Paradialychone ambigua, Capa, María & Murray, Anna, 2015

Capa, María & Murray, Anna, 2015, A taxonomic guide to the fanworms (Sabellidae, Annelida) of Lizard Island, Great Barrier Reef, Australia, including new species and new records, Zootaxa 4019 (1), pp. 98-167 : 140-146

Paradialychone ambigua n. sp.

(Figs 18–19)

Material examined. Queensland, Lizard Island: Holotype: AM W.45165, MI QLD 2444. Paratypes: AM W.44211, MI QLD 2376; AM W.44217, MI QLD 2376 (2, 1 on SEM); AM W.47393, MI QLD 2444 (2, 1 on SEM).

Description. Holotype 5 mm long, 0.3 mm wide, with eight thoracic and 28 abdominal chaetigers. Live specimens with radiolar crown almost transparent with radioles with broad irregular white pigmented bands alternating with thin orange bands, and white radiolar lobes and base (Fig. 18A). Body transparent, with visible yellow gut and bright orange eggs, in gravid females, along the thoracic and midanterior abdominal chaetigers (Fig. 18A). Preserved specimens whitish, opaque, with no pigment in radioles, gut or eggs. Methyl blue stains ethanol-fixed specimens lightly all over body with a darker and not well delimited transverse blue band around the peristomium (Fig. 18B, D–E). Glandular ridge on chaetiger 2 becomes more conspicuous (white) due to pigmentation of anterior thoracic chaetigers (Fig. 18B). Holotype a gravid female. Radiolar crown with semicircular lobes each with five radioles, with long pinnules gradually decreasing in length distally, radioles with long bare filiform tips (Figs 18C, 19A). Dorsal and ventral basal flanges absent (Fig. 19A–B). Basal membrane FIGURE 18. Paradialychone ambigua n. sp. A. Live specimen, holotype, female filled with eggs; B–E. Preserved specimens stained with methyl blue; B. Anterior end with detached crown showing the first ventral shield (white arrow) and glandular ridge on chaetiger 2 (black arrow); C. Detached radiolar crown; D. Whole specimen, showing staining pattern; E. Posterior abdominal chaetigers and pygidium, with cirrus. F. Detail of pygidium and posterior chaetigers; G. Midthoracic notopodia with superior narrowly-hooded chaetae, inferior paleate chaetae with medium length mucro and bayonet chaetae (arrow); H. Thoracic uncini acicular, with rows of teeth diminishing in size, first larger and medially arranged, covering 3/4 of the length of main fang; I. Anterior abdominal uncini avicular, with 4–6 rows of similar-sized teeth, occupying 1/2 the length of main fang; J. Posterior abdominal uncini modified, with main fang surmounted by five rows of almost similar-sized teeth, occupying most of the length of main fang, breast hooked, rectangular, handle absent; K. Drawing, anterior abdominal uncinus; L. Drawing, posterior abdominal uncinus. Photograph A by Alexander Semenov.

FIGURE 19. Paradialychone ambigua n. sp., scanning electron micrographs. A. Anterior end showing half of the crown and anterior thoracic chaetigers; B. Same, shown details of the base of the radiolar lobe, with the dorsal lips and radiolar appendages (arrow), and the collar dorsal margins fused to the faecal groove; C. Anterior end, lateral view, of a specimens with a detached crown; apparent glandular ridge around chaetiger two (arrow); D. Thoracic notopodium with narrowly-hooded superior chaetae, paleate inferior chaetae and an additional bayonet chaetae (arrow); E. Detail of inferior thoracic chaetae, dorsal view and neuropodial uncinus; F. Thoracic uncini with a large medial tooth above main fang and several rows of teeth diminishing in size distally; front view; G. Same, side view; H. Abdominal neurochaetae, narrowly hooded; I. Anterior abdominal uncini with 4–6 rows of similar-sized teeth, occupying 1/2 the length of main fang; J. Posterior abdominal uncini modified, with main fang surmounted by five regular rows of almost similar-sized teeth, occupying most of the length of main fang; K. Posterior abdominal chaetigers and pygidium, with an incipient cirrus.

extends 1/4 the length of radioles; narrow radiolar flanges to tips of radioles (Figs 18C, 19A–B). Two rows of vacuolated cells supporting radioles basally, not prolonged to radiolar flanges. Radiolar eyes absent. Dorsal lips triangular and erect, only slightly longer than wide (Fig. 19B), without dorsal radiolar appendages; one or two pairs of pinnular appendages. Ventral lips and parallel lamellae present; ventral sacs absent. Anterior peristomial ring lobe triangular, slightly exposed beyond collar. Posterior peristomial ring collar with dorsal margins fused to faecal groove, anterodorsal margins entire and ventral margin slightly higher than dorsal, not incised midventrally (Figs 18B, 19A–C). Narrow glandular ridge all around chaetiger 2 (Figs 18B, D, 19B–C). Thoracic ventral shields not conspicuous; first shield with rounded convex anterior margin ( Fig. 17 B). Interramal eyespots absent (Fig. 18D). Collar chaetae narrowly-hooded, arranged in oblique rows. Following thoracic chaetigers with slightly elevated notopodia narrowly-hooded superior chaetae, paleate inferior chaetae with medium length mucro and an additional anterior row of bayonet chaetae (Figs 18G, 19D–E). Six to eight thoracic neuropodial uncini acicular, with 5–6 rows of teeth diminishing in size, first larger and medially arranged, covering 3/4 of the length of main fang (Figs 18H, 19F–G). Companion chaetae absent. Abdominal chaetigers with inconspicuous neuropodia with elongate, narrowly-hooded chaetae (Fig. 19H). Anterior abdominal uncini avicular, with 4–6 rows of similar-sized teeth over 1/2 the length of main fang, breast rectangular and handle absent (Figs 18I, K, 19I); posterior abdominal uncini modified, with main fang surmounted by five regular rows of almost similar-sized teeth, occupying most of the length of main fang (Figs 18J, L, 19J), breast rectangular and hooked, handle absent (Fig. 18J). Pre-pygidial depression absent (Figs 18D–F, 19K). Pygidium conical, with incipient cirrus (Figs 18D–F, 19K); pygidial eyespots not seen. Mucous tube, very thin and fragile with some muddy particles attached.

Variation. Paratypes up to 8 mm long, including a 2 mm crown, and 0.3 wide. Paratypes have five or six radioles on each radiolar lobe. The number of thoracic chaetigers in examined specimens is eight and number of abdominal chaetigers varies between 25 and 32. The holotype is a gravid female with eggs in inferior thoracic and most abdominal chaetigers.

Remarks. The present species shares several of the diagnostic features typically attributed to Chone Krøyer, 1856 , Dialychone Claparède, 1870 and Paradialychone , according to Tovar-Hernandez ′s (2008) revision of the group. The placement of this new taxon into one of them, based on external morphology, is ambivalent and will remain uncertain until new evidence (most likely molecular) is found. Paradialychone ambigua n. sp. shares with other members of Paradialychone the presence of a short radiolar membrane, elongated dorsal lips (also shared with Chone and Dialychone ), dorsal pinnular appendages (also shared with Chone ), pinnules similar in length along radioles, thoracic uncini with teeth occupying 3/4 of the length of main fang and with a proximal larger tooth surmounted by rows of smaller teeth, and the presence of modified posterior abdominal uncini with teeth covering 3/4 of main fang ( Table 5 ). Nevertheless, it does not possess some of the features defined as typical of species of Paradialychone , that are contrarily present in the other genera. For example, similarly to other Chone , Paradialychone ambigua n. sp. does not have a pre-pygidial depression, but unlike Chone , it does possess modified uncini in the posterior abdominal segments ( Table 5 ). Moreover, in anterior abdominal chaetigers the uncini teeth decrease in size distally (unlike members of Paradialychone or Chone ) occupying about one half the length of main fang, similar to the pattern found in Dialychone ( Table 5 ).

This species is therefore characterised by its unique combination of features, highlighted by the dentition of the uncini of anterior abdominal chaetigers, lacking a single proximal tooth larger than the rest over the main fang and instead having rows of teeth decreasing in size distally.

A similar species present in Australian waters is Dialychone australiensis ( Hartmann-Schröder, 1979) , described from Western Australia, but it differs from P. ambigua n. sp. in the presence of a simple pre-pygidial depression (absent in the new species) and the dentition of the anterior abdominal uncini with similar-sized teeth instead of rows of teeth decreasing in size distally. New record of the genus for Australia.

Etymology. The name of this species, from the Latin word “ ambigua ”, refers to the ambiguity of its generic placement due to the mixed combination of morphological traits.

Habitat. Sand with mangrove detritus or seagrass, in depths of 0.5– 24 m.

Type locality. Lizard Island.

Distribution. Australia (Queensland: Lizard Island).

Chone Dialychone Paradialychone Paradialychone

ambigua n. sp.

Sabella aberrans Augener, 1926: 245 –253, fig. 18.

Sabella porifera .— Augener 1914: 106 –109 (in part).

Demonax aberrans .— Knight-Jones & Perkins 1998: 404.

Parasabella aberrans .— Tovar-Hernández & Harris 2010: 14; Capa & Murray 2015.

Material examined. Queensland, Lizard Island, AM W.197045, 14°40′S 145°27′E, Apr 1977; NTM W. 023122 (2), patch reef near lagoon entrance, 14°41′20′′S, 145°28′12′′E, 2 m, 1 Apr 2008; AM W.43880, MI QLD 2331; AM W.43941, MI QLD 2358; AM W.47743, MI QLD 2354; AM W.45162, MI QLD 2446.

Comparative material examined. Holotype of Sabella aberrans Augener 1926 , ZMUC –POL–2115, Little Barrier Island, New Zealand, 55 m, 29 Dec 1914, Dr Th. Mortensen Pacific Expedition.

Description of material examined. Up to 35 mm long and 3 mm wide, 5–8 thoracic and numerous abdominal chaetigers. Live specimens examined completely white ( Fig. 20A–B ) or showing some brown scattered spots on crown and white spots on body ( Fig. 20C ). Preserved specimens with variable colour pattern, some show pigment spots present along longitudinal axis of radioles and groups of pigmented pinnules and brown thorax (pigment absent from ventral shields and neuropodial tori). Spots between neuro- and notopodial rami, superficially resembling interramal eyespots, present in some specimens.

Radiolar crown with semicircular lobes or slightly involuted ventrally ( Fig. 20A ). Dorsal and ventral flanges absent ( Fig. 20A–B ). Basal membrane absent ( Fig. 20A–B ). Radioles with smooth outer margins, without flanges. Around 14–20 vacuolated cells in cross section at base supporting the radioles ( Fig. 20A–B ). Radiolar eyes absent. Dorsal lips with long radiolar appendages and 0–2 dorsal pinnular appendages. Ventral lips and parallel lamellae present; ventral sacs absent. Posterior peristomial ring collar separated by a wide gap, with broad ventral lappets separated by a midventral incision ( Fig. 20A–C ). Fleshy swelling with a transverse ridge, occupying the dorsum of first two chaetigers, forming either two posterior-facing sinuses or pockets separated by the faecal groove or continuous across faecal groove forming one large posterior-facing pocket (autapomorphy for the species, Fig. 20B–C ). Thoracic ventral shields in contact with adjacent neuropodial tori ( Fig. 20A ); first one with anterior margin m-shaped. Interramal eyespots absent. Collar chaetae elongate, narrowly-hooded in two oblique rows. Notopodia as conical lobes; superior thoracic notochaetae elongate, narrowly-hooded, inferior group with two rows of shorter broadly-hooded chaetae of type B. Uncini with around 10 rows of similar-sized teeth above main fang covering more than half its length, well developed breast and medium length handles. Companion chaetae with enlarged subdistal end with dentate appearance, and with thin distal mucro compressed laterally. Abdominal neuropodial chaetae narrowly-hooded in both anterior and posterior rows. Abdominal uncini with around 10 rows of similar-sized teeth above main fang covering more than half its length, well developed breast and short handles. Pygidium with rounded rim around ventral anus, with scattered eyespots present on both sides, only visible in some specimens. Pygidial cirrus absent. Tube not studied.

Remarks. This species is easily distinguished from other congeners by the fleshy swellings on the dorsum of the first two chaetigers ( Augener 1926; Capa & Murray 2015).

Habitat. Natural and artificial hard subtrates, intertidal to 80 m depth (see Capa & Murray 2015, for more information on the ecology and distribution of this species).

Type locality. Little Barrier Island, New Zealand.

Distribution. New Zealand, Australia (Queensland, New South Wales, South Australia, Western Australia).

Figures

FIGURE 17. Notaulax sp. 3, live specimens. A. Radiolar crown showing general colour pattern; B. Detail of radiolar pigmentation, basal membrane edges (white arrows) and radiolar ocelli arranged in compact groups (black arrows); C. Thoracic chaetigers, lateral view, showing collar morphology and chaetal arrangement.

FIGURE 20. A – C. Parasabella aberrans. A – B. Live specimens; A. Anterior end, ventral view; B. Same, dorsal view, showing the fleshy swelling with a transverse ridge on first two chaetigers (arrow); C. Preserved specimens, showing a detail of the dorsal swelling, divided in two by a longitudinal incision; D – F. Parasabella sp. cf. P. japonica live specimens; D. Anterior end, side view; E. Radiolar crown, side view; F. Anterior chaetigers with detached radiolar crown; conspicuous ventral shields separated from neuropodial tori; G – J. Perkinsiana anodina, preserved specimens; G. Anterior end, lateral view. H. Same, dorsal view, showing collar margins separated dorsally; I. Specimen stained with methyl blue, anterior chaetigers, with detached crown, showing the length of thorax (arrow), and the stained ventral shields separated from neuropodial tori; J. Anterior chaetigers showing collar ventral lappets and well developed ventral sacs.

Tables

TABLE 5. Diagnostic features for Chone, Dialychone, Paradialychone and the new species

Basal membrane	long short-long	long	short
Dorsal lips	broadly rounded elongated	elongated	elongated
Dorsal pinnular appendages	present absent	present	present
Pinnules	longest at mid radiole longest at mid radiole	equal in length	equal in length