Hippothoa catophilia Gordon 2020, n. sp.

Hippothoa catophilia n. sp.

(Figs 1 A–D; 2A, B)

Etymology. Alluding to the substratum; species of the bryozoan family Catenicellidae are popularly called ‘cats’ by specialists of the group; plus - philia, Greek, affection, fondness.

Material examined. Holotype: NIWA 132781, epizoic on the catenicellid bryozoan Costaticella solida (Levinsen, 1909), NIWA Stn B 272, 46.7333° S, 168.5233° E, 21 m, Foveaux Strait, New Zealand, coll. 29 May 1960. No paratypes.

Description. Colony encrusting, uniserial, branching. Length c. 4 mm, crossing several catenicellid segments.

Autozooids mostly restricted to abfrontal sides of autozooidal segments of catenicellid host, scarcely encroaching past lateral walls onto frontal side. Dilatation of autozooid strongly sloping upwards distad into an elongated suboral umbo (Fig. 1A) that has an oval or slit-like pseudopore on its distal face (virtually its underside), which partly conceals the orifice from frontal view (Fig. 1D). Cauda of autozooid about as long as dilatation, and jointed (cuticular) if it crosses a catenicellid joint (Fig. 1C), otherwise very short. Zooids of uniserial runner tend to be on one side of catenicellid basal wall, budding a pair of zooids laterally across the rest of the catenicellid wall (Fig. 1B); hence generally three, sometimes four, zooids epizoic on each catenicellid segment. Autozooidal gymnocyst smooth, often with some faint transverse growth lines. Free lateral pore-chamber openings small, round, two on each side. Basal zooidal wall with elongate-oval window in calcification. ZL 525±80, 341–608 (15); ZW 171±17, 136–188 (6).

Orifice (Fig. 1D) steeply sloping distad at about angle of 45°, a little longer than wide viewed en face; anter widest midlength, narrowing proximad toward stout angular condyles set below short shoulders of orifice; welldeveloped sinus a broadly rounded V shape. OL 70±8, 63–79 (4); OW 63±6, 55–70 (4).

No zooeciules.

Female cystids budded laterally (Fig. 1C) from parent autozooids in linear runner chains; similar to parent autozooids in size and also having an inclined frontal shield with stout suboral umbo; dilatation straight, the ta- pered proximal portion generally curving towards parent zooid, actual cauda very short. A pair of small round pore-chamber openings on each lateral wall. Ovicell prominent, terminal, cleithral; ooecium formed by flat distal (ooecial) kenozooid, ooecial frontal surface somewhat flattened, very smooth; distal profile of ooecium rounded, tapered, somewhat truncate, or medially notched depending on whether apical pseudopores (Fig. 2A) are fused or double with short median suture line. Periphery of ooecial kenozooid with 1–2 pore-chamber openings. Dimorphic combined maternal aperture proportionally broader than autozooidal orifice; common (combined) orifice about same size as autozooidal orifice (Fig. 1D). ♀ ZL 413±39, 352–494 (10); ♀ ZW 179±11, 169–200 (7); OoL 135±10, 120–148 (7); OoW 155±20, 137–193 (6); ♀ OrL 59±12, 49–74 (4); ♀ OrW 56±4, 53–59 (2).

Ancestrula kenozooidal, broadly oval (Fig. 2B). One seen on basal wall of catenicellid zooid doublet at branch bifurcation, with two pairs of budding loci; an ovicelled female zooid produced on each side proximolaterally, and a pair of long-caudate autozooids budded distolaterally, each cauda crossing a catenicellid joint to produce a chain of zooids along each daughter branch of host. AncL 236 (1); AncW 204 (1).

Remarks. Hippothoa species generally encrust hard substrata (shell gravel, dead coral, stones, rock), less often ‘leafy’ macroalgae (Gordon 1984) and rhodoliths (Souto et al. 2014), and rarely living animal hosts. Exceptions include Hippothoa musivaria Hayward & Fordy, 1982 (obligately on a living species of Adeonella) and Hippothoa aruensis Morris, 1980 on a species of Triphyllozoon. It was not stated if the Triphyllozoon host was dead or alive at the time of settlement; insofar as H. aruensis has a wide trans-Pacific distribution in warm water and can occur on non-fenestrate substrata (see Morris 1980, pl. 1, figs 3, 4, 6) the association is not obligate.

Hippothoa catophilia n. sp. is not only unique among hippothoids in encrusting a catenicellid host, it is also exceptional among cheilostomes in precociously budding two ovicellate zooids directly from the ancestrula; previously, Ostrovsky (1998) described the budding of an ovicellate zooid from an ancestrula in Cribrilina annulata (Fabricius, 1780).

Distribution. Endemic; known only from the type locality, Foveaux Strait, New Zealand, 21 m, presumably restricted to bushy catenicellid bryozoans.