Imbricaverruca yamaguchii Newman 2000, n. sp.
Creators: name: Newman, William A.
Publisher: name: Zenodo
Year: 2000
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Maxillopoda
Sessilia
Neoverrucidae
Imbricaverruca
Imbricaverruca yamaguchii

description: Imbricaverruca yamaguchii n. sp.
(Figs 1A; 2; 3; 4C; 5; 6)
MATERIAL. — Specimens were collected by the French submersible Nautile, BIOLAU Cruise of 1989 to the Lau Basin, Tonga (A.-M. Alayse-Danet, chief scientist), and they were received from the Centre national de tri d’Océanographie biologique (CENTOB), IFREMER, Brest. Two adult specimens on round stones partially coated with sulfide deposits, plus several juveniles about to shed their cyprid shells, inferred to belong to this species (Jensen’s x-juveniles of HØeg & Newman 1997; see below), all from station 1 (Hine Hina, 22°32’S, 176°43’W, at 1900 m depth). Two of these samples (BL-01 & BL-03) contained other vent barnacles and other vent organisms (Newman & Yamaguchi 1995; Yamaguchi & Newman 1997; Southward & Newman 1998; cf. Desbruyères et al. 1994).
ETYMOLOGY. — Named for Toshiyuki Yamaguchi in appreciation of his numerous and exacting works on the systematics and ecology of the living and fossil cirripeds, especially the vent barnacles.
DIAGNOSIS. — As for the genus.
R-C rostro-carinal diameter
W width, both in mm.
COMPARATIVEDESCRIPTION
Hard parts
The low-conic profile of the new genus, Imbricaverruca, is similar to Neobrachylepas Newman & Yamaguchi, 1995, whose representatives were relatively young, and to the juveniles of Neoverruca and Eochionelasmus Yamaguchi & Newman, 1990. The operculum forms a flat lid, as in the Proverrucidae and Verrucidae, but the hinge line is curved rather than essentially straight as in Neoverruca, and in higher verrucomorphs (cf. Figs 1A; 2A). Therefore, in order for the operculum to open, there is likely some flexibility to the wall as well as some freedom in the arthrodial membrane forming the hinge, and it must be able to bend along the scuto-tergal articulation, an ability likely facilitated by the basal gap protected by the median latus (Fig. 2C). Like Neoverruca, the scutal adductor muscle inserts in a pocket below the apex of the movable plate (Fig. 2E), and its origin on the fixed scutum, near the centre of the plate (Figs 2G; 4C), is supported by an adductor ridge or “myophore” as in Metaverruca Pilsbry, 1916 and Verruca Schumacher, 1817 (cf. Young 1998 for revision) (Fig. 4 G-H).
The fixed scutum and tergum are much reduced in height (Fig. 2 F-G, J-K) and there is a complex articulation between them. Together with the rostrum and carina, which are also much wider than high, they form a ring-like wall supporting the operculum. Therefore, the imbricating plates between this primary wall and the substratum form a substantially greater proportion of the body chamber than in Neoverruca. The principal three tiers of lateral imbricating plates, standing four plates high (rl 1-4, l 1-4 and cl 1-4), are fully represented in these two apparently adult Imbricaverruca (Figs 1A; 2A; 4C), as they are in brachylepadomorphs (Newman 1987: fig. 4A) and in the juveniles of Neoverruca (Newman & Hessler 1989; Newman 1989).
Soft parts
The trophi and cirri (Fig. 3) are similar to those of other hydrothermal vent barnacles (Scalpellomorpha, Brachylepadomorpha, Verrucomorpha and Balanomorpha), reflecting adaptations to feeding on very fine particles, presumably small, suspended bacterial clumps and filaments (cf. Southward & Newman 1998). The slightly bullate, indented but unnotched labrum of I. yamaguchii (Fig. 3F) supports the usual row of fine teeth and relatively large palps provided with relatively fine, stiff setae. The mandible (Fig. 3G, right exterior, H, I, left interior) is comparable to that of other hydrothermal vent forms, especially that of Neoverruca brachylepadoformis, in having one superior incisiform tooth above a setose area, followed by two low teeth each supporting a row of numerous, short, sharp spines along their superior curvatures, several of the uppermost of which roll over onto the inner or posterior surface (Fig. 3I), and the upper margin of the inferior angle supports a row of similar spines.
Maxillae I and II (Fig. 3 J, K and L, respectively) each support a relatively uniform comb of slender setae along the cutting edge, but maxillae I of I. yamaguchii differs from Neoverruca in having a single strong spine among the ordinary setae inside and just below the superior angle (Fig. 3K).
What could be seen of the cirri (Fig. 3 A-D) suggested they were typical of most vent barnacles, but unfortunately those of the paratype were badly damaged or missing. The right side was in the best condition and the cirral counts are as follows (a, anterior ramus; p, posterior ramus; –, ramus absent; +, terminal articles missing):
As can be observed (Fig. 3A, B), the first two pairs of cirri are modified as maxillipeds and at least the posterior ramus of the first as well as of the second are antenniform. The posterior four pairs of cirri are normal (ctenopod), but the lesser curvature of the intermediate articles of cirrus VI each have as many as five pairs of moderately long setae, fewer than Neoverruca, and their s/a ratios are markedly different, that for Imbricaverruca falling within the range for other vent barnacles while that for Neoverruca is the lowest known (Table 1).
The caudal appendages, while multiarticulate in Eochionelasmus and minute and uniarticulate in Neolepas Newman, 1979 and Neobrachylepas, are absent in Imbricaverruca as well as Neoverruca (Fig. 3C). Both adults were hermaphroditic; penis long, conspicuously annulated, and sparsely clothed with short, stiff setae (Fig. 3C, E). While the generally well-developed penes of vent barnacles have a well-developed pedicel, there is no basidorsal point (Fig. 3C). Well-developed testes extend into the pedicels of cirrus I & II (Fig. 3A, B), and to a lesser degree into at least those of cirrus III & IV. Ovigerous frena were not seen, but no ovigerous lamellae were being incubated and in their absence frena may be easily overlooked.
The x-juvenile
A number of attached cyprids found on sulfide deposits associated with hydrothermal activity were included with the collection from the Lau Basin sent by CENTOB. Some were sent to Peter G. Jensen for the study of lattice organs (cf. Jensen et al. 1994) who removed the cyprid shell covering the first juvenile stage inside, when preparing them for SEM. Some of these were neolepadines but two were the first juvenile stage of an unusual thoracic cirriped. It was studied and dubbed “Jensen’s x-juvenile” by HØeg & Newman (1997) (Fig. 5). Its capitulum, supported by a peduncle of comparable length, is armored by the five primordial valves commonly found in juvenile thoracicans, except iblomorphs.
The position and shape of the carinal primordium and a slight asymmetry between the scuta suggested the juvenile was a verrucomorph (HØeg & Newman 1997).
The early juveniles of Neoverruca (Newman, 1989) can be distinguished from the x-juvenile in being more generalized; e.g. in having a carinal primordium that is higher than wide extending up between the terga (Fig. 6; cf. Table 2). The only first juvenile of a verrucid known is that of Verruca stroemia Müller, 1776 described by Runnström (1927) and it differs from the x-juvenile in the scutal primordia being grossly unequal rather than nearly equal in size. Therefore it was concluded the x-juvenile could represent 1) a verrucid more primitive than V. stroemia such as an Altiverruca, 2) an advanced neoverrucid such as the one described from Lau herein, or 3) a yetto-be discovered population of the presumably extinct proverrucid, and it was thought that, because of these uncertainties, determining the affinities of Jensen’s x-juvenile would require further sampling of the Lau Basin fauna (HØeg & Newman 1997). However, the Lau neoverrucid, now known as Imbricaverruca, turned out not only to be more highly evolved than Neoverruca, but the adult has an autapomorphy, a carina that is much wider than high, which is the most notable characteristic of the x-juvenile. Therefore it seems highly likely that Jensen’s x-juvenile is the first juvenile of Imbricaverruca.
description: Published as part of Newman, William A., 2000, A new genus and species of barnacle (Cirripedia, Verrucomorpha) associated with vents of the Lau Back-Arc Basin: its gross morphology, inferred first juvenile stage and affinities, pp. 71-84 in Zoosystema 22 (1) on pages 74-81, DOI: 10.5281/zenodo.5391395