Amathia acervata Lamouroux, 1824

Hirose, M. & Gordon, D. P., 2020, New seriated Amathia species in Japan, with a redescription of A. acervata Lamouroux, 1824 (Bryozoa: Ctenostomata), Zootaxa 4742 (2), pp. 311-331 : 314-317

Amathia acervata Lamouroux, 1824

( Fig. 2 )

Amathia acervata Lamouroux, 1824: p. 45 ; Jelly, 1899: p. 10; d’Hondt, 1991: p. 165 (part).

Serialaria acervata: Blainville, 1834: p. 476 ; Deshayes & Milne Edwards, 1836: p. 170; d’Orbigny, 1853: p. 595.

Non Amathia acervata: d’Hondt, 1979: 10 , 16; d’Hondt, 1983: p. 65, fig. 36E; d’Hondt, 1991: p. 163, 165 (part); Gordon et al., 2009: p. 288. [These all refer to Amathia bicornis Tenison-Woods, 1880 .]

Amathia vidovici: d’Hondt, 1991: p. 165

Material examined. Holotype: Muséum national d’Histoire naturelle ( MNHN), Herbarium Sheet 86 (dried specimen; Fig. 2A ), with original handwritten label ( Fig. 2B ); a reconstituted fragment of the holotype, now in 70% ethanol, accompanies the herbarium sheet. Collected in Japanese waters by Wilhelm Gottlieb Tilesius (during the first Russian circumnavigation on the Nadezhda), October 1804 (see Barratt 1981).

Description (of reconstituted sample from holotype). Colonies erect, comprising relatively short (c. 12.0– 12.5 mm), sparsely branching tufts from small attachment points on algal substratum, these a little broader than the stolon and apparently somewhat triangular in cross section or roundly so; rhizoids not evident. Branching dichotomous ( Fig. 2 C–F), at angles of 20–45°. Stolon segments more or less straight or very gently curving, sinuous where the autozooid pairs are clustered ( Fig. 2E ); mean stolon length 1.74± 0.38 mm (range 1.41–2.35 mm, n = 5). Mean stolon width 0.10± 0.01 mm (range 0.09–0.13 mm, n = 11). Stolon with refringent yellow granules ( Fig. 2D ).

Autozooid clusters disposed in anticlockwise spirals on the stolon segments, comprising c. 12–15 ‘pairs’ per cluster, each cluster describing c. 1.6 turns about the stolon from its commencement to its completion; mean cluster length on stolon 1.00± 0.18 mm (range 0.75–1.29 mm, n = 8), terminating at the next stolon septum or branch node; mean inception distance of proximalmost zooid in cluster from bifurcation 0.82± 0.10 mm (range 0.66–1.00 mm, n = 9), zooid cluster occupying 54–75% of stolon length. Autozooids tilted distad from the perpendicular ( Fig. 2 C–F), with a mean length of 0.44± 0.03 mm (range 0.37–0.48 mm, n = 9) in reconstituted dried retracted specimens, connate, the outermost half of each zooid wall with thicker cuticle (hemispherical when viewed apically or in optical section); zooid width (as measured in lateral view of zooid cluster) averaging 0.12± 0.01 mm (range 0.11–0.14 mm, n = 8); owing to the zooid tilt, the distal end of each cluster generally leans past the point of termination of the zooid insertions at each branch node.

Remarks. Lamouroux (1824, p. 45) gave a diagnosis: “ Amathia dwarf, little branched, subdichotomous; hairlike branches, thin; subseparated cells (i.e. zooids) in distinct groups, together standing apart” (authors’ translation from the French). The fuller description of A. acervata given by Deshayes & Milne Edwards (1836) was translated by Tenison-Woods (1880) from the French thus: “the groups of cells are distant a millimetre from one another. They are composed of nearly 20 cells, heaped without order around the subdichotomous stems, which are not much branched, and isolated during the greater part of their length.”

Not enough material is available (or able to be reconstituted) to determine the full range of characters or dimensions based on the type. There is considerable concordance or overlap of characters (see Table 2 ) between A. acervata and Amathia brevisilva n. sp., though there are some differences, such as the direction of spiral of the autozooid clusters.

Lamouroux (1824) stated that his material came from the Sea of Japan (in French as “la mer du Japon ”) and that it had been collected by Wilhelm Gottlieb Tilesius (who visited Japan in 1804); subsequent French authors accepted this information ( Blainville 1834; Deshayes & Milne Edwards 1836; d’Orbigny 1853).

In recent decades, owing to a misunderstanding based on historic specimens in European museums, the binominal A. acervata was misapplied. d’Hondt (1979, 1983, 1991) inadvertently equated the species with Australian A. bicornis Tenison-Woods, 1880 , treating the latter as a junior subjective synonym. However, the earliest descriptions of A. acervata sensu Lamouroux do not match published descriptions and illustrations of A. bicornis , which is a highly distinctive species. Lamouroux (1824) described the autozooids as heaped/stacked/accumulated without order, which is not at all true of the Australian taxon, which has highly ordered, connate biserial clusters of autozooids that spiral distinctively for 1.5 turns about the stolon segment. Each autozooid also carries a conspicuous pair of spine-like processes, hence the epithet bicornis ; these are not mentioned in the diagnosis of A. acervata sensu Lamouroux.

Neither specimen name ( acervata or bicornis ) is given in any of the comprehensive published 20th-century lists of Bryozoa from Japan (e.g. Mawatari 1965; Mawatari 1986) or anywhere else in East Asian seas subsequently (e.g. Liu et al. 2001; Seo 2005, 2011), until Seo et al. (2018) reported it from Korea’s ‘South Sea’ coast (based on advice from the present authors). Harmer (1915), however, had tentatively included A. acervata in the synonymy of putative A. distans , noting that, “It is not impossible that the present species is identical with A. acervata , described by Lamouroux (1824) from Japan.” d’Hondt (1979, p. 16) came to his conclusion concerning the synonymy of A. acervata and A. bicornis based on the examination of a specimen labelled ‘Sirinx spinosa’ by Charles-Alexandre Lesueur, according it the corrected name of “ Amathia acervata ( Lamouroux, 1816 [sic]) (Holotype)” and “Nouvelle- Hollande?” as the provenance. However, he did not examine a Lamouroux specimen from Japan at that time as Lamouroux’s type was then thought lost (or destroyed in the Second World War).

Subsequently, d’Hondt (1991) reported on a collection of Lamouroux Bryozoa rediscovered in the herbarium at the Université de Caen. The dried bryozoans were kept between dust covers in the manner of dried plant or algal specimens. Dust cover 86 pertained to Amathia acervata ( Fig. 2A ) retaining an original label from the time of Lamouroux ( Fig. 2B ); the specimen is clearly not like A. bicornis . Assuming A. acervata had been lost, d’Hondt (1991, p. 165) interpreted this material as belonging to a completely different species, Amathia vidovici ( Heller, 1867) . He incorrectly determined another specimen LBIMM-BRY- 4531 in the same collection that looks like A. bicornis as the syntype of A. acervata .

In the information accompanying his original description, Lamouroux (1824) noted that A. acervata is ‘parasitic’ on Fucaceae . There is only one species of Fucus in Japan, viz. F. distichus subsp. evanescens , which occurs on the coast of Hokkaido, where Amathia has not been recorded in the published literature (see Mawatari 1972; Mawatari & Mawatari 1981). On the other hand, there are numerous species of Sargassum ( Fucales , Sargassaceae ) in Japan.

Based on the discrepancies between the original descriptions and geographical distributions of A. acervata and A. bicornis , we conclude: 1) the specimen in dust-cover 86 labelled Amathia acervata and resembling A. vidovici (which would be not dissimilar from A. distans or look-alikes in the dried state) was in fact genuine A. acervata from Japan (redescribed in this study); 2) a specimen in the same collection (LBIMM-BRY-4531) that looks like A. bicornis came not from Japan but from Australia (from Tasmania via a Mr Cummings).

Based on the dried holotype, d’Hondt (1991) noted that the European species Amathia vidovici ( Heller, 1867) resembles A. acervata . Now that the characters of the latter have been clarified based on the reconstituted fragment, it is possible to make a more precise comparison: A. vidovici differs in having both clockwise and anticlockwise spirals that complete only a single turn about the stolon owing to fewer autozooid pairs in each cluster (8–9) and both Prenant & Bobin (1966) and Hayward & McKinney (2002) state that stolon diameter is 0.2 mm, rather larger than in any of the Japanese specimens discussed in this paper (see Table 2 ).

Figures

FIGURE 2. Amathia acervata Lamouroux, 1824, holotype, Herbarium Sheet 86, MNHN, Paris. A. Entire type specimen. B. Original label in Lamouroux’s handwriting. C. Reconstituted fragment of holotype. D. Part of C, direct illumination. E, F. Part of C, in transmitted light, E showing distinct sinuosity of stolon within the autozooid cluster (same scale).