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

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Haywardozoon pacificum

n. sp.

Haywardozoon pacificum   n. sp.

( Figs 47 View FIGURE 47 , 48 View FIGURE 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 View FIGURE 47 , 48 View FIGURE 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 View FIGURE 47 ).

Orifice wider than long ( Figs 47I, J View FIGURE 47 , 48G View FIGURE 48 ), 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 View FIGURE 48 ).

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 View FIGURE 47 ). 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 View FIGURE 47 ). 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 View FIGURE 48 ). Orifice of small zooid ( Fig. 48J View FIGURE 48 ) identical in form to that of large zooids).

Measurements (mm). Holotype, ZIRAS 1/50726 ( Figs 47 View FIGURE 47 , 48 View FIGURE 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.