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

Abstract

This work describes Bryozoa of the orders Cyclostomata and Ctenostomata found associated with polymetallic nodules collected by box-coring in the eastern part of the Russian exploration area of the Clarion-Clipperton Fracture Zone (CCFZ) under contract to Yuzhmorgeologiya. Scanning electron microscopic study of 358 cyclostome colonies and 14 ctenostome colonies from 4510–5280 m depth has resulted in the recognition of two new species of Ctenostomata, and 14 new species, nine new genera and two new families of Cyclostomata; three additional species of Cyclostomata are left in open nomenclature pending the discovery of missing reproductive characters. The taxonomic novelty is thus notable. One of the new Ctenostomata represents the first living example of the previously monotypic Late Cretaceous genus Pierrella. Twelve of the new cyclostome taxa have well-developed gonozooids, indicating that embryonic cloning (polyembryony) is normal in this deep-sea environment. On the other hand, one indeterminate tubuliporine and two rectangulates have dimorphic peristomes. In the latter two cases, enough mature colonies were found to suggest that this feature is normal, and that the dimorphic zooids are possibly female—in other words, capacious incubation chambers are apparently lacking, and therefore polyembryony would also be lacking or reduced. In one of these species, evidence is presented to suggest that the ancestrular zooid can reproduce precociously. Of the species reported here, only one has previously been found outside the exploration area, highlighting both the limited knowledge we have of bryozoans in the deep Pacific and/or a fauna that is largely endemic to the nodule environment. An additional 31 species of Cheilostomata have also been discovered that will be described in a subsequent publication. Most bryozoans are macrofaunal-sized, so are both inadequately determinable and overlooked in images obtained by remotely operated vehicles; yet, with 50 species, Bryozoa is the most speciose sessile macrofaunal phylum on the nodules. Nodules constitute hard substrata in an area otherwise mostly inhospitable for Bryozoa, hence mining would lead to loss of critical habitat. Further, as suspension-feeders, bryozoans are highly susceptible to smothering by suspended sediment, and non-mined areas closely adjacent to extraction zones would likely also be affected and their associated bryozoan fauna obliterated. More data are required on the distribution of the CCFZ bryozoan species elsewhere in the east Central Pacific to determine if mining would lead to local taxon extirpation or global extinction at both low and high taxonomic levels.

Morphology of ctenostome bryozoans: 2. Haywardozoon pacificum, with implications of the phylogenetic position of the genus

“…bbw, basal body wall; bce, basal cuticular extension; blc, basal lip cuticle; c, collar; coe, collar epithelium; cui, cuticular inclusions; d, diaphragm; fbw, frontal body wall; o, orifice; v, vestibulum; vw, vestibular wallAlthough generally assumed long-living, larvae of such broadcasters might also be short-living and undergo metamorphosis shortly after their release. In the original description, an ancestrula of Haywardozoon pacificum was found close to other zooids(Grischenko et al, 2018). This indicates that either larvae from the same or different spawnings settled on the same substrate.…”

“…The tentacle number was not determined byGrischenko et al (2018), but determined as 17 in the current study. This number is within known range of the two other congeners and ranges between 12 and 18 (12 in H. atlantae, 14-18 in H. inarmatum (d'Hondt, 1983)).F I G U R E 1 Haywardozoon pacificum, light microscopical images.…”

“…bryozoans. Herein, we analyze the newly described deep-sea species Haywardozoon pacificum Grischenko, Gordon, & Melnik, 2018. Haywardozoon inarmatum is the type species of the genus Haywardozoon, which is even often allocated to a separate family. Originally described as Flustrellidra inarmata, it was collected from 2,939-3,213 m depth in the Norwegian Sea (Hayward, 1978).…”

“…Haywardozoon atlantae d 'Hondt & Hayward, 1981 has been described from the southwestern Atlantic (36 S, 52 W) from 2,440-2,480 m depth. The most recently described Haywardozoon pacificum Grischenko, Gordon, & Melnik, 2018 has been documented from eight stations within the Russian exploration area of the Clarion-Clipperton Fracture Zone, eastern Central Pacific, from a depth range 4,741-5,050 m. All species are characterized by simple, uniserial colonies with flattened zooids, and the aforementioned specific closure mechanism of the aperture.…”

Modularity is the mother of invention: a review of polymorphism in bryozoans

“…The gonozooid consists of a proximal undifferentiated section, an enlarged area forming the brood cavity where the embryos are incubated, and the brood chamber aperture (ooeciostome) homologous to the autozooidal peristome (Ström, ; Schäfer, ). Typical cyclostome gonozooids are lacking in only two families: Cinctiporidae, which has very large autozooids (Boardman, McKinney & Taylor, ) that might function reproductively (unconfirmed) and Anyutidae, which has autozooids possessing modified peristomes with inferred reproductive function (Grischenko, Gordon & Melnik, ).…”