A new species of Agelas from the Zanzibar Archipelago, western Indian Ocean (Porifera, Demospongiae)

Abstract

A new sponge species (Demospongiae: Agelasida: Agelasidae) is described from the eastern coast of Unguja Island in the Zanzibar Archipelago. Agelas sansibarica sp. n. is compared to all other Agelas species described so far. The new species differs from its congeners mainly in its three categories of verticillate spicules (acanthostyles, acanthostrongyles, and acanthoxeas) and their sizes. Acanthostrongyles, well represented in the spicular complement, are an exclusive trait of the new species widening the morphological range of the genus. Summarizing on spicular complement and spicular morphotraits of 36 species belonging to the genus Agelas: i) 32 species show only acanthostyles from Indo-Pacific (n = 14), Atlantic (n = 17), and Mediterranean (n = 1); ii) three Indo-Pacific species show acanthostyles and acanthoxeas; iii) one species Agelas sansibarica sp. n. from the western Indian Ocean is characterised by the unique trait of three categories of verticillate spicules (acanthostyles, acanthostrongyles and acanthoxeas). A key for the Indo-Pacific species is supplied together with short descriptions, illustrations, and geographic range; literature on chemical bioprospecting of the genus Agelas is also provided.

Keywords: Biodiversity; Unguja Island; diagnostic key; geographic range; morpho-taxonomy; sponges.

Figure 1.

Genus Agelas. Biogeographic pattern (grey areas). The red dot indicates the type locality of the new species Agelas sansibarica sp. n. at Jambiani (06°18'44.8"S, 39°33'32"E), eastern coast of Unguja Island, Zanzibar Archipelago, United Republic of Tanzania.

Figure 2.

Agelas sansibarica sp. n. Type specimen (alcohol preserved, colour different from in vivo) from the Zanzibar Archipelago.

Figure 3.

Agelas sansibarica sp. n. Spicular complement of verticillate acanthostyles, acanthoxeas and acanthostrongyles (SEM).

Figure 4.

Agelas sansibarica sp. n. Spicular complement of verticillate acanthostyles, acanthoxeas and acanthostrongyles (LM).

Figure 5.

Agelas sansibarica sp. n. a skeletal network of spongin fibres echinated by spicules (SEM) b detail of fibres surface echinated by verticillate spicules (SEM) c section of a primary fibre cored by a verticillate acanthostrongyle d–e skeletal network (LM).

Figure 6.

Agelas axifera. a living specimen b skeleton fragment with two spicular types, axially embedded in a fibre and arming the surface c acanthostyles d acanthoxea (a modified from an original underwater shot by J. Hooper b–d modified from Hentschel 1911).

Figure 7.

Agelas bispiculata. Spicular complement of acanthostyles of two size categories (modified from Vacelet et al. 1976).

Figure 8.

Agelas braekmani. a schematic drawings of two specimens b spicular complement of verticillate acanthostyles c skeleton architecture with echinate fibres, sponge surface on the right (modified from Thomas 1998).

Figure 9.

Agelas carpenteri. Drawing of the reticulate network with spongin fibres echinated by verticillate spicules perpendicularly arranged (modified from Carpenter 1856).

Figure 10.

Agelas cavernosa. The original illustration of verticillate acanthostyles ornate by spiny whorls by Thiele (1903).

Figure 11.

Agelas ceylonica. a very low quality image of the specimen studied by Dendy 1921 b schematic drawing of a branched specimen by Van Soest 1989 c skeleton architecture with echinate fibres d–e spicular complement of verticillate acanthostyles (c modified from Thomas 1981 d modified from Dendy 1921 e modified from Lévi 1961).

Figure 12.

Agelas dendromorpha. a the sponge specimens of the type series b spicular complement of two spicular types, acanthostyles and acanthoxeas; small oxea-like spicules (bottom, right) are not reported in the original description (modified from Lévi 1993).

Figure 13.

Agelas gracilis. a ramose slim dry specimen b–c spicular complement of verticillate acanthostyles of different dimensional categories (a–b modified from Lévi and Lévi 1983 c modified from Whitelegge 1897).

Figure 14.

Agelas linnaei. a type series specimens (liquid preserved) b a living shallow water specimen c spongin skeleton with spicules d verticillate acanthostyles (modified from de Voogd et al. 2008).

Figure 15.

Agelas marmarica. a–b spicular complement (a modified from Vacelet and Vasseur 1965 b modified from Lévi 1958).

Figure 16.

Agelas mauritiana. a drawing of a massive specimen b skeleton fragment c–g spicular complement b–d Agelas mauritiana var. oxeata a modified from Van Soest 1989; b–d modified from Thomas 1979 c modified from Carter 1883 e modified from Vacelet and Vasseur 1965 f modified from Lévi 1964 g modified from Lévi 1961).

Figure 17.

Agelas nakamurai. a skeleton architecture b close up of spicules insertion in the spongin fibres c acanthostyles (modified from Hoshino 1985).

Figure 18.

Agelas nemoechinata. a skeleton architecture b spicular complement (modified from Hoshino 1985).

Figure 19.

Agelas novaecaledoniae. a type specimen b spicular complement with two spicular types (modified from Lévi and Lévi 1983).

Figure 20.

Agelas robusta. a type specimen (dry) b spicular complement of acanthostyles very stout, verticillate by blunt spines (modified from Pulitzer-Finali 1982).

Figure 21.

Agelas semiglabra. Spicular complement with two dimensional categories of acanthostyles; long acanthostyles spiny only at the tips (modified from Pulitzer-Finali 1996).