Dercitus Gray, 1867

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 : 7-8

Genus Dercitus Gray, 1867

Battersbyia Bowerbank 1874

Stoeba Sollas 1888

Calcabrina Sollas 1888

Halinastra de Laubenfels 1936

Dercitancorina Topsent 1902

Type species:

Halina bucklandi Bowerbank, 1858.

Definition (emended):

Pachastrellidae (?) with calthrops or dichocalthrops as megascleres and possessing irregular acanthomicrorhabd-like sanidasters with a thick central axis relative to the actines; further microscleres may include smooth toxa-like forms and aster-like compressed forms; no structural oxea megascleres.

Comments:

Many authors have pointed out the similarities of Dercitus and Stoeba , the distinction of which rests entirely on the presence of unique toxa-like microscleres in the type species of the former. The similarities are the shape and size of the calthrops/short-shafted triaenes, the shape of the irregular sanidasters, the absence of any structure in the skeleton, the compressible liver-like texture, and the presence of large cells (60 µm) with inclusions reported for various Stoeba species as well as Dercitus bucklandi . The majority of past authors recognized only Dercitus , but Maldonado (2002) insisted on retaining the distinction at the genus level. Since there are dozens of species conforming to the above given definition and only a single North Atlantic species possesses the toxas, it appears unnecessarily formal to keep the use of two genus names for such similar species. It also would confound biogeographical analysis having a single unique character place an endemic genus in an area of the world (Celtic Seas and Lusitanian waters) where such higher taxa endemism in sponges is virtually nonexistent. Ultimately, we need independent molecular evidence to demonstrate that both are members of the same clade, but pending such results, we propose here for practical reasons to lower the status of the genera Dercitus and Stoeba to the level of subgenera. Dercitus being the senior name, the subgenera will be Dercitus (Dercitus) and Dercitus (Stoeba) . A third subgenus proposed is the suppressed Halinastra de Laubenfels (1936). The subgenera will be defined below and are keyed out in Fig. 1.

Calthrops are characteristically variable in size (cladi measuring from 25 - 648 µm), and shape, with conical-straight, curved, stunted, deformed, bifid cladi, frequently one of the cladi being longer than the others, sometimes lacking one ( ‘tripods’) cladus or with one or more reduced cladi, occasionally with five or more cladi. Short-shafted dichotriaenes (dichocalthrops) are present in twelve of the currently named and recognized species, and in five of these have replaced the calthrops entirely. When both megasclere types are combined in a single species, dichocalthrops are often distinctly smaller than the calthrops and the proportion of the two varies among individuals of the species.

Natural products: three unrelated compounds with biological actitivity, such as anti-tumor or antibiotic activity, have been extracted from species of Dercitus , viz. methylaplysinopsins from a Belize specimen of Dercitus sp. (cf. Djura and Faulkner 1980) and the acridine alkaloid dercitine and a dimethyldihydroxylindoliniumchloride from Dercitus (Stoeba) bahamensis sp. n. ( Gunawardana et al. 1988; Burres et al. 1989; Kohmoto et al. 2005 as Dercitus sp.). The furanosesterpene shinsonefuran was reported from Dercitus (Halinastra) japonensis sp. n. ( Phuwapraisirisan et al. 2004, as Stoeba extensa ).

Key to the subgenera of Dercitus (see Fig. 1)

.