Heterospio longissima Ehlers, 1874

Blake, James A. & Maciolek, Nancy J., 2023, New species and records of Heterospio (Annelida, Longosomatidae) from continental shelf, slope and abyssal depths of the Atlantic Ocean, Pacific Ocean, Indian Ocean and adjacent seas, Zootaxa 5260 (1), pp. 1-74 : 7-10

Comments on Heterospio longissima Ehlers, 1874

The original account of Heterospio longissima . The genus Heterospio was first described by Ehlers (1874, 1875) based on a single anterior fragment collected off SW Ireland (51.017°N, 11.35°W) in 458 fathoms (837 m). Ehlers (1874) introduced the genus and species names briefly in Latin as part of a summary of new or little known polychaetes collected as part of the Porcupine Expedition. The full description, however, with illustrations was not published until a year later ( Ehlers 1875). Ehlers placed his new genus in the Spionidae and named the new species H. longissima . He provided relevant details and an illustration of the anterior end. Based on Ehlers’ original description and figures ( Ehlers 1875: Pl. 25, figs. 10–11) and our interpretation of his illustrations ( Fig. 1 ), the type species can be characterized as follows:

Description of Heterospio longissima Ehlers, 1874 . A 12-setiger anterior fragment, 25 mm long, 0.5–0.8 mm wide. Body with a short anterior or thoracic region about 2 mm long with prostomium, peristomium, and eight short setigers each wider than long ( Fig. 1A–B ); these followed by setiger 9, the first elongate segment, about as long as first 8 setigers combined ( Fig. 1A–B ). Branchiae present on setigers 2–9 posterior to setal fascicles, one long branchia on setiger 4, with rest mostly stubs or scars. Setigers 10–12 (abdominal) each long, with setiger 10 being 4.5 times as long as setigers 1–9 combined; last two segments each about 8 times as long as anterior segments. Prostomium short, broadly rounded on anterior margin ( Fig. 1A ), flattened dorso-ventrally. Peristomium a single ring without dorsal crest; mouth surrounded by lobes ( Fig. 1A ). Setae arise from anterior border of each segment ( Fig. 1A–B ); setigers 1–9 with setae in discrete, narrow, fan-shaped fascicles; setigers 10–12 with setae arising in rows producing broad transverse fascicles along anterior and lateral margins, with dorsal, ventral, and lateral gaps; all setae capillaries. Presence of other types of setae not observed on available segments.

Remarks. This description is based on Ehlers’ (1874, 1875) text and illustrations and is the best we can present based on the limited available information. Ehlers (1874, 1875) states that the mouth has two transverse lobes on the anterior lip but his Pl. 25, fig. 11 suggests that additional lateral lobes may also be present.

Based on information published by Laubier et al. (1974) and Borowski (1994) as well as correspondence by the first author with the late Drs. M.E. Petersen and G. Hartmann-Schr̂der (in litt.), Ehlers’ type-specimen is not present in the Museum of Natural History, London, or the Zoological Museum of Hamburg and is presumed lost. It is noteworthy that despite additional surveys and collections from near the type locality off SW Ireland, no additional specimens that agree with Ehlers’ (1874, 1875) description have been found. Although Amoureux (1982) reported specimens that he identified as H. longissima , he did not describe them. Conversely, specimens that agree well with a Mediterranean species, H. reducta , have been identified from the same general area and depths ( Amoureux 1982; Parapar et al. 2014; this study).

Hartman’s (1965) concept of H. longissima . Hartman (1965), as part of a monograph on deep-water polychaetes from the North Atlantic Basin collected by H.L. Sanders and R. R. Hessler, described and illustrated specimens she assigned to Heterospio longissima . As noted in the Introduction, Hartman’s concept of the species has been used by many investigators to characterize the type species .

Laubier et al. (1974), as part of a paper describing two new species of Heterospio from the Mediterranean Sea, examined several specimens of H. longissima from the Sanders/Hessler collections loaned to them by Dr. Hartman but did not specify which stations they were from. This omission is problematic because there are two distinct species in Hartman’s material (see below).

Laubier et al. (1974) determined that Hartman’s concept of H. longissima differed from Ehlers’ (1874, 1875) original description in that setiger 9, the first elongate segment, was only about 2.5 times longer than setiger 8 instead of setiger 9 being as long as the preceding eight setigers. However, there are additional differences between Ehlers’ original description, brief as it is, and Hartman’s version, which itself contains several errors. One is that Ehlers found only capillary setae on his 12-setiger specimen, whereas Hartman reported acicular spines. Nevertheless, the morphological concept presented by Hartman (1965) and slightly modified by Laubier et al. (1974) has been perpetuated and modified in several subsequent studies as “ H. longissima sensu Hartman ” ( Laubier et al. 1974; Borowski 1994; Bochert & Zettler 2009; Parapar et al. 2014, 2016). It is generally assumed, although not specifically stated by these authors, that Hartman’s (1965) concept of H. longissima represents the actual morphology of Ehlers’ species.

However, based on an examination of Hartman’s original materials, it is clear that the description presented by Hartman (1965) is incorrect in several aspects. There are major differences between Hartman’s (1965) description of the specimens and our observations of the same material. The most striking differences are:

(1) The branchial distribution reported and illustrated ( Hartman 1965: Pl. 30, fig. f) for a specimen from R/V Atlantis Sta. II-2 indicates long filamentous branchiae on setigers 2–9, whereas the present observations of more than 50 specimens, including five from the same sample (R/V Atlantis II-2), consistently have branchiae on setigers 2–5 with no evidence of scars or stubs of additional branchiae on more posterior setigers on any specimen.

(2) The prostomium on Hartman’s Pl. 30 fig. f is shown as narrow and pointed; whereas none of the specimens examined from that station or others have such a prostomium. The conical prostomium, while narrowing anteriorly, definitely has a rounded, not pointed, tip.

(3) Hartman’s Pl. 30, fig. f illustrates two dorsal tentacles arising from the peristomium. In the present study, no specimens from the Sanders/Hessler’s collections had attached dorsal tentacles; however, one small specimen from ACSAR Sta. 16 had one dorsal tentacle arising from the right side of the peristomium. Hartman (1965:163) does indicate in the text that “several long grooved palpi are present in the sample”. These were probably added to the illustration.

(4) The main illustration of the anterior end, Pl. 30, fig. f, does not correctly depict the relationship of the emergence of the setal fascicles on the segments of this species or Heterospio in general. The parapodia are depicted with the setal fascicles emerging from the middle of each segment rather than on or near the anterior margin, a character that defines the genus (and family). This incorrect depiction of the origin of the setal fascicles also includes an additional segmental furrow suggesting that an additional setigerous segment is present due to its placement after the eighth pair of branchiae. This error was pointed out by Laubier et al. (1974) who diagramed the correct segmental sequence. However, these authors did not comment on the number or placement of branchiae on the specimens they examined.

Contributing to the confusion is that Hartman (1965) wrote only of acicular spines and capillaries in abdominal parapodia and did not indicate that spines having an arista or other type of terminal extension were present. Borowski (1994) specifically stated that H. longissima sensu Hartman did not have aristate setae but mistakenly reported subuluncini in his Table 2 when referring to Hartman (1965). Parapar et al. (2014) evidently followed Borowski’s table and included subuluncini in their description of H. longissima sensu Hartman based on specimens from off Iceland in bathyal depths (784–834 m). The specimens from Hartman’s collection reported here as H. hartmanae n. sp. are from lower continental slope and abyssal depths (2470–4950 m) and have only acicular spines and capillaries in the abdominal cinctures from setiger 10. The specimens reported by Parapar et al. (2014) most likely represent an undescribed species.

There is no obvious reason why the account of H. longissima by Hartman (1965) contains so many errors. However, the collection date of the last sample used in the study was April 1963, leaving only two years between the final collection date and the release of the monograph in April 1965 to process over 27,000 specimens and identify, describe, and illustrate more than 265 species, 70 of which were new to science. Further, four different illustrators were employed to assist Dr. Hartman on the project, including at least two technical assistants, perhaps students, one of whom is acknowledged as preparing Plate 30. It seems likely that morphological details in the illustrations and text were not rechecked against the actual specimens, or the text was edited after the illustrations were prepared and details were not confirmed.

Part of the problem may also be that the Sanders/Hessler collections examined by Hartman (1965) were from different locations. The main collections along the Gay-Head-Bermuda transect from off New England to Bermuda were mostly from abyssal depths and included the species with branchiae on setigers 2–5 described here as H. hartmanae n. sp. These collections differ from the original account as noted above. However, specimens were also collected from ca. 550 m off Suriname (then Dutch Guiana) and were also listed as H. longissima by Hartman (1965). These, however, are a different species, here described as H. guiana n. sp. These latter specimens agree more closely with Hartman’s Pl. 30, fig. f in that some long branchiae were present and branchiae or stubs were found from setigers 2–8. It seems possible that Hartman and/or her illustrator may have consulted specimens from both areas and assumed that observed differences were variations of the same species. In those days, Heterospio was rare, nothing was known about morphological variability, and many polychaete species were often assumed to have global distributions. Since the first two described species of Heterospio , Ehlers’ H. longissima and Hartman’s H. catalinensis had branchiae on setigers 2–9 and we recently learned that specimens from New Zealand that the late Dr. George Knox carried with him during a visit with Dr. Hartman in 1959 also had branchiae on setigers 2–9 (see Heterospio knoxi n. sp. below), it might be that Dr. Hartman assumed that this was typical for the genus.

A final issue is that Ehlers’s specimen came from an upper continental slope or bathyal site of about 837 m, whereas Hartman’s North Atlantic collections were largely from abyssal depths of 3000 m and greater. In our experience, upper slope or bathyal species rarely range into abyssal depths.

Summary. Ehlers’ type-specimen is apparently lost and no specimens having the same morphology described and depicted by Ehlers (1875) have been reported from the type-locality. Hartman’s (1965) concept of H. longissima is shown in the present study to represent two different species, neither of which agrees with Ehlers’ original account.

Figures

FIGURE 1. Heterospio longissima Ehlers, 1874. A, anterior end, right lateral view; B, anterior end, dorsal view. Redrawn from Ehlers (1875).