Echinocardium, Gray, 1825

Madeira, Patrícia, Kroh, Andreas, Cordeiro, Ricardo, De, António M., Martins, Frias & Ávila, Sérgio P., 2019, The Echinoderm Fauna of the Azores (NE Atlantic Ocean), Zootaxa 4639 (1), pp. 1-231 : 127-128

Echinocardium sp.

( Figs. 30 B–H)

Material examined: DBUA-ECH 084 ( SMG, AZO; 1 damaged spm, TL = 24 mm) ; DBUA-ECH 086 (off Vinha da Areia , SMG, AZO, 37°42’11”N, 25°25’04”W, 2006.09.05, 66 m; 3 spms, TL = 11–14 mm) ; DBUA-ECH 091 ( Vila Franca do Campo, SMG, AZO, 37°42’33”N, 25°24’35”W, 2006.07. 25, 36 m; 2 spms, TL = 7–9 mm) ; DBUA- ECH 093 ( Vila Franca do Campo, SMG, AZO, 37°42’37”N, 25°24’34”W, 2006.07. 25, 23 m; 1 spm, TL = 9 mm) ; DBUA-ECH 094 ( Azores , 20 m; 2 broken spms, TL = 18 mm) ; DBUA-ECH 097 (off Ribeira das Tainhas , Vila Franca do Campo, SMG, AZO, 37°42’04”N, 25°25’02”W, 2006.07. 24, 48–117 m; 1 spm, TL = 7 mm) ; DBUA- ECH 278 (off Vinha da Areia , Vila Franca do Campo, SMG, AZO, 37°42’12”N, 25°25’15”W, 2006.09.05, 63 m; 1 spm, TL = 13 mm) ; DBUA-ECH 419 (off Vinha da Areia , Vila Franca do Campo, SMG, AZO, 37°42’00”N, 25°25’15”W, 2006.09.05, 81 m; 1 spm, TL = 14 mm) ; DBUA-ECH 420 (off Vila Franca do Campo, SMG, AZO, 37°42’12”N, 25°25’08”W, 2006.10.03, 58 m; 1 spm, TL = 14 mm) .

Description: test very fragile, round to oval, moderately high (61–67%TL); anterior contour high and truncated in lateral view. Frontal ambulacrum somewhat sunken, being more obvious in larger specimens. Larger tubercles mostly absent, except for a few at the edge of ambulacrum III. Apical disc posterior of centre; genital pores not visible in specimens of 14 mm or smaller. Paired petals slightly depressed with pore-series somewhat convergent; petals IV and V with 5–9(IVa), 8–14(IVb) and 7–11(Vb), 7–11(Va) pore pairs, respectively. Oral side flattened with relative large peristome (21–23%TL) slightly anterior; labrum rounded, slightly projecting, reaching the second adjoining ambulacra plate; plastron keeled toward a sharp posterior point; presence of phyllodal tube feet. Periproct round and truncate; Internal fasciole shield-shaped, wider in the smaller specimens (width Ξ 70% length; TL ± 9 mm) becoming narrower in larger specimens (width = 50% length; TL = 24 mm; DBUA-ECH 084); the overall size of the internal fasciole larger in the larger specimens (48%TL; DBUA-ECH 084) than in the smaller individuals (33%TL, TL ± 9 mm); pores of frontal ambulacrum within the fasciole in regular single series with specialized penicillate tube feet; pore size increasing towards the anterior end (size difference more apparent in smaller individuals). Number of pores on each side of the anterior ambulacrum within the fasciole increases from the smallest size class (TL = 7 mm) to the largest specimen (TL = 24 mm, DBUA-ECH 084), from 9 to 22, respectively. Subanal fasciole diamond shaped, acute at its lower end and with up to two pore pairs per ambulacrum in the larger individuals. Anal fasciole expanding along the sides of the periproct onto the aboral side, adjoining but separate from subanal fasciole. Spines relatively uniform through the aboral region with the exception of the conspicuous presence of elongated spines forming an apical tuft in the frontal ambulacrum adapically. No pedicellaria were found. Colour (in ethanol): white test and spine and brown tube-feet.

Remarks: in the Atlantic the genus Echinocardium is represented by 12 extant species ( Mironov 2006), five of which are known to occur in the NE Atlantic: E. cordatum , E. flavescens , E. pennatifidum , E. mediterraneum and E. meteorense ( Mortensen 1951b; Mironov 2006). Jesus & Fonseca (1999) reported two additional species previously thought to be endemic to the Mediterranean Sea from the south of Portugal: E. fenauxi and E. mortenseni . Echinocardium species typically live in shallow waters, though most could be characterized almost as eurybathic by having a bathymetric range that extends to waters below the 200 m ( Tortonese 1965). E. meteorense is an exception as it occurs at waters between 300–450 m ( Mironov 2006).

In general, the genus Echinocardium is characterised by rather difficult systematics with many morphological diagnostic characters overlapping interspecifically and showing great intraspecific variability (individual or ontological variation; David & Laurin 1996). The first record of Echinocardium in the Azores was made by Barrois (1888) based on very small specimens dredged in S„o Miguel Island. Later Koehler (1909) re-examined Barrois’ material and commented that it contained only very small and fragile specimens, lacking many diagnostic structures such as the pedicellaria. Curiously, both authors’ remarks could be used to characterise the material presently housed in the DBUA-ECH collection. Most of these specimens were collected during the Third International Workshop of Malacology and Marine Biology (2006). Echinocardium was a frequent presence in the tows but few individuals survived the sediment weight while handling the dredge. The material stored at the DBUA-ECH collection is composed by heavily damaged tests, not exceeding 23 mm in size. Nevertheless, these specimens can be easily distinguished from E. mediterraneum and E. pennatifidum as both species lack specialized tube feet in the anterior ambulacrum. This feature is reflected by the shape and arrangement of the pores inside the internal fasciole, which in both species is characterised by widely spaced small sized pores ( Mortensen 1907). Our specimens from the Azores can also be distinguished from E. flavescens by the presence of a depressed frontal ambulacrum and almost complete absence of larger tubercles on the aboral side. Moreover, the number of pore pairs in the pair petals appears to be significantly higher in our individuals than what was published in the bibliography for E. flavescens of similar size classes (e.g., Mortensen 1907). A closely resembling species of E. flavescens , E. mortenseni , is also distinct from our material by having a relatively longer test contour, slightly lower test height, with no obvious frontal depression, a relative shorter inner fasciole (±33%TL) and shorter anterior petals (±10 pores) at comparable size classes ( Mortensen 1907; Koehler 1909, as E. intermedium ). The deep-water E. meteorense can be ruled out by being characterized by relative small and inconspicuous internal fasciole (<25–27%TL) and by a parallel arrangement in the pore columns of the paired petal ( Mironov 2006). Also E. meteorense known depth range is significantly deeper than the reported depth for DBUA-ECH specimens. In contrast, the diagnostic features mentioned above place the examined material close to E. cordatum . However, none of the examined specimens presented the pores in the frontal ambulacrum in an irregular double series arrangement, a feature unique in E. cordatum ( Mortensen 1951b) . On the other end, E. fenauxi has the pores in the frontal ambulacrum disposed in a similar fashion as our specimens, i. e. in a single series. At first instance the examined specimens appear to belong to this species. However, E. fenauxi is also characterised by having a large depressed test and a periproct wider than long, which is not consistent with the observations on the specimens from the Azores.

The validity of E. fenauxi has been contested ( Egea et al. 2016), since its original description by Péquignat (1963). In a preliminary genetic study, E. cordatum and E. fenauxi were ordered on the molecular trees according to their geographic origin, failing to separate the morphospecies ( Laurin et al. 1994). Féral et al. (1998) also failed to genetically differentiate E. fenauxi from E. cordatum . Furthermore, the diagnostic characteristics listed above for E. fenauxi appear to fall well in the known variability the polymorphic E. cordatum as was demonstrated the studies by Higgins (1974, 1975). In contrast, available genetic data on E. cordatum indicates that it is a cryptic species complex ( Egea et al. 2016).

Mortensen (1936) tentatively identified a damaged specimen of about 20 mm from Cape Verde (7–11 m of depth) as E. connectens . This species is still known only by the fragmentary type material from Saint Helena ( Mortensen 1933c). Nevertheless, Mortensen’s description and figures of the specimen from Cape Verde are in every aspect consistent with the material examined here, particularly when comparing specimens of similar size ( DBUA-ECH 94, TL = 18–19 mm). Unfortunately, no further material of Echinocardium from Cape Verde has been recorded to date. In the future it would be interesting to compare specimens from these archipelagos as new and better-preserved material becomes available.

Figures

FIGURE 30. Echinocardium cordatum (Pennant, 1777) (DBUA-ECH 083: A) and Echinocardium sp. (DBUA-ECH 084: B–D; DBUA-ECH 278: E–H). Apical view (A, B, E); oral view (C, F); posterior view (G); lateral view (D, H).