Lamellibrachia donwalshi, Mccowin & Rouse, 2018

Mccowin, Marina F. & Rouse, Greg W., 2018, A new Lamellibrachia species and confirmed range extension for Lamellibrachia barhami (Siboglinidae, Annelida) from Costa Rica methane seeps, Zootaxa 4504 (1), pp. 1-22 : 5-14

Lamellibrachia donwalshi sp. nov.

( Figs. 6–11 )

urn:lsid:zoobank.org:act:BECD07F4-55CD-499B-B371-32AB404A2DEF

Lamellibrachia sp. ( Levin et al. 2015)

Type-locality: Costa Rica, Eastern Pacific , methane seep known as Mound 12, ~1,000 meters depth ; 8.93°N, 84.32°W.

Material Examined. Holotype: (SIO-BIC A8382) from type locality, collected by HOV Alvin, Dive 4917, 1 June 2016; fixed in 10% SW formalin, preserved in 50% ethanol, putative male.

Paratypes: (SIO-BIC A1341) from type locality, collected by HOV Alvin Dive 4503, 24 February 2009; fixed in 10% SW formalin, preserved in 50% ethanol, two males, seven putative females, (see Table 2). One specimen ( MZUCR 402-01 ) from type locality, collected by HOV Alvin; fixed in 10% SW formalin, preserved in 50% ethanol .

Description. Tubes incomplete (broken in sampling), 24–26.5cm long, 9–10mm diameter anteriorly (n = 2; photo of tubes in-situ Fig. 6A ). Anterior end of tube slightly curved with mostly long tube collars, occasionally interrupted by two or three short tube collars, but varying among specimens ( Fig. 6B ). Posterior of tubes smooth, curled, without obvious tube collars ( Fig. 6B ).

Obturaculum length 2.5–9mm (n = 11; holotype 7mm); width 2–8mm (n = 11; holotype 6mm), with bare anterior face, lacking any secreted structures ( Figs. 6 C–G). Lateral surface of obturaculum surrounded by branchial plumes ( Fig. 6 E–G). 5–11 pairs sheath lamellae (holotype 11 pairs; Figs 6 E–G, 7–9) enclose 10–23 pairs branchial lamellae (holotype 23 pairs; Figs 6G , 8–10 ) with ciliated pinnules. Ratio of number of branchial lamellae pairs to obturaculum width varied from 1–3.3.

Vestimentum length 22–70mm (holotype 70mm), width 3–12mm with vestimental folds curled ( Figs 6 C–G, 8A–B, 9B). Anterior vestimentum edge slightly curled forming collar ( Figs 8A , 9A ); posterior ends of vestimental folds rounded with slight separation at center ( Figs 6 , 7 A–B, 8A, 9A). Dorsal paired vestimental ciliated grooves run down length of vestimentum ( Figs 8B , 9B ). In males, grooves flanked by ridge-like, conspicuous epidermal folds, spermatozeugmata observed in trunk ( Figs 7 D–E, 8B); conspicuous epidermal folds not present in putative females ( Figs 7 A–B, 9B, 10A–D). Both males and females have a few scattered epidermal processes on the internal epidermis of the vestimental cavity ( Fig. 10 C–D).

All specimens lacking posterior trunks. Anterior portion of trunk ( Figs 6 C–D, 7C) filled with fragile trophosome tissue ( Fig. 7C ). Ventral surface of vestimentum covered in cuticular plaques ( Figs 11 A–B), noticeably smaller than those on trunk ( Figs 11 C–D). Vestimental plaques measure 33.2–74.7µm in diameter (holotype 41.5– 49.8 µm, Fig. 11B ). Surface of trunk covered entirely by cuticular plaques, measuring 51.5–83µm in diameter (holotype 41.5–83µm, Fig. 11D ). No plaques on middorsal and midventral lines of trunk. Opisthosoma not recovered.

Etymology. Don Walsh was one of the first people to descend to the bottom of the Challenger Deep aboard the bathyscaphe Trieste in 1960. He went on to a distinguished career in oceanography and marine policy. We name Lamellibrachia donwalshi sp. nov. in honor of his contributions to deep sea research and exploration.

Distribution. Lamellibrachia donwalshi sp. nov. has only been recovered from a single small area (varies by 0.01 N) and depth range of 999 to 1,040 meters. It was previously noted by Levin et al. (2015) as Lamellibrachia sp.

Remarks. Lamellibrachia donwalshi sp. nov. differs morphologically from other Lamellibrachia species in that it has 5–11 sheath lamellae, 10–23 branchial lamellae, and vestimental plaque diameters of 33.2–74.7µm ( Table 4). It is not uncommon for ranges of sheath lamellae, branchial lamellae, and plaque diameters to overlap among Lamellibrachia species ( Table 4), but no previously described species encompasses the entire range of these morphological traits in L. donwalshi sp. nov. We found no significant correlation between the body size (length and width of obturaculum and vestimentum) and the number of sheath lamellae, branchial lamellae, or plaque diameters (Spearman rank correlation, 11 specimens, P> 0.05). This supports the findings of Kobayashi et al. (2015) that the number of lamellae and the diameters of plaques are independent of growth in adults and can be used for morphological comparison across species. Due to a lack of morphological data for L. sp. 2, we cannot say at this time whether L. donwalshi sp. nov. differs morphologically from this close genetic relative ( Fig. 3 ). However, it clearly differs morphologically from its other close relative, L. anaximandri ( Fig. 3 ), in having greater numbers of sheath lamellae and branchial lamellae and a shorter obturaculum length ( Table 4). Lamellibrachia donwalshi sp. nov. also demonstrates some of the smallest vestimental plaque diameters reported for the genus (lower bound of 33.2µm, Table 4), though this range is very close to that of L. sagami and falls partially within the range of plaque diameters for L. anaximandri (also shown in Table 4). Lamellibrachia donwalshi sp. nov. also closely resembles L. sagami in the range of trunk plaque diameters, but numbers of lamellae more closely resemble those of L. columna ( Table 4).

Figures

FIGURE 3. Maximum likelihood trees of the combined analysis from two mitochondrial genes (16S, COI) aligned with MAFFT and then concatenated, with three different rooting options: A Escarpia sp., B Ridgeia piscesae, C Riftia pachyptila. Bootstrap support percentages from Maximum Likelihood and Maximum Parsimony analyses (separated by slashes) are followed by Bayesian posterior probabilities. Support values of 95%/0.95 or greater for all analyses are indicated by stars. Nodes with support values less than 50%/0.5 or not recovered in one of the analyses are indicated by a hyphen.

FIGURE 6. In situ photograph and micrographs of live Lamellibrachia donwalshi sp. nov. A In situ photo of Lamellibrachia donwalshi sp. nov. holotype (SIO-BIC A8382) taken from the HOV Alvin, indicated by arrow. B Tubes (incomplete) of Lamellibrachia donwalshi sp. nov. paratypes (SIO-BIC A1341). C Holotype, ventro-lateral to dorsal, live. D Holotype, ventrolateral, live. E Holotype, left side, live. F Holotype, right side, post-preservation. G Holotype, dorsal, post-preservation. G Holotype, dorsal, post-preservation. Scale bars, B=5cm; C–F=10mm; G=1mm.

FIGURE 7. Micrographs of vestimental and trunk regions of Lamellibrachia donwalshi holotype (SIO-BIC A8382), male paratype (SIO-BIC A1341), and putative female paratype (SIO-BIC A1341). A 10 µm transverse section through anteriormiddle part of vestimentum, male paratype. B 10µm transverse section through anterior-middle part of vestimentum, female paratype. C 10µm transverse section through trunk, male paratype. D Light micrograph of additional spermatozeugmata dissected from male paratype. E Close-up of spermatozeugmata in 10µm transverse section through trunk, male paratype. F 10µm transverse section through crown, male paratype. VG, vestimental groove; DV, dorsal blood vessel; VV, ventral blood vessel; VN, ventral nerve cord (Worsaae et al. 2016); G, gland; SZ, spermatozeugmata; OB, obturaculum; OV, obturacular blood vessel; OC, coelom of obturacular blood vessel; BL, branchial lamellae; SL, sheath lamellae. Scale bars, A–C=1mm; D=100µm; E–F=1mm.

FIGURE 8. Illustration of Lamellibrachia donwalshi sp. nov. (male), holotype (SIO-BIC A8382). A Ventral. B Dorsal. Scale bar represents ~10mm.

FIGURE 9. Illustration of Lamellibrachia donwalshi sp. nov. (female), paratype (SIO-BIC A1341). A Ventral. B Dorsal. Scale bar represents ~5mm.

FIGURE 10. Micrographs of Lamellibrachia donwalshi sp. nov. male and female paratypes (SIO-BIC A1341). A Female dorsal anterior and vestimentum. B Male dorsal anterior and vestimentum. C Female vestimental grooves. D Male vestimental grooves. OB, obturaculum; SL, sheath lamellae; VF, vestimental fold; VG, vestimental groove. Scale bars, A–B=5mm; C– D=0.5mm.

FIGURE 11. Interference contrast micrographs of plaques from Lamellibrachia donwalshi sp. nov. holotype (SIO-BIC A8382). A–B vestimental plaques, indicated by arrows. C Trunk plaques, indicated by arrows. D 10µm transverse section through epidermis showing trunk plaques, indicated by arrows. Scale bars 35µm.