Sabellomma collinae, Nogueira, João Miguel De Matos, Fitzhugh, Kirk & Rossi, Maíra Cappellani Silva, 2010

Nogueira, João Miguel De Matos, Fitzhugh, Kirk & Rossi, Maíra Cappellani Silva, 2010, A new genus and new species of fan worms (Polychaeta: Sabellidae) from Atlantic and Pacific Oceans — the formal treatment of taxon names as explanatory hypotheses, Zootaxa 2603, pp. 1-52 : 16-23

Sabellomma collinae spec. nov.

( Figs 7–10 , 16 G–K; Table 2)

Material examined. Holotype and 8 paratypes coll. 7 Aug 2003, shallow subtidal (3.05 m) coral-sponge rubble, by G. Hendler, K. Fitzhugh, J. Sanchez, W. Keel, at south side of Cayo Swan (= Isla de Pájaros) (9.453o N 82.3o W), Bahia Almirante, Bocas del Toro Archipelago, Bocas del Toro Province, Caribbean side of Panamá. All type material deposited at the NHMLAC (holotype: LACM-AHF POLY 2404; paratypes: LACM-AHF POLY 2405–2412). Details of each spec. of type series are provided in Table 2.

Additional specimens. USNM 042793: Puerto Rico, Caribbean Sea, 1 spec.; USNM 044906: Key West, Florida, USA, 1 spec.

Comparative material examined. Demonax microphthalmus (CB–T–259–2001; 39027): 1 spec. Slides: radiole; notochaetae, chaetiger 7; uncini, chaetiger 7.

Definition. Two possibilities, depending on character transformation series in the phylogenetic hypothesis involving individuals to which Sabellomma collinae spec. nov., S. minuta , and S. harrisae spec. nov., refers (see Remarks on Specific-level Hypotheses in Sabellomma ): (1) A specific hypothesis, accounting for the absence of dorsal lip pinnular appendages among observed individuals. Dorsal lips without pinnular appendages originated by an unspecified mechanism(s) in a reproductively isolated population of individuals with pinnular appendages almost completely fused to dorsal lips, subsequent to which the new character became fixed in the population by an unspecified mechanism(s), leading to individuals observed in the present, all with dorsal lips lacking pinnular appendages. (2) There are no autapomorphies to provide a basis for the specific hypothesis.

As is discussed below (see Remarks on Specific-level Hypotheses in Sabellomma ), the formal definition of S. collinae as an explanatory hypothesis is tenuous since the explanation of the absence of pinnular appendages is not an autapomorphy in some transformation series.

Description. Measurements. Medium-sized individuals; crown 1–3 mm long, with 4–9 pairs of radioles (Table 2). Complete specimens with trunk 2–10 mm long, 0.2–0.75 mm wide, with 4–5 thoracic, and 18–53 abdominal chaetigers (Table 2).

Pigmentation. Living specimens not observed. Except for radiolar and interramal eyespots, body unpigmented or with very faint brownish pigmentation at base of crown and up to 4–5 radiolar bands. Small interramal eyespots present in all chaetigers, frequently faint and inconspicuous ( Fig. 7 L).

Crown. Radiolar flanges and palmate membrane both absent. Each radiole with four rows of skeletal cells. Radioles with two irregular rows of eyespots along lateral margins; eyespots as single units, each with large lens, more numerous along distal-most two thirds to one-half of radioles, especially in association with transverse pigment bands ( Fig. 7 E–K), less abundant near radiolar tips. Dorsal lips about one-fifth total crown length, basally broad, distally tapering, with radiolar appendages lacking internal skeletal cells; pinnular appendage absent ( Fig. 8 F). Ventral lips low, distally rounded, each continuing ventrally as parallel lamella with large ventral sac above collar ventral lappets ( Figs 7 A, C–G, I–K; 8B–C, E, G–H). Mid-dorsally, branchial lobes with thickened ridges extending along dorsal-most pair of radioles ( Fig. 8 A, D).

Body. Collar fused to body dorso-laterally, well separated from faecal groove, extending anteriorly to level of first pair of parapodia; laterally low, slightly oblique, covering bases of radiolar crown but not origins of radioles; ventrally with one pair of triangular, distally pointed, non-overlapping lappets reaching anterior margin of chaetiger 1, separated from each other by short parallel lamellae; ventrally, between termination of parallel lamellae and anterior margin of first ventral shield, ciliated patch present ( Figs 7 A–K; 8A–E, G–H). Trapezoidal ventral shields, posteriorly indented by neuropodia on thorax, anterior margin of first shield medially indented ( Figs 7 D–E, J–K; 8B–C, G–H). Mid-dorsal faecal groove deep on anterior chaetigers ( Figs 7 B, H; 8A, D). Collar chaetae narrowly hooded, arranged in two rows ( Fig. 9 A); subsequent thoracic notopodia with narrowly hooded superior chaetae, arranged in arc, inferior notochaetae paleate, with long, gently tapering tips, arranged in two rows partially enclosed by superior arc ( Figs 8 A–E; 9B; 10A–B). Thoracic neuropodia with slightly higher than long avicular uncini, crest with 4–5 irregular rows of secondary teeth, covering proximal half of main fang, breast distinct, not extending distally to tip of main fang ( Figs 9 F; 10E, G–H); companion chaetae with rounded, symmetrical, denticulate heads and long, tear drop-shaped, slightly asymmetrical, gently tapering membranes ( Figs 9 F; 10E, G, I–K). Abdominal neuropodia with narrowly hooded chaetae, arranged in two rows, anterior row with shorter chaetae ( Figs 9 C–E; 10C–D). Abdominal uncini similar to thoracic ( Figs 9 G–H; 10F). Triangular, distally rounded pygidium, with 1–3 small, red ocelli at each lateral margin ( Figs 7 M; 8I).

Variation. The specimens of S. collinae sp. nov., examined for the present study presented considerable variation in size, but most other characters did not vary between specimens (Table 2). One specimen (paratype 7), probably a juvenile, has a different number of radioles in right and left halves of the crown. All specimens have the same numbers of thoracic and abdominal noto- and neuropodia on both sides of the body, but there is also slight variation in the number of thoracic chaetigers, the holotype and paratype 7 having 4 thoracic chaetigers, all other specimens having 5 (Table 2). All this may indicate the occurrence of asexual reproduction by scissiparity, as said above for S. minuta .

Etymology. This species is named for Dr. Rachel Collin, director of the Bocas del Toro Marine Station, Smithsonian Tropical Research Institute, Panama, who coordinated the Panamanian survey.

TABLE 2. Morphological variation among the type-series of Sabellomma collinae gen. nov., sp. nov. (variation within parentheses is only shown when there is difference from one side of the body to the other).

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Distribution. Knight-Jones (1983) assigned to S. minuta specimens with short thorax from Florida (Key West) and Puerto Rico. We have examined those specimens and, although the generic characters of Sabellomma are conspicuous, they do not present dorsal pinnular appendages. Therefore, those specimens are here referred to S. collinae and this species is considered to occur throughout the Caribbean.

Figures

FIGURE 7. Sabellomma collinae gen. nov., sp. nov. A: total worm, left lateral view; B: total worm, dorsal view; C: total worm, right lateral view; D: total worm, ventral view; E: anterior end, ventral view; F: anterior end, left ventro-lateral view; G: anterior end, left lateral view; H: anterior end, dorsal view; I: anterior end, right lateral view; J: detail of anterior end, ventral view; K: detail of anterior end, left ventro-lateral view; L: anterior to mid-abdominal segments; M: posterior end, right lateral view. All photos from holotype (LACM-AHF 2404). vs = ventral sacs. Scale bars: A – D = 1 mm; E – I, K = 0.7 mm; J = 0.4 mm; L – M = 0.3 mm.

FIGURE 8. Sabellomma collinae gen. nov., sp. nov. A: anterior end, dorsal view; B: anterior end, left lateral view; C: anterior end, ventral view; D: detail of anterior end, dorsal view; E: detail of anterior end, left lateral view; F: dorsal lip (dissected crown); G – H: details of collar and base of crown, ventral view; I: posterior end, left lateral view. Unspecified arrows point to ciliated patch; bp = basalmost pinnule; br = branchial ridge; dl = dorsal lip; pl = parallel lamellae; ra = radiolar appendage; vs = ventral sacs. Photos A – E, G – H from paratype 7 (LACM-AHF 2411); photo F from paratype 6 (LACM-AHF 2410). Scale bars: A – B = 0.4 mm; C – E = 0.2 mm; F – G, I = 0.1 mm; H = 60 µm.

FIGURE 9. Sabellomma collinae gen. nov., sp. nov. A: collar chaetae; B: notochaetae from segment 4; C: neurochaetae from segment 13; D: notochaeta from anterior row from segment 13; E: notochaeta from posterior row from segment 13; F: neurochaetae from segment 4; G – H: uncini from segment 15. All photos from paratype 6 (LACM-AHF 2410). Scale bars: A – B, D = 30 µm; C, E = 25 µm; F = 20 µm; G – H = 10 µm.

FIGURE 10. Sabellomma collinae gen. nov., sp. nov. A: notochaetae from segment 4; B: inferior thoracic notochaetae (paleae) from segment 2; C – D: mid-abdominal neurochaetae; E: neurochaetae from segment 3; F: mid-abdominal uncini; G: neurochaetae from segment 2; H: uncini from segment 3; I – K: companion chaetae from segments 4, 3 and 2, respectively. All photos from paratype 6 (LACM-AHF 2410). Scale bars: A = 30 µm; B = 10 µm; C – D = 12 µm; E = 20 µm; F = 5 µm; G – H = 8 µm; I, K = 4 µm; J = 2 µm.

FIGURE 16. Methyl green staining. Sabellomma minuta gen. nov., comb. nov. (spec. 16 [ZUEC-POL 7444], photographed after ~ 2 hours in ethanol after immersion in methyl green solution). A: total worm, ventral view; B: total worm, dorsal view; C – D: anterior end, ventral views; E: posterior end, ventral view; F: posterior end, dorsal view. Sabellomma collinae gen. nov., sp. nov. (holotype [LACM-AHF 2404], photographed after ~ 2.5 hours in ethanol after immersion in methyl green solution). G: total worm, right lateral view; H: anterior end, dorsal view; I – J: anterior end, ventral views; K: posterior end, right lateral view. Scale bars: A – B, G = 1 mm; C, I = 0.7 mm; D – F, K = 0.3 mm; H, J = 0.4 mm.