Contributions to Zoology, 86 (3) – 2017Daniel Martin; Miguel A. Meca; João Gil; Pilar Drake; Arne Nygren: Another brick in the wall: population dynamics of a symbiotic species of Oxydromus (Annelida, Hesionidae), described as new based on morphometry

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In this section, the specimens of Oxydromus living symbiotically with the tellinid bivalves Scrobicularia plana and Macoma cumana in the Atlantic coasts of the Iberian Peninsula are described as a new species. The new species was previously confused with the congeneric Oxydromus humesi, which also lives symbiotically with a tellinid bivalve, Tellina nymphalis, in Congolese Atlantic coasts. To allow comparisons, a morphometric diagnosis of O. humesi and a general morphological and morphometric descriptions of the new species are provided. The type series of the two species are deposited at the Smithsonian Museum (USNM), the Museo nacional de Ciencias Naturales of Madrid (MNCN), the Annelida Polychaeta research collection of the Centre d’Estudis Avançats de Blanes (CEAB.A.P.), the Museu Nacional de História Natural e da Ciência of Lisboa (MUHNAC), the Biological Research Collection of the Departamento de Biologia of the Universidade de Aveiro (DBUA), the Senckenberg Forschungsinstitut und Naturmuseum of Frankfurt (SMF) and the National Museum of Wales, Cardiff (NMW).

Taxonomic account

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Family Hesionidae Grube, 1850

Genus Oxydromus Grube, 1855

Oxydromus humesi (Pettibone, 1961) 8453A918-89A8-4EEB-B78D-F9C452A39FA5


Parasyllidea humesi Pettibone, 1961. Pettibone (1961): figs. 4a-4h.

Oxydromus humesi (Pettibone, 1961). Martin et al. (2015) 434-441, figs. 4 (A, C, E), 5 (C, D, E, H) - 6 (A, C) - 7.


Material examined. Paratypes: USNM 30012, ca. 50 specimens fixed in formalin and preserved in 70% ethanol, Loango, Republic of Congo. (West Africa, approximately 4°37’42.6”, 11°49’30.0”); intertidal, mangrove muddy bottoms.


Morphometric diagnosis. Based on the average proportions being significant different from O. okupa sp. nov. (Table 8); “long” and “short” refer to parapodia of chaetigers 10 and 15, bearing long and short cirrostyles, respectively. General morphological description same as O. okupa sp. nov. Ratios number of segment and body width (without parapodia) vs. body width (with parapodia) ca. 0.03 and 0.5, respectively. Lateral antennae, palpophores and palpostyles ca. 0.5, 0.25 and 0.4 as long as prostomium length, respectively. Distance between anterior and posterior eyespots ca. 0.21 as long as prostomium length. Distance between anterior eyespots ca. 1.06 as long as that between posterior ones. Long and short dorsal cirrostyles 9 and 8 as long as cirrophores and 1.5 and 1.2 as long as dorsal lobes, respectively. Ventral lobe twice as long as dorsal one. Serration near blade tip less than twice short as blade width.


Table 8. Comparative table of the morphometric measurement proportions in the Iberian and Congolese populations. Differences expressed as percentages, with bold characters indicating significant differences (according to Benjamini and Hochberg, 1995) that may be higher (normal text) or lower (italics) in the Iberian than in the Congolese population. Measurement abbreviations as in Fig. 1. Min: minimum; Max: maximum; Mean: average ± standard deviation; F: Fisher’s F index; p: significance level.

Oxydromus okupa Martin, Meca and Gil sp. nov. D97B28C0-4BE9-4C1E-93F8-BD78F994A8D1

Figures 7-8-9


Fig. 7. Oxydromus okupa sp. nov. Light microscopy micrographs of the holotype in dorsal view. a. Whole worm. b. Anterior mid-body. c. Anterior end. Scale bars are µm.


Fig. 8. Light microscopy micrographs of paratypes in dorsal view. Oxydromus okupa sp. nov. a. Whole worm. b. Anterior mid-body. c. Anterior end. Oxydromus humesi. d. Whole worm. e. Anterior mid-body. f. Anterior end. Scale bars are µm.


Fig. 9. Oxydromus okupa sp. nov. a. Chaetiger 10, posterior view. b. Chaetiger 30, posterior view. c. Typical articulated chaeta. d. Tip of articulated chaeta. Oxydromus humesi. e. Chaetiger 10, posterior view. f. Chaetiger 30, posterior view. g. Tip of articulated chaeta. Scale bar is µm.


Parasyllidea humesi [non Pettibone, 1961]. Martin et al. (2012): 147-148, fig. 2b-2c;

Oxydromus humesi [non (Pettibone, 1961)]. Martin et al. (2015): 434-441, figs. 3, 4 (B, D, F), 5 (A, B, F, G), 6 (B, D), 7.


Material examined: Holotype MNCN 16.01/17760, 1 specimen. Paratypes: MNCN 16.01/17761, 24 specimens. Collected at Río San Pedro (Cádiz Bay, southern Atlantic coast of the Iberian Peninsula, 36°31’56.28”, 6°12’53.28”), intertidal muddy bottoms. All specimens fixed in a 4% formalin–seawater solution and preserved in 70% ethanol.


Additional material: Paratypes: MNCN 16.01/16090, 20 specimens, and CEAB.A.P. 854 A, 20 specimens. MUHNAC, MB29-000343 to MB29-000357, 15 specimens; DBUA0002020.01 to DBUA0002020.13, 13 specimens; SMF 24348 to SMF 24353, 6 specimens; NMW.Z.2017.010.0001 to NMW.Z.2017.010.0006, 9 specimens. Collection, fixation and preservation as for holotype.


General morphological description: Body rusty orange to tan (pale yellowish when preserved), flattened dorso-ventrally, tapering gradually posteriorly. Prostomium subrectangular, without posterior incisions, with two pairs of small reddish-brown eyes (dark brown when preserved), a median ridge, biarticulated palps and three smooth antennae inserted frontally; palpophores cylindrical, palpostyles flask-shaped, about twice the length of palpophores; median antenna very small, button like; lateral antennae conical, with tapering tips. Nuchal organs on lateroposterior prostomial margin. Facial tubercle present. Lip pads absent. Proboscis with two smooth rings and a terminal ciliated one. Jaws absent. Segment 1 dorsally reduced. Parapodial lobes and chaetae absent on segments 1-3. Long and short dorsal cirrophores distinct, ventral ones often indistinct. Dorsal and ventral cirrostyles smooth, distally tapering, slightly alternating short and long, ventral cirri shorter than dorsal, with blunt tip. Parapodia subbiramous from segment 4 onwards; notopodial lobe achaetous, half as long as neuropodial one, alternating elevated and non-elevated, with cirrophore on tip, with up to five aciculae; neuropodial lobes chaetigerous, elongated, subconical, with blunt tips, with long digitiform prechaetal lobe, rounded postchaetal lip, up to three aciculae and numerous compound neurochaetae, with heterogomph shafts, unidentate blades (middle ones much longer than dorsal and ventral) with curved, blunt tips, finely denticulate cutting edges, and a long subdistal spine reaching tip of curved end. One pair of pygidial cirri, similar to dorsal cirri. Pygidial papilla absent. Anus terminal.


Morphometric description. This description is based on the holotype (MNCN 16.01/17760); “long” and “short” refer to parapodia of chaetigers 10 and 15, bearing long and short cirrostyles, respectively). Tables 3 and 6 summarizing population ranges and averages. Body 11.6 mm long, 2 mm wide at the level of chaetiger 10, with 48 segments. Body width (without parapodia) ca. 0.35 as wide as with parapodia, ca. 5.8 as wide as body length. Ratio number of segments vs. body width (with parapodia) = 0.02. Prostomium 287 µm long and 499 µm wide; lateral antenna 226 µm long; palpostyles almost twice as long as palpophores, 150 µm and 74 µm long, respectively. Lateral antennae (226 µm long), palpophores (74 µm long) and palpostyles (159 µm long) 0.8, 0.3 and 0.5 as long a prostomium length, respectively. Distance between anterior eyespots 386 µm; distance between posterior eyespots 356 µm; distance between anterior and posterior eyespots 61 µm. Distance between anterior eyespots ca. 1.09 as long as that between posterior ones. Distance between anterior and between posterior eyespots ca. 0.7 and 0.8 as long as prostomium width, respectively. Distance between anterior and posterior eyespots ca. 0.21 as long as prostomium length. Long and short dorsal lobes similar in size, ca. 210 µm long, tips almost reaching those of ventral lobes. Long and short dorsal cirrophores 41 and 30 µm long, 0.14 and 0.2 as long a dorsal lobe. Long and short dorsal cirrostyles 530 and 512 µm long, ca. 2.4, 2.5 as long as dorsal lobes, and 17.8 and 12.8 as long as cirrophores. Long and short posterior neurochaetal lobe similar in size, ca. 136 µm long. Long and short ventral cirri 206 and 198 µm long, ca. 1.5 as long as posterior neurochaetal lobes.


Remarks: Oxydromus okupa sp. nov. and the morphologically-similar O. humesi share a virtually identical general morphological description, which resulted in them being initially identified as the same species (Martin et al. 2015). There was a single chaetal type, compound ones with heterogomph unidentate blades, which were very similar in both species. The blade serration seemed to be longer in the new species than O. humesi, although this character is highly variable and depends on the observed chaetae so that we strongly suggest not relying on it to differentiate the two species. Specimens corrected for body size (as body width including parapodia) show significant quantitative differences in body measurements (Table 6). Among these differences, the new species has significantly fewer segments and a narrower body width (without parapodia). The head is almost 4% wider, and the cephalic appendages are significantly longer in O. okupa sp. nov., with the latter including dimensions of palpophores (12% longer), palpostyles (14% longer), lateral antennae (19% longer) and distances between eyes (particularly between the anterior and posterior pairs). Some parapodial measurements are also significantly longer (6 to 9.6% long), while the dorsal lobe is the only character being shorter in O. okupa sp. nov. (8.5% and 13% shorter in parapodia bearing long and short cirrostyles, respectively). Moreover, dorsal and ventral lobes are similar in length, with the tip of the former reaching the tip of the latter in O. okupa sp. nov., while the dorsal lobe is much shorter than the ventral one in O. humesi.

Oxydromus okupa sp. nov. differs from O. humesi in body measurement proportions (Table 8). Accordingly, O. okupa sp. nov. has the body width measured without parapodia proportionally narrower with respect to the body width measured with parapodia, and it has also fewer segments. The new species also has the cephalic appendages proportionally longer with respect to prostomium length, particularly in the case of lateral antennae (more than 16% longer), and the distance between anterior and posterior eye pairs is also significantly longer, too. All ratios concerning parapodial measurements are also higher for O. okupa sp. nov., with the most marked differences being at the level of the dorsal cirrostyle vs. the corresponding dorsal lobe (15-22%) and the cirrophore (9-13.5%). Serration near blade tip as long as blade width.


Etymology: The specific epithet “okupa” refers to the Okupas (i.e., the Spanish squatters), a movement that emerged in the 80s as a response to the ever-increasing difficulty of housing opportunities. Okupation means squatting in empty buildings for the own use of the okupas, which implies self-organisation and alternative relationship mechanisms, in a parallel way as symbiotic polychaetes interact with their hosts and with the whole ecosystem.


Geographical distribution: Despite the wide distribution of S. plana in European waters (Santos et al., 2011), Oxydromus okupa sp. nov. is currently only known from the type locality, the intertidal of Río San Pedro saltmarshes, and the nearby subtidal environments of Cádiz Bay (southern Atlantic coast of the Iberian Peninsula).