Bomba Kelly, Reiswig & Samaai

Kelly, Michelle, Sim-Smith, Carina, Stone, Robert, Reiswig, Toufiek Samaai Henry & Austin, William, 2016, New taxa and arrangements within the family Latrunculiidae (Demospongiae, Poecilosclerida), Zootaxa 4121 (1), pp. 1-48 : 28-29

Genus Bomba Kelly, Reiswig & Samaai gen. nov.

Type species. Bomba endeavourensis gen. et sp. nov., designated herein.

Diagnosis. Small, low-lying hemispherical to pedunculate Latrunculiidae with a smooth or wrinkled surface which may be raised in places into tough, horn-like bundles of megascleres. Megascleres are large sinuous styles that are lightly terminally spined. Microscleres are unusual anisodiscorhabds with only three whorls of projections: a basal whorl, a median whorl, and an apical whorl. The basal whorl is composed of bifurcate projections that may be terminally rounded or sharp. The median whorl, located slightly above centre on the shaft, is similar to the basal whorl in all aspects of morphology except that the bifurcate projections may be splayed horizontally. The apical whorl consists of doublet cylindrical projections, the tips of which may be sharp or bluntly terminated in the form of a chiaster, the edges ringed with minute spines. The doublet projections of the basal and median whorls are horizontally arrayed perpendicular to the shaft, while those of the apical whorl are vertically orientated, parallel with the spicule shaft. Projections are generally smooth but may be sparsely acanthose with spines in patches and linear arrays. The basal whorl is orientated obliquely and slightly away from the median and apical whorls which are orientated obliquely and slightly forward. The anisodiscorhabd progenitor consists of differentiated basal, median, and apical whorls from the earliest stages. Ectosome forms a leathery casing formed by a tangential crosshatching of megascleres topped with a patchy palisade of single, well-spaced microscleres. Choanosome is soft, detaching easily from the ectosome, permeated with thick, strong fibres. Megascleres and microscleres are scattered between the fibres.

Etymology. Named for the holotype which has the morphology of a floating sea mine as seen from above the water (bomba, mine; L.).

Remarks. The anisodiscorhabds of Bomba gen. nov. are very unusual in that they appear to be a highly reduced form with only three whorls of projections; there is no evidence of a manubrium or subsidiary whorl or apex. Although the microsclere appears superficially to be the same at each end, the basal and apical whorls are at slightly different angles to the shaft (the apical whorl projecting forwards) and the doublet projections on the apical whorl are on a different plane compared to those of the median and basal whorls. The megascleres in this genus are the longest known to date in the Latrunculiidae , averaging over 600 µm and reaching well over 700 µm in the case of the type species B. endeavourensis gen. et sp. nov.

Type species Bomba endeavourensis gen. et sp. nov. can be compared to species of Tsitsikamma (Family Latrunculiidae ) from South African waters, which also have an ectosomal casing that is extraordinarily tough and leathery and composed of a thick, paratangential cross-hatch of megascleres. However, Tsitsikamma type species, T. favus Samaai & Kelly, 2002 , and T. scurra Samaai, Gibbons, Kelly & Davies-Coleman, 2003 , differ in that they are constructed of large, rigid chambers, not a single sack as B. endeavourensis gen. et sp. nov. Both genera also have species with unusual anisodiscorhabds featuring three rings of uniform doublet projections (or triplets in the case of Tsitsikamma species) with chiaster-like terminations. The specific form and ornamentation of the microscleres in Bomba gen. nov. are quite different, however, and no other Latrunculiidae has been recorded with protruding, horn-like spicule tracts.

The microscleres of B. endeavourensis gen. et sp. nov. are grossly comparable to species of the South African genus Cyclacanthia Samaai, Govender & Kelly, 2004 (Family Latrunculiidae ), which have acanthose isospinodiscorhabds with three whorls of spines positioned equidistantly along the shaft, but which also bear a manubrium and apical spike. Figure H illustrates the diagnostic microscleres that define Bomba gen. nov.