Sabellastarte fallax (Quatrefages, 1866)

Knight-Jones, Phyllis & Mackie, Andrew S. Y., 2003, A revision of Sabellastarte (Polychaeta: Sabellidae), Journal of Natural History 37 (19), pp. 2269-2301 : 2282-2285

Sabellastarte fallax (Quatrefages, 1866)

(figure 5)

‘ Sabella penicillus Sav. ?’. (Grube, 1846: 55, plate 2, figure 2), one specimen without tube ( ZMHUB 138 , now additionally labelled type of Sabella fallax ), no location given.

Sabella fallax Quatrefages (1866: 444) .

Description. Body without crown about 60 mm long, 8 mm wide with about 130 segments, of which eight on left and nine on right are thoracic (figure 5A); crown about 17 mm long with shallow base and shallow interradiolar web forming a full circle each side; crown radioles 39 on right, 37 on left with a few partially developed ones on the ventral margins, none interdigitating, each subquadrangular in crosssection (without ridges) and with short, blunt tips beyond pinnules (figure 5A); dorsal lips damaged, but Grube noted lengths about one-third length of radioles; thorax as wide as long (figure 5A), first segment scarcely longer than following thoracic segments (viewed from side and discounting height of collar, figure 5C); collar short, lateral margins just above junction of crown and thorax and transverse to body axis (figure 5B, C), ventral lappets rounded and overlapping medially (figure 5A, D), dorsal collar margins joining bases of prominent obtuse ridges, flanking midline groove but scarcely forming pockets (figure 5B); first ventral shield with indistinct anterior margin; all thoracic tori abutting ventral shields (figure 5A), thoracic torus 6 (on left) with 53 uncini, posterior thoracic tori half length of 1st thoracic pair and twice length of adjacent abdominal tori (figure 5C, C); thoracic uncini each with crest of numerous fine teeth covering less than half of distal ‘head’, distance between end of shaft and breast similar to distance between breast and crest (figure 5G); thoracic chaetae scarcely geniculate with knees a little wider than shafts, superior chaetae much longer above knee (figure 5E) and with shafts more slender than those of inferior chaetae (figure 5F), thoracic fascicle 6 with about 60 chaetae; abdominal uncini (ca 22 per torus) and abdominal chaetae (ca 18 inferior and eight superior in parapodium 48 on right) similar to thoracic uncini and chaetae; interramal spots not apparent, but surface sloughing present.

Grube (1846) noted that most of the body was a dirty grey with brown ventral shields, violet pigment on the dorsal side of the collar and small dark violet semicircles round the base of each chaetal fascicle. The crown was pale yellow without bands or spots and with a somewhat darker base. Some of these pigments have now faded.

Remarks. Savigny’s description (1822: 78, 79) of Sabella penicillus was based on material from Dieppe in Cuvier’s collection ‘au Museum d’histoire naturelle’ Paris. None of the three holdings in the Paris museum labelled ‘ Sabella penicillus Cuv. ’ have labels giving the location as Dieppe, but one is labelled La Manche (MNHN A 245, 306g). That material is Sabella pavonina Savigny (see Knight-Jones and Perkins, 1998: 400). Quatrefages (1866) also looked at the Dieppe material and compared it with Grube’s (1846) published figures of ‘ Sabella penicillus Sav. ?’. He realised that the latter had different proportions and gave it a new name, Sabella fallax .

Neither Grube (1846) nor Quatrefages (1866) noted that companion chaetae were absent from this species, although later Grube (1870b) was the first to note that the genus Sabellastarte has ‘thoracic tori with a single row of hooks’. Earlier Grube (1846) was happy to leave the sabellid in Sabella , a genus which at that time was ill defined. He seemed, however, uncertain about the specific identification since his 1846 paper included a question mark after Sabella penicillus Sav. He also noted that the length of the crown is one-fifth of the length of the body, whilst Savigny’s Dieppe material had length of crown half that of body. Only a few of the radioles of Sabellastarte fallax show distal damage (predation?), which might account for the short crown. Two of these show regeneration which accounts for the unusual fine filament on the tip of a radiole (figure 5H), seen by Grube (1846, plate 2, figure 2a).

Grube described the collar as being ‘lowly and in two halves, not further subdivided’ and indeed the usual dorsal lamellae are missing, but represented by the two ridges flanking the midline groove. This type of collar is reminiscent of the dorsal collar of Megalomma heterops Perkins (1984, figure 42D) where ‘the dorsomedial parts of collar lamellae [are] not produced on most specimens’. Similar obtuse, thick, ridges flanking the midline groove also show in that figure (42D). Such a collar is clearly intermediate between collar lamellae with free dorsal margins separated by a wide gap, as in Sabella , and collar lamellae fused to the sides of the groove, as in other Sabellastarte , some specimens of Megalomma heterops (Perkins, 1984, figure 42A) and most species of Megalomma . Such variations of dorsal collar lamellae could well occur within Sabellastarte fallax .