Semiodera tenera ( Grube, 1868 ) Salazar-Vallejo, 2012

Salazar-Vallejo, Sergio I., 2012, 3562, Zootaxa 3562, pp. 1-62 : 34-36

Semiodera tenera ( Grube, 1868) n. comb.

Figure 13

Siphonostomum tenerum Grube 1868:636–637 ; Grube 1869:506 (partim).

Stylarioides xanthotrichus: Monro 1937:301–302 , Textfig. 20 (non Schmarda).

Pherusa tenera: Wehe & Fiege 2002:50 (partim).

Type material. Red Sea. Four syntypes of Siphonostomum tenerum (ZMB-512), Ehrenberg, coll.

Additional material: Northwestern Indian Ocean, Yemen. One specimen ( SMF-15401 ), Ras Qatanian Bay , Socotra, Stat. 725 (12°21'17" N, 53°32'07" E → 12°20'18" N, 53°31'39" E), dredge, 18–20 m, 9 Apr. 2000, T. Wehe, coll. (11 mm long, 2.5 mm wide, cephalic cage chaetae 5 mm long, 42 chaetigers). Five specimens ( SMF- 15403 ), Hawlaf Bay , off dune, Socotra, Cruise MAP-151, Stat. ST-092 (12°40.519’N, 54°4.170E), 4–5 m, 21 Mar. 1999, M. Apel, coll. (9–14 mm long, 1.5–2.5 mm wide, cephalic cage chaetae 4.5–8.0 mm long, 50–55 chaetigers; falcate neurohooks from chaetiger 4). Three specimens and an anterior fragment ( SMF-15404 ), Mafrihin, Socotra (12°24.971' N, 54°14.364' E), 22 Apr. 2000, M. Apel, coll. (19 mm long, 2 mm wide, cephalic cage chaetae 5.0– 5.5 mm long, 58–59 chaetigers; mature female without posterior end, with dark oocytes, each about 100 µm). Three specimens ( SMF-15405 ), Alansiyah (Qualansiyah) Bay , Socotra, Cruise MAP-78A, Stat. 18 (12°41.026’N, 53°28.309’E), 10 Mar. 1999, M. Apel, coll. (5.0– 16.5 mm long, 1.0– 2.5 mm wide, cephalic cage chaetae 4–6 mm long, 35–57 chaetigers; falcate neurohooks from chaetiger 4). Six specimens ( SMF-15406 ), three mature females and three mature males, Ras Qatanih Bay, Socotra, Stat. 726 (12°21.293' N, 53°32.659' E), 8–10 m, 9 Apr. 2000, T. Wehe, coll. (9–20 mm long, 1.5–2.5 mm wide, cephalic cage chaetae 4–7 mm long, 44–54 chaetigers; falcate neurohooks from chaetiger 4). Southwestern Indian Ocean , Moçambique Channel. One specimen (LACM- AHF-4867), complete, International Indian Ocean Expedition, RV Anton Bruun, Stat. AB 371G (24º49' S, 35º13' E), 72 m, rock dredge on rocky sediments, 18 Aug. 1964 (17 mm long, 2 mm wide, cephalic cage 8 mm long, 54 chaetigers) .

Description. Four syntypes (ZMB-512), two complete, the others without posterior ends ( Fig. 13A); all greyish, slightly or markedly twisted, integument variously broken. Body cylindrical, tapering posteriorly into a cauda; complete syntypes 6–9 mm long, 1.0– 1.5 mm wide, cephalic cage 5.5–6.0 mm long, 42–45 chaetigers (others 1.0– 1.5 mm wide, cephalic cage 4.5–5.0 mm long). Tunic thin, without sediment cover; body papillae medium-sized, globose, arranged in two rows per segment, with more papillae in anterior row ( Fig. 13B, C), disappearing in median and posterior chaetigers (more prominent in smaller and more contracted specimens).

Cephalic hood not exposed; anterior end not dissected to avoid further damage. One additional specimen dissected (SMF-15404). Prostomium depressed; central area dark, individual eyes and caruncle not seen. Palps whitish, large; palp keels not seen. Lateral lips well-developed, rounded. Dorsal and ventral lips reduced.

Branchiae cirriform, sessile on branchial plate, filaments arranged in one posterior continuous row with 4 filaments, and two lateral small groups with filaments arranged in spiral, decreasing in size ventrally; each group with 6–8 filaments, larger on outer row, 10 filaments per side ( Fig. 13D); larger filaments about as long as palps. Nephridial lobes thin, positioned lateral to prostomium, about its middle region, between the spiral and the continuous branchial filaments groups.

Cephalic cage damaged, chaetae as long as body (2/3 body length), or 4–5 times longer than body width. Chaetigers 1–2 involved in cephalic cage; chaetiger 1 with chaetae arranged in longer rows than chaetiger 2; chaetiger 1 with notochaetae dorsal, neurochaetae ventral; chaetiger 2 with chaetal lobes lateral. Chaetiger 1 with 6–8 noto- and 6–8 neurochaetae; chaetiger 2 with 6 noto- and 6 neurochaetae.

Anterior dorsal margin of first chaetiger projected anteriorly ( Fig. 13B, C), slightly damaged, two large lateral papillae (trifid lobe in SMF-15401), covered by sediment. Anterior chaetigers without especially long papillae; chaetal lobes with ovoid papillae, as long as body ones. Chaetigers 1–2 short, chaetiger 3 longer, as long as following ones. Sand cemented anterior shield reduced, extended over anterior lobe of chaetiger 1 and chaetigers 1–2, with sparse sediment particles. Chaetal transition from cephalic cage to body chaetae abrupt; long pseudocompound hooks in chaetiger 3 ( Fig. 13E). Falcate simple neurohooks from chaetiger 4, one per ramus. Gonopodial lobes present in chaetiger 5, slightly oblique, ovoid, darker areas, slightly elevated ( Fig. 13C).

Parapodia poorly-developed, chaetae emerge from body wall ( Fig. 13F). Parapodia lateral, median neuropodia ventrolateral. Notopodia and neuropodia without projections, lobe or long papillae. Noto- and neuropodia distant to each other, with a medium-sized interramal papilla.

Median notochaetae multiarticulate capillaries, about as long as 1/3 body width, occurring singly, articles tenuous, long, increasing in length distally. Neurochaetae multiarticulate capillaries in chaetigers 1–2; pseudocompound hooks present in chaetiger 3 only; falcate dark brown neurohooks from chaetiger 4, only one per ramus in anterior to posterior chaetigers ( Fig. 13G), more falcate in median chaetigers, almost straight in caudal chaetigers.

Posterior end tapering to a blunt lobe; pygidium with terminal anus; no anal cirri.

Remarks. Semiodera tenera ( Grube, 1868) n. comb. was described in two successive papers ( Grube 1868:636–637, 1869:506), with very little modifications in the second paper, but additional material was examined. The diagnosis would be: body swollen anteriorly, posteriorly markedly tapering; papillae ovoid, arranged in 2 transverse rows dorsally, one row ventrally; cephalic cage made by chaetigers 1–2; neurochaetae falcate dark hooks, one per ramus; eight branchiae.

However, the two syntypes lots deposited (ZMB-512) belong to two different species; one corresponds with the original description since it has the transverse rows of ovoid papillae, while the other has abundant long digitate papillae, and is more closely allied to Stylarioides delle Chiaje, 1831 and is described elsewhere ( Salazar-Vallejo 2011b). According to the publication dates, the first lot was collected by von Frauenfeld, and the second lot by Ehrenberg; however, the first lot was not used in the description of the species. This discrepancy was explained by Grube himself (1869:506) in the last paragraph: “Die obige in der Publication der Frauenfeld’schen Anneliden gegebene Beschreibung ist hauptsächlich nach dem besten der im Berliner Museum aufgestellten Exemplare von Ehrenberg entworfen; das von Frauenfeld eingeschickte hatte zwar ähnliche Dimensionen, war aber nicht so vollständig erhalten“. This translates as the above description given in the publication of the Frauenfeld’s Annelids is based on material in the Zoologisches Museum, Berlin, Germany collected by Ehrenberg; Frauenfeld’s single specimen had similar dimensions, but was not so complete. Semiodera tenera ( Grube, 1868) n. comb., and S. laevis differ from other species in the genus by having pseudocompound neurohooks only in chaetiger 3 and neurohooks occurring singly throughout the body. They differ in the number of branchial filaments, there are about 10 filaments per side in S. tenera , whereas there are 20 filaments per side in S. laevis . Also S. tenera has a single medium-sized interramal papillae whereas S. laevis has two minute ones.The record of Stylarioides xanthotrichus by Monro (1937:301) was based on specimens collected off the South Arabian coast and match the description of the species.

Variation: Falcate neurohooks always start in chaetiger 4; however, the neurochaetae of chaetiger 3 can be multiarticulate capillaries numbering 1–3 or a long (rarely 2) pseudocompound hook. As both types of chaetae were found in the same lot ( SMF-15406 ), it suggests that this is not a useful dignostic character..

Distribution. Originally described from the Red Sea. Wehe & Fiege (2002:50) regarded it as endemic to the region. The additional specimens were from the Northwestern and Southwestern Indian Ocean.