Arabella aracaensis, a new species with growth rings on its mandibles, and some remarks on the endoparasitic Labrorostratus prolificus (Polychaeta: Oenonidae) from southeast Brazil Author Steiner, Tatiana M. Author Amaral, Antonia Cecília Z. text Journal of Natural History 2009 2009-10-05 43 41 - 42 2537 2551 http://dx.doi.org/10.1080/00222930903219988 journal article 10.1080/00222930903219988 1464-5262 5217505 Labrorostratus prolificus Amaral, 1977 ( Figures 1–2 ; Table 1 ) Labrorostratus prolificus Amaral, 1977 , p. 285 , figures 1–8. Material examined Araçá Beach , São Sebastião Channel , State of São Paulo , Brazil , 45°24′28″W ; 23°48′55″S , August 1996 , intertidal; 1–10 setigers: ZUEC-POL-1886 ( 4 specimens ), ZUEC-POL-1887 ( 4 specimens ), ZUEC-POL-1888 ( 4 specimens ), ZUEC-POL-1889 ( 4 specimens ), ZUEC-POL-1890 ( 8 specimens ); 11–30 setigers: ZUEC-POL- 1891 ( 4 specimens ), ZUEC-POL-1892 ( 5 specimens ); 31–45 setigers: ZUEC-POL-1893 ( 3 specimens ), ZUEC-POL-1894 ( 4 specimens ). Slides: ZUEC-POL-2174 ( 14 specimens , in different stages), ZUEC-POL-2173 ( 3 specimens , 11–30 setigers), ZUEC-POL-2172 ( 1 specimen , 3 setigers) . Material used for SEM: ( 2 specimens , in different stages). Additional material: 3 slides with jaws (ZUEC-POL-2174A1, ZUEC-POL-2174A2, ZUEC-POL-2174A3), 2 slides with parapodia (ZUEC-POL-2174A4, ZUEC-POL-2174A5). Host: Perinereis cultrifera (Grube 1840) – ZUEC-POL-824. Complete female specimen, 46 mm long, 3 mm wide, 105 setigers. Figure 1. Labrorostratus prolificus . (A) Specimen with 3 setigers (dorsal view, ZUEC-POL- 2172); (B) specimen with 5 setigers (dorsal view, ZUEC-POL-2174); (C) specimen with 7 setigers (dorsal view, and terminal stolon, ZUEC-POL-2174); (D) specimen with 10 setigers (lateral view, ZUEC-POL); (E) specimen with 43 setigers (dorsolateral view, ZUEC-POL). Notes: PR1, first peristomial ring; PR2, second peristomial ring; arrow indicates the triangular simple parapodium. Description Body without evident pigmentation. Smallest specimen 285 µm long, 122 µm wide, three setigers ( Figure 1A ). Largest specimen 3330 µm long, 495 µm wide, 45 setigers. Stage 1 (1–10 setigers). Eyes, jaws, aciculae and setae absent. Prostomium compressed dorsoventrally, with rounded anterior end in specimens with three setigers ( Figure 1A ), and others with a triangular shape ( Figure 1B and C ). First peristomial ring fused to prostomium ( Figure 1D ); second ring well-defined, shorter than (in specimens with more than four setigers) or as long as (in specimens with three to four setigers) the first setigers. Body slightly flattened dorsoventrally, wider in setigers where parapodia are larger. Setigers with one pair of broad triangular parapodia, without distinct pre- and post-setal lobules ( Figure 1D , arrow), well developed in the first setigers and reduced near the pygidial region. Cylindrical pygidium, as long as the prostomium, without pygidial cirri. Figure 2. Labrorostratus prolificus . (A) Parapodium from median region (anterior view, specimen with 40 setigers); (B) parapodium from anterior region (specimen with 35 setigers) and detail of the limbate geniculate seta; (C) specimen with 65 setigers; (D) specimen with 17 setigers; (E) specimen with 39 setigers. Notes: Figures C–E from Amaral (1977) ; arrows indicate the beginning of formation of a terminal stolon. Table 1. Measurements of individuals of L. prolificus (length, width and number of setigers) found in the present study and in Amaral (1977) , including number of individuals with stolon.
No. setigers Length (µm) Width (µm) No. individuals No. individuals Reference
with stolon
1–10 285–563 122–225 32 1 present study
11–20 675–800 260–270 8 1 present study
21–30 1900–2500 – 10 – Amaral (1977)
21–30 1125–1687 270–315 6 3 present study
31–40 1800–3000 360–450 13 4 present study
41–45 3195–3330 450–495 2 1 present study
41–45 3200 – 4 – Amaral (1977)
46–65 8500–11000 – 19 – Amaral (1977)
The only distinguishable peristomial ring is the second; the first peristomial ring is fused to the prostomium ( Figure 1D ). At the end of this stage, while new setigers are added in the pre-pygidial zone, only the parapodia of the first setigers grow, and it is possible to observe the beginning of the differentiation between the pre- and post-setal lobules. Aciculae of the first setigers begin its development at the end of this stage. Stage 2 (11–20 setigers). Anterior end cylindrical, with the posterior third of the body without evident parapodia, tapering abruptly ( Figure 2D ). Prostomium triangular; eyes and setae not evident. First peristomial ring well defined, distinct from prostomium in specimens with more than 15 setigers, being as long as the second ring. A rudimentary jaw is present ( Figure 2D ). Specimens with 18–20 setigers with one aciculum only on the first 3 pairs of parapodia. The post-setal lobe is developed in the first setigers, but is inconspicuous in the posterior region. The median parapodia are well developed, but aciculae are absent. The last 5–10 setigers are very short and narrow, and without apparent parapodia. In general, the body is narrow where there are no well-developed parapodia. Stage 3 (21–30 setigers). Anterior end of the prostomium rounded, inflated dorsoventrally. Beginning of formation of lateral pair of eyes. Setae apparently absent. At the beginning of this stage, the aciculae of median and posterior parapodia appear more rapidly, and most of the parapodia already have evident acicula. Stage 4 (31–40 setigers). Second pair of eyes (inner pair) well developed ( Figure 2E ). Maxillae and mandibles easily visible and well formed. Parapodia of anterior region uniform in size; post-setal lobule conical, and pre-setal lobule truncate. One neuropodial aciculum and one short, simple, limbate geniculate seta present on each parapodium of the first 5–15 setigers. Stage 5 (41–45 setigers). Prostomium as wide as long. Two pairs of reddish eyes, inner pair shorter and more superficially located. Peristomial rings as long as the following setigers ( Figure 1E ). Body uniform in width, tapering near pygidial region. Sub-biramous parapodia, notopodium with a very short papilla and one internal aciculum. Neuropodium of the first setigers with rounded pre-setal and conical postsetal lobule ( Figure 2A ), with one aciculum and one to two simple limbate capillary setae with a serrated blade ( Figure 2B ). Jaws amber-coloured, with flat and slender paired mandibles. Maxillae with one pair of broad maxillary plates, attached to a single, elongated basal support, almost twice as long as the maxillae ( Figure 2E ). Remarks Some specimens with about 30–40 setigers have eyes, whereas others with the same number of setigers have none. Some individuals with three to 30 setigers have a clearly delimited longitudinal area in the median portion of the prostomium, which can be seen under SEM observation ( Figure 1D ). A peculiar characteristic in specimens with three to 15 setigers is the fusion of the first peristomial ring with the prostomium. This aspect has not been described previously in oenonids. In these specimens, the parapodia of the anterior region are a simple triangular projection, without differentiation into pre- and post-setal lobules ( Figure 1D , arrow). The lobules begin to appear together with the arising of the aciculum; that is, lobules are present where aciculae are being formed. Discussion Information on length and width variation of specimens in their different stages is given in Table 1 . In this study we found individuals with up to 45 setigers, and more than 50% had between three and 10 setigers. The specimens collected by Amaral (1977) had between 17 and 65 segments, which indicates that the host was in a more advanced stage of infection ( Figure 3 ). Amaral (1977) found stolons only in specimens with about 65 setigers. In this study we found specimens in different stages with stolons, with the highest frequency in individuals with 21–40 setigers ( Table 1 ). Because of this, and considering that the pygidium of these polychaetes is a simple cylinder, it is possible that the specimens with fewer than 65 setigers that were studied by Amaral (1977) also had stolons beginning to form, as in Figures 2D and E . Even though there is no pygidial cirrus in worms with up 45 setigers, one pair of small cirri is present in longer individuals, as in Figure 2C. A large number of gametes (possibly oocytes) 240 µm in diameter was found in the coelomic cavity, mainly in the posterior half of the host’s body. Emerson (1974) described a species of the genus Arabella in the coelomic cavity of Diopatra ornata , which was completely full of eggs. According to the author, the parasites feed on the eggs to grow, and consequently come to occupy less space in the coelom. The youngest worms, without developed jaws, feed on coelomic fluid. In this study, both young and adults occupied the anterior half of the host’s body, and no specific location was noted for each stage, as mentioned by Amaral (1977) , who found young specimens (with about 17 setigers) in the anterior region and adults (with 50 setigers) in the median region. Figure 3. Frequency distribution of the size (number of setigers) of L. prolificus found in the present study and in Amaral (1977) . Distribution Atlantic Ocean: Brazil (State of São Paulo ).