Haywardozoon pacificum, Grischenko & Gordon & Melnik, 2018

Grischenko, Andrei V., Gordon, Dennis P. & Melnik, Viacheslav P., 2018, Bryozoa (Cyclostomata and Ctenostomata) from polymetallic nodules in the Russian exploration area, Clarion - Clipperton Fracture Zone, eastern Pacific Ocean-taxon novelty and implications of mining, Zootaxa 4484 (1), pp. 1-91 : 69-74

Haywardozoon pacificum n. sp.

( Figs 47 , 48 )

Material examined. Holotype: ZIRAS 1/50726, colony encrusting tube of serpulid polychaete detached from nodule, YMG R.V. Yuzhmorgeologiya cruise YMG4–04, Stn 39, 16 August 2005, 13.61415° N, 130.82158° W, 5017 m. Additional material: YMG4–07, Stns 134, 143; GLD4–11, Stns 214, 220; GLD4–12, Stns 245, 267; YMG4–14, Stn 322. Total specimens examined eight.

Etymology. Alluding to the first description of the genus in the Pacific Ocean.

Description. Colony encrusting, diffuse, comprising up to c. 12 large zooids, partly uniserially arranged and disjunct ( Figs 47 , 48 ), adjacent zooids connected distally and laterally by very small contact points; highly transparent and apparently colorless in life. Zooids generally mostly elongated, their lateral outlines weakly convex to subparallel or even slightly diverging; bilaterally symmetrical or one side extending outwards as a triangular skirt. Daughter zooids budded distolaterally. Membranous frontal wall gently rising to highest point of zooid at orifice ( Fig. 47G ).

Orifice wider than long ( Figs 47I, J , 48G ), having slightly thickened cuticularized rim with two components—proximal rim more or less transversely C-shaped, concave on inner side; distal rim more or less straight but produced proximally as D-shaped flap that superficially resembles operculum and fits into concavity of proximal rim; edge of flap slightly thickened ( Figs 48G, H ).

Vestibule more or less parallel-sided, a little longer than broad, 28–33% polypide length, with strongly developed parieto-diaphragmatic musculature at proximolateral corners ( Fig. 47I, J ). Vestibule 0.097–0.123 mm long; retracted tentacle crown 0.265–0.311 mm long, tentacle number not determined. No stomach gizzard. Small brown bodies or fragments of brown bodies retained in cystid ( Fig. 47I, J ). Anchor point of polypide retractor muscles not clearly seen.

One very small oval zooid encountered that may be ancestrula, very close to proximal curved ‘tail’ of large zooid that may have budded from it ( Fig. 48I ). Orifice of small zooid ( Fig. 48J ) identical in form to that of large zooids).

Measurements (mm). Holotype, ZIRAS 1/50726 ( Figs 47 , 48 ): ZL 0.703–1.450 (1.048 ± 0.211); ZW 0.438–0.852 (0.714 ± 0.117); OrL 0.088–0.140 (0.120 ± 0.018); OrW 0.150–0.203 (0.172 ± 0.019). Ancestrula (n = 1): AnL 0.322; AnW 0.221; AnOrL 0.027; AnOrW 0.059.

Remarks. We follow Jebram (1986) in including Haywardozoidae in superfamily Hislopioidea, and Reverter- Gil et al. (2016) concerning the emended spelling of the family name.

Our material conforms to the overall characters of the two described Atlantic species of Haywardozoon , especially H. inarmatum , which has a similar budding pattern and zooid shape, but from which it differs in details of the orifice. D’Hondt (1983) characterized the polypide of Haywardozoon species as “minute … inhabiting only a very small portion of the zoecial cavity”, which is not the case in H. pacificum n. sp. The CCZ colonies were found only on tubes of serpulid polychaetes attached to nodules.

Distribution. Recorded from eight stations within coordinates 12.26676– 13.61415° N, 130.82158– 134.59811° W, at depth range 4741–5050 m.

Figures

FIGURE 47. Haywardozoon pacificum n. sp. Specimens stained in Rose Bengal. A, specimen GLD4–11, Stn 214, zooids on a serpulid tube; B–G, holotype, ZIRAS 1/50726, different views of zooids on a serpulid tube; H–J, specimen GLD4–12, Stn 245, respectively showing very lightly stained zooids on serpulid tube and two zooids seen in transmitted light. Abbreviations: bb, brown body; d, diaphragm; dmd, dilator muscles of diaphragm; g, gut; olf, operculum-like flap; rmtc, retractor muscles of tentacle crown; t, tentacle cluster; v, vestibule. Scale bars: A–H, 500 µm; I, J, 100 µm.

FIGURE 48. Haywardozoon pacificum n. sp. Holotype, ZIRAS 1/50726. A–F, autozooids disposed on serpulid tube, all slightly collapsed through drying; G, H, orificial region showing operculum-like flap; I, autozooid, with dwarf ancestrular at lower right; J, close-up of ancestrula. Scale bars: A, F, 500 µm; B–E, I, 250 µm; G, 200 µm; H, I, 100 µm.