BAERIIDA, Borojevic & Boury-Esnault & Vacelet, 2000

Borojevic, Radovan, Boury-Esnault, Nicole & Vacelet, Jean, 2000, A revision of the supraspecific classification of the subclass Calcaronea (Porifera, class Calcarea), Zoosystema 22 (2), pp. 203-263 : 249-251

Order BAERIIDA n. ord.

DIAGNOSIS. — Leuconoid Calcaronea with the skeleton either composed exclusively of microdiactines, or in which microdiactines constitute exclusively or predominantly a specific sector of the skeleton, such as choanoskeleton or atrial skeleton. Large or giant spicules are frequently present in the cortical skeleton, from which they can partially or fully invade the choanoderm. In sponges with a reinforced cortex, the inhalant pores can be restricted to a sieve-like ostiabearing region. Dagger-shaped small tetractines (pugioles) are frequently the sole skeleton of the exhalant aquiferous system. Although the skeleton may be highly reinforced by the presence of dense layers of microdiactines in a specific region, an aspicular calcareous skeleton is not present.

DESCRIPTION

Dendy & Row (1913) already wrote that “aberrant genera [such] as Leucopsila , Baeria, Kuarraphis , Leucyssa and Trichogypsia can only be included in the Grantiidae provisionally. The difficulty of arranging the genera probably arises from the fact that great gaps exist in the family owing to extinction of intermediate forms”. This

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statement clearly outlines the major arguments for separating the above-named sponges from the Leucosoleniida . We now propose to create a new order, the Baeriida in the Calcaronea, for a group of sponges with quite a distinct type of organization, in which no traces of radial symmetry can be observed, and which apparently has not followed the sycettid pathway of evolution.

The aquiferous system of the Baeriida is always leuconoid, with choanocyte chambers distributed irregularly throughout the sponge wall and often arranged in groups around large exhalant canals ( Figs 41 ; 42). No true atrial skeleton, reminiscent of the central tube, is found in the exhalant aquiferous system, nor does a clear subatrial skeleton indicate the original position of the radial tubes. We found no sponges with an asconoid or syconoid type of aquiferous system, which could be included in this order. The postlarval development of the Baeriida is not known, and the presence of an early olynthus stage in their development has not been established. It is noteworthy that a comparison of the morphogenesis of diamorphs, obtained after dissociation and reaggregation of Sycon vigilans and Grantia compressa (representing the Leucosoleniida ) and Baeria (Leuconia) nivea (representing the Baeriida ) (Sarà et al. 1974; Peixinho 1980) have disclosed clear differences. During morphogenesis both Sycon and Grantia pass through the olynthus stage, acquiring a sycettid grade of organization by the subsequent formation of radial tubes, similar to the postlarval development of the Leucosoleniida . Conversely, Baeria does not pass through olynthus and sycettid stages during morphogenesis, but develops a leuconoid type of aquiferous system by the formation of a rhagon, similar to that described for the Demospongiae by Lévi (1956) ( Fig. 43 ). Consequently, we assume that in the Baeriida , as in the Demospongiae, the development of the aquiferous system involves the formation of spherical choanocyte chambers, simultaneous with the formation of the inhalant and exhalant aquiferous systems.

Apart from these aspects of the aquiferous system and the associated skeleton, the Baeriida are characterized by having two distinct categories of spicules, which correspond to the megascleres and microscleres in Demospongiae. Small spicules (most frequently microdiactines) are found throughout the sponge and giant spicules are limited to the cortical region (e.g. Baeria johnstoni and Lamontia zona ), or invade the choanosome from the cortex and form a scattered skeleton throughout the body (e.g. Baeria nivea ). One or several types of very small spicules may be present. A very particular type of tetractine termed “unicorvo-cruciform” by Bowerbank (1864), “kreuzförmigen Vierstrahlern” by Haeckel (1872), “dagger-shaped tetracts” by Grant (1826), Dendy (1892b) and Kirk (1895), or harpoon-like tetractines by more recent authors is found in the skeleton of exhalant surfaces. We propose to name these spicules “pugioles” (pugiolus, in Latin small dagger). Typical pugioles are found in Baeria and Lamontia . They constitute the exhalant canal skeleton, in which the paired actines are adjacent to the canal surface, the unpaired actine is perpendicular to it lying inside the adjacent tissue, and the apical actine is free in the canal lumen ( Figs44 ; 45 ). Consequently, they have the main axis (the one passing through the unpaired angle of the basal triactine system) perpendicular to the exhalant canal surface, as opposed to atrial spicules in the Leucosoleniida where this axis is parallel to the atrial surface oriented longitudinally with the unpaired angle in most of the cases turned towards the osculum. The position and function of pugioles are not unlike those of the equally“cruciform” large spicules named chiactines (Jenkin 1908a) that are characteristic of the family Staurorrhaphidae . We consider that this is a consequence of the same need for reinforcement and protection of the surface of the exhalant system. In both cases, the atrial surface is devoid of skeleton, and consequently is bald and exposed to invasion. Chiactines are modified subatrial spicules and thus participate both in forming the proximal part of the choanoskeleton and in the protection of the atrial cavity through long apical actines bent centripetally across the atrial surface of the sponge. However, pugioles are present only in the Baeriidae , where they point their apical actine towards the inside of the atrium. Apparently, they are derived from spicules that were tangential to the surface of exhalant canals, but which have subsequently acquired the particular position and orientation observed in Baeria johnstoni and B. nivea . The second type of small spicules are microdiactines, often termed “Stäbchen-Mörtel” (Haeckel 1872) or “mortar spicules” (Dendy 1892b) ( Fig. 45 ). These spicules apparently derive from small triactines, in which one of the paired actines is rudimentary, giving the spicule a lanceolate-like shape. Similar spicules can be found among sponges in the Leucosoleniida , but in the Baeriida they may be the sole spicule type present, or can constitute a specific part of the skeleton, either alone or as its major component, such as choanoskeleton (e.g. Baeria , Lamontia , Eilhardia , Lepidoleucon ) or atrial skeleton (e.g. Leucopsila ).

There may also be small triactines with two short or rudimentary paired actines, bent together to form a club-shaped spicule, often with a more or less pronounced hole adjacent to the centre of the spicule; these are the “needle-eye” spicules seen in the genus Kuarraphis and in Baeria ochotensis .

Baeria gladiator Dendy, 1892 also has typical trichodragmas. To our knowledge, this is the only calcareous sponge with this type of microdiactine. The external skeleton of the Baeriida may have a thick and continuous layer of reinforced cortical spicules that obstructs the free flow of inhalant water and causes the inhalant pores to be restrict- ed to a specific cribriform region (e.g. Lamontia , Lepidoleucon ).

In the subclass Calcaronea, continuous evolutionary lineages with all the intermediate forms are observed in Leucosoleniida , suggesting a recent evolutionary radiation. In contrast, the Baeriida and Lithonida are represented by wellcharacterized and very distinct genera, with no intermediate forms, suggestive of long-term evolution in which a small number of only the most specialized forms are conserved. Similarly, in the subclass Calcinea, all the transitional forms are found in Clathrinida but not in Murrayonida (Borojevic et al. 1990) .

Figures

FIG. 41. — Transverse sections through the wall of Baeria johnstoni (Carter, 1871) (light micrograph). Abbreviations: ex, large exhalant canals; ch, choanosome; cx, cortex. Scale bar: 230 µm.

FIG. 43. — Diagram of the formation of choanocyte chambers of diamorphies during the process of reconstitution from dissociat- ed cells; drawing from original micrographs by Peixinho (1980); A, pre-sycon stage of Grantia compressa; B, pre-leucon stage in Baeria nivea. Scale bar: A, 26 µm; B, 45 µm.

FIG. 44. — Pugioles (p) in an exhalant canal (ex) of Baeria nivea (Johnston, 1842). Scale bar: 90 µm.

FIG. 45.— Diagram of pugioles and microdiactines;A, Baeria gladiator; B, Lamontia zona; C, Baeria nivea; D, Baeria ochotensis.