Euchone glennoi, 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 : 116-119

Euchone glennoi n. sp.

( Figs 6 A–G, 7)

Material examined. Queensland, Lizard Island: Holotype: AM W.36485 (1/2 crown on SEM), Outer Barrier, Yonge Reef, 14°36′25′′S, 145°37′52′′E, coarse coral rubble, 30 m, 21 Feb 2009. Paratypes: AM W.47336 (on SEM), same collection data; AM W47340, MI QLD 2445 (with half crown).

Comparative material examined. Holotype of Euchone variabilis , AM W.196901, New South Wales, Botany Bay, 33°59′36′′S, 151°12′12′′E, sand, 4 m, 12 Feb 1975. Paratypes of Euchone variabilis , AM W.196902 (7), New South Wales, Botany Bay, 33°59′30′′S, 151°09′36′′E, sand, 8 m, 17 Jan 1975.

Description. Holotype 7.5 mm long (crown 3 mm), 0.8 mm wide, with eight thoracic and 18 abdominal chaetigers. Live specimens not studied. Preserved specimens are white, without pigment. When stained with methyl green, holotype specimen shows biannulate dorsal and ventral glandular bands on each segment in both thorax and abdomen, with darker ventral shields, and single glandular bands on segments in the pre-pygidial area of the posterior abdomen including patches on the lateral flanges surrounding the depression ( Fig. 6 A–C). Body with biannulate segments, autapomorphy for Euchone . Radiolar crown with two semicircular lobes, each with seven radioles. Dorsal and ventral basal flanges absent. Basal membrane short, about a tenth of radiole length (Fig. 7B). Narrow radiolar flanges along radioles (Fig. 7A–C). Radiolar eyes absent. Dorsal lips with short radiolar appendage, dorsal pinnular appendages absent. Ventral lips and parallel lamellae present, ventral sacs absent. Two pairs of ventral radiolar appendages present (Fig. 7A). Posterior peristomial ring collar with dorsal margins fused to faecal groove and ventral margin with short midventral incision (Fig. 7C, E). Narrow glandular ridge present on chaetiger 2, slightly broader on lateral and dorsal sides ( Fig. 6 A–B). Ventral shields indistinct ( Fig. 6 A). Interramal eyespots absent. Thoracic prechaetal and postchaetal lobes well developed, autapomorphies for Euchone . Collar chaetae narrowly-hooded, in two oblique rows (Fig. 7F). Following thoracic chaetigers with slightly elevated notopodia; superior thoracic notochaetae narrowly-hooded, inferior, elongated broadly-hooded chaetae (type B), additional anterior row of bayonet chaetae present (Fig. 7G). Thoracic neuropodial uncini acicular with rows of similar-sized teeth over main fang covering half its length (Fig. 7H), poorly developed breast and long handle ( Fig. 6 D). Companion chaetae absent. Abdominal neuropodia low and inconspicuous, with narrowly-hooded chaetae in transverse rows. Anterior abdominal uncini avicular with rows of similar-sized teeth above main fang, occupying half its length, quadrangular breast, handle absent ( Figs 6 E–F, 7J); posterior chaetigers with similar-sized teeth over main fang, occupying 3/4 of its length ( Figs 6 G, 7K), smaller rectangular breast, handle absent. Abdomen with 10 anterior chaetigers, and posteriorly with pre-pygidial flanged depression of eight chaetigers, lateral flanges surrounding depression joined anteriorly by a flap which is folded inwards, has a straight to rounded medial margin and which, when expanded, is subequal in height to the adjoining lateral flanges ( Figs 6 C, 7L–M). Pygidium as a triangular lobe with an incipient cirrus, half the length of the pygidial lobe ( Figs 6 C, 7L–M). Pygidial eyespots not seen. Tube unknown.

Variation. Paratype smaller (5.5 mm long, 0.5 mm wide), with 19 abdominal chaetigers. Holotype female with eggs in last four thoracic and first two abdominal segments. It also has seven pairs of radioles, whereas one paratype possesses six pairs.

FIGURE 7. Euchone glennoi n. sp., scanning electron micrographs. A. Half of the radiolar crown showing ventral radiolar appendages (arrow); B. Detail of base of radiolar crown with short basal membrane; C. Detail of collar, ventral view, with a ventral incision; D. Anterior end of specimen regenerating radiolar crown; E. Collar, with dorsal margins fused to faecal groove; F. Collar chaetae narrowly hooded; G. Thoracic notochaetae, narrowly-hooded, inferior, elongated broadly-hooded chaetae (type B) and anterior row of bayonet chaetae (arrow); H. Thoracic neuropodial uncini acicular with rows of similarsized teeth over main fang covering half its length; I. Abdominal neuropodial chaetae, narrowly-hooded; J. Anterior abdominal uncini with rows of similar-sized teeth above main fang, occupying half its length; K. Posterior chaetigers with similar-sized teeth over main fang, occupying 3/4 of its length; L. Posterior abdominal uncini with pre-pygidial depression, side view; pygidium with incipient cirrus; M. Flanged pre-pygidial depression with an enlarged rounded anterior margin; pygidial cirrus present.

Remarks. This small Euchone species has several distinctive features that differentiate it from congeners: the presence of a low basal membrane, a posterior peristomial ring collar with a midventral incision, inferior thoracic chaetae of type B, about 18–19 abdominal chaetigers with a pre-pygidial depression in the posteriormost 7–8 chaetigers, provided with raised lateral flanges, and the pygidium bears a pygidial cirrus ( Table 2 ). The most similar species is Euchone variabilis Hutchings & Murray, 1984 , a species common in southeastern Australia, as both species share the same type of inferior thoracic chaetae (type B), greater than seven chaetigers forming the pre-pygidial depression, raised flanges around the pre-pygidial depression, and the presence of an incipient pygidial cirrus ( Table 2 , Fig. 6 F). However, the basal membrane is much shorter the new species (about one tenth of the length of the crown compared to 1/4– 3/4 of the length of radioles in E. variabilis ), the shape of the collar differs (entire in E. variabilis and with a midventral incision in these specimens) and the morphology of the prepygidial anterior flanges is also different (with two triangular flaps on either side of a U-shaped anterior medial gap in E. variabilis , which are absent in these specimens). The staining pattern with methyl blue/green also differs between the two species – the flanged area in Euchone variabilis stains uniformly blue ( Wong et al. 2014), whereas this species displays a single strong glandular band per segment, even on the raised flanges. Other species showing similar features such as eight or more chaetigers occupying the pre-pygidial depression as well as type B inferior thoracic notochaetae include E. cochranae , E. heterochaetosa , E. pallida and E. danieloi n. sp ( Table 2 ). The new species differs from all these by the presence of an incised ventral collar margin (as compared with E. cochranae and E. danieloi n. sp.), the presence of high flanges around the pre-pygidial depression (as compared with the low short rim reported in E. pallida ) and the lack of elongate flaps on either side of the anterior margin of the flanged depression (as compared with their presence reported for E. heterochaeta and E. variabilis ) ( Rullier 1972, Hutchings & Murray 1984, Fitzhugh 2002). Some other characters differentiating the species are shown in Table 2 .

Etymology. This species is dedicated to Glenn Ferguson, for his support and encouragement for one of us (AM), over many years.

Type locality. Lizard Island.

Distribution. Australia (Queensland: Lizard Island).

Habitat. Coral rubble at shallow subtidal depths to 30 m.

Figures

FIGURE 6. Euchone glennoi n. sp. A – C. Preserved specimens stained with methyl blue; A. Anterior thoracic chaetigers with a conspicuous first ventral shield and narrow glandular ridge on chaetiger two (arrow); B. Same, dorsal view; glandular ridge, evident (arrow); C. Posterior abdominal chaetigers and pygidium, lateral view; D. Thoracic acicular uncini; E. Posterior abdominal uncini; F. Drawing, anterior abdominal uncinus; G. Drawing, posterior abdominal uncinus; H. Euchone variabilis, posterior abdominal segments, with flanged pre-pygidial depression, and pygidium.