Olisthella occlusa n. sp.

(Fig. 9)

Material examined. Holotype: AU.J62, from RV Vulkanolog Stn B 36/37 #64 (Collection Sample AU 12299), 35.4383° S, 175.7167° E, 445 m, deep outer shelf off NE North Island, 25 February 1990.

Etymology. Latin occlusus, closed, shut, alluding to the kenozooids that occupy autozooidal cystids, occluding their cavities.

Description. Unique colony unilaminar, multiserial, but made up of coalescing pluriserial lobes of zooids in quincunx, leaving some zooids slightly disjunct and some interzooidal spaces occupied by well-developed kenozooids; maximum spread 6.5 mm. Autozooids more or less elongate-oval, many with tapering gymnocystal ‘tails’ [ZL 500–921 (642); ZW 387–472 (428)]. Gymnocyst encircling entire autozooid, generally narrow throughout but may be a little broader proximally or proximolaterally. Cryptocyst and opesia encircled by a continuous raised granular rim (CrL 365–656 (500); CrW 299–361 (299)]; cryptocystal shelf moderately broad, gently sloping towards opesia, attenuating in width towards orificial area, evenly granular except for a smooth band bordering opesia. Opesia more or less narrowly elongate-oval, generally broader proximally, proximal margin evenly rounded or obliquely so [OpL 231–500 (353)]. Articulated pericryptocystal spines 17–27 in number; the distalmost 6–7 spines slightly thicker, bordering the orifice in an arcuate series; 5–17 additional spines on the surrounding gymnocyst, the maximum number of spines seen on any one zooid = 44. No avicularia. Ooecium hyperstomial, smooth-surfaced, about as wide as long or wider; tilting reveals a narrowly transverse or compressed subarcuate ectooecial excavation facing proximad, not seen in frontal view [OoL 176–221 (208); OoW 211–223 (213)]. Ooecial kenozooid wholly concealed by ooecium. Interzooidal kenozooids generally well developed, infilling spaces between disjunct autozooids, each with a sloping gymnocyst surrounding a small central opesial foramen surrounded by a concentric area of granular cryptocyst; similar kenozooids form within some autozooidal cystids by regenerative budding, superficially appearing as opesial closure plates. Position of frontally damaged ancestrula indicated only by a thin lateral wall.

Remarks. Olisthella occlusa n. sp. is characterised by the large number of pericryptocystal and gymnocystal spines, frontally featureless ooecium, wholly concealed ooecial kenozooid and distinctive inter- and intrazooidal kenozooids. It appears most closely related to O. mimica n. sp. (below), which has far fewer spines and a smooth cryptocyst.

Distribution. Endemic to the New Zealand EEZ; known only off the NE coast of North Island at 995 m depth, where it encrusted the inner face of an unidentified bivalve shell.