Dercitus Stoeba simplex (Carter, 1880)

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 : 15

Dercitus Stoeba simplex (Carter, 1880) Figs 6 A–B

Samus simplex Carter 1880: 60, pl. V fig. 26.

Stoeba simplex ; Sollas 1888: 102; Maldonado 2002: 155, fig. 12 A–B.

Dercitus simplex ; Thiele 1900: 20, pl. II fig. 1.

Stoeba plicata var. simplex; Annandale 1915: 458.

Dercitus plicatus var. simplex ; Burton and Rao 1932: 309.

Halina plicata ; Thomas 1972: 353, pl. II figs 6 A–B.

Material examined.

BMNH 1931.1.1.31a, Invisible Bank, Andaman Islands, slide only of which it is uncertain whether it represents the present species. Type: Indian Museum Calcutta? (not seen).

Description

(from Carter and Sollas). "Sponge excavating. Spicules: Megasclere dichotriaene, rhabdome 0.210 × 0.042 mm. Microsclere rod-like with numerous small spines 0.0127 mm in length. Habitat: Gulf of Manaar".

Remarks.

The exact properties and variation of this species have not been established so far, so we can only provide a discussion pending a proper revision. The type material has not been reexamined and its precise whereabouts are uncertain.

Annandale (1915) described specimens from the Mergui Archipelago (now Myanmar) as similarly ‘excavating’ (they are insinuating dead corals and filling spaces presumably made by clionaid sponges) and having dichocalthrops, and a single calthrops, as megascleres (sizes not given); sanidasters 16.2 µm.

Thomas (1972) described 'coral boring’ material from the Gulf of Manaar, insinuating, with dichocalthrops having protocladi 33 × 2, deuterocladi 79 × 16, rhabdome 63 × 16 and cladome 210 µm. The rhabdome is clearly shorter than in the other described specimens.

In contrast to previous descriptions, Thiele (1900) recorded this species from Ternate (Indonesia, Halmahera) as forming a black encrustation likened to Dercitus (Dercitus) bucklandi . Spicule dimensions provided were: rhabdome of dichocalthrops 150 × 25 µm, cladome also similar in size, sanidasters 9 µm, provided with 'numerous clear spines’. Thiele also mentions the presence of large (12-35 µm) pigment cells.

Maldonado (2002) gave a description of an Indian specimen from the Andaman Islands, supposedly of this species, but not the Gulf of Manaar type specimen itself. It is presumed that he described the specimen mentioned in Burton and Rao (1932). We borrowed the same slide from the NHM collection (BMNH 31.1.1.31a). It is possible that this specimen which according to Burton and Rao (l.c.) in external form resembled Dendy’s (1905) Dercitus (Stoeba) extensus more than Dercitus (Stoeba) simplex may indeed have been of another species as there is a big difference between the original description of Carter and the Burton and Rao slide in the size of the microrhabds: 12.7 µm in the type, 18-28 × 3-7 µm in the Andaman specimen (Fig. 6B). The rhabd of the dichocalthrops of the type is given as 210 × 42 µm whereas Maldonado gives 40-225 × 60-75 µm in the Andaman specimen (remeasured by us 75 –251.5– 317 × 12 –39.8– 52 µm) (Fig. 6A). Maldonado additionally gives protocladi as 30-50 × 12-60 µm (remeasured by us: 53 –84.3– 117 × 14 –39.7– 51) and deuterocladi as up to 150 × 35-40 µm (remeasured 15 –105.0– 157 × 8 –29.4– 38 µm). Cladomes 128 –386.8– 492 µm. Small dichocalthrops were rare in the slide.

If all these specimens are members of a single species, then it occurs on both sides of the Gulf of Bengal as well as on the islands in the middle of it and to the east into Indonesia. However, specimens need to be reexamined.