Aricidea (Acmira) hirsuta, Arriaga-Hernández, Stefan, Hernández-Alcántara, Pablo & Solís-Weiss, Vivianne, 2013

Arriaga-Hernández, Stefan, Hernández-Alcántara, Pablo & Solís-Weiss, Vivianne, 2013, Description and distribution of two new species of Paraonidae (Annelida: Polychaeta) from a lagoon-estuarine ecosystem in the Southern Gulf of Mexico, Zootaxa 3686 (1), pp. 51-64 : 55-58

Aricidea (Acmira) hirsuta n. sp.

Figures 2 A–E, 3A–I

Material examined. Type material. Holotype: National Polychaete Collection, ICML, UNAM (CNP– ICML POH– 02–001): Station 22, 18° 39' 40.40”N, 91° 32' 44”W, 2.6 m. Paratypes: National Polychaete Collection, ICML, UNAM (CNP– ICML POP–02–001): 7 paratypes, one of them coated with gold for SEM studies, Station 22, 18° 39' 40.40”N, 91° 32' 44”W, 2.6 m. Museo Nacional de Ciencias Naturales de Madrid ( MNCN 16.01/14719): 6 paratypes, Station 24, 18° 34' 30”N, 91° 29' 54”W, 3.9 m. Stations located in Términos Lagoon, Campeche, Southern Gulf of Mexico; collected October 20, 2009, by P. Hernández-Alcántara.

Additional material. National Polychaete Collection, ICML, UNAM (CNP– ICML PO–02–040), 1112 specimens: Station 18, 21 specimens, 18° 33’ 40”N, 91° 36’ 10”W, 4 m. Station 22, 201 specimens, 18° 39’ 40”N, 91° 32’ 44”W, 2.6 m. Station 23, 619 specimens, 18° 37’ 00”N, 91° 31’ 10”W, 3.9 m. Station 24, 199 specimens, 18° 34’ 30”N, 91° 29’ 54”W, 3.9 m. Station 25, 5 specimens, 18° 32’ 30”N, 91° 28’ 39”W, 3.8 m. Station 26, 51 specimens, 18° 34’ 30”N, 91° 22’ 40”W, 3.2 m. Station 28, 15 specimens, 18° 40’ 13”N, 91° 26’ 34”W, 3.3 m. All the stations located in Términos Lagoon, Campeche, Southern Gulf of Mexico; collected October 20, 2009, by P. Hernández-Alcántara.

Description. Holotype complete with 102 chaetigers, body length 11.82 mm, width 0.28 mm; paratypes with 61–112 chaetigers, 4.45–14.16 mm long and 0.22–0.35 mm wide. Body wide, dorsoventrally flattened in branchial region, cylindrical in postbranchial region ( Figs 2 A, 3A). Prostomium triangular, distally rounded, slightly wider than long, with no eyes ( Fig. 2 A). Nuchal organs as pair of oblique, deep slits. Median antenna proximally inflated, tapering to short blunt end, extending to posterior margin of prostomium ( Figs 2 A, 3A). Three prebranchial chaetigers ( Figs 2 A, 3A, B). First two notopodial postchaetal lobes short, subtriangular ( Fig. 2 A, 3B), cirriform from chaetiger 3 ( Figs 2 A, 3B), progressively longer in branchial region ( Figs 2 A, 3C) to long, thin, filiform in posterior region ( Fig. 3 E, H, I). Neuropodial postchaetal lobes absent. Ciliated branchiae arranged on dorsum, starting from chaetiger 4, 15 pairs, basally inflated, foliaceous, distally pointed, as long as body width when posterior-most ( Fig. 3 A, C, E). Notochaetae all slender capillaries, with numerous thin filaments on their internal margin. Neurochaetae including slender capillary and modified chaetae from chaetiger 18 ( Figs 2 C, D, E, 3D, F, G). Modified chaetae appearing as curved spines with blunt shaft surrounded by pubescence ( Fig. 3 D); pubescent filaments numerous and inserted in median and distal end of chaetae ( Figs 2 D, 3F); some spines with one or two distal filaments clearly longer ( Figs 2 C, D, 3D). Up to seven modified chaetae per neuropodium ( Fig. 3 G), which increase in size and decrease in number towards posterior end of body; about 14 segments before the pygidium, only one or two modified chaetae per parapodium, stouter and longer ( Fig. 2 B). Pygidium rounded, with three anal cirri of similar size, ventrally situated ( Fig. 3 H, I).

Remarks. Currently the family Paraonidae includes about 150 described species worldwide, of which only 17 species (including the new species described in this study) belong to the subgenus Aricidea (Acmira) . The main characters used to distinguish the different species (see Table 1) are the length and shape of the median antenna and the features of modified neurochaetae (teeth, hood, distal arista and pubescence). A. (Acmira) hirsuta n. sp., can be clearly distinguished from other members of this genus by the short median antenna, which reaches only to the posterior margin of the prostomium, and by the presence of curved unidentate spines with no arista or distal hood, but with dense distal and subdistal pubescence.

The presence of a fine distal arista, distal or subdistal pubescence, and/or a distal or subdistal hood in modified neurochaetae is a common feature in this subgenus. Most of its members (13 species) have some or all of these diagnostic characters (Table 1). In fact, A. (Acmira) simonae Laubier and Ramos , from the Eastern Mediterranean, A. (Acmira) simplex Day , widely distributed in the world seas, A. (Acmira) strelzovi Hartmann-Schröder and Rosenfeldt , from Antarctica, and A. (Acmira) trilobata Imajima , from Japan, are the only species with no hood and with curved spines entirely lacking a distal arista and pubescence.

Pubescence in modified chaetae is a feature less common in the subgenus; even so, in half of the described species, spines with distal or subdistal filaments of different size are present. Particularly, among the species with spines bearing pubescence but with no hood, A. (A.) hirsuta n. sp., can be considered close to A. (Acmira) mirifica Strelzov , from the Antarctic, New Guinea and Southern California, A. (A.) horikoshi Imajima , from Japan and California, and A. (A.) catherinae Laubier and A. (A.) finitima Strelzov , widely distributed in the Atlantic and Pacific Oceans, since they all have neuropodial spines with numerous fine filaments around the apex. But A. (A.) hirsuta n. sp., is distinguished from A. (Acmira) mirifica because the latter bears spines sometimes with a short distal arista and its median antenna is very long (reaching down to chaetiger 6); nevertheless, the irregular distribution found in A. (Acmira) mirifica could suggest that its records belong to a group of species rather than only to one. Besides the presence of modified chaetae starting on posterior chaetigers (27–33) and the fact that it has a narrow sheath in the convex side, A. (A.) horikoshi differs from A. (A.) hirsuta n. sp,. in having long cirriform antennae (reaching down to chaetigers 4–5) and a large number of branchiae (30 pairs). On the other hand, in the modified chaetae of A. (A.) catherinae and A. (A.) finitima , distal pubescence is also present, but they also bear an arista distally attached to the shaft. These distal aristae may be lost easily, and therefore difficult to detect ( Gaston 1984; Montiel et al. 2002), which could be confused for the modified chaetae present in A. (A.) hirsuta n. sp.; however, it is clear that the spines in the new species entirely lack the distal arista or sheath. Besides, in A. (A.) catherinae the median antenna is proximally inflate, tapering to a blunt end, similar in shape to A. (A.) hirsuta n. sp., but longer (reaching to chaetigers 1–3), and its modified chaetae also bear a weakly expanded sheath. Finally, A. (A.) finitima can also be distinguished from the new species, because it bears dorsal papillae on the branchiferous segments, and its median antenna reaches down to chaetigers 1–3.

Etymology. Aricidea (Acmira) hirsuta is named for its particular traits linked to the presence of curved unidentate spines with no arista or distal hood, but with dense distal and subdistal pubescence.

Habitat. In mud and fine sands, depth 2.6 to 4 m, temperature 27.20 to 28.09°C, salinity 33.93 to 35.84 psu, pH 8.2 to 9.2.

Distribution. Central and southern regions of Términos Lagoon, southern Gulf of Mexico.

Figures

FIGURE 2. Aricidea (Acmira) hirsuta n. sp. (A) anterior region, lateral view; (B) posterior region, ventrolateral view; (C) modified posterior neurochaetae, redrawn from scanning electron microscopy photographs; (D) modified postbranchial neurochaetae; (E) modified medium neurochaetae, redrawn from scanning electron microscopy photographs. Scale bars: A, B 0.05 mm; C, E 5 µm, D 15 µm.

FIGURE 3. Aricidea (Acmira) hirsuta n. sp. (A) anterior region, dorsal view; (B) notopodia 1 to 3, lateral view; (C) parapodia 2 to 6, lateral view; (D) modified medium neurochaetae; (E) branchial-postbranchial region, dorsal view; (F) modified posterior neurochaetae; (G) modified postbranchial neurochaetae; (H) posterior end, lateral view; (I) posterior end, ventrolateral view. Scale bars: A 0.2 mm; B, I 0.02 mm; C, H 0.05 mm; D, F, G 5 µm; E 0.01 mm.