Armandia opisthoculata, Moreira, Juan & Parapar, Julio, 2017

Moreira, Juan & Parapar, Julio, 2017, New data on the Opheliidae (Annelida) from Lizard Island (Great Barrier Reef, Australia): five new species of the genus Armandia Filippi, 1861, Zootaxa 4290 (3), pp. 483-502: 493-496

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Armandia opisthoculata

n. sp.

Armandia opisthoculata   n. sp.

( Figs 1 View FIGURE 1 , 7–8 View FIGURE 7 View FIGURE 8 )

Material examined. Nine specimens in three samples. Holotype: AM W.49296, MI QLD 2414. Paratypes: AM W.49297, MI QLD 2373 (4); AM W.49298, MI QLD 2373 (1, on SEM stub); AM W.45402, MI QLD 2441 (3).

Diagnosis. Parapodia biramous, with prechaetal lobe and ventral lobe; dorsal cirrus not present; prechaetal lobe asymmetrical provided with well-defined tip pointing ventro-posteriorly; ventral lobe wide, becoming larger in mid-body to posterior chaetigers. Anal tube short, about as long as last 2–3 chaetigers, opening directed posteroventrally; posterior margin provided with up to 9 pairs of digitiform marginal papillae, one pair of basal papillae and unpaired anal cirrus. One pair of large groups of small reddish spots in ventral side of anal tube at both sides of anal cirrus.

Description. Based on holotype. Specimen complete, 5.7 mm long and 0.5 mm wide, with 27 chaetigers. Body slender, slightly tapering at anterior end and truncated at posterior end ( Figs 7 View FIGURE 7 A, 8A, D). Prostomium somewhat contracted, longer than wide; palpode well developed, with narrow palpophore and palpostyle conical. One dorsal eye and two reddish lateral eyes embedded in prostomium. One pair of ring-shaped nuchal organs; pharynx eversible, tentacles not seen. Segmental limits among chaetigers poorly defined. Branchiae digitiform, present from CH 2 to CH 25, chaetigers CH 26– CH 27 abranchiate; branchiae surpassing level of parapodia of following chaetiger or reaching that of second following chaetiger, not meeting at dorsal midline, decreasing in length towards posterior chaetigers. Parapodia biramous, with prechaetal lobe and ventral lobe on each parapodium ( Figs 7 View FIGURE 7 B–F, 8B, C); dorsal cirrus not seen. Prechaetal lobe asymmetrical, provided with conspicuous tip in ventroposterior angle and directed posteriorly; ventral lobe wide, becoming larger in mid-body to posterior chaetigers. Simple capillary chaetae in two bundles of 5–7 each; notochaetae longer than neurochaetae, as long as branchiae in first chaetigers and longer in subsequent ones. Lateral orange eyespots anterior to parapodia on 11 chaetigers ( CH 7– CH 17); eyespots of CH 1 and CH 17 smaller than others. Ventral groove deep, well defined along all body. Anal tube short, as long as last 2–3 chaetigers, somewhat contracted, about as long as wide ( Figs 7 View FIGURE 7 G, H, 8D, E). Anal tube opening directed posteriorly and ventrally; ventral incision extending posteriorly along all ventral side of tube ( Fig. 8 View FIGURE 8 F). Posterior margin provided with 9 pairs of digitiform marginal papillae of different length (0.5–0.8 times length of anal tube); one pair of basal papillae wider at mid-length and narrower basally, about as long as longer marginal papillae; unpaired anal cirrus ringed, about as long as anal tube. One pair of conspicuous, large groups of small reddish spots in ventral side of anal tube at both sides of anal cirrus, resembling eye spots ( Fig. 7 View FIGURE 7 G, I).

Variation. Paratypes measuring between 4.0 and 7.2 mm in length, 0.3–0.5 mm in width and with same number of chaetigers (27) as holotype. Palpode is long and thin in most paratypes. One paratype shows eight digitiform oral tentacles protruding from mouth. Last 2–3 chaetigers may lack branchiae and are much smaller than the precedent ones ( Fig. 8 View FIGURE 8 D, E). Lateral eyes number 10–11 pairs depending on the specimen. Anal tube is contracted in several specimens and bears about 5–9 paired marginal papillae ( Fig. 8 View FIGURE 8 E, F); paired basal papillae may be longer than others; the pair of ventral anal spots can be easily distinguished.

Remarks. Armandia opisthoculata   n. sp. is characterised by the features of the anal tube which is about as long as wide and is provided with two conspicuous large pigmented spots in the ventral side. Similarly, Armandia sampadae Gopal, Jaleel, Parameswaran and Vijayan, 2016 (Andaman Sea)   also bears two ventral pigmented spots in the anal tube; however, A. sampadae   differs from the new species in having up to 32 chaetigers and lacking anal cirrus, paired marginal papillae are thin and long, and the paired basal papillae are pigmented, leaf-like, and much larger than other papillae. Other species with similar anal tube dimensions (length of tube/width at base) and bearing paired marginal papillae and one pair of basal papillae are A. intermedia   ( Senegal), A. amakusaensis Saito, Tamaki and Imajima, 2000   ( Japan), A. laminosa   and A. paraintermedia   (both also from Lizard Island ). However, A. intermedia   has 29 chaetigerous segments (vs 27), the last three abranchiate (vs last 2), 13 pairs of lateral eyes, and the anal tube has a pair of basal papillae much thicker than marginal papillae; A. amakusaensis   bears an anal tube that is provided with long, thin unpaired cirrus and ventral incision is short (about 1/3 of anal tube length), and most parapodia bear dorsal cirrus ("dorsal small projection" sensu Saito et al. 2000); A. laminosa   has the first three chaetigers with parapodia provided with wide, foliose prechaetal lobe; finally, A. paraintermedia   have parapodia that bear dorsal cirrus and anal tube has an unpaired cirrus that is not ringed.  

Etymology. The epithet opisthoculata   (“ opistho -” G.: “back”, “ oculatus ”, L.: “with eyes”) refers to the pair of conspicuous pigmented spots that resemble eyes in the ventral side of the anal tube.

Habitat / Distribution. Subtidal (5–15 m) in sandy and muddy sand bottoms in three localities north (Holotype, Mermaid Cove ), east ( Watson’s Bay ) and South (Vicki’s Reef) of LI ( Fig. 1 View FIGURE 1 , Table 1).