Megapogon crucifer ( Poléjaeff, 1883 )

Alvizu, Adriana, Xavier, Joana R. & Rapp, Hans Tore, 2019, Description of new chiactine-bearing sponges provides insights into the higher classification of Calcaronea (Porifera: Calcarea), Zootaxa 4615 (2), pp. 201-251 : 224-226

Megapogon crucifer ( Poléjaeff, 1883)

( Figs 9 A–B; Table 8 )

Original description. Poléjaeff 1883, p. 60, pl. VII, figs 5a–5d.

Type locality. Azores .

Synonyms and citations. Leuconia crucifera, Poléjaeff 1883, p. 60 (pl. VII, figs 5a–5d); Megapogon cruciferus Jenkin 1908, p. 36 (pl. XXXVI, figs 114); M. cruciferus Dendy & Row 1913, p. 768 ; not M. cruciferus Burton 1956, p. 117 ; Leuconia crucifera Burton 1963, p. 117 .

Material examined. Holotype: BMNH-1884.4.22.46a (one section slide), Challenger collection, St. 75, collection date: 02.07.1873, at 822 m depth (450 fathoms), off the Azores (38º37’N, 28º30’W) ( Poléjaeff 1883) . Additional material: BMNH-1948.3.8.2: wet material (three pieces), Atlantide—Danish Expedition to the Coasts of Tropical West Africa.

Morphology. It was not possible to present a proper morphological description for this species because the only material available is one slide of the holotype. The only morphological character visible from this slide is the presence of big diactines protruding the surface and crossing the entire choanosome ( Fig 9A ).

Skeleton. Based on the material examined, we could record that the cortical skeleton seems to be composed of triactines and long and thick diactines ( Fig 9A ). Microdiactines were observed in the atrial skeleton ( Fig 9B ; Table 8 ).

Spicules. Few spicules were measured from the slide (see Table 8 ). The type of spicules distinguished from the slide were long diactines, microdiactines and triactines ( Figs 9 A–B).

Distribution and depth. The first record of this species is from Azores, at 822 m depth (450 fathoms) ( Poléjaeff 1883), and a second record was found in the tropical coast of West Africa ( Senegal), at 65–89 m depth ( Burton 1956). However, this second record does not correspond to M. crucifer (see remarks section).

Molecular identification. Not available.

Remarks. According to the original descriptions presented by Poléjaeff (1883), the skeleton of M. crucifer consists of: atrial chiactines, tubar triactines, cortical triactines, stout acerate diactines, which are piercing the choanosome obliquely and projecting their distal ends, and slender acerate diactines, scattered on the “outer surface” (cortex) in small bundles. The presence of minute spined diactines (microdiactines) was reported by Jenkin (1908) after the re-examination of the original material.

The original description of M. crucifer is based on a single fragment “belonging to the interior part” of the sponge ( Poléjaeff 1883), and for this reason there are some morphological characters, such as the type of aquiferous system, that are not mentioned by the author. New material is urgently needed to present a better description of this species which is the type species of the genus Megapogon .

After re-examining specimens and slides (BMNH-1948.3.8.2) of M. crucifer collected in the tropical coast of West Africa and identified by Burton (1956), we consider the specimen from West Africa as non-conspecific with M. crucifer . The West Africa sample consists of three fragments with tubular shape, and a slightly hispid surface. These fragments present two different types of triactines, the first one has longer unpaired actines and the paired actines are bent upwards forming a round angle. The second type of triactines are “T” shaped but with paired actines much longer than the unpaired actines. Similar to the first type of triactines, some tetractines have the paired actines bent upwards forming a round angle. Some of these tetractines look like chiactines but we could not confirm their presence in this sample. The diactines were difficult to measure because all of them were broken, but they are slender and shorter than the stout diactines reported by Topsent (1907) in the original description of M. crucifer . All these characteristics differ from the holotype of M. crucifer and its original description, suggesting that the specimen from the tropical West Africa is not conspecific with M. crucifer from the Azores Island. However, further analyses of the holotype and additional material (if available) is necessary to make a better re-description of this species.

Figures

FIGURE 9A–B. Megapogon crucifer. A–B: sections of the holotype BMNH-1884.4.22.46a. Abbreviations: Di = diactines; Mic = microdiactines.

Tables

TABLE 8. Spicule measurements from specimens of Megapogon crucifer (holotype BMNH 1884.4.22.46; additional material BMNH 1948.3.8.2). Measurements from the original description by Poléjaeff (1883) are included below. BMNH 1884.4.22.46

Spicules	Length (µm)				Width (µm)
	Min	Mean	Max	SD	Min	Mean	Max	SD	n
Diactines*	at least 1442.7		--	--	55.2–85.4			--	1
Microdiactines Triactines	37.3	40.0	42.7	3.8	2.4	3.0	3.6	0.8	2
Unpaired actines Paired actines BMNH 1948.3.8.2	276.7 187.8			-- --	14.7 16.2			-- --	1
Spicules Diactines Microdiactines Triactines I	Min 906.53 --	Mean 678.4* 57.9	Max 1483.6 --	SD 104 --	Min 28.1 --	Mean 26.6 3.2	Max 45.4 --	SD 3.7 --	n 11 1
Unpaired actines Paired actines Triactines II	90.8 108.7	158.9 139.1	239.4 167.7	46.2 18.1	6.0 4.4	8.2 7.5	10.8 12.0	1.9 2.4	6
Unpaired actines Paired actines Chiactines	71.8 140.6	90.6 207.9	116.9 308.4	17.6 61.6	4.2 6.7	6.1 6.9	7.4 7.2	1.1 0.1	4
Unpaired actines Paired actines Apical actines	173.2 173.7 51.7	186.4 212 70.6	199.6 313.8 80.0	13.2 47.3 11.2	7.6 6.3 5.8	7.8 7.9 7.7	7.9 10.3 9.2	0.1 1.3 1.2	2 6 5
Measurements from the original description ( Poléjaeff 1883)
Spicules			Length (µm)			Width (µm)
Diactines I: stout acerate, spindle-shaped, either straight			3000			100 (30:1)
or slightly curved Diactines II: slender acerate, spindle-shaped or more or			800			2.5
less cylindrical, straight. Cortical triactines
Unpaired actine: straight, tapering from the base to			200–300			18
sharp points. Paired actines: curved forwards			200			18
Chiactines
Unpaired actine			250			15
Paired actines			200			15
Apical actine: same length as the paired actines, often rather shorter and thinner