Leucandra irregularis ( Burton, 1930 ), 2015

Leucandra irregularis ( Burton, 1930) View in CoL comb. nov.

Figures 49a–b View FIGURE 49 , 50a–e View FIGURE 50

Anamixilla irregularis Burton, 1930: 6 , fig. 5.

Not: Hôzawa, 1940: 155, pl. VII fig. 12.

Material examined. Holotype ZMA Por. 00144, Indonesia, Nusa Tenggara, Sumbawa, Bay of Bima near South Fort , 8.505°S 118.695°E, depth 55 m, trawled, bottom mud with patches of coral sand, coll. Siboga Expedition stat. 047, 8 April 1899; BMNH 1929.8 .30.6, five slides made from the holotype. GoogleMaps

Description. Hispid thick-walled pear-shaped tube ( Fig. 49a View FIGURE 49 ), size approximately 2.5 cm high, 1 cm in widest diameter, dirty white in color (alcohol), with rather soft consistency. The original specimen had a narrow apical opening with naked rim, but this has been cut off and mounted in one of the slides, kept in the Natural History Museum.

Skeleton. ( Fig. 49b View FIGURE 49 ) Due to the poor preservation, histological sections show a jumbled skeleton, but here and there rounded choanocyte chambers are apparent indicating a leuconoid aquiferous system. There is a cortex of smaller triactines ( Fig. 49b View FIGURE 49 top) overlying a choanosomal skeleton of confusedly arranged giant triactines, with occasional giant diactines at sharp angles to the surface. The atrial skeleton ( Fig. 49b View FIGURE 49 bottom) is predominantly formed by tetractines. The specimen orginally was in the possession of a naked osculum, supported by tangential lengthwise arranged diactines, but this has not survived in the present remains. One of the slides made by Burton and kept in the Natural History Museum collection shows the oscular skeleton to be formed by a dense mass of tetractines similar to those of the atrial skeleton.

Spicules. ( Figs 50a–e View FIGURE 50 ) Giant triactines, intermediate and smaller triactines, smaller tetractines, giant diactines.

Cortical triactines ( Fig. 50d View FIGURE 50 ), actines relatively thin, usually sagittal or parasagittal, rarely regular equiangular and equiactinal, paired actines not infrequently somewhat wobbly, unpaired actines 84– 221.2 –311 x 7– 10.7 –15 µm, paired actines, 123– 263.2 –510 x 6– 10.4 –15 µm.

Choanosomal giant or large triactines ( Figs 50a–b View FIGURE 50 ), usually slightly sagittal, but with actines almost invariably strongly different in length, even when equiangular. The shape somewhat resembles pseudosagittal triactines. Size quite variable but recognizable by relatively thick actines, 270– 597.1 – 1080 x 23 – 38.4 –52 µm.

Atrial tetractines ( Figs 50c View FIGURE 50 ), rather irregular in shape, apical actine prominent, unpaired actines, 174– 293.3 – 420 x 5– 10.3 –13 µm, paired actines 120– 287.2 –438 x 4– 10.8 –17 µm, apical actines 20– 60.8 –120 x 4– 6.8 –10 µm.

Oscular diactines ( Fig. 50e View FIGURE 50 ), occasionally also in the tubar skeleton, 820– 1242.9 –2100 x 45– 55.5 –63 µm.

Ecology. On soft bottom at 55 m.

Distribution. Indonesia, known only from the type locality off the island of Sumbawa.

Remarks. Burton assigned this species to Anamixilla probably because of the similarity of the complement of giant triactines, which also often show a parasagittal shape with unequal actine lengths. However, the structure of the skeleton and the aquiferous system differ clearly from Anamixilla torresi Poléjaeff, 1883 (see below). Remarkably, at a later date (1963) Burton omitted to report the presence of giant diactines in this species, which is one of the distinguishing features.

There is a compelling general similarity with Sri Lankan Leucandra donnani Dendy, 1905 , which shares the shape, skeletal organization and spiculation. Differences are found in the sizes of the various spicule types, with overall smaller lengths and widths .

It also shows similarity with Japanese Leucandra rigida Hôzawa, 1940 , which shares the giant triactines and diactines, differing in the presence of small choanosomal diactines. Northeast Australian Leucandra sphaeracella Wörheide & Hooper, 2003 has giant triactines and diactines, differing likewise from L. irregularis by having small diactines, but these are found in the ectosomal cortex. Both species have the spicule sizes in the same range as those of L. irregularis , so they are to be regarded as members of a regional complex of closely similar species. Leucandra nicolae Wörheide & Hooper, 2003 is also similar in spicule sizes, but it lacks the giant diactines, and has two types of microdiactines. A further close form probably is Leucandra tropica Tanita, 1943 from Palau (also reported by De Laubenfels, 1954). It differs by the presence of cortical tetractines, in addition to atrial tetractines.

Hôzawa (1940) recorded this species from Haiti (Caribbean), but provided no description of the spicules. The habitus figure he provided differs in shape from the holotype. Its identity is unclear, but in view of the localities at opposite parts of the globe it is not likely conspecific with the Indonesian specimen .

The resemblance of the choanosomal triactines to pseudosagittal spicules is perhaps attributable to the possible polyphyletic nature of these spicules, occurring in Grantiidae and Heteropiidae as discussed in Voigt et al. (2012).