Hillerella bisepta Simon, Logan & Mottequin

Simon, Eric, Logan, Alan, Zuschin, Martin, Mainguy, Jerome & Mottequin, Bernard, 2016, Lenticellaria and Hillerella, new kraussinoid genera (Kraussinoidea, Brachiopoda) from Indo-Pacific and Red Sea waters: evolution in the subfamily Megerliinae, Zootaxa 4137 (1), pp. 1-34 : 26-30

Hillerella bisepta Simon, Logan & Mottequin , sp. nov.

(Pl. 12. Figs. 1–7)

Megerlia echinata ( Fischer & Oehlert, 1890) — Logan, Tomašových, Zuschin & Grill, 2008, p. 305, Figs. 2P, R, S, T (not Q).

Diagnosis. Micromorphic kraussinoid, wider than long, biconvex, ventral valve with tuberculate radial costae; dorsal valve with less prominent radial ornamentation; ventral valve interior with single central septum not interrupted in its posterior part, hinge line with prominent teeth; dorsal valve hinge line with sockets but without cardinal process or crura; dorsal valve floor with usually a single commissural row of tubercles, dorsal valve interior with two prominent subparallel septa directed posteriorly from loop and slightly converging towards the hinge line, loop consisting of an arch supported by two slightly outwardly-inclined plates attached to valve floor, with a thin ventral bridge and with ventro-anterior expansions not strongly developed.

Diagnose. Brachiopode kraussinoïde micro-morphique, plus large que long, biconvexe; valve ventrale avec côtes radiales tuberculées; valve dorsale avec côtes moins proéminentes; valve ventrale avec septum central non interrompu dans sa partie postérieure; ligne de charnière avec des dents proéminentes; ligne de charnière de la valve dorsale avec sockets mais sans processus cardinal ni crura; surface interne de la valve dorsale avec deux septa subparallèles proéminents dirigés postérieurement du brachidium jusqu’à la charnière; brachidium consistant en une arche supportée par deux plaques divergentes attachées à la surface interne de la valve avec une partie ventrale extrêmement fine et avec des expansions ventro-antérieures peu développées.

Etymology. Specific epithet describes the diagnostic subparallel septa in the interior of the dorsal valve.

Type locality (locus typicus). Station 100/8 at 90m depth off Port Sudan, Red Sea (18º 57.5’ N, 38º 15.8’ E) ( Grill & Zuschin 2001; Logan et al., 2008, Fig. 1).

Holotype. Ventral and dorsal valves of an articulated specimen, Pl.12, Figs.1a–f from type locality, with dimensions indicated in Table 3 ( NHMW 87192/GP 253).

Paratypes. (Pl. 12, Figs. 2–6) all from the type locality except Pl. 12, Fig. 7 which has been collected from Toliara (SW. of Madagascar). Measurements are indicated in Table 3 . ( NHMW 87192/GP 254–255 and NBM— 0 10321, NBM—008251).

Material. Seven articulated specimens, 90 dorsal valves often fragmented and rarely intact, 88 ventral valves often fragmented too, all from the type locality 100/8 at 90 m depth off Port Sudan, Red Sea (Fig. 3 and see Grill & Zuschin 2001 and Logan et al., 2008 for details of exact location, substrate type and depth).

Also a single bivalved specimen collected by Jacques Picard c.1965 from dredged sediments in the vicinity of shallow coral reefs (to which the specimen was presumably attached) at Toliara, south-western Madagascar.

Description. Shell small, wider than long, maximum width about 3 mm at mid-line, usually biconvex, but occasionally verging on plano-convex; shell surface of ventral valve costate (Pl. 12, Figs.1a,c), with between 10– 14 radiating ribs, shallow, furnished with strong tubercles, some with spinose tips (Pl. 12, Fig.1c,d). Anterior commissure rectimarginate, occasionally sulcate. Hinge line orthocline, with prominent abraded beak (Pl. 12, Fig. 2a) with large amphithyrid foramen. Shell surface of dorsal valve with less prominent radial costae, and with fewer tubercles (Pl. 12, Fig.1b).

Ventral valve interior with prominent pedicle collar, strongly folded laterally when seen in anterior view (Pl. 12, Fig. 2a). Narrow striated interarea, very small triangular disjunct deltidial plates and prominent teeth (Pl. 12, Fig. 2b). Median septum extending anteriorly to about half length of valve (Pl. 12, Fig. 2a). No tubercles. Shell endopunctate.

Dorsal valve interior without cardinal process, outer socket ridges very low, much higher inner socket ridges excavate below but without crura, dental sockets deep. Strong divergent ridges sustain the sockets in the bottom of the valve (Pl. 12, Figs. 4, 5a–b). Two prominent parallel septa extend posteriorly on valve floor from about the midpoint, lengthening with age but present in even the smallest specimens (Pl, 12, fig.3). Anterior ends of septa attached to two slightly outwardly-inclined narrow plates anchored to, and emerging upwards from, the valve floor (Pl. 12, Fig. 5c).

An ontogenetic sequence shows the gradual development of the loop from a very early stage (Pl. 12, Figs. 1e– f) to later mature stages (Pl. 12, Figs. 4, 5a–d, 6, 7a–b). Plates support an arch or cross-bar which, with ontogeny, gradually builds inward from the top of either plate to eventually join, completing the cross-bar, which bridges the gap and acts as a support for the lophophore. The lateral terminations of the cross-bar may be bulbous (Pl. 12, Figs. 6, 7a–b). Anterior margin of dorsal valve with a single row of tubercles (Pl. 12, Figs. 1e, 5a, b, 7a), with excavated tips (Pl. 12, Fig. 1e, 5a, 7a). Shell endopunctate (Pl. 12, Fig. 5c).

PLATE 12. Hillerella bisepta sp. nov. all collected from Port Sudan at 90 m. Station 100, Fig. 3, except specimen figured in fig. 7, which comes from Toleara, Madagascar.

Fig.1. Hillerella bisepta sp. nov. Holotype (NHMW 87192/GP 253). 1a: External view of ventral valve showing radial ornament of costae, tubercles and small spines. 1b: External view of dorsal valve showing radial ornament of faint ribbing, no tubercles or spines. 1c–d: Profile view of both valves attached, showing differences in ornament between the two valves. 1e–f. Interior of dorsal valve. 1e: early stage development of septal ridges and arch of loop of brachial skeleton. Note single row of marginal tubercles with excavated tips. 1f: enlargement of brachial skeleton and septal ridges shown in previous figure. Fig.2. Paratype 1. (NHMW 87192/GP 254). 2a; Interior of ventral valve, with pedicle collar, hinge area, teeth, median septum and tuberculate margin. 2b: enlargement of part of hinge area (H) of previous specimen, showing tooth (T) and disjunct deltidial plate (D) outlined in black.

Fig 3. Paratype 2. (NHMW 103331-5). Interior of early juvenile stage in ontogeny of dorsal valve, showing biseptal development preceding loop.

Fig. 4. Paratype NBM- 010321. Interior of juvenile dorsal valve, anterior view of loop of immature form showing progressive development of arch of loop towards fusion.

Fig.5. Paratype 4. (NHMW 87192/GP 255). 5a: ventral view. 5b: anterior view. 5c: oblique lateral view. 5d: detail of the ventral bridge. Note marginal tubercles with excavated tips in 5a.

Fig. 6. Paratype NHMW 103335. Detailed view of a mature loop with bulbous extremities.

Hillerella bisepta sp. nov. Specimen collected from Toliara (SW Madagascar), c1965, dredged by J. Picard (no depth data). Fig.7. Paratype NBM-008251. Interior of a dorsal valve. 7a: general ventral view showing brachidium and marginal tubercles with excavated tips. 7b: thickened mature loop and bulbous extremities.

Remarks. This species was briefly described and illustrated by Logan et al. (2008) from specimens collected by Zuschin and others from a wide variety of localities in the northern and central areas of the Red Sea, including the Port Sudan area. It was misidentified as Megerlia echinata ( Fischer & Oehlert 1890) at that time. Consequently we have now established the new genus Hillerella . While this genus has some of the attributes of the other members of the family Kraussinidae ( Kraussina , Megerlia , Megerlina and Pumilus (Lee & MacKinnon, 2006) it differs from other members of this family mainly in its small size typical of Red Sea brachiopods in general ( Zuschin & Mayrhofer, 2009), the possession of subparallel septal ridges on the floor of the dorsal valve and the unique structure of the loop. Unlike Hillerella , Lenticellaria has a single central pillar with a bifurcate loop on either side to support the lophophore, while the separate claws never conjoin. The single example from Toliara, Madagascar (Pl. 12, Fig. 7a, b) shows a thicker crossbar than typical Red Sea specimens, with more bulbous lateral terminations and the space between the underlying supports is narrower at the base, but nevertheless has the diagnostic subparallel septal ridges and loop structure to justify being assigned to H. bisepta .

Homeomorphy and comparison with other kraussinid brachiopods. Homeomorphy is common among brachiopods and is often an important cause of misinterpretation. The most striking homeomorphy for Lenticellaria gregoryi sp. nov. is observed with the recently erected Annuloplatidia curiosa Bitner, 2014 (see Bitner, 2014, Fig. 9 A–H, p. 257). This micromorphic species is easily confused with a young Megerlia or with our new species. The brachidium is however typical of the genus Annuloplatidia Zezina, 1981 .

The homeomorphy between L. gregoryi sp. nov. and young different species of Megerlia (Pls. 1–5) is clearly visible.

Controversies concerning the validity of certain Megerlia species are still discussed in the literature and most are due to homeomorphy.

M. echinata ( Fischer & Oehlert, 1890) , for instance, is considered as an ecological variant of M. truncata by Logan (1979) and Logan et al. (2004). For Miocene specimens Bitner (1990, 1993) has the same opinion. For Emig et al. (2015) this species is a synonym of M. truncata . On the contrary M. echinata was regarded as a separate species by Brunton & Curry (1979), Cooper ( 1973 b, 1981a, 1981b), Brunton (1989) and Anadón (1994). It is reconsidered again as a valid species by Logan et al. (2007, 2008).

Detailed morphological observations of the type specimen and SEM illustrations have not been published until now (Plate 10). The type specimen shows all the characters proposed independently by Atkins (1961a, p. 89) for her M. echinata material collected by the R.V. Sarsia (1958 & 1959) at depths between 556– 882 m. The flat dorsal valve is smooth (without any radial costae) with numerous concentric growth lines (Pl.10, Fig. 1) whereas the ventral valve is ornamented by long spines (Pl.10, Figs.2a–b). All these spines are not only placed on radial costae but they can be developed on the whole surface of valve (Pl.10, Fig. 2c). Broken spines show a typical alveolar structure (Pl.10, Fig. 2d). The differences between the lophophore of M. echinata and M. truncata were discussed by Atkins (1961b).

A problem of zoogeographical order remains. The original specimen of M. echinata collected by “Le Travailleur” has been trawled off Cape Bojador ( Sudan) between 640–782 m deep. The material studied by Atkins came from the western Atlantic. Phylogenetic analyses should establish definitively the taxonomic status of M. echinata and its relationship with other megerlinid species and also will confirm if the material from Cape Bojador and from the western Atlantic are the same species.

Similar problems in regard to Megerlia gigantea ( Deshayes, 1863) were discussed by Cooper (1981) and still no definitive solution has been found. For Bitner (2007, 2008) and Emig et al. (2015) M. gigantea is regarded as a synonym of M. truncata whereas it is a distinct species for Laurin (1997), Cooper (1981) and Gaspard (2003).

The specimen illustrated by Laurin as M. echinata (1997, fig. 38, p. 452 and fig. 39, p. 453) is quite unusual. No complete description of this material is given and the illustrations consist of two drawings. His fig. 38 may be “synthetic” as no details of the tuberculation and of the ventral ornamentation are provided. The loop represented in fig. 39 is quite different from the loop seen in Megerlia at the same stage of growth (Pl. 4, Figs. 3a–e and Pl. 5, Figs. 1a–g). These drawings probably represent another genus. Recently, Bitner (2014, p. 258) placed these specimens in synonymy with her newly-erected species Annuloplatida curiosa from French Polynesia. She suggests that Laurin made a wrong interpretation of his material. However, this material should be re-studied again in regard to its taxonomic position.

The specimen reported by D’Hondt (1987) is more problematic and this material should be revised because his determination is based only on Cooper’s description (1981) and no description and illustration of this single specimen was provided. Note that among the morphological characters drawn on the original figure of Deshayes (1863, p. 37, pl. 2, figs. 10, 11) no “ring” is visible. Only a bifurcate septum producing a fork is apparent which is joined by descending branches. The ring is probably broken.

The specimen of Megerlia echinata illustrated by Cooper (1973, pl. 1, figs. 1–3) collected from southwest Cape of Good Hope has a width of 10 mm and is much larger than L. gregoryi sp. nov. The dorsal valve is smooth and the ventral valve has radial tuberculation. The surface between the radial rows of tubercles is covered with straight small spines which differ from the scales observed in L. gregoryi sp. nov.

Megerlia representatives and also M. truncata appear to have an almost global distribution (Logan, 2007; Bitner, 2007, 2008). This species is common in the Mediterranean Sea and seems to be widely distributed in the Caribbean Sea, along the West African coast (though not as far south as Cape Verde as indicated in Logan, 1988), Canary Islands and Madeira ( Logan, 1983 & Logan, 1988) and as far as Japan, Philippines, Hawaii and other Pacific zones (see references in Logan, 2007, p. H3114). Such a wide distribution, interrupted by vast gaps, is difficult to explain, and is in need of revision.

Specimens from the Persian Gulf were assigned to this species by Jackson (1921) under the name Megerlia truncata var. paucistriata (see also Bitner, 2008, p. 279 and Bitner et al., 2008). They are not illustrated but the description fits perfectly with L. marerubris sp. nov. We put M. truncata var. paucistriata in synonymy with L. marerubris sp. nov.

Some specimens of M. truncata should be revisited, for instance the specimen from French Polynesia described by Bitner (2007, fig. 3, I–J). This is a small specimen but its loop is unknown as dried soft parts are present. Bleaching this material should be useful for knowing the brachidium structure to aid in the generic identification. A similar question concerns the specimen illustrated in Bitner (2008, fig. 19, D–E) as it is very small. Its attribution to Megerlia or Annuloplatidia should be reconsidered. Recently, Bitner (2014) suggested that all her described Megerlia specimens from Pacific waters are in fact Annuloplatidia curiosa Bitner, 2014 and she placed these Megerlia specimens in synonymy with this platidiid brachiopod. However, as Lenticellaria gregoriae sp. nov is also quite similar to Annuloplatidia externally, bleaching this material is necessary for knowing the real brachidium structure and to aid in the generic identification.

Megerlia acrura Hiller, 1986 may be another problematic species from the eastern coast of South Africa. The external outline is similar to Megerlia species but the brachidium which develops a complete ring does not possess crura and descending branches. Studying the brachiopods collected from the BENTHEDI– cruise in the Mozambique, Zezina (1987) suggested the name Megerlina gigantea ( Deshayes, 1863) for a kraussinid specimen devoid of crura. She did not give any comments concerning the presence of a ring (or the presence of a broken ring?). Her description is quite short and no illustration is available for this material. Bitner (2007) suggested that this kraussinid brachiopod could be an M. acrura . This opinion has been adopted again by Hiller et al. (2008).

To know if M. acrura should be placed in a new genus was considered "a moot point" by Hiller et al. (2008, p. 381).

Tables

TABLE 3. Hillerella bisepta sp. nov. Morphometric measurements made on holotype and paratypes all collected from Port Sudan, Red Sea at a depth of 90 m except specimen NBM- 008251 which was dredged by J. Picard, c. 1965, at Toleara, SW of Madagascar (no depth indicated). L: length (mm); LDV: length of dorsal valve; W: width (mm); T: thickness (mm); ØF: maximal width of the foramen (mm); Wbrach: maximum width of the brachidium (mm); L / W = ratio length to width, T / W = ratio thickness to width; ØF / W: ratio width of foramen to width.

	L or (LDV)	W	T	ØF	L/W	T/W	ØF/W Wbrach
Specimens from Port Sudan, 90m.
Holotype NHMV 87192/GP 253	1.78	2.15	0.75	0.56	0.83	0.35	0.26 0.52
Paratype NHMV 87192/GP 254	2.70	3.08	n.m.	n.m.	0.88	n.m.	n.m. n.m.
Paratype NHMW 103331-5	(1.18)	1.25	n.m.	n.m.	n.m.	n.m.	n.m. 0;28
Paratype NBM-010321.	(1.65)	2.60	n.m.	n.m.	n.m.	n.m.	n.m. 0.50
Paratype NHMW 87192/GP 255	2.38	2.67	1.10	0.64	0.89	0;41	0.24 0.89
Paratype NHMW 103335	2.64	2.65	n.m.	0.55	0.99	n.m.	0.21 1.30
Specimen from Toleara
SW of Magascar (dorsal valve)
Paratype NBM-008251.	n.m.	5.65	n.m.	n.m.	n.m.	n.m.	n.m. 2.16