Semiodera laevis ( Stimpson, 1856 ) Salazar-Vallejo, 2012

Salazar-Vallejo, Sergio I., 2012, 3562, Zootaxa 3562, pp. 1-62 : 27-29

Semiodera laevis ( Stimpson, 1856) n. comb.

Figure 9

Siphonostomum laeve Stimpson 1856:391 .

Trophonia xanthotricha Schmarda 1861:16 , Pl. 19, Fig. 165, textfig. a–f.

Stylarioides xanthotrichus: Ehlers 1908:119–121 , Pl. 16, Figs 1–2.

Stylarioides laevis: Day 1955:421–422 (syn.).

Stylarioides monroi Day 1957:103 , textfig. 6n–p, South Africa.

Pherusa monroi: Day 1961:505 ; Day 1967:660, Fig. 32.2d–g.

Pherusa laevis: Day 1967:661–662 , Fig. 32.3a–c.

Type material. South Africa. Two syntypes of Stylarioides monroi ( BMNH- 1961.16.71–72), Natal (29º S, 31º E), shore, Stat. 190C (Imboyte, 27.2 km N of Port St. Johns in Day 1957), J.H. Day, coll.

Additional material: South Africa. Three specimens ( LACM-AHF-4864 ), University of Cape Town Ecological Survey, Port Nolluth (20.5–23.0 mm long, 1.8–3.0 mm wide, cephalic cage 4.5–7.0 mm long, 61–68

chaetigers; one with anterior end everted shows 17 branchial scars per side, spirally arranged). Two specimens (USNM-1191184), RV Mering Meude, Stat. SM185 (33°39.3' S, 27°11.6' E), 90 m, in dead dendrophyllid coral, 31 May 1978, H. Zibrowius, coll. (13–22 mm long, 2 mm wide, cephalic cage 5.5–7.0 mm long, 58–69 chaetigers).

Description. Syntypes (BMNH-1961.16.71–72), complete, pale, one breaking into two pieces, the other a mature female, bent backwards, both dissected and some parapodia previously removed ( Fig. 9A). Body anteriorly swollen, tapering posteriorly into a cauda; 12–13 mm long, 3 mm wide, cephalic cage 5–6 mm long, 53–54 chaetigers. Tunic thin, free from sediment cover; body papillae small, globose, arranged in two rows per segment, both with abundant papillae (except chaetigers 2–3, which have one row each).

Anterior end not exposed; one syntype dissected. Prostomium low cone; four dark large eyes. Caruncle low, wide, not reaching the branchial plate margin. Palps pale, large; palp keels not seen. Dorsal lip projected as a small conical lobe. Lateral lips well-developed, rounded. Ventral lip reduced ( Fig. 9E).

Branchiae cirriform, sessile on branchial plate, filaments arranged in one posterior continuous row, and two proximal lateral, small groups; each proximal group with 16 filaments (18 filaments per side); larger filaments about as long as palps. Nephridial lobes in branchial plate placed between the distal branchial row and the convoluted proximal branchial filaments ( Fig. 9E, F).

Cephalic cage chaetae about half as long as body length or about twice as long as body width. Chaetigers 1–2 involved in the cephalic cage ( Fig. 9D); chaetae arranged in short rows about the body corners; chaetiger 1 with about 10 chaetae per ramus, chaetiger 2 not displaced dorsally, 6 chaetae per ramus.

Anterior dorsal margin of first chaetiger truncate ( Fig. 9B), projected ventrally, with two large digitate papillae ( Fig. 9C). Anterior chaetigers without especially long papillae; chaetal lobes with digitate papillae, slightly longer than body papillae. Chaetigers 1–2 of about the same length, shorter than chaetiger 3. Sand cemented anterior shield extended ventrally, mostly eroded. Chaetal transition from cephalic cage to body chaetae abrupt; one long pseudocompound hook in chaetiger 3. Falcate simple neurohooks from chaetiger 4. Gonopodial lobes present in chaetiger 5, transverse ovoid slits.

Parapodia poorly-developed, chaetae emerge from body wall. Parapodia lateral, median neuropodia ventrolateral. Noto- and neuropodia without any projection, lobe, or longer papillae ( Fig. 9G). Noto- and neuropodia distant to each other, with two tiny interramal papillae.

Median notochaetae restricted to a single capillary, multiarticulate, as long as ¼–1/6 body width, articles medium sized basal- and medially, distally not defined. Neurochaetae thick multiarticulate capillaries in chaetigers 1–2; neuropodia 3 with a long pseudocompound hook; falcate yellow neurohooks from chaetiger 4, one per ramus throughout the body, decreasing in size posteriorly. Each neurohook with a dark ovoid spot about the limit between the internal and external or exposed portions ( Fig. 9H).

Posterior end tapering to a hemispheric lobe; pygidium with terminal anus; no anal cirri. Oocytes about 150 µm.

Remarks. The type material of Siphonostomum laeve Stimpson,1856 was destroyed during the great 1871 Chicago fire because Stimpson had brought his collections from Washington to his new job as director of the local Academy of Sciences in 1866. (http://www.si.edu/oahp/ScientificIllustrators/WStimpson.html).

Semiodera laevis ( Stimpson, 1856) n. comb., belongs in the group of species with a poorly developed dorsal shield. It resembles S. tenera ( Grube, 1868) n. comb., by having a single hook per neuropodia; they differ because S. laevis has up to 40 branchial filaments, whereas S. tenera has only about 20 branchial filaments. However, an easier character to observe is that S. laevis has two tiny interramal papillae whereas in S. tenera there is a single large one.

Day (1955:421) regarded S. laevis as a senior synonym for S. xanthotrichus Ehlers , and he recognized some differences to Monro’s record, which he later named as S. monroi . Day (1957:103–104) noticed that his Stylarioides monroi was very close to S. laevis . He regarded the presence of a long neurohook in chaetiger 3 of S. monroi and the number of “anterior antennae” as distinguishing features. He was following Monro’s (1937) account of S. xanthotrichus collected from Southern Arabia, but that record belongs in S. tenera (see below). In fact, the three known species with a poorly developed dorsal shield ( S. curviseta , S. laevis , S. tenera ) have a long neurohook in chaetiger 3, but as shown below, this is not a consistent feature because it may be broken and there may even be some capillary chaetae instead. The “anterior antennae” are the projections on the dorsal margin of chaetiger 1; they are often covered by cemented sand grains, their removal may break them apart, and they may also regenerate, rendering their number unsuitable to separate similar species. Therefore, the number of branchial filaments remains as the only useful feature, and while it may be size dependent, the difference in their number is so high that it may be employed until additional characters are found.

Distribution. Restricted to South Africa in shallow water, boring in calcareous substrates.