Armandia parva, 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 : 496-500

Armandia parva n. sp.

( Figs 1 , 9–11 )

Material examined. Seven specimens in six samples. Holotype: AM W.44244, MI QLD 2368. Paratypes: AM W.49299, MI QLD 2334 (1); AM W.49300, MI QLD 2374 (2); AM W.44558, MI QLD 2395 (1, on SEM stub); AM W.45407, MI QLD 2443 (1); AM W.49301, MI QLD 2444 (1).

Diagnosis. Prostomium distinctly short, truncated, with conspicuous anterior incision before palpode. Parapodia biramous, with prechaetal lobe and ventral lobe on each parapodium; dorsal cirrus from CH2. Prechaetal lobes with distinct tip, short and oval. Anal tube square-shaped, about as long as wide at base; tube as long as last 2 chaetigers; posterior and ventral margins open, provided with short unpaired anal cirrus, projecting outwardly. Posterior border provided with several elongate paired marginal papillae, some larger and inflated; pair of basal papillae large, slightly shorter than anal tube, provided with several protuberances distally resembling small papillae.

Description. Based on holotype (longest specimen available) complemented with features of paratypes (no specimen was fully complete regarding branchiae and anal tube papillae). Holotype complete, 6.6 mm long and 0.37 mm wide, with 29 chaetigers. Body slender, slightly tapering towards anterior end, posterior end truncated ( Figs 9 A, 10A). Prostomium short, truncated anteriorly, with conspicuous incision before palpode ( Figs 9 A, 10A); palpode well-developed, digitiform. Prostomium with one dorsal eye and two lateral conspicuous reddish eyes. One pair of evaginated nuchal organs; pharynx and oral tentacles not seen ( Fig. 10 A, B). Branchiae highly deciduous, lacking in several chaetigers; present from CH 2 to CH 22–25, absent in last 4–7 chaetigers (considering all type series); short in most chaetigers, not reaching chaetal bundle of next chaetiger ( Fig. 10 C, D), sometimes longer in mid-body and then meeting mid-dorsally ( Fig. 9 F). Parapodia biramous, with prechaetal lobe and ventral lobe on each parapodium ( Fig. 11 A–D); dorsal cirrus present from CH 2. Prechaetal lobe distally rounded provided with distinct oval, short tip directed posteriorly ( Fig. 9 C–G). Lateral reddish eyespots anterior to parapodia on 11 chaetigers ( CH 7–17), those of CH 7 and CH 17 smaller than others. Numerous simple capillary chaetae, arranged in two rows in each noto- and neuropodium; each row with up 6–8 chaetae, chaetae of anterior row shorter; notochaetae longer than neurochaetae, those of first chaetigers longer than those of subsequent chaetigers. Anal tube square-shaped, about as long as wide at base ( Figs 9 H, I, 10E, F); tube as long as last 2 chaetigers; posterior and ventral margins open, provided with short, digitiform unpaired anal cirrus, projecting outwardly. Posterior border in holotype provided with several elongate paired marginal papillae, apparently lacking some ( Fig. 9 H); two paratypes with pair of large basal papillae, slightly shorter than anal tube, provided distally with four protuberances resembling small papillae, one paratype also with two large dorsal inflated papillae, distally pointed, shorter than basal pair ( Fig. 9 I).

Variation. Paratypes are shorter than holotype, ranging from 2.0 to 2.75 mm in length with 25–28 chaetigers. Apart from other features mentioned in the previous section, paratypes show a short prostomium that is truncated anteriorly as it happens in the holotype. Anal papillae (marginal and basal) seem highly deciduous and the anal tube of two paratypes (including that used for SEM, Fig. 10 E, F) appears somewhat contracted. Ventral groove was detected in the expected place along body but it was usually filled by protruding tissue ( Fig. 10 A, B) (consequence of fixation?).

Remarks. Armandia parva n. sp. is a small-sized species (<7 mm in length) and unique among the genus because of the shape and length of the prostomium (short and truncated, with anterior incision), the shape of the prechaetal lobe and the proportions of length/width at base of the anal tube and the features of anal papillae. In general, in Armandia species the prostomium is conical, long and is usually continuous with palpode, sometimes showing a constriction corresponding to the palpophore; on the contrary, the prostomium of A. parva n. sp. appears truncated anteriorly with an incision where the palpode is inserted. This feature is shared by all specimens and does not seem to be an artifact derived of contraction of specimens after fixation. On the other hand, the number and shape of anal papillae vary among specimens, perhaps due to state of preservation or development/regeneration of any given specimen at time of collecting; the shape and proportions of the anal tube is, however, mostly similar among specimens. Interestingly, two paratypes bear a pair of basal papillae that resemble those of A. secundariopapillata and A. casuarina n. sp. (see above) as they are provided with small protuberances resembling secondary papillae, but less numerous (about four) and not as well defined as in the aforementioned species. Anyway, A. parva n. sp. mostly differs from those species because of the shape of the prostomium as it was stated above, and in the shape of the prechaetal lobe that is provided with a tip that is short and conical instead of elongated or triangular.

Etymology. The epithet parva (L.: “small”) refers to the small size of this species when compared to other Armandia species.

Habitat / Distribution. Most specimens were found in the West coast of LI, mostly in front of Casuarina Beach and Vicki’s Reef (e.g. holotype), from the intertidal to 15 m depth in several types of sediments ( Fig. 1 , Table 1).

Figures

FIGURE 1. Map of the study area showing collecting sites of new species described herein. Arrow in Yonge Reef symbol facing to cross-shelf site.

FIGURE 9. Armandia parva n. sp. A – H, holotype AM W. 44244; I, paratype AM W. 49300. A, anterior end, dorsal view; B, anterior end, ventral view. (C – G) Parapodia, ventral (v, left) and dorsal view (d, right) (C – E) and dorsal view only (F – G): C, CH 1; D, CH 2; E, CH 4; F, CH 18 (showing branchia in full); G, CH 23 (C – F, right side of body; G, left side). H, last chaetigers and anal tube, ventral view; I, posterior end, lateral view. A – B, C – E, same scale.

FIGURE 10. Armandia parva n. sp. SEM micrographs (paratype AM W. 44558). A, anterior end, ventral view; B, mouth and ventral groove, detail; C, CH 1 – 3, ventral view; D, CH 6 – 8, ventral view; E, posterior end, lateral view; F, posterior end, ventral view.

FIGURE 11. Armandia parva n. sp. SEM micrographs (paratype AM W. 44558). Parapodia, right side: A, CH 12, ventral view; B, CH 15, anterolateral view; C, CH 16, anterolateral view; D, CH 21, anterolateral view.