Dercitus Stoeba fijiensis, Van Soest, Rob W. M., Beglinger, Elly J. & De Voogd, Nicole J., 2010

Van Soest, Rob W. M., Beglinger, Elly J. & De Voogd, Nicole J., 2010, Skeletons in confusion: a review of astrophorid sponges with (dicho-) calthrops as structural megascleres (Porifera, Demospongiae, Astrophorida), ZooKeys 68, pp. 1-88 : 25-27

Dercitus Stoeba fijiensis sp. n. Figs 12 A–C

Halina plicata ; Tendal 1969: 34, figs 2 A–B.

Material examined.

Holotype ZMUC unnumbered, Fiji Islands, Vitu Levu, Suva Harbour, coll. T. Wolff, 18 May 1965.

Description.

According to Tendal (1969) the sponge formed an irregular mass of 2 ×5× 4 mm, situated in a crevice in a dead piece of coral. Smooth surface. Colour dark grey, oscules and pores not visible. Consistency hard. The material available to us consisted of a tiny fragment, approx. 1 mm3, half of which was sacrificed for SEM and a residue spicule slide.

Skeleton: unknown but presumably confused, with an ectosomal cover of microscleres.

Spicules: calthrops and dichocalthrops megascleres in approximately equal quantities, sanidasters.

Calthrops (Fig. 12A), with cladi occasionally crooked or bifid at the apex, size relatively uniform with few smaller spicules, cladi 96 –222.7– 258 × 19 –31.2– 37 µm, cladome 186 –347.1– 420 µm.

Dichocalthrops (Fig. 12B), with smaller sizes normal shaped, but characteristically with very short protocladi and long conical deuterocladi when larger, protocladi 19 –26.5– 30 × 13 –25.2– 42 µm, deuterocladi 55 –112.5– 192 × 9 –20.2– 31 µm, rhabdomes 58 –84.6– 132 × 11 –13.6– 21 µm, and cladomes 129 –248.4– 361 µm.

Sanidasters (Fig. 12C), relatively thick, pointed-fusiform at low magnifications, in SEM mostly with blunt endings, relatively uniform in size and shape, 15 –16.9– 21 × 3 –3.6– 4 µm.

Etymology.

Named after its type locality.

Habitat.

Shallow-water, in crevices in dead corals.

Distribution.

Known only from the Fijian type locality.

Remarks.

The distinctive feature of this new species, apart from details of spicule sizes, is the characteristic shape of the larger dichotriaenes with very short protocladi and long conical deuterocladi (represented most clearly in the dichocalthops at the right of Fig. 12B). Tendal (1969) assigned this material to Dercitus (Stoeba) plicatus (as Halina ), but this Mediterranean species has much smaller dichocalthrops (cladomes only up to approx. 200 µm) in a lower quantity than the calthrops, and is white in colour. Tendal’s measurements of the spicules differs slightly from our measurements. We did not see any sanidasters thinner than approx. 3 µm, whereas Tendal mentions 1-4 µm in thickness and protocladi of the dichocalthrops were never longer than 30 µm, whereas Tendal gives 24-66 µm. Possibly, the limited size of our fragment and the few spicules we could measure explains the differences. Even with Tendal’s measurements included, the differences with Dercitus (Stoeba) plicatus in the size of the dichocalthrops and calthrops remain clear. Furthermore, Tendal stressed that the deuterocladi are always longer than the protocladi and gave an excellent drawing of the characteristically shaped dichocalthrops. Thus the differences with Dercitus (Stoeba) plicatus are distinct and unambiguous.

The species closest to Dercitus (Stoeba) fijiensis sp. n. is probably Dercitus (Stoeba) extensus from Sri Lanka. Colour and other macroscopic features appear similar, as is the shape of the microscleres. Calthrops and dichocalthrops are slightly smaller (cladomes of both approx. 200 µm, against up to 400 and 300 µm respectively in Dercitus (Stoeba) fijiensis sp. n.). The characteristic shape of the dichocalthrops of Dercitus (Stoeba) fijiensis sp. n. is not found in Dercitus (Stoeba) extensus .

Dercitus (Stoeba) occultus Hentschel (1909) has its dichocalthrops shaped rather similarly to Dercitus (Stoeba) fijiensis sp. n. but cladome size is distinctly smaller; moreover this species lacks calthrops.

Other species with a complement of both calthrops and dichocalthrops, Dercitus (Stoeba) lesinensis , Dercitus (Stoeba) dissimilis , Dercitus (Stoeba) pauper , Dercitus (Stoeba) reptans , and Dercitus (Stoeba) bahamensis sp. n. likewise differ in (dicho-)calthrops size and shape.