserved specimens, Figs 3D –F, 4A–C) but retain the colour bands on operculum described above, now dark brown instead of bright orange ( Figs 3A –E).

Body. Holotype incomplete but well preserved, 39 chaetigers (32–43), 32 mm long (30–43 mm), and 4 mm maximum width excluding parapodia (6–8 mm); posterior abdominal chaetigers and cauda missing.

Operculum. Operculum completely divided into two free long lobes ( Fig. 2 D) with distal ends oblique ( Figs 2 B, 3A, B). Two rows of golden paleae, outer row with 19 (18–19) pairs of paleae, cylindrical at base and flattened, with curved tips, and some fine thecal sculpture ( Figs 5 A, B, 6A–C); inner row with 7 (7–8) pairs of paleae, cylindrical shafts with blunt tips and smooth surface ( Figs 5 C, 6D, E). Opercular papillae, 10 pairs (10–12), peripheral to outer paleae of each lobe, conical, similar in size except for the 2–3 pairs closer to nuchal spines larger than the rest ( Figs 2 B, 3A–B, D, F, 6A). One pair of brown nuchal spines on each side ( Figs 2 A, C–D, 3C–D), stout, strongly recurved without sharp limbations on concave margin ( Fig. 6 A). Tentacular filaments compound, arranged in 11 rows (11–12) ( Figs 2 B, 3B). Median ridge inconspicuous. Well-developed median organ, arising abruptly from the base of opercular lobes, near edge of upper lip; slightly shorter than lobes. Median organ cylindrical, with a planar, teardrop coronal shape when viewed head on. A row of eyespots along both sides of its stalk ( Figs 3 E–F, 4A–C), and tufts of cilia on its surface, more densely arranged on coronal distal end ( Fig. 4 D–G). Pair of grooved, ringed palps, half the length of opercular lobes ( Fig. 3A–B ).

Thorax. Chaetiger 1 with lobe-shaped neuropodia and elongated cirrus ( Figs 2 B, 3A–B); capillary chaetae with fibres forming distal hood ( Fig. 6 F). Chaetiger 2 with three pairs of elongated triangular-shaped lateral lobes, connecting branchiae to neuropodia ( Figs 2 A–B, 3A); capillary chaetae similar to those in chaetiger 1. About 15 pairs of branchiae present from segment 2 ( Fig. 2 A).

Parathorax. Chaetiger 3–6, with notopodia bearing small, conical dorsal cirrus ( Figs 2 A–B, 3A, C). Two types of notochaetae arranged transversely, six lanceolate (6–7), distally concave, with frayed twisted tips ( Figs 2 B, 5D–E, 6G), and interspersed with minute capillaries (6–7) ( Figs 5 F, 6G). Neuropodia with large, rounded lobes directed anteriorly ( Figs 2 B, 3A); two alternating transverse rows of 6 (5–6) chaetae, lanceolate with frayed tips ( Figs 5 G–H, 6H), and thin capillaries ( Figs 5 I, 6H).

Abdomen. Abdominal notopodia lobe-like, each with a transverse row of uncini decreasing in number posteriorly. Uncini of anterior abdominal chaetigers with 8–9 transverse rows of teeth with characteristic arrangement: single basal tooth, median 5–6 rows with two teeth each (not aligned but alternating), and distal 2–3 rows with 3–4 teeth each ( Figs 5 K–L, 7A–B). Uncini of posterior chaetigers with two rows of seven teeth each, thicker than those of anterior uncini ( Fig. 7 C–D). Abdominal neuropodia with capillaries, arranged in two longitudinal rows; dorsal row with slightly larger chaetae, ornamented with irregular thecal laminar extensions and ventral row with thinner and with fibres forming distal hood ( Figs 5 J, 7E–F). Last 5–7 abdominal chaetigers thinner and compacted ( Figs 2 E, 7G), not bearing chaetae or uncini. Branchiae diminishing in size posteriorly, present to chaetiger 14 (12–18), and absent in posterior-most abdominal chaetigers.

Cauda. Cauda smooth, about the length of ten posterior abdomen segments, with no signs of segmentation but some longitudinal ridges ( Figs 2 E, 7G).

Gut. Straight tube running from mouth to anus, with a broadened structure or ‘proventriculus’ between the last parathoracic segment and the first abdominal. Not obvious in preserved specimens.

Remarks. Lygdamis nasutus n. sp. is distinguished from its congeners by a unique combination of features: well-developed cylindrical median organ distally pigmented, with a flattened, teardrop corona, outer paleae (18–19 pairs) with asymmetrical pointed tips and subtle thecal sculpture, inner paleae (7–8 pairs) with blunt tips and smooth surface, three elongated and pointed lateral lobes on chaetiger 2, and abdominal chaetigers with two types of neurochaetae and notopodial uncini with three or four distal teeth.

The three species of Lygdamis previously reported in Australia are characterised by a small or medium size, conical and unpigmented median organ. In contrast, the new species bears a conspicuous, well-developed, cylindrical and strongly pigmented median organ. Lygdamis nasutus n. sp. is provided with rows of eyespots along both sides of the median organ, whereas L. augeneri Kirtley, 1994 and L. giardi ( McIntosh, 1885) , two of the species previously reported from Australia, bear eyes on the median ridge, not the median organ (free distal end) (Hutchings et al. 2012: Figs 8 A, B), and in the third one, L. wambiri Hutchings et al., 2012 , eyespots seem absent both on the median organ and median ridge. Moreover, L. augeneri and L. giardi bear symmetrical outer paleae, unlike the new species. Other differences between the Australian species of Lygdamis can be found in Table 1.

There are several attributes that are outstanding in L. nasutus n. sp., but seem not to have been noticed and described in other congeners. A comprehensive revision of these features in Lygdamis species and other sabellariids may provide informative characters for taxonomic purposes and phylogenetic reconstruction. These are:

1) The new species has small and conical cirri on the distal dorsal margin of parathoracic notopodia ( Figs 2 B, 3A). These structures have also been described in other Lygdamis species (i.e., L. indicus Kinberg, 1867 sensu Kirtley, 1994 , L. splendidus Lechapt & Kirtley, 1998 , and L. japonicus Nishi & Kirtley, 1999 ) but have often not been reported in the literature.

2) Lygdamis nasutus n. sp. bears chaetae of two different morphologies on abdominal neuropodia ( Figs 5 J, 7E, F), similar to those described in L. curvatus ( Johansson, 1922) and also Bathysabellaria spinifera Lechapt & Kirtley, 1996 . Remaining Lygdamis species have been described with a single type of abdominal neurochaetae (i.e., the other Australian species), but it is probable that in other species this feature has been overlooked.

3) Posterior abdominal chaetigers in L. nasutus n. sp. specimens examined lack uncini in their notopodial tori. Since new abdominal segments are added between the abdomen and the cauda during development ( Eckelbarger 1975), it is possible that uncini are formed after the addition of chaetigers, but it could also be a species specific feature.

4) Abdominal uncini are generally described as having two longitudinal rows of teeth ( Lana & Gruet 1989; Lechapt & Gruet 1993; Kirtley 1994). However, variations to this typical pattern have been found after reviewing the literature, suggesting it has not always been studied in detail. For instance, Lygdamis indicus Kinberg, 1867 , L. giardi , L. wirtzi and L. nasutus n. sp. have up to three or four longitudinal rows of teeth at the distal end of the uncini. Moreover, Lygdamis japonicus Nishi & Kirtley, 1999 , L. augeneri and the new species present a single tooth proximally. This structural variation in uncini has not always been formally described but is clearly visible in species illustrations (e.g., Uebelacker 1984; Nishi & Kirtley 1999; Nishi & Núñez 1999; Hutchings et al. 2012). Other sabellariids, for example Phalacrostemma maloga , have been described as having uncini with three rows of teeth (Hutchings et al. 2012). Moreover, Lygdamis nasutus n. sp. shows a large variation range in the morphology of uncini along the abdominal chaetigers, a character not often commented in the literature. The structural complexity in morphology of uncini is due to the development and linked to differences in chaetoblasts and chaetogenesis ( O’Clair & Cloney 1974; Bartolomaeus 1995, 2002; Hausen 2005) and is considered a diagnostic feature among other polychaete families (e.g., Bartolomaeus 1995, 2002; Garraffoni & Lana 2004; Hausen 2005; ten Hove & Kupriyanova 2009; Capa et al. 2011). Since the variability of uncinial morphology seems to be greater than previously documented among sabellariids, further detailed revisions are required to reveal the morphological traits among species not previously analysed.

5) The presence of an abdominal expansion of the gut often referred to the ‘proventriculus’ (e.g., Kirtley 1994) has been observed in Lygdamis nasutus n. sp. and other Lygdamis species, but not as conspicuous as found in other Sabellariidae (e.g., Hutchings et al. 2012: Fig 14C). Since this organ is involved in the food processing, its morphology and development may be related to some functional traits (i.e., feeding preferences or digestion).

6) The median organ described for this species resemble that described for L. ehlersi ( Caullery, 1913) , L. rayrobertsi Kirtley, 1994 , and Lygdamis wirtzi Nishi & Núñez, 1999 . In these species, the median organ is welldeveloped, arising from the dorsal sagittal suture between opercular lobes and is cylindrical with a planar coronal shape. In at least L. wirtzi , this organ is provided with eyespots on both sides, but these have not been described in the other two species ( Kirtley 1994; Nishi & Núñez 1999; Dos Santos et al. 2014). The new species differs from L. ehlersi in the relative size of the median organ, which is thinner in the former species ( Kirtley 1994). Lygdamis rayrobertsi is distinguished from L. nasutus n. sp. in the morphology of the outer paleae, with more pointed tips in the former. The most similar species is L. wirtzi and both species also share the opercular colour pattern, with a white stalk and dark distal end, and a similar morphology of the parathoracic lanceolate notochaetae with concave blades. Differences between L. nasutus n. sp. and L. wirtzi include the shape of the outer paleae with a thinner and acute tip in the new species and the number of eyespots on the median organ ( L. wirtzi bears only two at the base and L. nasutus n. sp. has numerous ones along both sides of the organ) ( Nishi & Núñez 1999). Lygdamis wirtzi seems to be a larger species (three times the size of L. nasutus n. sp.) also bearing a larger number of paleae than the new species. Even though L. wirtzi was described as presenting over 100 pairs of tentacular filaments, these are clustered in around 13 oblique compound rows ( Nishi & Núñez 1999: Fig. 3 ), a similar number to that found in L. nasutus n. sp.

Lygdamis augeneri Lygdamis giardi Lygdamis wambiri Lygdamis nasutus n. sp.

Colour pattern colourless* some pigmentation on colourless* as described above operculum in some

specimens

Length (mm; excl. 15–20 12–43 14 30–43

cauda)

Max width (mm) 2–3 2–5 2 6–8

Number of outer 42–44 16–20 27–29 18–19

paleae (pairs)

Morphology of outer flattened shafts, flattened shafts, flattened shafts, flattened shafts, margins

paleae distally tapering, with distally tapering͵ with margins symmetrical, asymmetrical, progressively nearly symmetrical nearly symmetrical progressively tapering tapering to acute tip with abruptly pointed tips abruptly pointed tips to acute tip with small fine chaetal sculpture and smooth surface and smooth surface distal denticles

Number of inner 30– 36 10–14 12–16 7–8

paleae (pairs)

Morphology of inner cylindrical, distally cylindrical, distally cylindrical, distally cylindrical, distally

paleae tapering, smooth tapering, smooth tapering, smooth tapering, smooth surface surface surface

......continue on next page Lygdamis augeneri Lygdamis giardi Lygdamis wambiri Lygdamis nasutus n. sp.

Opercular papillae 12 8–12 18 10–12

(pairs)

Nuchal spines 1 1 1 1

(pairs)

Morphology of strongly recurved, strongly recurved, strongly recurved, strongly recurved, margins

nuchal spines margins smooth, margins smooth, margins smooth, smooth, without limbation

without limbation without limbation without limbation

Tentacular filaments 15–19 15– 19 15–30 12–19

(rows)

Median ridge present present, short, not present, as a basal present, as a basal reaching the distal continuation of MO continuation of MO, margin of operculum reaching the distal margin of operculum

Median organ present? small, conical; at small, conical; at large, cylindrical, with junction of lobes of junction of lobes of planar teardrop-shape opercular stalk, as a opercular stalk, as a corona; at junction of lobes continuation of continuation of of opercular stalk. median ridge median ridge

Eyespots present along sides of present on either side absent present along either sides of

median ridge of median ridge median organ

Segment 2 (lateral 3 elongate triangular 3 elongate triangular 3 elongate triangular 3 elongate triangular lateral

lobes)** lateral lobes (short) lateral lobes (short) lateral lobes (long) lobes (long)

Branchiae (pairs) 8 9–10 12 15

Segments 3–6 6 lanceolate chaetae, 7–8 lanceolate chaetae 8 lanceolate chaetae 6–7 lanceolate chaetae and (notochaetae) and 6 capillaries in and 7–8 capillaries in and fine capillaries in 6–7 capillaries in between

between between between

Segments 3–6 4 lanceolate chaetae 5–6 lanceolate chaetae 5 lanceolate chaetae 5 lanceolate chaetae and (neurochaetae) and 4 fine capillaries and 5 fine capillaries and fine capillaries in fine capillaries in between

with thin flattened with compact thecae between

blades with short in between

narrow thecae, in

between

Uncinal rows of 1–3 rows from 2 rows of teeth after a?2 2–3 rows from proximal to teeth proximal to distal end first proximal single distal end on anterior

tooth chaetigers, 2 in posterior

uncini Number of teeth/ 6–8 7–9 8 7

row ......continue on next page

Lygdamis augeneri Lygdamis giardi Lygdamis wambiri Lygdamis nasutus n. sp.

Abdominal one type of capillaries, one type of capillaries, one type of capillaries, dorsal row ornamented with

neuropodia ornamented with ornamented with ornamented with irregular thecal laminar irregular fibres irregular fibres irregular fibres extensions; ventral row (‘pilose type’) (‘pilose type’) (‘pilose type’) with irregular fibres (‘pilose type’)

* Pigmentation may be related to methods of preservation and subsequent storage.

** Short or long is just a relative comparison between the species dealt with herein (based on Hutchings et al. 2012).

Etymology. This species is named nasutus (big-nosed and sensory, in Latin) in reference to the well-developed median organ, considered to have a sensory function.

Habitat. This solitary species was collected at 5–12 m, from coral rubble.

Type locality. Mermaid Cove, Lizard Island, Great Barrier Reef.

Distribution. Only known from Lizard Island. Specimens were collected twice (in 1995 and 2013), in spite of extensive collecting for polychaetes over the last 40 years at Lizard, indicating this species is rare. The type locality is an easily accessible site which has been dived at many times by Pat Hutchings since Lizard Island Research Station was established in 1973.

Figures

FIGURE 2. Lygdamis nasutus n. sp., paratype, AM W. 47750, live. A. Whole specimen, dorsal view, arrowheads point to notopodial cirri; B. Anterior end, lateral view, with median organ protruding from operculum (arrow); C. Anterior end, dorsal view; D. Operculum, frontal view; E. Posterior abdominal chaetigers and cauda, ventral view. Photos by A. Semenov.

FIGURE 3. A – D. Lygdamis nasutus n. sp., holotype, AM W. 47372, preserved. A. Operculum, thoracic and parathoracic chaetigers, lateral view; arrowheads point to notopodial cirri; B. Anterior end, ventral view; C. Same, dorsal view; D. Same, but with exposed well-developed median organ. E – F Paratype AM W. 44467. E. Detail of median organ, dorsal view; F. Cross section of paratypes, showing half of the operculum with whole median organ. Abbreviations: br = branchia, bo = building organ, cn 1 = cirrus neuropodia segment 1, chn 1 = chaetae neuropodium segment 1, dc = dorsal cirrus, es = eyespots, ip = inner paleae, li = lips, m = mouth, mo = median organ, nh = nuchal hook, op = outer paleae, opa = opercular papillae, pa = palp, rtf = row of tentacular filaments, tf = tentacular filaments. Small arrow indicates conical dorsal cirrus. Photo: A – D—E. Wong.

FIGURE 4. Median organ, Lygdamis nasutus n. sp., paratypes, AM W. 44467. A. Lateral view with a close up of the eyespots along its length; B. Details of the distal tip, showing the flat corona; C. Distal end, showing teardrop coronal shape frontal view. D – G. SEM images, AM W. 47750. D. Complete median organ, lateral view; E. Distal end, lateral view; F. Detail of the base of median organ with a few sparsely distributed ciliary tufts; G. Close up of ciliary tufts.

FIGURE 5. Chaetae, Lygdamis nasutus n. sp., paratypes. A. Outer paleae; B. Detail of tips of outer paleae; C. Inner paleae, distal end; D. Notopodium, parathoracic chaetiger; E. Detail of tips of lanceolate parathoracic notopodial chaeta; F. Parathoracic notopodial simple capillaries, interspersed with lanceolate chaetae; G. Neuropodium, parathoracic chaetiger; H. Detail of tips of lanceolate parathoracic neuropodial chaetae; I. Parathoracic neuropodial simple capillaries, interspersed with lanceolate chaetae; J. Abdominal notochaetae (two types); K. Neuropodial abdominal uncini; L. Detail of abdominal uncinus, side view.

FIGURE 6. Chaetae, Lygdamis nasutus n. sp., paratypes, SEM images, AM W. 44467. A. Operculum, lateral view; B. Outer paleae; C. Thecal sculpture, outer paleae; D. Inner paleae; E. Close up of distal end, inner paleae; F. First thoracic neuropodial chaetae; G. Parathoracic notopodia; H. Parathoracic neuropodium. Abbreviations: cn 1 = cirrus neuropodia segment 1, chn 1 = chaetae neuropodium segment 1, ip = inner paleae, mo = median organ, nh = nuchal hook, op = outer paleae, opa = opercular papillae, pa = palp.

FIGURE 7. Chaetae, Lygdamis nasutus n. sp., paratypes, SEM images, AM W. 44467. A. Anterior abdominal uncini with number of rows of teeth provided in one uncinus, close up of distal dentition; B. Detached uncini, with number of rows of teeth provided in one uncinus; C. Posterior abdominal uncini; D. Detail of posterior abdominal uncini; E. Abdominal notopodium; F. Detail of the two types of abdominal notochaetae; G. Posterior abdominal chaetiger and cauda.

FIGURE 8. Median organ and ridge diversity in Australian Idanthyrsus. A. Idanthyrsus australiensis, AM W. 201770, with conical median organ (MO), eyespots (white arrow) along median ridge (MR); B. Idanthyrsus sp. cf. I. australiensis AM W. 29153, with flattened, triangular median organ; eyespots absent along median ridge; C. Idanthyrsus sp. cf. I. australiensis, AM W. 29125 with flattened, triangular median organ, eyespots present along median ridge; D. Idanthyrsus willora, scanning electron micrograph, with inconspicuous median organ.